Assimilating Aircraft Humidity in the U.S. Navy's Global Data Assimilation System

Over 100 U.S. commercial aircraft are now including humidity in automated meteorological reports distributed as MDCRS data. These data are measured by the WVSS-II sensor and have been shown by previous studies to be of high quality. Currently, radiosonde data are the only source of in-situ humidity profiles in the U.S. Navy's data assimilation system, so the addition of MDCRS humidity profiles would not only increase the number of profiles overall, but would also provide profiles at 0600 and 1800 UTC, when few radiosonde launches are available. This paper reports on results from testing that was performed at the Naval Research Laboratory in preparation for assimilating these observations operationally at Fleet Numerical Meteorology and Oceanography Center.

Given that preliminary testing of MDCRS humidity was promising, a full data assimilation test is being performed for the period 30 March to 30 June 2013 using NAVGEM, the U.S. Navy's operational global data assimilation and modeling system. NAVDAS-AR, the 4DVAR data assimilation system that is part of NAVGEM, is able to take advantage of off-time observations as it assimilates data throughout the six-hour data assimilation window at the actual time of the observation. In addition, NAVGEM has the ability to compute observation impacts based on the adjoint of the modeling and data assimilation systems. Previous results show that humidity plays a large role in the observation impacts. Results will be presented in terms of comparisons of MDCRS humidity observations with nearby radiosonde data and with model analysis and forecast values, comparisons of forecasts made with and without MDCRS humidity, and observation impacts.