mete08001 meteorology: atmosphere & …dstevens/teaching/metae... · a large part of...

Examination number: _______________________

METE08001 METEOROLOGY: ATMOSPHERE & ENVIRONMENT

2013/2014

Mark

%

1

.

CONTENTS

General information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Lecture and lab schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Useful equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Table of constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Interpreting weather charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

Stations plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Cloud identification and classification . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Calculations with the Saturation Vapour Pressure diagram . . . . . . . . . . . . . . . . . . . . . 22

Lab 1: Weather observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Lab 2: Plotting observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Lab 3: Wind chill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Lab 4: Passage of a cold front . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Lab 5: Convection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Lab 6: The skew T – ln P diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Lab 7: Thunderstorm analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Lab 8: Radiation instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Spare observations sheets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Use of plagarism detection software and ‘Own Work Declaration’. . . . . . . . . . . . . . . . 59

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Meteorology: Atmosphere and Environment Lab Book Assessment

Lab Mark Comments

Observations and plotting

/ 20

Wind chill

/ 10

Frontal analysis

/ 10

Convection tank

/ 10

Skew T – ln P diagram

/ 10

Thunderstorms

/ 10

Radiation

/ 10

Overall lab-book presentation

/ 20

Total %

1

Course Organizer: David Stevenson ([email protected]) Crew Building 314

Course Secretary: Meredith Corey ([email protected]) Crew Building 215

Entrance requirements

There are no specific entry requirements, but a physical approach to the subject is adopted throughout and some background in physics and maths, for example at SCE Higher grade (or equivalent), is desirable. Students who anticipate problems in this respect should discuss the matter with the Course Organizer.

Class locations and times

Lectures are 10:00-10:50 on Mondays, Wednesdays and Fridays in the Joseph Black Building (Chemistry) Lecture Theatre 100. Please collect a clicker from the new Murray Library and remember to bring it to all lectures; most lecturers will ask clicker questions. Lecture notes and other information will be posted on Learn.

A large part of meteorology involves measurements, observations and practical experiments. This is the purpose of the laboratory classes, which commence during the second week of Semester 1 and are for 1½ hours a week on either Monday 14:00-15:30, Tuesday 10:00-11:30 or Thursday 14:00-15:30. You need to sign up for one of these sessions on Learn. The lab is room 8216 on the top (8th) floor of the James Clerk Maxwell Building (JCMB). The lift only goes to the 7th floor, and you need to ascend an extra flight of stairs. There is a separate lift between floors 7 and 8; let the Course Organizer know if you need to use this. Lab results should be recorded in this book, which you will hand in for marking at the end of the course. You will need a ruler, a pencil, a rubber and a calculator for every lab. Note that the only calculators approved by the College of Science and Engineering for use in exams are Casio fx82, fx83 or fx85.

Recommended textbooks

The main recommended text is ‘Introducing Meteorology: A Guide to Weather’ by Jon Shonk (2013 £9.99; also available as an e-book). This is a new book, and although the course doesn’t exactly follow its contents, it covers much of the material at the correct level. There should be good stocks of this in Blackwell’s, but it may not be in the library yet.

In previous years, we have recommended “Meteorology Today” by C. Donald Ahrens (ISBN 0495555746), however this text has suddenly increased in price (£104 in Blackwells!), so we no longer recommend students buy this. The 9th edition (2009) is fine, and a free PDF can be easily downloaded (google: meteorology today 4shared). Second hand or library copies of earlier editions are fine, but be aware that any page references in lectures will differ between editions.

“Atmospheric Science: An Introductory Survey” by J.M. Wallace and P.V. Hobbs is also recommended for students keen to take further Meteorology courses; this takes a more detailed maths/physics approach and goes beyond what is required for this particular course, but it is nevertheless an excellent book. There are copies ofthese latter two books in the library.

Learning outcomes

By the end of the course you will be able to: • interpret weather maps in terms of local weather • recognise cloud types and be able to describe their formation mechanisms • plot and interpret vertical temperature and moisture soundings • describe the basic processes occurring in the atmospheric boundary layer • describe and explain the structure, physics and dynamics of thunderstorms, tornadoes and

hail formation

mailto:[email protected]


2

• describe the layers of the atmosphere from the surface to 100 km + • explain the basic physics of atmospheric processes, such as radiation at the surface, water in

the atmosphere and its phase changes • observe and plot weather elements in standard format

Assessment The course is assessed by coursework (30%) and an exam (70%) in mid-December. The coursework is divided equally between three components:

a mid-term assignment (10%)

a weather observations test in the last lab class (10%)

this completed lab book, which must be handed in after the last lab class (10%). In addition, your lab book should be handed in after the third lab and you will be given feedback on the first three labs – this will not count towards your overall mark, and you can subsequently revise your lab book for these three labs.

The mid-term assignment will be posted on Learn on 7th October and should be returned by 18th October. The exam has two sections: Section A consists of 20 multiple-choice questions, together worth 40% of the paper, and Section B consists of 8 longer questions in 4 groups of 2; you must answer one question from each group, 4 in total, worth 15% each (NB this exam format was introduced in December 2012; earlier papers are slightly different). If more than 4 questions are answered in Section B, the highest marks from each group are counted. You will need an approved calculator (Casio fx82, fx83 or fx85) in the exam.

To pass the course, you must obtain an overall mark above 40%, and get over 40% in both the exam and the coursework. There is a resit exam in August if you fail the exam. If you fail the coursework, your only option is to resit the coursework when it is offered the next year (NB this option requires the additional permission of the Head of School). The only exception is if you fail the coursework but have relevant special circumstances, in which case an alternative to the coursework will be offered.

Past exam papers are available from http://www.exampapers.lib.ed.ac.uk/Meteorology0405.shtml. Note (i) that the course content has varied slightly from year to year, and (ii) the new exam format.

All items which count towards the degree assessment will be marked anonymously. You should enter your examination number, and not your name, on all such items (including this lab book). Please hand in items to the Course Secretary (Merdith Corey, Room 215, Crew Building) by 12 noon on the due date. There are penalties for late submission of work: a reduction in the maximum possible mark of 5% per day up to 5 days late, and zero marks for work that is more than 5 days late. University policies on plagiarism and other forms of cheating will be rigorously enforced for all assessments.

Class Student Representative(s)

One or more volunteers are sought to act as class representatives. The role of class reps is to help communicate any problems related to the course between the student group and the course team. In addition to ad hoc communications, you would be expected to collate any comments from students and present them at the staff-student liason meeting, held mid-semester. Contact the CO if you would like to volunteer.

Problems If you are having problems with any part of the course, there are various things that you can do:

1. discuss it with a class colleague, and/or the class representative; 2. if the query is short, ask after a lecture or in a lab class; 3. arrange a time to see a member of staff.

In the event of illness for more than a few days, or other disruption of study, please inform your Student Support Coordinator and the Course Organizer promptly.

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Accessibility We welcome disabled students (including those with specific learning difficulties such as dyslexia) and are working to make all our courses accessible. If you wish to talk to a member of academic staff about the course requirements and your particular needs please contact the Course Organizer. You can also contact the Student Disability Service (Main Library, telephone 650 6828, email [email protected]) and an Advisor will be happy to meet with you. The Advisor can discuss possible adjustments and specific examination arrangements with you, assist you with an application for Disabled Students' Allowance, give you information about available technology and personal assistance such as note takers, proof readers or dyslexia tutors, and prepare a Learning Profile for your School which outlines recommended adjustments. You will be expected to provide the Student Disability Service with evidence of disability - either a letter from your GP or specialist, or evidence of specific learning difficulty. For dyslexia or dyspraxia this evidence must be a recent Chartered Educational Psychologist's assessment. If you do not have this, the Student Disability Service can put you in touch with an independent Educational Psychologist. If you feel that you need to use a calculator that is not on the currently permitted list, the Student Disability Service can assess your needs and suggest what alternative form of calculator may be appropriate as part of

an agreed schedule of adjustments. If you require this document in an alternative format, such as large print or a coloured background, please contact the Course Organizer.

The Course Team The course is delivered by three lecturers from the School of GeoSciences:

Weather maps, observations and air pollution – 12 lectures Prof David Stevenson ([email protected]) Crew 314 (Course Organiser)

Air masses, fronts and radiation –8 lectures Dr Hugh Pumphrey ([email protected]) Crew 313

Atmospheric processes, clouds, thermodynamic diagrams and storms – 10 lectures Dr Massimo Bollasina ([email protected]) Grant Institute 303

Course secretary:

Meredith Corey ([email protected])

Crew 215


[email protected]

[email protected]

4

Feedback

The University launched new Feedback Standards and Guiding Principles for staff and students in September 2010 (http://www.enhancingfeedback.ed.ac.uk/). For this course, individual written feedback and model answers will be provided for the mid-term exercise three weeks after the hand-in date. Preliminary written feedback on the lab books will be given in Week 5, and overall feedback on the lab books, weather observations test and exam will be available at the beginning of semester 2, and there will be an open feedback meeting on 5th February. Lecturers will lead many of the laboratory classes and a post-graduate demonstrator will be present in all of the labs to give immediate feedback on work.

Early in the semester, one or more volunteers will be sought to act as class representatives. They will have meetings with the Course Organizer to consider difficulties, complaints, suggestions etc. regarding the course. Make use of these representatives as a channel for your comments and feedback about the course. There will be a staff-student liason meeting mid-way through the course (date to be announced) to discuss any problems.

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Lecture and lab schedule

Monday 10am

Wednesday 10am

Friday 10am

Weekly lab class (Mon, Tue or Thu)

Week 1 16 Sept

DS Introduction

DS Weather maps

Satellite images

DS Cloud

classification

No lab

Week 2 23 Sept

DS Structure of the

atmosphere

DS Temperature

measurements

DS Humidity

measurements

DS 1. Weather

observations

Week 3 30 Sept

DS Precipitation

measurements

DS Pressure and wind

measurements

DS Gas laws and

thickness charts

DS 2. Station plots

Week 4 7 Oct

HP Air masses and

fronts 1

HP Air masses and

fronts 2

HPAir masses and fronts 3

DS 3. Wind chill

Week 5 14 Oct

MB Condensation of cloud droplets

MB Fog and cloud

formation

MB Precipitation from

clouds

HP 4. Weather fronts

Week 6 21 Oct

MB Physics of dry air

MB Atmospheric

moisture

MB Atmospheric

stability

MB 5. Convection

Week 7 28 Oct

MB Atmospheric inversions

MB Thunderstorms

MB Hail, lightning and

tornadoes

MB 6. The skew T-ln P

diagram

Week 8 4 Nov

MB The Föhn effect

Review

HP Importance and

nature of radiation

HP Perfect radiators Kirchhoff's law

MB 7. Thunderstorm

analysis

Week 9 11 Nov

HP Solar radiation and terrestrial

radiation

HP Energy balance at

the surface Diurnal variations

HP Rainbows and other optical phenomena

HP 8. Radiation instruments

Exam tutorial

Week 10 18 Nov

DS Air Pollution 1

DS Air Pollution 2

DS Review/exam preparation

DS Weather

observations test

6

Useful Equations The ideal gas law:

constantT

pV

relates pressure (p), volume (V) and Kelvin temperature (T) of a gas. Rather than volume, it is more

convenient for meteorological applications to work with air density (ρ = mass/volume) found from … The equation of state:

RTp

R is the specific gas constant. The dependence of the gas constant on specific humidity (q) in air is made explicit by

TqRp d )61.01(

where Rd = 287 JK-1kg-1 is the gas constant for dry air. The hydrostatic equation:

gdz

dp

gives the vertical gradient in pressure with height (z), assuming balance between pressure gradient

and gravitational forces. Acceleration due to gravity, g = 9.81 ms-2. Combining the hydrostatic equation and the first law of thermodynamics gives the dry adiabatic lapse rate:

1

adiabatic

kmC8.9

pc

g

dz

dT

This is the rate at which a parcel of air will cool as it is lifted without becoming saturated (“dry”) or exchanging energy with its surroundings (“adiabatic”). The heat capacity of dry air at constant

pressure is cp = 1004 JK-1kg-1. Combining the hydrostatic equation with the gas law and integrating over height gives … The altimeter equation:

H

zp

TR

gzpzp expexp)( 00 ,

which gives the decrease in pressure with height in a column of air with average temperature T .

The scale height H = g / (RT) ≈ 8 km for the lower atmosphere, and p0 is the pressure at height z =0. Inverting the altimeter equation gives … The hypsometric equation:

2

112 ln

p

p

g

TRzz ,

which gives the difference in height (“thickness”) between two pressure levels. For small differences, this can be approximated by … The thickness equation:

p

p

g

RTz

Δz is the thickness of a layer and Δp is the pressure drop across the layer.

7

The Clausius-Clapeyron equation:

2

1

TR

L

dT

de

e v

vs

s

relates saturation vapour pressure (es) to temperature. Lv = 2.47 x 106 Jkg-1 is the latent heat of

vapourization for water and Rv = 461 J kg-1K-1 is the gas constant for water vapour. Integrating the Clausius-Clapeyron equation gives:

TTes

1

273

1104.5exp11.6)( 3

for es in hPa as a function of temperature in Kelvin. Amongst other applications, this gives the curved saturation line on the SVP diagram.

For actual vapour pressure e, the relative humidity is RH = 100 × e / es(T) and the dew point

temperature Td is such that e = es(Td). The psychrometer equation:

])([1

eTeATT wspw

Wet-bulb temperature Tw is the temperature of a wet surface cooled by evaporation. The

psychrometer “constant” Ap depends on ventilation and pressure: Ap = 0.66 hPa°C-1 at 1000 hPa for

a ventilated surface, and Ap ~ 0.8 hPa°C-1 for an unventilated wet-bulb thermometer in a Stevenson screen. Rearranging the psychrometer equation gives

)()( wws TTATeep

,

which is the equation of the sloping lines on the SVP diagram. Specific humidity and mixing ratio:

Specific humidity q and mixing ratio w are related by

ww

wq

1

Specific humidity q, vapour pressure e and air pressure p are related by

p

eq 622.0

The Stefan-Boltzmann equation:

4

sTL

gives the longwave radiation (Wm-2) emitted by a surface with emissivity (dimensionless) and

temperature Ts (Kelvin). Stefan-Boltzmann constant σ = 5.6710-8 Wm-2K-4. Wien’s displacement law:

T

2897max

gives the wavelength for peak emission from a black body at Kelvin temperature T.

8

Table of Constants

Acceleration due to gravity, g = 9.8 ms-2

Constant in Wien’s displacement law = 2897 μm K = 2.897 ×10-3 m K

Rotation rate of the Earth, Ω = 7.29 × 10-5 rad s-1

Gas constant for dry air, R = 287 J kg-1K-1

Gas constant for water vapour, Rv = 461 J kg-1K-1

Latent heat of vapourization of water, Lv = 2.47 × 106 J kg-1

Latent heat of melting of ice, Lf = 3.35 × 105 J kg-1

Mean radius of the Earth = 6370 km

Solar constant, S = 1370 Wm-2

Specific heat of air at constant pressure, cp = 1004 J kg-1K-1

Speed of light, c = 3 × 108 ms-1

Stefan-Boltzmann constant, σ = 5.6710-8 W m-2K-4

Typical density of air at the Earth surface, ρ = 1.2 kg m-3

Conversion between C and K: 0C = 273.15 K

Conversion between inches and mm: 1 in = 25 mm

Conversion between feet and metres: 1 foot = 0.3048 m

1 mb = 100 Pa = 1 hPa

A table of constants and a list of equations will be supplied in exams.

9

Interpreting weather charts

(based on Met Office Fact Sheet 11: www.metoffice.gov.uk/learning/library/publications/factsheets)

Weather charts consist of curved lines drawn on a geographical map in such a way as to indicate weather features. These features are best shown by charts of atmospheric pressure, which consist of isobars (lines joining points of equal sea-level pressure) drawn around depressions (or lows) and anticyclones (or highs). Other features on a weather chart include fronts, troughs and ridges. These are drawn to highlight the areas of most significant weather, but that does not mean that there is nothing of significance elsewhere on the chart.

Figure 1: Isobars, weather systems and fronts on a weather chart.

Low pressure or depression

Depressions are areas of low pressure, usually with a well-defined centre, and are usually associated with frontal systems and unsettled weather. Winds blow in an anticlockwise direction around depressions in the northern hemisphere, and clockwise in the southern hemisphere.

High pressure or anticyclone

Anticyclones are areas of high pressure, whose centres are often less well defined than depressions, and are associated with quiet, settled weather. Winds blow in a clockwise direction around anticyclones in the northern hemisphere, and this is reversed in the southern hemisphere.

Fronts

Early weather charts consisted simply of station plots and isobars, with the weather being written as comments, like “Rain, heavy at times”. During the 1920s, a group of Scandinavian meteorologists, known collectively as the Bergen School, developed the concept of representing the atmosphere in terms of air masses. Since the air masses could be considered as being in conflict with each other, the term “front” was used to describe the boundary between them. Three types of front were identified which depend on the relative movement of the air masses.

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Cold Front

A cold front marks the leading edge of an advancing cold air mass. On a synoptic chart a cold front appear as a line with triangles. The direction in which the triangles point is the direction in which the front is moving.

Warm Front

A warm front marks the leading edge of an advancing warm air mass. On a synoptic chart a warm front appears as a line with semi-circles. The direction in which the semi-circles point is the direction in which the front is moving.

Occlusion (or occluded front)

Occlusions form when the cold front of a depression catches up with the warm front, lifting the warm air between the fronts into a narrow wedge above the surface. On a synoptic chart an occluded front appears as a line with a combination of triangles and semi-circles. The direction in which the symbols point is the direction in which the front is moving.

Troughs

Fronts describe thermal characteristics and also happen to be where there is significant precipitation, but precipitation is not confined to fronts. Drizzle in warm sectors or showers in cold air occur fairly randomly, but lines of more organized precipitation can develop; these are called troughs and are shown by lines on a synoptic chart.

Frontogenesis

Development or marked intensification of a cold or warm front

Frontolysis

Disappearance or marked weakening of a cold or warm front

Relationship between isobars and wind

Wind is a significant feature of the weather. A fine, sunny day with light winds can be very pleasant. Stronger winds can become inconvenient and, in extreme cases, winds can be powerful enough to cause widespread destruction. The wind can easily be assessed when looking at a weather map by remembering that:

closer isobars mean stronger winds;

the wind blows almost parallel to the isobars;

in the northern hemisphere, the wind blows round a depression in an anticlockwise direction and around an anticyclone in a clockwise direction. In the southern hemisphere, the opposite is true;

winds around anticyclones can sometimes be even stronger than indicated by the isobars;

in warm air, the wind is relatively steady and tends to blow at about two-thirds the speed that the chart would suggest, though there are exceptions to this;

in cold air, the wind is usually as strong as indicated by the isobars and can be very gusty.

11

Station plots

Good quality observations are one of the basic 'tools of the trade' for weather forecasting. The weather conditions at each individual station for a given time can be represented on a surface chart by means of station plot. This means that information which would take up a lot of space if written on a chart can be displayed in a quick and easy to understand format. Figure 2 shows an example of a plotted chart.

Figure 2: An example of a plotted chart

The land station plot can represent all the elements reported by a station, which typically include:

• Air temperature • Cloud amounts • Dew-point temperature • Cloud types • Wind speed • Cloud heights • Wind direction • Present weather • Visibility • Past weather • Atmospheric pressure and three-hour tendency

Traditionally station plots for manned observing sites are based around a central station circle. Automatic weather observations are increasingly replacing these and being plotted on weather charts. To differentiate between the two, automatic observations are plotted around a station triangle. Each element of the observation, with the exception of wind, is plotted in a fixed position around the station circle or triangle so that individual elements can be easily identified. The plotting positions and an example are given in Figure 3.

12

Figure 3: Plotting positions and an example of a manual land station circle

Total cloud amount

The total amount of the sky covered by cloud is expressed in oktas (eighths) and is plotted by the amount of shading within the station circle for manned observations or station triangle for automatic stations. The symbols used for manual and automatic observations are shown in Tables 1 and 2, respectively.

Table 1: Symbols for recording manual cloud cover observations

Table 2: Symbols for recording automatic cloud cover measurements

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Wind speed and direction

The surface wind direction is indicated on the station plot by a line in the direction that the wind is coming from. Direction is measured in degrees from true North. Therefore a wind direction of 180 is blowing from the south. The wind speed is given by the number of “feathers” on the arrow. Half feathers represent 5 knots whilst whole feathers indicate 10 knots. A wind speed of 50 knots is indicated by a triangle. Combinations of these can be used to report wind speed to the nearest 5 knots. The symbols used are given in Table 3.

Table 3: Symbols for wind speed

Gust speed

Gust speeds are measured in knots and are plotted as whole knots preceded by the letter G. i.e. G35 indicates a gust of 35 knots. Gust speeds are normally only recorded if they exceed 25 knots.

Air temperature

Air temperature is plotted to the nearest whole degree Celsius, i.e. 23 would indicate 23C

Dew point temperature

Dew point temperature is plotted to the nearest whole degree Celsius, i.e. 18C.

Pressure

Pressure is recorded in hectopascals and tenths and the last three digits are plotted. Therefore 1003.1 hPa would be plotted as 031 and 987.1 hPa would be plotted as 871.

14

Present weather

In total the Met Office has 100 codes for recording the current weather at the time of the observation. Different types of weather are represented using different weather symbols, a key to which can be found in Table 4.

Table 4. Symbols for present weather (continued on next page)

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Past weather

Simplified versions of the present weather symbols, shown in Table 5, are used to indicate weather in the time since the last observation. No symbol is plotted on the station circle if the past weather is recorded as codes 0, 1 or 2.

Table 5. Past weather symbols.

Pressure Tendency

Pressure trend shows how the pressure has changed during the past three hours, i.e. rising or falling, and pressure tendency shows by how much it has changed. The tendency is given in tenths of a hectopascal, therefore '20' would indicate a change of two hPa in the last three hours. Pressure tendency is indicated by the symbols in Table 6.

Table 6. Symbols for pressure tendency

17

Visibility

Visibility, which is how far we can see, is given in coded format, in either meters or kilometres. Visibilities below five kilometres are recorded to the nearest 100 metres, whilst those above five kilometres are given to the nearest kilometre.

Codes for visibilities of less than five kilometres

Code Distance (km) Code Distance (km) Code Distance (km)

00 <0.0 18 1.8 36 3.6

01 0.1 19 1.9 37 3.7

02 0.2 20 2.0 38 3.8

03 0.3 21 2.1 39 3.9

04 0.4 22 2.2 40 4.0

05 0.5 23 2.3 41 4.1

06 0.6 24 2.4 42 4.2

07 0.7 25 2.5 43 4.3

08 0.8 26 2.6 44 4.4

09 0.9 27 2.7 45 4.5

10 1.0 28 2.8 46 4.6

11 1.1 29 2.9 47 4.7

12 1.2 30 3.0 48 4.8

13 1.3 31 3.1 49 4.9

14 1.4 32 3.2 50 5.0

15 1.5 33 3.3 51-55 Not Used

16 1.6 34 3.4

17 1.7 35 3.5

Codes for visibilities of more than five kilometres

Code Distance (km) Code Distance (km) Code Distance (km)

56 6 68 18 80 30

57 7 69 19 81 35

58 8 70 20 82 40

59 9 71 21 83 45

60 10 72 22 84 50

61 11 73 23 85 55

62 12 74 24 86 60

63 13 75 25 87 65

64 14 76 26 88 70

65 15 77 27 89 >70

66 16 78 28

67 17 79 29

18

Low cloud type symbols Medium cloud type symbols

High cloud type symbols

19

Cloud height

Cloud heights are measured in feet. The way these are plotted varies depending on whether the station is an automatic or manned observing site.

Cloud heights for automatic stations

Code Height in feet

00 <100

05 500

10 1000

15 1500

20 2000

... ...

50 5000

60 6000

Cloud heights for manned stations

0 0-149

1 150-299

2 300-599

3 600-999

4 1,000-1,999

5 2,000-2,999

6 3,000-4,999

7 5,000-6,499

8 6,500-7,999

9 8,000 or above

/ Cloud height unknown

Example

Type of observation: Manned

Total cloud amount: 8 oktas

Wind Speed: 28-32 knots

Wind direction: South-westerly

Air temperature: 23C

Dew point temperature: 18C

Pressure: 1004.2 hPa

Present weather: Continuous moderate rain

Past weather: Rain

Pressure tendency: Falling 0.5 hPa in past three hours

Visibility: 6 km

Low cloud type: Stratus

Low cloud amount: 6 oktas

Low cloud height: 1000-1999 feet

Medium cloud type: Altostratus

High cloud type: Cirrus

Gust speed: 45 knots

20

Cloud height can be estimated in several different ways: (i) if objects of known altitude are obscured by clouds (e.g., Arthurs Seat – 250m or 830 ft; Pentland Hills are ~450m or 1500ft); (ii) a useful ‘rule of thumb’ is Cloud base height (in meters) = 125 (T – Td); (iii) determine the lifting condensation level using a skew T-ln p chart.

Visibility objects from JCMB

Object Bearing Distance Code

Refectory chimney 355 110 m 01

Royal Observatory 282 1.0 km 10

Commonwealth Pool 005 2.0 km 20

Appleton Tower 343 2.5 km 25

Edinburgh Castle 333 3.3 km 33

Pentland Hills (Caerketten) 215 5.5 km 50

Corstorphine Hill 298 7.0 km 57

(Queen Mary’s Mount) (110) (11.5 km) 61

Cockenzie power station 068 14 km 64

Lufness Point 062 28 km 78

Berwick Law 064 32 km 80

Lomond Hills 348 36 km 81

Bass Rock 063 38 km 82

Ochil Hills 314 45 km 83

May Island 053 49 km 84

The Beaufort Wind Scale

Force Description Speed (knots)

0 Calm – smoke rises vertically 0

1 Light air – direction of wind shown by smoke drift but not by wind vanes 1-3

2 Light breeze – wind felt on face; leaves rustle; ordinary wind vane moved by wind 4-6

3 Gentle breeze – leaves and small twigs in constant motion; wind extends light flag 7-10

4 Moderate breeze – raises dust and loose paper; small branches are moved 11-16

5 Fresh breeze – small trees in leaf begin to sway 17-21

6 Strong breeze – large branches in motion; umbrellas used with difficulty 22-27

7 Moderate gale – whole trees in motion; inconvenience felt when walking against wind

27-33

8 Fresh gale – breaks twigs off trees 34-40

9 Strong gale – slight structural damage (chimney pots and slates removed) 41-47

10 Whole gale – trees uprooted 48-55

11 Storm – rarely experienced inland; widespread damage 56-63

12 Hurricane 64-71

21

Cloud Identification and Classification

Clouds contain large numbers (typically 106-109 m-3) of very small drops (~ 20 m in diameter). Clouds are continuously in a process of evolution and therefore appear in an infinite variety of shapes and sizes. Nevertheless it is possible to define a limited number of characteristic types or genera, each with a Latin name and standard abbreviation, applicable all over the world. The names are based on five Latin words: cumulus (heap), stratus (sheet), cirrus (lock of hair), altus (high), nimbus (rain). Each genus is assigned to one of three height bands - low, medium and high - based on the height of the cloud base. Low-level clouds (0-2 km) Stratus (St) - grey, structureless, extensive sheet of cloud, but sometimes in ragged patches. Stratocumulus (Sc) - grey/whitish patch or sheet of cloud composed of rounded masses or rolls, usually having an apparent width of 5o or more. Cumulus (Cu) - detached, dense clouds with sharp outlines, forming mounds or towers with flat bases. The clouds are brilliant white where lit by the sun. Cumulonimbus (Cb) - heavy and dark clouds of large vertical extent. Their tops are usually fibrous and spread out. Precipitation is often seen falling from their bases. Medium-level clouds (2-4, 7, 8 km in polar, mid-latitude and tropical regions) Altocumulus (Ac) - shallow sheet of cloud composed of rounded masses or rolls, having an apparent width generally in the range 1 to 5o. Altostratus (As) - largely featureless, greyish sheet, usually thin enough to reveal sun at least vaguely, as through ground glass. No halo phenomena. Nimbostratus (Ns) - extensive sheet of diffuse, precipitating grey cloud, thick enough to blot out the sun. Often accompanied by ragged low cloud (stratus). The base of nimbostratus may be in the low-cloud range at times. High-level clouds (3-8 km polar, 5-14 km mid latitudes, 6-18 km tropical) Cirrus (Ci) - clouds composed of ice crystals, usually in delicate filaments. Cirrocumulus (Cc) - thin white patch or sheet of cloud with dappled or rippled appearance, often fibrous in places and having an apparent width generally less than 1o. Cirrostratus (Cs) - largely transparent white sheet of cloud of fibrous or smooth appearance, generally producing halo phenomena. Genera may be supplemented by adding a description name called a species. Some common species are: Fractus (fra) - broken or ragged (applied to Cu and St). Lenticularis (len) – elements shaped like a lens or almond (applied to Sc, Ac and Cc).

22

Calculations with the Saturation Vapour Pressure Diagram

e.g. air temperature (T) 15C and wet-bulb temperature (Tw) 11C

esat = 17 hPa

e = 10 hPa

RH = 100×(10/17) = 59%

Td = 7C

TdTw T

e

esat

TdTw T

e

esat

23

Lab 1: Weather observations

Record your observations here and use the SVP diagram on the next page to calculate the humidity variables. (Do your values have the correct number of significant figures and do they have units?)

Date and time:

Air temperature:

Max. temperature:

Min. temperature:

Wet-bulb temperature:

Dew-point temperature:

Vapour pressure:

Relative humidity:

Total cloud cover:

Low level cloud cover:

Low level cloud type(s):

Middle level cloud type(s):

High level cloud type(s):

Cloud base height:

Wind speed:

Wind direction:

Current weather:

Past weather:

Visibility:

Pressure (measured in lab):

Pressure (corrected to Mean Sea Level):

Pressure tendency:

For this week only, you also have to submit your results on-line; instructions for how to do this will be sent to your university email. Please submit your results as soon as possible after you have attended your lab, and by 5pm on Friday 27th September at the latest. It should only take 5-10 minutes. It is important to submit your results, as the data will be used as part of the mid-term exercise. If you have no values for a particular category, leave it blank. Don't worry if some of your values appear to be incorrect; just enter what you have recorded.

24

SVP diagram for humidity calculations

Skew-T ln p diagram for predicting cloud base heights; you will learn how to use this in Lab 6

25

Lab 2: Plotting observations

Decode these station plots

Type of observation: Total cloud amount: Wind Speed and direction: Air and dew point temperatures: Pressure: Pressure tendency and trend: Present and past weather: Visibility: Low cloud type, amount and height: Medium cloud type: High cloud type: Gust speed:


26



Plot station circles for these observations

27

Type of observation: Manual Total cloud amount: 7/8 Wind Speed and direction: 5 knots SW Air temperature: 13ºC Wet bulb temperature: 10ºC Pressure: 1022.5 hPa Pressure tendency and trend: 2 hPa, rising then steady Present and past weather: Continuous drizzle, drizzle in last 3 hours Visibility: 4 km Low cloud type, amount and height: 1/8 shallow cumulus at 1500 feet Medium cloud type: Dense altostratus

High cloud type:

Gust speed: Type of observation: Manual Total cloud amount: 8/8 Wind Speed and direction: Calm Air temperature: 12ºC Wet bulb temperature: 11ºC Pressure: 1018.8 hPa Pressure tendency and trend: 4 hPa, rising Present and past weather: Continuous rain, rain in last 3 hours Visibility: 7 km Low cloud type, amount and height: 8/8 stratus at 200 feet

Medium cloud type:

High cloud type:

Gust speed: Type of observation: Automatic Total cloud amount: 8/8 Wind Speed and direction: 20 knots NW Air temperature: 13ºC Wet bulb temperature: 10ºC Pressure: 998.7 hPa Pressure tendency and trend: 2.1 hPa, rising then steady Present and past weather: Continuous rain, more than 50% cloud cover in last 3

hours Visibility: 40 km Low cloud type, amount and height: 5/8 at 500 feet

Medium cloud type:

High cloud type:

Gust speed:

29

Lab 2 Observations

Use this sheet and the SVP diagram on the next page to record and plot your observations from Lab 2. More observation sheets are available at the back of this book for practice.

Date and time:

Air temperature:

Max. temperature:

Min. temperature:



Vapour pressure:

Relative humidity:

Total cloud cover:





Cloud base height:

Wind speed:

Wind direction:

Current weather:

Past weather:

Visibility:



Pressure tendency:

Station circle:

31

UK surface observations at 11:00 on Sunday 30 September 2007. Pick a few to decode for practice.

33

Lab 3: Wind chill

The purpose of this experiment is to investigate the effect that wind and evaporation have on heat loss from an object. This is related to wind chill in humans and the measurement of wet-bulb temperature. Wind chill is the apparent temperature, if the air were still, felt on the exposed human body due to a combination of air temperature and wind speed. Wind chill does not affect inanimate objects, only warm-bodied humans and animals.

A recent version of a wind chill table was derived from extensive studies by the meteorological services of Canada and the U.S. and is appropriate for heat loss from an exposed human face, taking account of physiological changes which occur when a person is exposed to cold stress. The wind speed in this table is appropriate to face level rather than normal anemometer level of 10 metres (see the section Air Temperature and Human Comfort in Ahrens).

WIND SPEED

(ms-1)

AIR TEMPERATURE (C)

calm 0 -2 -4 -6 -8 -10 -12 -14 -16 -18 -20 -22 -24 -26 -28 -30

2 -3 -6 -8 -11 -13 -16 -18 -20 -23 -25 -28 -30 -32 -35 -37 -40

4 -5 -8 -11 -13 -16 -18 -21 -23 -26 -28 -31 -33 -36 -38 -41 -44

6 -7 -9 -12 -15 -17 -20 -22 -25 -28 -30 -33 -36 -38 -41 -43 -46

8 -8 -10 -13 -16 -18 -21 -24 -26 -29 -32 -35 -37 -40 -43 -45 -48

10 -9 -11 -14 -17 -19 -22 -25 -28 -30 -33 -36 -39 -41 -44 -47 -50

12 -9 -12 -15 -17 -20 -23 -26 -29 -31 -34 -37 -40 -42 -45 -48 -51

14 -10 -12 -15 -18 -21 -24 -27 -29 -32 -35 -38 -41 -43 -46 -49 -52

16 -10 -13 -16 -19 -22 -24 -27 -30 -33 -36 -39 -42 -44 -47 -50 -53

18 -10 -13 -16 -19 -22 -25 -28 -31 -34 -37 -39 -42 -45 -48 -51 -54

20 -11 -14 -17 -20 -23 -26 -28 -31 -34 -37 -40 -43 -46 -49 -52 -55

22 -11 -14 -17 -20 -23 -26 -29 -32 -35 -38 -41 -44 -47 -50 -53 -55

24 -12 -15 -18 -21 -24 -26 -29 -32 -35 -38 -41 -44 -47 -50 -53 -56

26 -12 -15 -18 -21 -24 -27 -30 -33 -36 -39 -42 -45 -48 -51 -54 -57

28 -12 -15 -18 -21 -24 -27 -30 -33 -36 -39 -42 -45 -48 -51 -54 -57

30 -13 -16 -19 -22 -25 -28 -31 -34 -37 -40 -43 -46 -49 -52 -55 -58

Frostbite in >> 30 min 10 min 5 min

What to do

Spend a few minutes reading these notes in full before you start so you know what to do. Ask if you are confused.

In this experiment we will look at the rate of heat loss from a metal cylinder in air at various wind speeds in order to investigate the cooling effect of wind. Get into groups of 2 or 3 people (we only have 10 fans to go around).

First determine the air temperature (Tair) in the lab using the temperature probe. Use a ruler to measure the (inner) dimensions of the tube you are using, and calculate the volume of water it will hold.

Fill the tube with water from the hot tap (it should be 35-40°C). Insert the cork and thermocouple in the top, locating the tip of the thermocouple as close to the middle of the tube as possible. Make sure the outside of the tube is dry. Make sure that the water is well-mixed before you take a temperature measurement by quickly inverting the tube. With the fan OFF, observe the water temperature (Twater) at regular intervals (~30 seconds) as it cools towards room temperature. About 7-8 minutes of measurements should be sufficient. Plot a graph of how Twater varies with time.

34

Now repeat the experimental procedure three more times, but with the fan switched on. Try to start from the same temperature and keep the tube at the same distance from the fan (about 50 cm). The three extra experiments are:

Tube exposed to a low wind-speed (about 0.5 m s-1)

Tube exposed to a high wind-speed (about 2 m s-1)

Tube exposed to a high wind-speed and wrapped in a wet paper towel

Plot your results on the same graph as the first experiment (use a different colour or symbol for each one).

Calculate how the cooling rate (C s-1) evolves in each experiment. Plot the cooling rate against

time. Use your results to determine by what factor the cooling rate at low and high speeds exceeds that in still air.

For specific heat capacity of water 4200 J kg-1 K-1 and density 1000 kg m-3, what is the cooling rate expressed in J s-1 (equal to Watts, W)? (You will need to use the volume of water to calculate this). Add another axis to the cooling rate graph that shows the cooling rate in Watts.

Lastly, but most importantly, write down a physical explanation of the range of results.

Notes and calculations

Room temperature = (you should record this at least twice)

Volume of tube =

Conversion factor between C s-1 and Watts =

Physical explanation of results:

Attach any additional pages securely

35

Temperature variation with time

Time Experiment 1 Experiment 2 Experiment 3 Experiment 4

36

Cooling rate with time

Time Experiment 1 Experiment 2 Experiment 3 Experiment 4

38

Lab 4: The passage of a cold front

On Saturday 4th October 2008 a cold front passed the UK sometime in the afternoon. Met Office surface pressure charts at 12 noon and 6 pm and station plots from 9 am until 8 pm on the 4th of October are shown on the next two pages. Examine each of the 12 station plots and enter data values on five graphs for the following variables at Leuchars in Fife: a) surface pressure (to nearest hPa)

b) air temperature (C)

c) wind direction (to nearest 45) d) wind speed (knots – plot only the central value of the range) e) cloud amount (fraction of 8ths) and low, medium and high cloud types

Then answer the following questions:

Q1) At what time did the cold front pass over Leuchars (to the nearest hour)? What other station symbol (not one of the variables in the graphs) would enable you to determine that time?

Q2) Describe the temperature change between the hour that the front passed and the hour after.

Q3) At what other time of day was there a similar variation in temperature between two consecutive hours and how do you explain this?

Q4) Describe the wind direction change between the hour that the front passed and the following hour. Did the wind veer or back? Is this to be expected?

Q5) Describe the variation in wind speed in the hours proceeding, at the time of, and the hour following the passage of the cold front.

Q6) At what time did the sky begin to clear (reduced cloud amount by 5/8 oktas or less) after the passing of the front?

Q7) What other cloud types appeared when the overall cloud amount reduced substantially (to 1/8 oktas) and what might this suggest?

42

Lab 5: Convection

The atmosphere is, in general, notably stable with respect to the dry-adiabatic lapse-rate, but sunshine heats the Earth’s surface and this heating is communicated upwards by turbulent convective motions in the atmospheric boundary layer. We can simulate this in the laboratory using a tank of water with a heating plate at its base. A stable stratification in the tank (increasing temperature with height) can be set up using an immersion heater and the temperature profile can be determined using thermistors. The motion of the fluid is made visible by introducing a potassium permanganate solution at the bottom of the tank. After switching on the heating, thermals will be seen to rise from the base, overshoot the level at which they have zero buoyancy (the level where the temperature of the thermal is equal to that in its surroundings) and sink back. Successive thermals rise higher as the warmed layer deepens. Preparation

Heat the upper layer of the water carefully so as not to disturb the lower layers.

Pour the potassium permanganate solution down the funnel carefully so that it spreads evenly across the bottom of the tank without mixing upwards.

Note heights of thermometers above the base and initial temperature readings.

Turn the heater dial to the voltage marked to give a 1 W cm-2 heat flux and start timing. Observations

Take temperature readings every minute.

When thermals start to rise, sketch their structure.

Sketch convection cells viewed by looking down into the tank.

Record temperatures and heights of the mixed layer as it develops; this will happen quickly, so take measurements more frequently.

Switch off the heating as the mixed layer approaches a constant height. Note the structure of the layer top.

Analysis

Plot temperatures against thermometer height for at least the starting and finishing times on the same graph.

Plot the depth of the mixed layer against time.

Calculate the average surface heat flux from the area between initial and final temperature profiles using the equation

iTt

zcH

0

c is the volumetric heat capacity of water (4.2 JC-1cm-3), δz is the distance between

thermistors (2 cm), Δt is the time between the initial and final measurements (in seconds),

ΔTi is the difference between initial and final temperatures for one thermistor, and Σ denotes the sum over all the thermistors. How well does your result compare with the expected 1 W cm-2? Why might they differ?

43

Temperature profiles

Time Temp. 1 Temp. 2 Temp. 3 Temp. 4 Temp. 5 Plume height

44

Plume height / mixed layer depth with time

Notes, calculations and sketches

Attach any additional pages securely

45

Lab 6: The skew-T ln p diagram

In this lab, we explore the make-up of the skew T – ln p diagram, and use it to plot and analyze vertical temperature and dew point measurements.

There are blank charts in this book, but extra copies will be handed out in the lab; make sure you stick/staple these securely into your lab book if you use them for plotting. You can also find a pdf of this chart to print off yourself on WebCT, or here:

http://www.geos.ed.ac.uk/homes/dstevens/TeachingMaterials.html

1. First, let’s try and identify what the different lines are on this complicated chart.

On the first blank skew T – ln p diagram:

(a) Colour and label three isobars (lines of constant pressure, p): 1000, 500 and 200 hPa.

(b) Using a different colour, label three isotherms (lines of constant temperature, T): -20, 0 and +20°C.

(c) Similarly, label dry adiabats with potential temperatures (θ): -20, 0 and +20°C.

(d) …and wet adiabats with wet-bulb potential temperatures (θw): -20, 0 and +20°C.

(e) Finally, label three lines of constant saturation mixing ratio (ws) (1, 2, 5 g kg-1).

2. Now let’s look at a set of measurements from Lerwick, Shetland, on 17 October 2009:

Pressure (hPa) 1000 950 930 850 800 700 600 500 400 300 200 100

Temperature (oC) 8.4 5.1 1.8 5.8 4.9 -1.7 -8.0 -19.3 -30.9 -42.9 -63.3 -55.5

Dew-point (oC) 3.4 2.5 1.4 -36.2 -26 -24.7 -34.3 -22.9 -37.9 -64.2 -74.3 -87.5

(a) Plot these data on the second blank chart - both dew point (Td) and temperature (T). Connect the points for each quantity with straight lines, ideally in different colours (if your lines cross, something went wrong: by definition Td must always be less than or equal to T).

(b) What is the moisture content (or saturation mixing ratio, ws) of the air at 930 hPa and 850 hPa? Estimate the range in moisture content of air near to the surface (1000-930 hPa) and compare this to the moisture content of air between 850-500 hPa. Why do they differ?

46

(c) Describe the main features of the temperature profile (you should find four distinct height ranges which show different behaviours). What do each of these layers correspond to? Estimate the potential temperature (θ), and thickness (in metres) of air in the lowermost layer.

(d) Replot the 1000 hPa points on the expanded diagram above (first label some pressures and heights on the vertical axis), and use Normand’s Law to estimate the lifting condensation level.

Lifting condensation level in hPa:

In m:

This level is approximately where rising surface air would condense and form a cloud. You can use this method to estimate cloud base height if you know T and Td.

(e) Finally, use the enlarged diagram to determine the wet-bulb temperature at 1000 hPa.


47

Chart for question 1

48

Chart for question 2(a)

49

Lab 7: Analysis of a typical thunderstorm in Edinburgh, 7th June 2011

On 7th June 2011, in mid-afternoon, I was looking out my office window and observed the sky blacken quickly; there was a sudden onset of torrential rain, then hail, accompanied by thunder. Shortly afterwards, the rain rapidly stopped. It was a typical example of a ‘single cell’ thunderstorm. In this lab, we will take a look at some meteorological data gathered on that day, and try and understand what conditions led to this thunderstorm. The figure below shows measurements from the University of Edinburgh weather station (on the roof of JCMB), for ~24 hours from 0800 on 7th June 2011. The first plot shows air temperature (from two different sensors in slightly different locations: one on the roof, one in the Stevenson screen); next shows rainfall amount (mm per 1 minute time interval); next shows solar flux; lowermost shows windspeed.

Air temperature (black line WS sensor, grey line Stevenson screen)

1. Exactly (to the nearest ~5 minutes) when was the thunderstorm? Using the data above, quantitatively describe what happened over the hour or so before the storm, during the storm, and in the hour or so afterwards.

50

2. The table below shows temperature and dew-point data from a vertical sounding taken near Newcastle (the nearest available station to Edinburgh) at 12Z (closest to the time of the storm).

Vertical sounding data from Albemarle (Northumberland) for 12Z 07 Jun 2011

Pressure, p (hPa) Temperature, T (°C) Dew-point, Td (°C)

983 15.2 5.2

968 12.2 4.3

925 8.6 3.6

887 5.4 2.8

850 2.6 0.1

811 -0.3 -1.8

755 -3.6 -5.9

700 -7.5 -9.7

657 -9.3 -24.8

590 -13.3 -44.3

550 -15.9 -38.9

500 -21.1 -38.1

400 -33.1 -43.1

300 -47.7 -57.7

200 -45.7 -80.7

(a) Plot the data on a skew T-ln p chart (make sure you give the chart a sensible title, and clearly label the two curves). (b) Apply Normand’s Law and graphically calculate the lifting condensation level (LCL) and the surface wet-bulb temperature (just like in the last lab). LCL (hPa) = Tw =

52

(c) Draw a saturated adiabat upwards from the LCL and shade the area of convective available potential energy (CAPE) – this is an indication of the likelihood of a thunderstorm, as it identifies unstable air. You should find that this profile has some CAPE, suggesting that thunderstorms may occur. Indicate the equilibrium level (EL) on the chart and note it below (in both hPa and m). EL (hPa) = EL (m) = (d) Let us suppose that surface temperature increases above that seen in the profile (but that the rest of the profile stays the same), for example due to strong solar heating of the surface. Show on your chart what would happen to CAPE and the EL if the surface temperature increased to 20°C, and then 25°C. Estimate the increase in CAPE relative to the value from the observed profile for each of the higher temperatures. (e) Now go back and look at what happened to surface temperature during the Edinburgh storm. Again, estimate what happens to CAPE for the observed change in temperature. Why do think the storm was short-lived?

53

Lab 8: Radiation Instruments

The purpose of this short lab session is to familiarise you with some radiation instruments and with the nature of solar and terrestrial radiation.

Campbell-Stokes Sunshine Recorder

This sunshine recorder has been used, and continues to be used, at many locations for measuring sunshine hours. It employs a glass sphere to focus the sun's rays to an intense spot, which will char a mark on a curved card mounted concentrically with the sphere. As the Earth rotates, the position of the spot moves across the card. When the sun is obscured, the trace is interrupted. At the end of the day the total length of the trace, less gaps, is proportional to the duration of sunshine.

The record cards are made from a special card which produces a clearly visible trace even in weak sunlight. The cards are treated to char rather than burn to ensure clarity of the trace. Different cards are used for different seasons. Each card is marked with hourly intervals. We have one of these instruments for you to inspect. In the unlikely event that it is sunny, we may even be able to show it in action.

Solarimeter

The solarimeter (or Moll-Gorczynski pyranometer) measures the intensity of solar radiation and gives a voltage output which can be measured with a multimeter. Use the solarimeter provided to measure the albedo of the surfaces provided. The albedo of a surface is the fraction (or percentage) of incident solar radiation that is reflected.

We have one of these instruments available which will be set up as a demonstration, with two different surfaces at which it can be pointed. Record the downward and upward radiation readings for each surface in the table and calculate the albedo for each

surface.

Surface Downward radiation Upward radiation Albedo

Thermal Radiation primer

In addition to the direct and scattered sunlight that surrounds us, we are also surrounded by a similar amount of radiation at much longer wavelengths. This is emitted by absolutely every object. The flux density, F, that leaves the surface of a body is given by Stefan's law: F = εσT4, where T is the temperature of the body in KELVIN. The constant σ is a fundamental constant called the Stefan-Boltzmann constant: it has the value 5.6704 × 10-8 Wm-2K-4. The emissivity ε is a property of the surface; it is a number lying between 0 and 1. A body whose emissivity is exactly 1 is called a perfect radiator or a black body. Note: To convert from Degrees Celsius to Kelvin, add 273.15.

54

Radiation Thermometers

We have three sorts of radiation thermometers: the large digitron instruments, a new pistol-style instrument and the small “palm-of-the-hand” ones (see picture). All of these instruments receive thermal radiation from the object they are pointed at and display this as the temperature of a black body that would emit the same amount of radiation.

The little instruments have a rather wide beam; the large ones (despite their clunky appearance) are better instruments for observing a small area from a large distance. The pistol-style instrument (if it is available) has an even narrower beam.

Take a radiation thermometer and measure the radiative temperature of a variety of objects. Calculate the flux density that the object is emitting, and record the results below.

Make sure that your test objects include the sky vertically above you and the roof of the building (or some other horizontal surface in the open air). What is the difference between the flux density leaving the roof and the flux density coming downwards from the sky?

Make sure that one of your objects is a kettle of boiling water, which you know has a temperature of 100°C. We should have a kettle available with a black side and a polished metal side. Comment on the radiative temperatures that you observe from both sides:

Surface Radiative temperature Flux density

WARNING: The small radiation thermometers contain a laser pointer to help you aim the thermometer at a target. When using this BE VERY CAREFUL to ensure that you are not aiming anywhere near anyone else's eyes.

NOTE: If your radiation thermometer seems to be giving odd results, check with one of your colleagues. If you are getting very different results, your instrument may have a flat battery, OR it may be set to assume an emissivity less than one. Ask a demonstrator for assistance.

55

Observation Sheet (extra blank copies)

Date and time:

Air temperature:

Max. temperature:

Min. temperature:



Vapour pressure:

Relative humidity:

Total cloud cover:





Cloud base height:

Wind speed:

Wind direction:

Current weather:

Past weather:

Visibility:



Pressure tendency:

Station circle:

57

Observation Sheet

Date and time:

Air temperature:

Max. temperature:

Min. temperature:



Vapour pressure:

Relative humidity:

Total cloud cover:





Cloud base height:

Wind speed:

Wind direction:

Current weather:

Past weather:

Visibility:



Pressure tendency:

Station circle:

59

Use of plagiarism detection software

Note that computers may be used to detect plagiarism, whether by using something as simple as a search engine such as Google (it is as easy for a marker to find online sources as it is for you) or something more complex for specialized comparisons of work. Some courses will use the JISC plagiarism detection service.

The plagiarism detection service is an online service hosted at www.submit.ac.uk that enables institutions and staff to carry out electronic comparison of students' work against electronic sources including other students' work. The service is managed by The University of Northumbria on behalf of the Joint Information Systems Committee (JISC) and is available to all UK tertiary education institutions by subscription.

The plagiarism detection service works by executing searches of the world wide web and extensive databases of reference material, as well as content previously submitted by other users. Each new submission is compared with all the existing information. The software makes no decisions as to whether a student has plagiarised, it simply highlights sections of text that are duplicated in other sources. All work will continue to be reviewed by the course tutor. As such, the software is simply used as a tool to highlight any instance where there is a possibly case of plagiarism. Passages copied directly or very closely from existing sources will be identified by the software, and both the original and the potential copy will be displayed for the tutor to view. Where any direct quotations are relevant and appropriately referenced, the course tutor will be able to see this and will continue to consider the next highlighted case.

Once work has been submitted to the system it becomes part of the ever growing database of material against which subsequent submissions are checked. The copyright in each work submitted remains with the original author, but a non-exclusive, non-transferable, licence is granted to permit use of the material for plagiarism detection purposes.

There is an on-line demonstration of the system available at

http://www.submit.ac.uk/

Own Work Declaration When you submit your work to the Teaching Office in Crew, please sign the ‘Own Work Declaration’ form at the submission box to indicate that you have adhered to the University’s policies. An example of what this form is on the next page.

60

OWN WORK DECLARATION

By signing below, you indicate that you have adhered to the University of Edinburgh’s Own Work Declaration

I confirm that all this work is my own except where indicated, and that I have:

1. I have read and understood the Plagiarism Rules & Regulations in the course sections and Programme Handbooks; 2. I have clearly referenced / listed all sources as appropriate; 3. I have referenced and appropriately indicated all quoted text of more than three words (from books, web, etc); 4. I have given the sources of all pictures, data etc that are not my own; 5. I have not made any use of the essay(s) of any other student(s) either past or present; 6. I have not submitted for assessment work previously submitted for any other course, degree or qualification; 7. I have not incorporated any work from or used the help of any external professional agencies other than extracts from attributed sources; 8. I have acknowledged in appropriate places any help that I have received from others (e.g. fellow students, teachers in schools, external sources); 9. I have complied with any other plagiarism criteria specified in the course and Programme handbooks; 10. I understand that any false claim for any of the above will mean that the relevant piece of work will be penalised in accordance with the University regulations

I understand that any false claim for this work will be penalised in accordance with the University regulations.

Course Name [Course Code]

Assignment Title Office Use

Matric Number Name Signature

s0000001 Last, First











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