Mitigation of Sri Lanka Island effects in colombo sounding data and its impact on DYNAMO analyses

Abstract

During the Dynamics of the MJO (DYNAMO) field campaign in 2011, upper-air soundings were launched in Colombo, Sri Lanka, as part of the enhanced northern sounding array (NSA) of the experiment. The Colombo soundings were affected at low levels by the diurnal heating of this large island and by flow blocking caused by elevated terrain to the east of the Colombo site. Because of the large spacing between sounding sites, these small-scale island effects are aliased onto the larger scale impacting analyses and atmospheric budgets over the DYNAMO NSA. To mitigate these local island effects on the large-scale budgets, a procedure was designed that used low-level ECMWF-analyzed fields in Sri Lanka’s vicinity to estimate open-ocean conditions at Colombo’s location as if the island were not present. These “unperturbed” ECMWF fields at low-levels were then merged with the observed Colombo soundings. Results indicate a beneficial impact of using these adjusted fields on several aspects of the budget analyses.