Model moist bias in the middle and upper troposphere during DEEPWAVE

Abstract

AbstractData from 279 dropsonde profiles collected during the Deep Propagating Gravity Wave Experiment (DEEPWAVE) over New Zealand between 4 June and 20 July 2014 were used to verify the relative humidity (RH) fields simulated by regional configurations of the UK Met Office Unified Model (MetUM) in the troposphere. Significant RH biases (predictions up to 28% too high) were found in the middle and upper troposphere during this period. This RH bias was found to be mainly caused by the errors in the simulated‐specific humidity. It is demonstrated here that evaporation from the lower boundary (mainly sea surface) is not a factor leading to the moist bias. A similar magnitude of moist bias was also found in the Global UM (the global configuration of the MetUM) and from a preliminary inspection is also very likely to occur in ERA‐interim and NCEP‐GFS reanalyses. This study suggests that the moist bias is very likely not a regional or a model specific issue.