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Published September 2013 | metadata_only
Journal Article

A decadal microwave record of tropical air temperature from AMSU-A/aqua observations


Atmospheric temperature is one of the most important climate variables. This observational study presents detailed descriptions of the temperature variability imprinted in the 9-year brightness temperature data acquired by the Advanced Microwave Sounding Unit-Instrument A (AMSU-A) aboard Aqua since September 2002 over tropical oceans. A non-linear, adaptive method called the Ensemble Joint Multiple Extraction has been employed to extract the principal modes of variability in the AMSU-A/Aqua data. The semi-annual, annual, quasi-biennial oscillation (QBO) modes and QBO–annual beat in the troposphere and the stratosphere have been successfully recovered. The modulation by the El Niño/Southern oscillation (ENSO) in the troposphere was found and correlates well with the Multivariate ENSO Index. The long-term variations during 2002–2011 reveal a cooling trend (−0.5 K/decade at 10 hPa) in the tropical stratosphere; the trend below the tropical tropopause is not statistically significant due to the length of our data. A new tropospheric near-annual mode (period ~1.6 years) was also revealed in the troposphere, whose existence was confirmed using National Centers for Environmental Prediction Reanalysis air temperature data. The near-annual mode in the troposphere is found to prevail in the eastern Pacific region and is coherent with a near-annual mode in the observed sea surface temperature over the Warm Pool region that has previously been reported. It remains a challenge for climate models to simulate the trends and principal modes of natural variability reported in this work.

Additional Information

© 2013 Springer-Verlag Berlin Heidelberg. Received: 6 June 2012; Accepted: 4 February 2013; Published online: 27 February 2013. We thank Dr. Dong L. Wu for critical comments and two anonymous referees for constructive criticisms that improved this paper. YS was supported by Overseas Research Fellowship of the Faculty of Science and Department of Physics, The University of Hong Kong. The extraction of the AMSU-A/Aqua data from the Atmospheric InfraRed Spectrometer (AIRS)/AMSU-A data archive was supported by a research grant administered by Dr. Ramesh Kakar, EOS Aqua Programme Scientist at NASA Headquarter and the Keck Institute for Space Studies at California Institute of Technology. We also thank Dr. Thomas Hearty for proofreading our paper and sharing his results on AIRS data. The TMI SST data were downloaded from ftp://ssmi.com/tmi/. The standardized zonal winds at 30 and 50 hPa (u30hPa and u50hPa) were downloaded from http://www.cpc.ncep.noaa.gov/data/indices/. The MEI index for ENSO was downloaded from http://www.esrl.noaa.gov/psd/enso/mei/. YLY designed the approach; HHA provided the monthly-averaged AMSU-A/Aqua data; TYH and ZS provided the DMP package; ZS and YS developed the EJME package; YS performed the time series decomposition; KFL, YLY, and YS interpreted the results and wrote most of the manuscript.

Additional details

August 22, 2023
August 22, 2023