Idealized simulation of hydrodynamic characteristics of Lake Victoria that potentially modulate regional climate

摘要

This study explores, through three-dimensional (3D)-lake model simulations, the unique thermodynamic and hydrodynamic characteristics of Lake Victoria that can potentially modulate the lake catchment climate. The simulations are mostly based on idealized forcing due to lack of sufficient observed data. A suite of simulations with an elliptic (oval) geometry and prescribed wind speed (surface wind stress), lake-atmosphere temperature difference and vertical temperature profile are performed. The time evolutions of lake temperature as well as the currents (circulation characteristics) at different depths and/or points are analysed to understand the lake's response to certain aspects of surface forcing conditions. Similarities and differences between the features simulated in a typical tropical lake (Lake Victoria) and typical mid-latitude lake based on the effects of the Coriolis force are also examined. Our simulations revealed a number of unique features in the time and space evolutions and profiles of the lake temperature. Considered at different points on the lake surface, the temperature of both runs with or without effect of Coriolis force equilibrates after almost the same time (between 30 and 40 clays). However, there is a conspicuous difference in the vertical temperature profiles of the two runs (cases). For example, the MIDLAT run is characterized by a 'dome-shaped' profile in the bottom layers (40 m and deeper) after 30 days of model integration, in contrast to the VICTORIA case which is nearly isothermal over the full water column. Perhaps one of the most significant outcomes of the present study is that the two-gyre circulation pattern shown in the VICTORIA case after 30 days of model integration is also present in the simulations with observed lake bathymetry. Even more significant is that our results with a fully coupled regional climate-3D lake hydrodynamics simulate more realistic evaporation/evapotranspiration and precipitation over the lake surface and immediate environs.