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Modulation of Precipitation over West Africa by Equatorial Waves

Schlueter, Andreas; Fink, Andreas H.; Knippertz, Peter; Vogel, Peter

Abstract:
Equatorial waves often couple with deep convection and this way modulate rainfall on the synoptic to subseasonal timescale throughout the tropics. Until now, however, no comparative study of the influence of all the different wave types on precipitation has been performed, specifically for West Africa.

To fill this gap, the following wave types are analyzed for the extended West African monsoon seasons April to October: (1) the Madden-Julian Oscillation (MJO), (2) Kelvin waves, (3) equatorial Rossby waves, (4) eastward-propagating inertio-gravity waves, (5) mixed Rossby-gravity waves and (6) tropical disturbances/African Easterly Waves. The different wave types are filtered in the wavenumber-frequency domain using outgoing longwave radiation. Eight different wave phases are defined from a phase diagram calculated from the time-derivative of the filtered wave signals following Yasunaga and Mapes (2012). Subsequently, composites of dynamical and thermodynamical fields for each wave phase of the different wave types are produced using the ERA Interim reanalysis from the European Centre for Medium-Range Weather Forecasts. Finally, the influence of equatorial waves on West African precipitation is quantified using three rainfall datasets: (1) the gauge-adjusted three-hourly combined microwave-infrared estimates from the Tropical Rainfall Measuring Mission (TRMM) 3B42 V.7 for the period 1998–2016, (2) the Karlsruhe African Surface Station Database, which provides daily data from an extended rain gauge network for a period from 1979 to 2013, and (3) the gauge-calibrated, infrared based Climate Hazards Group InfraRed Precipitation with Station data V.2 (CHIRP/S) precipitation estimation, also for the period from 1979 to 2013.

All aforementioned wave types significantly influence West African rainfall and dynamics. ... mehr



Zugehörige Institution(en) am KIT Institut für Meteorologie und Klimaforschung - Forschungsbereich Troposphäre (IMK-TRO)
Publikationstyp Vortrag
Jahr 2018
Sprache Englisch
Identifikator KITopen-ID: 1000085048
HGF-Programm 12.01.02 (POF III, LK 01)
Veranstaltung American Meteorological Society, 33rd Conference on Hurricanes and Tropical Meteorology, Ponte Vedra, FL, USA, 16 - 20 April 2018
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