The effects of orbital drift on spectral radiances from HIRS observations and GFDL climate model simulations

Title: The effects of orbital drift on spectral radiances from HIRS observations and GFDL climate model simulations.

Darren L. Jackson NOAA/ETL Boulder, CO Darren.Jackson@noaa.gov

Brian J. Soden NOAA/GFDL Princeton, NJ Brian.Soden@noaa.gov

Abstract: The 25-year HIRS data record (1979-2004) has become recognized in recent years as an important data set for examination of global climate change in temperature, water vapor and OLR. However, HIRS instruments reside on NOAA polar-orbiting satellites that are known to drift from their sun synchronous orbits such that local observations times can change by several hours over the lifetime of a satellite. This drift has its greatest impact on surface-sensing channels and adversely impacts the long-term time series for several HIRS channels. This study identifies the diurnal sampling bias on HIRS temperature (15 ìm), water vapor (6.7 ìm) and surface (11.1 ìm) channels and provides corrections to those channels affected by diurnal bias. HIRS radiances simulated from the GFDL climate model using a 3-hour time step to simulate the diurnal cycle were used to identify and correct the diurnal bias. The model diurnal cycle is validated with one year of geostationary data for surface (11.1 ìm) and water vapor (6.7 ìm) to verify the model diurnal cycle follows the observed climate. Identifying and removing the diurnal bias from the HIRS data will make these data more suitable for climate studies.

Poster presentation preferred