Microwave Sounding Unit Temperature Anomalies
Since 1978 Micowave Sounding Units (MSU) measure radiation emitted by the earth's atmosphere from NOAA polar orbiting satellites. The different channels of the MSU measure different frequencies of radiation proportional to the temperature of broad vertical layers of the atmosphere. Channel 2 mainly measures tropospheric temperatures, while Channel 4 measures temperatures in the lower stratosphere. The analysis of the satellite temperature record represented here begins in 1979.
Tropospheric and lower stratospheric temperature data are collected by NOAA's TIROS-N polar-orbiting satellites and adjusted for time-dependent biases by the Global Hydrology and Climate Center at the University of Alabama in Huntsville (UAH). An independent analysis is also performed by Remote Sensing Systems (RSS) and a third analysis has been preformed by Dr. Qiang Fu of the University of Washington (UW) (Fu et al. 2004).
Fu et al. (2004) developed a method for quantifying the stratospheric contribution to the satellite record of tropospheric temperatures and applied an adjustment to the UAH and RSS temperature record that attempts to remove the satellite contribution (cooling influence) from the middle troposphere record. This method results in trends that are larger than those from the respective source.
This adjustment to both the RSS and UAH datasets is accomplished by deriving separate weighting coefficients for the MSU T2 and T4 channels over the tropics (30N to 30S), Northern and Southern hemispheres, and for the global mean by fitting radiosonde troposphere anomalies to radiosonde-simulated T2 and T4 anomalies over the period from 1958-2004 as
T850-300 = a0 + a2*T2 + a4*T4
where T850-300 is the radiosonde 850-300 hPa layer; T2 and T4 are the radiosonde simulated MSU brightness temperature anomalies; and a0, a2, and a4 are the coefficients derived from this linear regression.
Analysis can be found in NCDC's monthly Upper Air State of the Climate Report and the Bulletin of American Meteorology Society's Annual State of the Climate Report.
Note: Beginning in December 2010, all lower troposphere, middle troposphere, and lower stratosphere satellite data are reported here with respect to the 1981–2010 base period. Prior to December 2010, data were reported with respect to the 1979–1998 base period. Remote Sensing Systems continues to provide data to NCDC with respect to the 1979–1998 base period; however, NCDC readjusts the data to the 1981–2010 base period so that the satellite measurements are comparable.