Title: Very preliminary synoptic evaluation of the ECMWF Nature Run at NASA GSFC Oreste Reale
1(Very) preliminary synoptic evaluation of the
ECMWF Nature Run at NASA GSFCOreste Reale
- The African Monsoon Region and the Tropical
Atlantic - Period May August 1 degree fields
2The African Easterly Jet (AEJ)
- Traditional ECMWF AEJ depition the AEJ appears
at higher elevation and is slightly more to the
north with respect to climatology and analyses,
as already pointed out for the operational model
(e.g. Tompkins et al., 2005). - Intensity (11m/s) compares well with observed
climatology (e.g Burpee 1972 and operational
analyses for the period) - Realistic clear separation between AEJ and
low-level Harmatthan flow - Realistically well-defined low level westerly
flow - Moderate horizontal cyclonic shear on the
southern flank of the AEJ, increasing towards the
end of the analyzed period
3The AEJ and the African Monsoon
- July and August means show a northward
displacement of the AEJ, an intensifcation of the
Harmatthan flow and of the low-level monsoonal
flow. - Realistically well-defined low level westerly
monsoonal flow in agreement with obs (e.g. Asnani
2005) - Realistically intense horizontal cyclonic shear
on the southern flank of the AEJ in July and Aug - Tropical Easterly Jet at 200-150 hPa is perhaps
stronger than climatology, thus creating
higher-than-observed vertical easterly shear,
which appears to inhibit the early development of
AEWs attempting to become vortices
4AEJ (cont.)
The AEJ has a realistic maximum of 11 m/s at 600
hPa but wind speed are too low at 750 and 700
hPa consistently with the altitude bias.
Meridional shear of zonal wind is realistic and
supportive of barotropic instability.
5African Easterly Waves (AEWs)
AEWs in July/Aug show a realistic propagation
speed of about 6-9 deg/day Realistic change in
wave speed and structure at transition (about
15W) Realistic amplitudes and scales Zonal wind
over the continent subject to strong (perhaps
excessive?) diurnal cycle
6Tropical Easterly Jet (TEJ)
The TEJ (200-150hPa) displays a perplexingly
strong diurnal cycle over land but also over
ocean. It also appear to produce a
stronger-than-observed vertical easterly shear
which may inhibit the early stages of development.
7Example of nondev. AEW due to Easterly Shear
In the early stages, 850 hPa vort. increases and
vort max becomes aligned with 650hPa circulation
center. Eventually upper-level easterly shear
suppresses development.
8Example of nondev. AEW due to Easterly Shear
(cont.)
The potentially favorable situation induced by a
vertically aligned structure between 800 and 500
hPa at 12-14N is counteracted by easterly
vertical shear of the order of 20 m/s.
9Hurricane-like (HL) vortices
Only two relatively strong HL vortices are
observed until Aug 31st. (slp mins of about
970 hPa and 975 hPa in the 1deg res. ).
10HL vortices horizontal structure
The 1 degree fields do not allow a full
evaluation of HL vortices. Pressure center and
low-level wind are realistic, but no evidence of
bands is seen, neither in the low-level
vorticity or in the specific humidity fields.
Full-resolution fields need to be analyzed.
11HL vortices vertical structure
Vertical structure of a HL vortex shows, even at
the degraded resolution of 1 deg, a distinct
eye-like feature and a very prominent warm core.
12Preliminary concluding remarks
- A preliminary synoptic assessment of the NR over
the AM region and the tropical Atlantic shows an
overall realistic African Monsoon, AEJ and wave
activity - However, only 2 systems appear to have acquired a
full hurricane-like development up to Aug 31st - More evaluations need to be done and the entire
season has to be investigated prior to any
conclusive statement on the NR representiveness
of the Atlantic tropical cyclone activity - Full-resolution fields need to be analyzed to
assess the realism of the HL vortices structure
13IN PROGRESS and FUTURE WORK
- Investigate the entire African Atlantic Season
and establish realism of AEW evolutions, perform
statistics of developing versus non-developing
systems, intensity/track of developing systems,
ET transitions. - Investigate Indian Ocean and Asian Monsoon with
emphasis on the Somali Jet, monsoon onset and
breaks - Investigate easterly waves on a planetary scale
assessing scales of motion, development
statistics, interaction with baroclinic systems,
transitions - Investigate mid-latititude activity, jet stream
structure and maintenance, cyclogenesis and
cyclolysis, perform cyclone development and scale
diagnostics