Studies of African wave distrubances with the GISS GCM

Journal Article · Tue Feb 01 04:00:00 EST 1994 · Journal of Climate; (United States)

DOI:https://doi.org/10.1175/1520-0442(1994)007<0261:SOAWDW>2.0.CO;2· OSTI ID:7067323

Druyan, L M; Hall, T M ^[1]

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1. NASA/Goddard Institute for Space Studies, NY (United States)

Simulations made with the general circulation model of the NASA/Goddard Institute for Space Studies (GISS GCM) run at 4[degrees] latitude by 5[degrees] longitude horizontal resolution are analyzed to determine the model's representation of African wave disturbances. Waves detected in the model's lower troposphere over northern Africa during the summer monsoon season exhibit realistic wavelengths of about 2200 km. However, power spectra of the meridional wind shown that the waves propagate westward too slowly, with periods of 5-10 days, about twice the observed values. This sluggishness is most pronounced during August, consistent with simulated 600-mb zonal winds that are only about half the observed speeds of the midtropospheric jet. The modeled wave amplitudes are strongest over West Africa during the first half of the summer but decrease dramatically by September, contrary to observational evidence. Maximum amplitudes occur at realistic latitudes, 12[degrees]-20[degrees]N, but not as observed near the Atlantic coast. Spectral analyses suggest some wave modulation of precipitation in the 5-8-day band, and compositing shows that precipitation is slightly enhanced east of the wave through, coincident with southerly winds. Extrema of low-level convergence west of the wave troughs, coinciding with northerly winds, were not preferred areas for simulated precipitation, probably because of the drying effect of this advection, as waves were generally north of the humid zone. The documentation of African wave disturbances in the GISS GCM is a first step toward considering wave influences in future GCM studies of Sahel drought. 36 refs., 14 figs.

• DOE Contract Number: FG02-92ER61477
• OSTI ID: 7067323
• Journal Information: Journal of Climate; (United States), Journal Name: Journal of Climate; (United States) Vol. 7:2; ISSN JLCLEL; ISSN 0894-8755
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
540110*
AFRICA
ATMOSPHERIC CIRCULATION
DAILY VARIATIONS
GENERAL CIRCULATION MODELS
MATHEMATICAL MODELS
VARIATIONS