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

Abstract

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 Tb. In the lower stratosphere these climatologies agree extremely well. Small differences between NCEP/NCAR and MSU Tb centered at about 80 mbar amount to ≤2 K year round across the tropics and ≤5 K in southern winter polar latitudes. Artificial land‐ocean outlines ≤2 K do appear in maps of the NCEP/NCAR lower stratospheric Tb between 30°S and 30°N. This NCEP/NCAR land‐ocean Tb 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 Tb. However, the experimental MSU channel 3R climatology has markedly cooler upper tropospheric Tb. 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 Tb.