What we’ve covered since the midterm

Nigam Wind: global systems; general circulation of the atmosphere: single cell model; three cell model; global pattern of winds and pressure systems at the surface and aloft

Chp. 10

Ruiz-Barradas

Air masses and fronts different type of air masses and associated weather; weather fronts; structure, weather and development of fronts

Chp. 11

Zeng Formation of the jet stream; formation of the polar front jet formation of the tropical jet

Chp. 12

Zeng Polar front theory-Bergen School cyclogenesis; developing cyclones and jet stream; upper level waves and surface storms; barotropic atmosphere; baroclinic atmosphere; vorticity; Rossby waves

Chp. 12

Carton global seasonal surface wind patterns; SST; ocean currents; upwelling; ocean water masses

Carton Atmosphere/ocean Interactions: ENSO, Indian dipole, Atlantic variability

Kalnay Weather Forecasting Chp 13

C. Kieu Hurricanes Chp. 15

C. Kieu Thunderstorms and tornadoes; atmospheric conditions that produce thunderstorms and tornadoes; air-mass thunderstorms; severe thunderstorms; lightning; tornadoes;

Chp 14

Carton Global Climate Climate Change Chp.16/17

Chapt 11: air masses

invasion of cold, moist mP air into the mid-Atlantic and New England states. (Green-shaded area represents light rain and drizzle; pink-shaded region represents freezing rain and sleet; white-shaded area is experiencing snow.)

Typical winter conditions

Cold-occluded front

The faster-moving cold front (a) catches up to the slower-moving warm front (b) and forces it to rise off the ground (c). (Green-shaded area in (d) represents precipitation.)

Conditions this morning

Chapt 12: Cyclogenisis

• Topic: Jet Streaks and Storms– Entrance and exit regions associated with

divergence and convergence, right exit allows divergence.

• Conveyor Belt Model: air constantly glides through storm; warm, cold, and dry conveyor belt

Chapt 13: Weather forecasting

Weather Forecasting Methods

• NWP– Types of Forecasts

• Now cast <6 hrs• Short range 12-65 hrs• Medium range 3-8.5 days• Long Range >8.5 days

– Accuracy and Skill• 12-24 hrs most accurate, 2-5 days good• Skill = more accurate than a forecast utilizing persistence

of climatology

• Other Forecasting Techniques– Persistence– Trend– Analogue– Statistical– Weather type– climatological

Chapt. 14: thunderstorms & tornadoes

Simplified model depicting the life cycle of an ordinary cell thunderstorm

Thunderstorms• Multi-cell Thunderstorms

– Thunderstorms that contain a number of convection cells, each in a different stage of development, moderate to strong wind shear; tilt, over shooting top

– Gust Front: leading edge of the cold air out-flowing air; shelf cloud, roll cloud, outflow boundary

– Micro-bursts: localized downdraft that hits the ground and spreads horizontally in a radial burst of wind; wind shear, virga

Lightning

When the negative charge near the bottom of thecloud becomes large enough to overcome the air’s resistance, a flow of electrons — the stepped leader — rushes toward the earth. (b) As the electrons approach the ground, a region of positive charge moves up into the air through any conducting object, such as trees, buildings, and even humans. (c) When the downward flow of electrons meets the upward surge of positive charge, astrong electric current — a bright return stroke — carries positive charge upward into the cloud.

Tornadoes

• Tornado Occurrence– US experiences most tornadoes– Tornado Alley (warm, humid surface; cold dry air aloft)– Highest spring, lowest winter

• Tornado winds– Measurement based upon damage after storm or Doppler radar– For southwest approaching storms, winds strongest in the northeast

of the storm, 220 kts maximum– Multi-vortex tornados

• Enhanced Fujita Scale

average annual number of tornadoes observed in each state over average annual number of tornadoes per 10,000 square miles in each state

classic tornadic supercell thunderstorm showing updrafts and downdrafts, along with surface air flowing counterclockwise and in toward the tornado. The flanking line is a line of cumulus clouds that form as surface air is lifted into the storm along thegust front.

Chapt 15: hurricanes

EyeEye wallSpiral rain bandAnticyclonic divergence

Intense storm of tropical origin with winds greater than 64kts; typhoon, cyclone, tropical cyclone

• light wind• 26.5°C sea

surface temperatures (June-November)

• Surface converge trigger (tropical wave)

• Coriolis effect: 5-20º latitude

Required environmental conditions

Tropical DisturbanceTropical Depression (22-34kts)Tropical Storm (35-64kts)Hurricane (> 65kts)

Chapt. 17: global climate

Chapt. 17 Climate var. & change

Possible Causes of Climate variability

• Plate Tectonics and Mountain Building– Theory of plate tectonics– Ridge and subduction– Mountain interaction with airflow and ocean

currents

• Changes in ocean circulation

• Variations in Solar Output• Variation on the Earth’s Orbit

– Milankovitch Theory• Eccentricity• Precession• Obliquity

Global Warming

• Radiative Forcing– Any change in average net radiation that occurs

at the top of the atmosphere which is due to some change in the climate system is called radiative forcing.

• Climate Models and Recent Temperature– It is difficult to unequivocally prove greenhouse

forcing due to the noise in the system.– Model well sulfate aerosols, greenhouse gases,

change in solar radiation

IPCC forecasts