Branch Seminar Series: Karen Mohr

Increasing the predictability of weather and short term climate phenomena is a key objective of operational forecasters. The work of my students and I in investigating the initiation/development of convective systems and their spatial-temporal variability is intended to improve the predictability of precipitation in West Africa. Because surface observing systems in this region are limited, microwave remote sensing from space and cloud-resolving numerical simulation are useful in providing insights into the characteristics of West African convective systems and the environments in which they form. Using TRMM Microwave Imager products, we have characterized the frequency, distribution, sizes, and intensities of West African convective systems since 1998. Along with gridded reanalysis, surface observations, and MODIS products, we have been able to link convective system characteristics to monsoon circulation features and trends in surface precipitation and streamflow. We have found that the variability of convective system characteristics is much greater regionally and intraseasonally than interannually. We conducted numerical studies using the Goddard Cumulus Ensemble/Parameterization for Land-Atmosphere-Cloud Exchange (GCE-PLACE) a coupled cloud-resolving/land surface process model. In our simulations, the strength of the monsoon moisture flux was the most important factor in determining fair or convective weather in each zone. However, the local land/atmosphere interaction influenced the timing, precipitation efficiency, and size of convective systems. We have detected statistically significant declines in observed daily precipitation and streamflow in the Guinea Coast region that we hypothesize is linked to trends in warming SSTs and decreasing monsoon moisture flux. Our work implies that a less favorable environment for the development of large convective systems may be emerging.