Error Structure and Atmospheric Temperature Trends in Observations from the Microwave Sounding Unit

Abstract

The Microwave Sounding Unit (MSU) onboard the National Oceanic and Atmospheric Administration polar-orbiting satellites measures the atmospheric temperature from the surface to the lower stratosphere under all weather conditions, excluding precipitation. Although designed primarily for monitoring weather processes, the MSU observations have been extensively used for detecting climate trends, and calibration errors are a major source of uncertainty. To reduce this uncertainty, an intercalibration method based on the simultaneous nadir overpass (SNO) matchups for the MSU instruments on satellites NOAA-10, -11, -12, and -14 was developed. Due to orbital geometry, the SNO matchups are confined to the polar regions, where the brightness temperature range is slightly smaller than the global range. Nevertheless, the resulting calibration coefficients are applied globally to the entire life cycle of an MSU satellite.Such intercalibration reduces intersatellite biases by an order of magnitude compared to prelaunch calibration and, thus, results in well-merged time series for the MSU channels 2, 3, and 4, which respectively represent the deep layer temperature of the midtroposphere (T 2 ), tropopause (T 3 ), and lower stratosphere (T 4 ). Focusing on the global atmosphere over ocean surfaces, trends for the SNO-calibrated T 2 , T 3 , and T 4 are, respectively, 0.21 6 0.07, 0.08 6 0.08, and 20.38 6 0.27 K decade 21 from 1987 to 2006. These trends are independent of the number of limb-corrected footprints used in the dataset, and trend differences are marginal for varying bias correction techniques for merging the overlapping satellites on top of the SNO calibration.The spatial pattern of the trends reveals the tropical midtroposphere to have warmed at a rate of 0.28 6 0.19 K decade 21 , while the Arctic atmosphere warmed 2 to 3 times faster than the global average. The troposphere and lower stratosphere, however, cooled across the southern Indian and Atlantic Oceans adjacent to the Antarctic continent. To remove the stratospheric cooling effect in T 2 , channel trends from T 2 and T 3 (T 23 ) and T 2 and T 4 (T 24 ) were combined. The trend patterns for T 23 and T 24 are in close agreement, suggesting internal consistencies for the trend patterns of the three channels.

Radiative and Dynamical Influences on Polar Stratospheric Temperature Trends

“…S1 in the supplemental material). Trends from MERRA were also compared to the National Oceanic and Atmospheric Administration's Center for Satellite Applications and Research (STAR) Stratospheric Sounding Unit, version 2 (SSUv2; Zou et al 2014), and MSU T4 (Zou et al 2009) data at higher altitudes, discussed further below (see Fig. S1).…”

Stratospheric ozone change and related climate impacts over 1850–2100 as modelled by the ACCMIP ensemble

“…Figure 6 shows recent stratospheric temperature decadal trends in polar regions during springtime (March-April-May in the Arctic and October-NovemberDecember in the Antarctic). The figure compares temperature in the lower stratosphere (TLS) in the ACCMIP, CMIP5 and CCMVal2 models with observational estimates based on Microwave Sounding Unit (MSU) retrievals by the Remote Sensing Systems (RSS -version 3.3) (Mears et al, 2011), the Satellite Applications and Research (STAR -version 3.0) (Zou et al, 2006(Zou et al, , 2009, and the University of Alabama in Huntsville (UAH -version 5.4) (Christy et al, 2003) ( Fig. 6a-c).…”

Recent slowdown of tropical upper tropospheric warming associated with Pacific climate variability

“…An intercalibration method, based on simultaneous nadir overpass matchups, was applied to reduce biases in the intersatellite MSU instruments [Zou et al, 2006[Zou et al, , 2009. We used the temperatures of the troposphere and stratosphere corresponding to measurements from MSU channels 2 and 4 (T 2 and T 4 ) covering the vertical layers of 0-15 and 12-26 km (with their weighting functions peaking near 550 and 100 hPa), respectively [Zou and Li, 2014].…”