ATM 521 Tropical Meteorology FALL 2009

ATM 521 Tropical Meteorology SPRING 2008

Instructor: Chris ThorncroftRoom: ES226Phone: 518 442 4555E-mail: chris@atmos.albany.edu

Aim of Course:To describe and understand the nature of tropical weather systems and their role in the

tropical climate, including emphasis on the interactions between dynamics and convection.

Course Assessment:1. Homework 15%2. Class exam on Wednesday 14th October 30% 3. Final exam on Tuesday 15th Dec. 8.00-10.00am 55%

Text Books:There is no recommended text book for this course.

ATM 521 Tropical Meteorology SPRING 2008

Lecture Plan:

1. Introduction 2. Tropical Convection (including MCSs)3. Large-scale Tropical Circulations4. Kelvin waves5. Easterly waves6. Tropical Cyclones

Dry spells Flooding: Ghana 07 Flooding: New Orleans 05

1. INTRODUCTION

Where are the tropics and what makes them special?Zonal and time mean circulationsAsymmetric circulations

2. TROPICAL CONVECTION

Conditional Instability, CAPE, tephigramsVertical profiles of conserved variables

MESOSCALE CONVECTIVE SYSTEMS

Structure, propagation and longevity issues will be discussed as well as their impact on larger scales.

See Houze, R. A., Jr., 2004: Mesocale convective systems Rev. Geophys., 42, 10.1029/2004RG000150, 43 pp.

TRMM based MCS climatology over Africa and tropical Atlantic for June-July-August

Rainfall Stratiform Rain Fraction

Percentage of MCSs with significant ice scattering

Average Lightning flash density

Schumacher and Houze (2006) QJRMS :Less stratiform rain over sub-Saharan Africa than Atlanticbut, Stratiform rain increases in monsoon season compared to pre-monsoon season due to (i) reduced upper-level shear?, (ii) reduced impact of dry SAL?, (iii) other?

MESOSCALE CONVECTIVE SYSTEMS

Cold Tongue

AEJ

SAL

ITCZ

Heat Low

Key features of the West African Monsoon Climate System during Boreal summer

3 LARGE-SCALE TROPICAL CIRCULATIONS

Observations and theory of monsoonsTheories for large-scale motionEmphasis given to West African Monsoon

4. KELVIN WAVES

Kelvin waves are the dominant synoptic weather system in the equatorial Africa sector in Spring but they also exist in other basins (e.g. Pacific, Amazon).

We will discuss their structure and theories for their existence and growth including how they interact with MCSs.

cat3

convergence

H L

convection

H L

Solution of the shallow water model

Evolution of Kelvin waveNegative phase

L H

OLR (W/m2)Shading: min convection max convection

Wind at 850 hPa (m/s)Vectors, significant at the T-test 99% level

Surface Pressure (Pa) Contours dashed: low L continue: high H

Evolution of Kelvin waveInitiation phase

L H

OLR (W/m2)Shading: min convection max convection

Wind at 850 hPa (m/s)Vectors, significant at the T-test 99% level

Surface Pressure (Pa) Contours dashed: low L continue: high H

Evolution of Kelvin waveActive phase

L

H

OLR (W/m2)Shading: min convection max convection

Wind at 850 hPa (m/s)Vectors, significant at the T-test 99% level

Surface Pressure (Pa) Contours dashed: low L continue: high H

Evolution of Kelvin wave Dissipation phase

H

OLR (W/m2)Shading: min convection max convection

Wind at 850 hPa (m/s)Vectors, significant at the T-test 99% level

Surface Pressure (Pa) Contours dashed: low L continue: high H

MCSs embedded in Kelvin wave

envelops

Brightness Temperature (K) Resolution spatial : 0.5° temporal : 3 hours

5. EASTERLY WAVES

Easterly waves are the dominant synoptic weather system in the Africa-Atlantic sector but they also exist in other basins (e.g. Pacific)

We will discuss their structure and theories for their existence and growth including how they interact with MCSs (see next slides).

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

Diagnostics for highlighting multi-scale aspects of AEWs

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

315K Potential Vorticity (Coloured contours every 0.1PVU greater than 0.1 PVU) with 700hPa trough lines and easterly jet axes from the GFS analysis (1 degree resolution), overlaid on METEOSAT-7 IR imagery.

6. TROPICAL CYCLONES

Observations and theory of tropical cyclones including issues that relate to genesis, structure and track

Key weather systems in the West African and Tropical Atlantic regions

An ideal region to study scale interactions including how they impact downstream tropical cyclogenesis

AEWs

MCSs

SAL

TC

6. TROPICAL CYCLONES

FINAL COMMENTS

The course is fundamentally about the interactions between dynamics and convection, combining observations, modeling and theory.

Ultimately a major motivation for research in this area is to improve our ability to predict tropical convection (over a range of space and timescales). This remains a major challenge and MUCH remains to be learned.

The above is a major motivation for the proposed Year Of Tropical Convection (YOTC) a WCRP/THORPEX supported virtual field campaign that began during 2008.

It is also a motivation for a joint AMMA-THORPEX Working Group that exists to evaluate and develop forecasting methods for the West African region.

More information about both these activities will be provided during the course.