Intersatellite Differences of HIRS Longwave Channels Between NOAA-14 and NOAA-15 and Between NOAA-17 and METOP-A

Intersatellite differences of the High-Resolution Infrared Radiation Sounder (HIRS) longwave channels (channels 1-12) between National Oceanic and Atmospheric Administration 14 (NOAA-14) and NOAA-15 and between NOAA-17 and METOP-A are examined. Two sets of colocated data are incorporated in the examination. One data set is obtained during periods when equator crossing times of two satellites are very close to each other, and the data set is referred to as global simultaneous nadir overpass observation (SNO). The other data set is based on multiyear polar SNOs. The examination shows that intersatellite differences (ISDs) of temperature-sounding channels from lower stratosphere to lower troposphere, i.e., channels 3-7, are correlated with their corresponding lapse rate factors. Many of the channels also vary with respect to channel brightness temperatures; however, for the upper tropospheric temperature channel (channel 4), the patterns of ISDs from low latitudes and high latitudes are very different due to the fact that the latitudinal variation of brightness temperature does not necessarily follow the latitudinal variation of the temperature lapse rate. The differences between observations in low latitudes and high latitudes form “fork” patterns in scatter plots of ISDs with respect to brightness temperatures. A comparison of ISDs derived from short-term global SNOs and those derived from multiyear polar SNOs reveals the advantage and the limitation of the two data sets. The multiyear polar SNO generally provides larger observation ranges of brightness temperatures in channels 1-4. The global SNO extends the brightness temperature observations to the warm sides for channels 5-12 and captures the occurrences of larger ISDs for most longwave channels.