Atmospheric Temperature Climate Data Records from Satellite Microwave Sounders - Satellite-based Applications on Climate Change - page 105

8.1 Introduction

Accurate determination of the atmospheric temperature variability and trends is an
important component in global change monitoring and research. The global atmo-
spheric temperature trend is an important indicator of whether the Earth is warming
or cooling. Additionally, knowledge of the atmospheric temperature trends at both
global and regional scales is crucial for validating consistencies of the simulated
atmospheric and surface changes in climate model simulations. For instance, moist
adiabatic theory predicts that the tropical troposphere warms faster than the surface,
which has been seen in most climate model simulations (Santer et al. 2005 ).
However, such a relationship needs to be verified by observations. Observational
verifications of climate model simulations affect scientific views on the reliability
of climate model projections of future climate changes, which in turn are
foundations for making policy decisions on prevention, mitigation, and adaptation
strategies for global change.
Development of climate data record (CDR) is desirable for reliably detecting
atmospheric temperature trends. A CDR is defined as “a time series of measurements
of sufficient length, consistency, and continuity to determine climate variability and
change” (NRC 2004 ). In this regard, the long-term observations from the microwave
sounders including microwave sounding unit (MSU) and advanced microwave
sounding unit-A (AMSU-A) onboard NOAA, NASA, and MetOp-A polar-orbiting
satellites provide unique opportunities for an atmospheric temperature CDR devel-
opment. The MSU and AMSU-A are cross-scanning instruments which make res-
pectively 11 and 30 Earth observations during each scan. The MSU observations
covered the period from 1979 to 2006, with four channels to measure the temperature
profiles from the surface to the lower stratosphere. As its successor, the AMSU-A
is a 15-channel instrument making temperature profile observations from the surface
to the upper stratosphere. The AMSU-A observations cover the period from 1998
to the present and onward into the future. The MSU/AMSU instruments were
designed primarily for weather monitoring; however, because of their long-term
continuity, global coverage, insensitivity to cloud effects, and frequency stability,
their observations have been widely used for atmospheric temperature variability and
trend investigations (Spencer and Christy 1992a , b ; Spencer et al. 2006 ;Trenberth
and Hurrell 1997 ; Hurrell and Trenberth 1997 , 1998 ; Hurrell et al. 2000 ; Christy et al.
1998 , 2000 , 2003 ; Prabhakara and Iacovazzi 1999 ; Prabhakara et al. 2000 ;Wentz
and Schabel 1998 ; Mears et al. 2003 ; Mears and Wentz 2005 , 2009a , b ; Vinnikov
and Grody 2003 ; Grody et al. 2004 ;Vinnikovetal. 2006 ;Fuetal. 2004 ;Fuand
Johanson 2004 , 2005 ; Johanson and Fu 2006 ; Zou et al. 2006 , 2009 ; Zou and Wang
2010 , 2011 ). The importance of the MSU/AMSU observations for climate change
detection and its related studies has been well reviewed in the US Climate Change
Science Program Synthesis and Assessment report (Karl et al. 2006 ) and the fourth
Intergovernmental Panel on Climate Change report (Solomon et al. 2007 ).