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Volume 9, issue 4 | Copyright

Special issue: Limb observations of the middle atmosphere by space- and airborne...

Atmos. Meas. Tech., 9, 1685-1699, 2016
https://doi.org/10.5194/amt-9-1685-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 15 Apr 2016

Research article | 15 Apr 2016

Interannual variability of temperature in the UTLS region over Ganges–Brahmaputra–Meghna river basin based on COSMIC GNSS RO data

Khandu1, Joseph L. Awange1,2,3, and Ehsan Forootan4,5 Khandu et al.
  • 1Department of Spatial Sciences, Curtin University, Perth, Australia
  • 2Geodetic Institute, Karlsruhe University of Technology (KIT), Karlsruhe, Germany
  • 3Department of Geophysics, Kyoto University, Kyoto, Japan
  • 4Institute of Geodesy and Geoinformation, Bonn University, Bonn, Germany
  • 5School of Earth and Ocean Sciences, Cardiff University, Cardiff, UK

Abstract. Poor reliability of radiosonde records across South Asia imposes serious challenges in understanding the structure of upper-tropospheric and lower-stratospheric (UTLS) region. The Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission launched in April 2006 has overcome many observational limitations inherent in conventional atmospheric sounding instruments. This study examines the interannual variability of UTLS temperature over the Ganges–Brahmaputra–Meghna (GBM) river basin in South Asia using monthly averaged COSMIC radio occultation (RO) data, together with two global reanalyses. Comparisons between August 2006 and December 2013 indicate that MERRA (Modern-Era Retrospective Analysis for Research Application) and ERA-Interim (European Centre for Medium-Range Weather Forecasts reanalysis) are warmer than COSMIC RO data by 2°C between 200 and 50hPa levels. These warm biases with respect to COSMIC RO data are found to be consistent over time. The UTLS temperature show considerable interannual variability from 2006 to 2013 in addition to warming (cooling) trends in the troposphere (stratosphere). The cold (warm) anomalies in the upper troposphere (tropopause region) are found to be associated with warm ENSO (El Niño–Southern Oscillation) phase, while quasi-biennial oscillation (QBO) is negatively (positively) correlated with temperature anomalies at 70hPa (50hPa) level. PCA (principal component analysis) decomposition of tropopause temperatures and heights over the basin indicate that ENSO accounts for 73% of the interannual (non-seasonal) variability with a correlation of 0.77 with Niño3.4 index whereas the QBO explains about 10% of the variability. The largest tropopause anomaly associated with ENSO occurs during the winter, when ENSO reaches its peak. The tropopause temperature (height) increased (decreased) by about 1.5°C (300m) during the last major El Niño event of 2009/2010. In general, we find decreasing (increasing) trend in tropopause temperature (height) between 2006 and 2013.

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Monthly accumulated COSMIC RO data is used to examine the interannual variability of UTLS temperature over the Ganges-Brahmaputra-Meghna river basin from 2006 to 2013. PCA analysis of tropopause temperatures and heights indicates that ENSO accounts for 73% of the interannual variability with a correlation of 0.77 with Niño3.4 index whereas the QBO explains about 10% of the variability. The tropopause temperature (height) increased (decreased) by about 1.5oC (300 m) during the 2009/2010 El Niño.
Monthly accumulated COSMIC RO data is used to examine the interannual variability of UTLS...
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