Modulation of Precipitation over West Africa by Equatorial Waves
Andreas Schlüter
Karlsruhe Institute for Technology, Karlsruhe, Germany
Thursday, Apr 26, 2018, 11:00 am
DSRC Room 1D403
Abstract
Equatorial waves often couple with deep convection and so modulate rainfall on the synoptic to subseasonal timescale throughout the tropics. Despite the importance of rainfall variability for vulnerable societies in tropical Africa, the relative influence of equatorial waves for this region is largely unknown. Here, we present the first systematic comparison of the impact of six wave types on precipitation over West Africa during the transition and full monsoon seasons, using two satellite products and a dense rain gauge network. Composites of rainfall anomalies generally reveal the theoretical wave patterns, but some deviations exist, which might be related to the West African Monsoon and tropical-extratropical interactions. African Easterly Waves (AEWs) and Kelvin waves dominate the 3-hourly to daily timescale and explain 10-30% locally. On longer timescales (7--20d), only the MJO and equatorial Rossby (ER) waves remain as modulating factors and explain about up to one third of rainfall variability.
Favorable conditions for organization of convection prevail in Kelvin waves, African Easterly Waves, and the MJO. In contrast, equatorial Rossby waves and mixed Rossby-gravity waves tend to trigger large-scale rainfall by dynamic lifting and large scale moistening. Finally, we will discuss a new statistical method for the prediction of African rainfall that uses spatio-temporal correlations of rainfall as well as the phasing and intensity of equatorial waves. Applied to northern tropical Africa, the new statistical model successfully forecasts precipitation probabilities and outperforms simple climatological as well as NWP forecasts. We believe that this method can be also applied to other tropical regions where convectively coupled equatorial waves modulate precipitation, and in particular for tropical countries with limited computational power.
(NOTE: This is a joint seminar with Michael Maier-Gerber)
You must provide an accepted form of identification at the Visitor Center to obtain a vistor badge. Security personnel also inspect vehicles prior to entrance of the site. Please allow extra time for these procedures.
After receiving a badge, you must arrive at the DSRC Lobby at least 5 minutes before the seminar starts to meet your security escort. If you arrive after that time, you will not be allowed entry.
Foreign Nationals: Please email the seminar contact at least 48 hours prior to the seminar to provide additional information required for security purposes.
Seminar Contact: Shannon.Kelly@noaa.gov