Lower Stratospheric Temperatures from CHAMP RO Compared to MSU/AMSU Records: An Analysis of Error Sources

A comparison of lower stratospheric temperatures (TLS) from (Advanced) Microwave Sounding Unit (MSU/AMSU) records with CHAMP radio occultation (RO) data was performed for September 2001–December 2006. Synthetic TLS temperatures were calculated by applying global weighting functions to monthly RO temperature climatologies and alternatively by applying the RTTOV_8.5 radiative transfer model to the individual CHAMP RO profile data set. The results published by Steiner et al. (2007) showed very good agreement of CHAMP TLS anomalies with MSU records from the University of Alabama in Huntsville (UAH, USA) and from Remote Sensing Systems (RSS, USA) for intra-annual variability. Statistically significant trend differences of UAH and RSS with respect to CHAMP TLS anomalies were found in the tropics (–0.40 K/5 years to –0.42 K/5 years). In this context error sources regarding the retrieval of RO data, the building of climatologies, and the related synthetic MSU computation procedure were analyzed and found to be of minor importance. In the NH extratropics the TLS specific sampling error showed a significant negative trend which is projected globally but tropical trends are small. In total, the contribution of errors from RO was found to be about an order of magnitude smaller than the trend differences and thus insufficient to account for them, especially in the tropical region. Their resolution, currently pursued in a further study, requires either the presence of currently unresolved biases in the MSU records or additional, so far overlooked, sources of error in the RO TLS record. SAC-C, GRACE, and COSMIC TLS temperatures were found to closely match CHAMP temperatures. The results underpin that inter-comparison of independent estimates of the same variable from different instruments is beneficial for the detection of residual weaknesses in otherwise high quality climate records.

[1]  A. Löscher,et al.  Error Characteristics of Refractivity Profiles Retrieved from CHAMP Radio Occultation Data , 2006 .

[2]  Vicky Chu,et al.  FORMOSAT-3/COSMIC science mission update , 2005 .

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

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

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

[6]  Holly A. Titchner,et al.  Assessing Bias and Uncertainty in the HadAT-Adjusted Radiosonde Climate Record , 2008 .

[7]  Gottfried Kirchengast,et al.  Retrieval of temperature profiles from CHAMP for climate monitoring: intercomparison with Envisat MIPAS and GOMOS and different atmospheric analyses , 2007 .

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

[9]  John R. Lanzante,et al.  Temporal Homogenization of Monthly Radiosonde Temperature Data. Part I: Methodology , 2003 .

[10]  U. Foelsche,et al.  Tropical tropopause climatology as observed with radio occultation measurements from CHAMP compared to ECMWF and NCEP analyses , 2007 .

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

[12]  J. Christy,et al.  Correcting Temperature Data Sets , 2005, Science.

[13]  Grzegorz Michalak,et al.  GPS radio occultation with CHAMP and GRACE: A first look at a new and promising satellite configuration for global atmospheric sounding , 2005 .

[14]  Leopold Haimberger,et al.  Toward Elimination of the Warm Bias in Historic Radiosonde Temperature Records—Some New Results from a Comprehensive Intercomparison of Upper-Air Data , 2008 .

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

[16]  Christian Rocken,et al.  COSMIC System Description , 2000 .

[17]  C. Rocken,et al.  Climatologies Based on Radio Occultation Data from CHAMP and Formosat-3/COSMIC , 2009 .

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

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

[20]  Douglas W. Nychka,et al.  Statistical significance of trends and trend differences in layer-average atmospheric temperature time series , 2000 .

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

[22]  John R. Christy,et al.  Uncertainty in Signals of Large-Scale Climate Variations in Radiosonde and Satellite Upper-Air Temperature Datasets , 2004 .

[23]  C. Ao,et al.  Sensitivity of GPS occultation to the stratopause height , 2007 .

[24]  Leopold Haimberger,et al.  Homogenization of Radiosonde Temperature Time Series Using Innovation Statistics , 2007 .

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

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

[27]  Jens Wickert,et al.  Observing upper troposphere–lower stratosphere climate with radio occultation data from the CHAMP satellite , 2008 .

[28]  J. Dykema,et al.  Climate Benchmarking Using GNSS Occultation , 2006 .

[29]  S. Hassol,et al.  Temperature Trends in the Lower Atmosphere: Steps for Understanding and Reconciling Differences , 2006 .

[30]  John R. Christy,et al.  UNCERTAINTIES IN CLIMATE TRENDS Lessons from Upper-Air Temperature Records , 2005 .

[31]  Peter W. Thorne,et al.  Revisiting radiosonde upper air temperatures from 1958 to 2002 , 2005 .

[32]  Lennart Bengtsson,et al.  An observing system simulation experiment for climate monitoring with GNSS radio occultation data: Setup and test bed study , 2008 .

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

[34]  Jens Wickert,et al.  Assessing the climate monitoring utility of Radio Occultation data: from CHAMP to FORMOSAT-3/COSMIC. , 2009 .

[35]  Lippincott Williams Wilkins,et al.  Part I , 1997, Neurology.

[36]  J. Wickert,et al.  Pre-Operational Retrieval of Radio Occultation Based Climatologies , 2006 .

[37]  Gottfried Kirchengast,et al.  A multi-year comparison of lower stratospheric temperatures from CHAMP radio occultation data with MSU/AMSU records , 2007 .

[38]  Gottfried Kirchengast,et al.  Local time influence in single‐satellite radio occultation climatologies from Sun‐synchronous and non‐Sun‐synchronous satellites , 2007 .