MSU as a four channel radiometer provided layer average brightness temperatures for four respective atmospheric layers. Channels 2 and 4 correspond to the temperature in the middle troposphere (TMT) and the lower stratosphere (TLS), respectively. Since 1998 AMSU samples the atmosphere using 20 spectral channels, with channels 5 and 9 closely matching MSU's channels 2 and 4, respectively, ensuring the continuation of the temperature time series (Christy et al. 2003). In parallel, MSU data have been processed through December 2004. AMSU data showed error characteristics indistinguishable from the earlier MSU products justifying the generation of a homogenous MSU/AMSU time series. The bias between AMSU9 and MSU4 was found to be about 0.3 K, which is a value within the range of biases determined amongst the MSUs themselves (Christy et al. 2003). Daily gridpoint (2.5° x 2.5° bins) noise estimates for TLS are < 0.2 K in the tropics, increasing to 0.3-0.4 K (0.5-0.6 K) in the Northern (Southern) Hemisphere mid-latitudes (http://ghrc.nsstc.nasa.gov/uso/readme/msulimb93.html#1). We used version 5.1 of MSU data produced by UAH. Data were available at http://vortex.nsstc.uah.edu/data/msu for December 1978-December 2006. We used version 2.1 of MSU data produced by RSS and sponsored by the NOAA Climate and Global Change Program. Data were available at www.remss.com for November 1978-December 2006. Monthly-mean brightness temperature anomalies are provided by UAH and RSS on a 2.5° x 2.5° latitude/longitude grid between ±82.5° together with 20 year monthly means over 1979-1998.
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