AMMA-UK WP3 – Convection and dynamics

Doug ParkerInstitute for Atmospheric ScienceSchool of Earth and Environment

University of Leeds29 November 2004

WP3 Objectives

To explain the basic dynamics and transport properties of the WAM system, including the diurnal cycle of the boundary layer control on the monsoon, and the response to shallow and deep cumulus convection.

Water vapour 17/6/97

Moist convection in the south, dry convection in the north (the Sahara): a ‘natural laboratory’ for tropical continental convection.

Monsoon winds

African Easterly Jet (AEJ) 600 hPa

Shallow cumulus

Mixed layer

Deep convection

1. The analysis of the African Easterly Jet is good

ECMWF analyses (Adrian Tompkins; in Thorncroft et al, BAMS 2003):

Sahara ITCZ

Courtesy Tompkins, ECMWF.

700 hPa zonal winds, averaged over August 2003

Systematic error! We need to represent the physics better.

2. The forecast has systematic error

3. Significnt errors in ECMWF PBL fields compared to observations

(Aida Diongue; in

Thorncroft et al., BAMS 03)

Potential temperature

Equivalent potential temperature

There is cool, humid air too far north.

Surface fluxes?Advective fluxes?Column radiation?

4. The monsoon flow is active at night and in the morning.

The observed monsoon (v-wind) is much more irregular.

Recent rainfall

Chris Taylor, CEH Wallingford

Surface temperature (1200 UTC) and boundary layer TKE in the afternoon (around 1500 UTC)

WAM dynamics

By day, the boundary layer ‘maps’ onto soil moisture

By night, airflow responds to pressure gradients

WP3 ObjectivesConvection-soil moisture-

diurnal WP3.1 To develop validated model case

studies of the diurnal cycle of convection in the continental WAM, and over anomalies of soil moisture (with WP1; using OWP1, OWP3 and OWP4 data).

WP3.2 To use case studies to quantify the response of the WAM dynamics to Mesoscale Convective Systems (MCSs) (using OWP1,3,4).

Mixing ratio – an atmospheric tracer showing nocturnal circulations

WP3 Objectives: Transport WP3.3 To quantify the transport properties

of dry and moist convective circulations, on the mesoscale and the continental scale, through model case studies and through use of chemical tracers that act as markers of source regions and of air mass ages (with WP4). Within this, to model mixing in the monsoon layer and its implication for the monsoon fluxes (using OWP1,3,4 data).

C. M. Taylor et al, QJRMS, 2005

WP3 Objectives: synoptic

WP3.4 To develop synoptic cases studies of AEW structure both north and south of the AEJ, and explore the interaction of these AEWs with soil moisture patterns (with WP1; using OWP1,3,4 data).

WP3.5 To describe the evolution of the SAL on synoptic and diurnal timescales.

Flight patterns

Stacked N-S legs in association with MCSs

Early morning / late evening Long straight legs in boundary

layer

Summary of ‘soundbites’

1. The analysis of the African Easterly Jet is good

2. The forecast has systematic error3. Significnt errors in ECMWF PBL

fields compared to observations4. The monsoon flow is active at

night and in the morning

African Monsoon Multidisciplinary Analyses

Afrikanske Monsun: Multidisiplinære Analyser

Afrikaanse Moesson Multidisciplinaire Analyse

Analisi Multidisciplinare per il Monsone Africano

Afrikanischer Monsun: Multidisziplinäre Analysen Analisis Multidiciplinar de los Monzones Africanos

Analyses Multidisciplinaires de la Mousson Africaine