Comparing upper tropospheric and lower stratospheric temperatures: Microwave sounding unit, radiosonde, COSPAR International Reference Atmosphere, and National Center for Environmental Prediction National Center for Atmospheric Research reanalysis monthly mean climatologies

Climate-modeling groups are having to assess their models' temperatures at high, thinly observed altitudes in order to investigate near-tropopause forcings with confidence. To support such analyses, the microwave sounding unit (MSU), GFDL/Oort radiosonde, COSPAR International Reference Atmosphere (CIRA), and new 13-year National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis Project climatologies are intercompared herein in terms of their monthly mean microwave brightness temperatures T-b. In the lower stratosphere these climatologies agree extremely well. Small differences between NCEP/NCAR and MSU T-b centered at about 80 mbar amount to less than or equal to 2 K year round across the tropics and less than or equal to 5 K in southern winter polar latitudes. Artificial land-ocean outlines less than or equal to 2 K do appear in maps of the NCEP/NCAR lower stratospheric T-b between 30 degrees S and 30 degrees N. This NCEP/NCAR land-ocean T-b distinction may be due to sparseness of inputed radiosonde data at lower stratospheric heights not compensated for by satellite retrievals in the NCEP/NCAR assimilation process. In the upper troposphere, good agreement again occurs between the GFDL radiosonde, the CIRA, and the NCEP/NCAR reanalysis T-b. However, the experimental MSU channel 3R climatology has markedly cooler upper tropospheric T-b. Coolness peaks at over 6 K across low latitudes and diminishes to a few kelvins at polar latitudes with little seasonal dependence. The cool bias of the MSU channel 3R is likely due to a combination of channel 3 receiver drift and limb-darkening problems. Latitudinal correction terms are suggested for this experimental, but valuable, MSU product based on comparisons with calculated NCEP/NCAR reanalysis T-b.