Calibration of temperature in the lower stratosphere from microwave measurements using COSMIC radio occultation data: Preliminary results

Accurate, consistent, and stable observations from different satellite missions are crucial for climate change detection. In this study, we use Global Positioning System (GPS) Radio Occultation (RO) data from the early phase of the FORMOSAT-3/Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) mission, which was successfully launched on 15 April 2006, to inter-calibrate Temperature in the Lower Stratosphere (TLS) taken from Advanced Microwave Sounding Unit (AMSU) microwave measurements from different satellites for potential improvements of stratospheric temperature trend analysis. With a limited number of COSMIC soundings in the early phase of the mission, these results are considered preliminary. In this study, we use COSMIC RO data to simulate microwave brightness temperatures, for comparison with AMSU Ch9 measurements (e.g., TLS) on board NOAA15, 16 and 18. Excellent correlation was found between synthetic COSMIC brightness temperatures (Tbs) and Tbs from NOAA15, NOAA16 and NOAA18, respectively. However, systematic differences on the order of 0.7 K to 2 K were found between COSMIC and AMSU observations over Antarctica. Our results demonstrate that synthetic COSMIC Tbs are very useful in identifying inter-satellite offsets among AMSU measurements from different satellites. To demonstrate the long-term stability of GPS RO data, we compare COSMIC dry temperature profiles to those from collocated CHAMP profiles, where CHAMP was launched in 2001. The fact that the CHAMP and COSMIC dry temperature difference between 500 hPa and 10 hPa ranges from -0.35 K (at 10 hPa) to 0.25 K (at 30 hPa) and their mean difference is about -0.034 K demonstrates the long-term stability of GPS RO signals. In order to demonstrate the potential usage of the GPS RO calibrated AMSU Tbs to inter-calibrate other overlapping AMSU Tbs, we examine the uncertainty of the calibration coefficients derived from AMSU-GPS RO pairs. We found the difference between COSMIC calibrated AMSU Tbs and those from CHAMP to be in the range of ±0.07 K with 0.1 K standard deviation. This demonstrates the robustness of the calibration

[1]  Ying-Hwa Kuo,et al.  Comparison of GPS radio occultation soundings with radiosondes , 2005 .

[2]  Rolf König,et al.  The Radio Occultation Experiment aboard CHAMP: Operational Data Analysis and Validation of Vertical Atmospheric Profiles , 2004 .

[3]  J. Angell,et al.  Variations and Trends in Tropospheric and Stratospheric Global Temperatures, 1958–87 , 1988 .

[4]  Steven Businger,et al.  GPS Sounding of the Atmosphere from Low Earth Orbit: Preliminary Results , 1996 .

[5]  Douglas Hunt,et al.  GPS profiling of the lower troposphere from space: Inversion and demodulation of the open‐loop radio occultation signals , 2006 .

[6]  John R. Christy,et al.  Error Estimates of Version 5.0 of MSU–AMSU Bulk Atmospheric Temperatures , 2003 .

[7]  Gottfried Kirchengast,et al.  Inversion, error analysis, and validation of GPS/MET occultation data , 1999 .

[8]  Benjamin M. Herman,et al.  Remotely Sensing the Earth’s Atmosphere Using the Global Positioning System (GPS)—The GPS/MET Data Analysis , 1999 .

[9]  J. Christy,et al.  Precision and Radiosonde Validation of Satellite Gridpoint Temperature Anomalies. Part I; MSU Channel 2. Pt. 1; MSU Channel 2 , 1992 .

[10]  P. Jones,et al.  Hemispheric and Large-Scale Surface Air Temperature Variations: An Extensive Revision and an Update to 2001. , 2003 .

[11]  Jens Wickert,et al.  Climatological validation of stratospheric temperatures in ECMWF operational analyses with CHAMP radio occultation data , 2005 .

[12]  Jens Wickert,et al.  Tropical tropopause parameters derived from GPS radio occultation measurements with CHAMP , 2004 .

[13]  Mitchell D. Goldberg,et al.  Temperature trends at the surface and in the troposphere , 2006 .

[14]  Ying-Hwa Kuo,et al.  A comparison of lower stratosphere temperature from microwave measurements with CHAMP GPS RO data , 2007 .

[15]  F. Wentz,et al.  The Effect of Diurnal Correction on Satellite-Derived Lower Tropospheric Temperature , 2005, Science.

[16]  S. Sherwood,et al.  Radiosonde Daytime Biases and Late-20th Century Warming , 2005, Science.

[17]  Anthony J. Mannucci,et al.  CHAMP and SAC-C atmospheric occultation results and intercomparisons , 2004 .

[18]  J. Schofield,et al.  Observing Earth's atmosphere with radio occultation measurements using the Global Positioning System , 1997 .

[19]  Roy W. Spencer,et al.  Precision and radiosonde validation of satellite gridpoint temperature anomalies , 1992 .

[20]  Thomas P. Yunck,et al.  A History of GPS Sounding , 2000 .

[21]  Changyong Cao,et al.  Recalibration of microwave sounding unit for climate studies using simultaneous nadir overpasses , 2006 .

[22]  X. Zou,et al.  Analysis and validation of GPS/MET data in the neutral atmosphere , 1997 .

[23]  John R. Christy,et al.  Analysis of the Merging Procedure for the MSU Daily Temperature Time Series , 1998 .

[24]  John R. Lanzante,et al.  Sensitivity of Tropospheric and Stratospheric Temperature Trends to Radiosonde Data Quality , 2000 .

[25]  T. V. Ommen,et al.  Observed climate variability and change , 2002 .

[26]  Mietek Jaroniec,et al.  Global Warming Trend of Mean Tropospheric Temperature Observed by Satellites , 2003 .

[27]  W. Collins,et al.  Amplification of Surface Temperature Trends and Variability in the Tropical Atmosphere , 2005, Science.

[28]  Q. Fu,et al.  Stratospheric Influences on MSU-Derived Tropospheric Temperature Trends: A Direct Error Analysis. , 2004 .

[29]  Matthias C. Schabel,et al.  A Reanalysis of the MSU Channel 2 Tropospheric Temperature Record , 2003 .

[30]  Douglas Hunt,et al.  Estimates of the precision of GPS radio occultations from the COSMIC/FORMOSAT‐3 mission , 2007 .

[31]  W. G. Melbourne,et al.  The application of spaceborne GPS to atmospheric limb sounding and global change monitoring , 1994 .

[32]  Martin Stendel,et al.  Validating the microwave sounding unit stratospheric record using GPS occultation , 2003 .

[33]  Estimation of Tropospheric Temperature Trends from MSU Channels 2 and 4 , 2006 .

[34]  John R. Christy,et al.  MSU Tropospheric Temperatures: Dataset Construction and Radiosonde Comparisons , 2000 .

[35]  Mitchell D. Goldberg,et al.  Calibration of multisatellite observations for climatic studies: Microwave Sounding Unit (MSU) , 2004 .

[36]  K. Hocke,et al.  Inversion of GPS meteorology data , 1997 .

[37]  Christian Rocken,et al.  Inversion and error estimation of GPS radio occultation Data , 2004 .

[38]  J. Christy,et al.  What may we conclude about global tropospheric temperature trends? , 2004 .