# Presentation: 677941

## Comparisons of Aura TES V004 temperature retrievals with sonde measurements

**Robert L. Herman****1****, ****Mark W. Shephard****2****, Karen E. Cady-Pereira****2****, Vivienne H. Payne****2****,**** **
**Brendan M. Fisher****1****, Susan S. Kulawik****1****, Annmarie Eldering****1****, Gregory B. Osterman****1****, Shepard A. Clough****3**
*1. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA, 91109, USA*
*2. Atmospheric and Environmental Research Inc., 131 Hartwell Ave., Lexington, MA, 02421-3626, USA*
*3. Clough Associates. 89 Hancock St. Lexington, MA, 02420, USA*

**Comparisons of Aura TES V004 temperature retrievals with sonde measurements**

_**TES Temperature Retrievals**_
**Updates to forward model and retrieval strategy in TES V004 improve agreement between TES temperature retrievals and radiosonde measurements.**
**What are the potential sources of the differences between TES and radiosondes?**
** ****TES Measurements: tenths of a K **(Shephard et al., 2008)
** ****Sonde Measurements**** **(most likely a small source)
**nighttime uncertainty of ~±0.2K (RS92)**
**daytime bias of ~(0.1 - 0.3) K (RS90) (**Luers, 1997)** **
** ****Forward model****: Spectroscopy, Land Surface emissivity, Cloud parameters**
**Sampling errors****: Coincidence and co-location of satellite/sonde observations leads to ~0.5 – 1 K uncertainty.**
** ****Retrieval Strategy**** ****(e.g. impact of water vapor on temperature)**

**TES Temperature Retrieval Strategy**
**TES uses an optimal estimation non-linear least squares retrieval **(Bowman et al., 2006, IEEE)
**Retrievals from passive TOA radiances are an ill-posed problem with a number of potential solutions**
** ****V003 (R10) used a simultaneous retrieval of TATM, H****2****O and O****3**
** ****CO****2**** v2 region (600-800 cm****-1****, TES 2B1 filter),**
** ****O****3**** region (950-1100 cm****-1****, TES 1A1 filter),**
** ****H****2****O**** region (1200-1600 cm****-1****, TES 2A1 filter).**
**Potentially has a number of advantages over a sequential retrieval:**
- Eliminates the need to account for interference between target species
- Obtains temperature information from the spectral information of all target species
** ****Increased number of solutions with increased number of retrieval parameters**
- Very sensitive to any inconsistencies in the measurements or forward model
- Inconsistencies: between bands, between species, within bands
** ****V004 (R11) uses a sequential retrieval: **
** ****Step 1: TATM retrieved using ****CO****2**** v2 region,**
** ****Step 2:  H****2****O and O****3**** jointly retrieved.**
**Sequential retrieval reduces the potential impact of systematic errors not adequately accounted for in the retrieval**
**Now an option due to improvements in 2B1 (CO****2**** v2 band) calibration and forward model **
** ****V004 significantly reduces the differences w.r.t. GMAO GEOS-5 (Shephard et al., 2008)**
-  The decrease in sensitivity accounts for <=0.5K of the improvement (Shephard et al., 2008)
** ****Radiance closure study showed reduced residuals in the CO****2**** v2 region**
** ****What else is new in V004:**
**TSUR initial guess refinement for daytime land when initial guess is too low.**
**Improved CO****2**** climatology based on 3D fields from PCTM model, scaled up by trend.**
***A priori *****constraint vector is based on interpolated 3D temperature fields from GMAO GEOS 5.1 (starting in October 2008 this has changed to GEOS 5.2).**
**Constraints changed from climatological to altitude-dependent Tikhonov constraints, as described in Kulawik et al., 2006, IEEE.**

**Forward Model Improvements Incorporated into V004**** **
**CO****2**
**Includes line mixing/coupling for all the CO****2**** bands (Niro et al., 2005)**
**Validation by AER using AIRS/IASI **
**Improved consistency between CO****2**** v****2**** (600-800 cm****-1****) and v****3**** (2200-2400 cm****-1****) **
**H****2****O**
** ****Included HITRAN updated H****2****O line width (Gordon et al., 2008) **
**Effect is of order of tenths of K in T****b**** in TES MWs (up to 0.5 K)**
** ****Investigating new H****2****O line strengths (from Coudert) using IASI**
**O****3**
**HITRAN 2004**** parameters are different than tes_v_1.3 (MIPAS)**
**Differences of order of 0.1K in T****b**** in TES O****3**** region**
**REDUCED THE TROPOSPHERIC BIAS (~200-400 hPa) BY ~0.5 K**

**New V004 TES / NCEP Radiosonde Comparisons**
**Sonde types include Vaisala RS80/RS90/RS92.  TES global surveys from 2004-2007 are matched with sonde profiles within 3 hr and 300 km except as described below.**
**Temporal Variability:**
**time difference of 3 hr vs 1 hr**
**changes bias near surface.**
**Spatial Variability: **
**distance of 300 km vs 200 km**
**has slight effect on rms and**
**on bias near surface.**
**Surface Type: **
**land vs ocean has an effect **
**on bias near surface**
**(land vs ocean emissivity)**
**Region:**
**midlat (30-60 N) **
**vs polar (60-90 N)**
**probably requires more **
**comparisons, but indicates**
**a warm TES bias in the **
**polar lower troposphere.**

**Previous V003 TES/ NCEP Radiosonde Comparisons**** **

**A global comparison with match-up criteria of 2 hr and 250 km for TES V003 and  Vaisala RS90/RS92 sondes yielded temperature biases of 1-2 K and temperature RMS of <4 K in the lower troposphere.  These results prompted improves to the TES forward model and retrieval strategy for V004 temperature.  **

**© 2008. All rights reserved.**

**ACKNOWLEDGMENTS**
**Many thanks to Pranjit Saha, Mariyetta Madatyan, and Hyejung Yun of the TES software team for developing the software tool to carry out sonde-TES matches and comparisons.  We acknowledge the NASA Aura Program for support.  Part of the research described here was was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.**

**Summary**
**New code to compare TES with sondes has been developed, and has been applied to matches between TES and NCEP sondes (RS80/RS90/RS92). **
**V004 sequential retrieval strategy improves TES/sonde temperature comparisons**
**Global TES/sonde statistics:**
**Bias < 1K is a significant improvement over V003 **(sometimes 1-1.5K near the surface)
**RMS ~1K in the stratosphere and UT but increases to ~2K in the LT.  ****RMS is probably elevated due to spatial and temporal variability, i.e., the sondes are not close enough in space or time to the TES retrieval.  **
**Near Future Plans**
**Reprocess more V004 TES data using the new retrieval strategy**
**Perform more TES/sonde comparisons**
**Determine whether the temperature RMS can be reduced through more stringent TES/sonde matching criteria.**
**Perform a radiance closure experiment on key TES/sonde matches.**