On the impact of dropsondes on the ECMWF Integrated Forecasting System model (CY47R1) analysis of convection during the OTREC (Organization of Tropical East Pacific Convection) field campaign

Abstract

Abstract. The Organization of Tropical East Pacific Convection (OTREC) field campaign, conducted August through October 2019, focuses on studying convection in the eastern Pacific and the Caribbean. An unprecedented number of dropsondes were deployed (648) during 22 missions to study the region of strong sea surface temperature (SST) gradients in the eastern Pacific region, the region just off the coast of Columbia, and in the uniform SST region in the southwestern Caribbean. The dropsondes were assimilated in the European Centre for Medium-Range Weather Forecasts (ECMWF) model. This study quantifies departures, observed minus the model value of a variable, in dropsonde denial experiments and studies time series of convective variables, saturation fraction which measures moisture and instability index and deep convective inhibition which quantify atmospheric stability and boundary layer stability to convection, respectively. Departures are small whether dropsondes are assimilated or not, except in a special case of developing convection and organization prior to Tropical Storm Ivo where wind departures are significantly larger when dropsondes are not assimilated. Departures are larger in cloudy regions compared to cloud-free regions when comparing a vertically integrated departure with a cloudiness estimation. Abovementioned variables are all well represented by the model when compared to observations, with some systematic deviations in and above the boundary layer. Time series of these variables show artificial convective activity in the model, in the eastern Pacific region off the coast of Costa Rica, which we hypothesize occurs due to the overestimation of moisture content in that region.