Transcript Observations of the African Easterly Jet and the West

AMMA-UK WP3 – Convection
and dynamics
Doug Parker
Institute for Atmospheric Science
School of Earth and Environment
University of Leeds
29 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.
Moist convection in the south, dry convection in the north
(the Sahara): a ‘natural laboratory’ for tropical continental
convection.
African
Easterly
Jet (AEJ)
600 hPa
Monsoon winds
Water vapour 17/6/97
Deep
convection
Shallow cumulus
Mixed layer
1. The analysis of the African Easterly Jet is good
Sahara
ITCZ
ECMWF analyses (Adrian Tompkins; in
Thorncroft et al, BAMS 2003):
2. The forecast has systematic error
Courtesy Tompkins, ECMWF.
700 hPa zonal winds, averaged over August 2003
Systematic error! We need to represent the physics better.
3. Significnt errors in
ECMWF PBL fields
compared to observations
Potential
temperature
Equivalent
potential
temperature
(Aida Diongue; in
Thorncroft et al., BAMS 03)
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
Surface temperature (1200 UTC) and boundary
layer TKE in the afternoon (around 1500 UTC)
Chris Taylor, CEH Wallingford
WAM dynamics


By day, the boundary layer ‘maps’ onto
soil moisture
By night, airflow responds to pressure
gradients
WP3 Objectives
Convection-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 error
3. Significnt errors in ECMWF PBL fields
compared to observations
4. 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