Evaluation of SSMIS Upper Atmosphere Sounding Channels for High-Altitude Data Assimilation

Abstract

Upper atmosphere sounding (UAS) channels of the Special Sensor Microwave Imager/Sounder (SSMIS) were assimilated using a high-altitude version of the Navy Global Environmental Model (NAVGEM) in order to investigate their potential for operational forecasting from the surface to the mesospause. UAS radiances were assimilated into NAVGEM using the new Community Radiative Transfer Model (CRTM) that accounts for Zeeman line splitting by geomagnetic fields. UAS radiance data from April 2010 to March 2011 are shown to be in good agreement with coincident temperature measurements from the Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) instrument that were used to simulate UAS brightness temperatures. Four NAVGEM experiments were performed during July 2010 that assimilated (i) no mesospheric observations, (ii) UAS data only, (iii) SABER and Microwave Limb Sounder (MLS) mesospheric temperatures only, and (iv) SABER, MLS, and UAS data. Zonal mean temperatures and observation 2 forecast differences for the UAS-only and SABER1MLS experiments are similar throughout most of the mesosphere, and show large improvements over the experiment assimilating no mesospheric observations, proving that assimilation of UAS radiances can provide a reliable large-scale constraint throughout the mesosphere for operational, high-altitude analysis. This is confirmed by comparison of solar migrating tides and the quasi-two-day wave in the mesospheric analyses. The UAS-only experiment produces realistic tidal and two-day wave amplitudes in the summer mesosphere in agreement with the experiments assimilating MLS and SABER observations, whereas the experiment with no mesospheric observations produces excessively strong mesospheric winds and two-day wave amplitudes.

Comparison of co‐located independent ground‐based middle atmospheric wind and temperature measurements with numerical weather prediction models

“…Between 10 and 0.1 hPa, comparative spectral analyses confirm the lack of variability on shorter time scales (up to 20 days and in the order of~10 dB at 5 day period) that is neither present in ECMWF and MERRA products nor in the free-running MPI-ESM-LR climate model. These results are in line with a recent study by Hoppel et al [2013], who showed that assimilation of microwave imager/sounder data could provide reliable large-scale constraints throughout the mesosphere for operational high-altitude analysis.…”

“…The MLT is a dynamic medium with variability over time scales ranging from minutes to days. Both the mean state and the variability within the MLT are subject to inaccuracies both in current operational analyses and reanalyses [Rienecker et al, 2011;Hoppel et al, 2013]. troposphere and lower stratosphere (i.e., below~35 km) because their weighting function peaks are generally in those regions [Hoppel et al, 2013].…”

“…Both the mean state and the variability within the MLT are subject to inaccuracies both in current operational analyses and reanalyses [Rienecker et al, 2011;Hoppel et al, 2013]. troposphere and lower stratosphere (i.e., below~35 km) because their weighting function peaks are generally in those regions [Hoppel et al, 2013]. There are no direct routinely operational meteorological wind measurements presently available above~30 km where few radiosondes reach; thus, winds are derived from thermal wind balance and wind data assimilated at lower levels.…”

“…Assimilation of temperatures in the MA into current operational models is still developing for a number of reasons [Hoppel et al, 2013]: (i) satellite observations with weighting functions that peak in the mesosphere are typically not provided in real time as most of these observations come from research instruments, (ii) biases in the assimilation of satellite radiance observations [Derber and Wu, 1998], and (iii) data assimilation systems are affected by the different biases originating from the combination of multiple data sources or by limitations of the assimilating model [Dee, 2005;Polavarapu et al, 2005].The assimilation of these data in reanalyses up to an~50 km altitude further influences upper regions through model calculations [Sakazaki et al, 2012].…”

Zeeman effect in atmospheric O<sub>2</sub> measured by ground-based microwave radiometry

“…These measurements were used to validate a fast model developed from the radiative transfer model of Rosenkranz and Staelin (1988). Moreover, the measurements were also used together with data from the Microwave Limb Sounder (MLS) on board the Aura spacecraft for assimilation in a numerical weather prediction (NWP) model (Hoppel et al, 2013). Schwartz et al (2006) also reported a comparison of another radiative transfer model with measurements of the 118 GHz oxygen line from MLS.…”