# Presentation: 483896

## Validation of MLS OH measurements with FTUVS total OH column measurements at Table Mountain (TMF), California

- Shuhui Wang, Herbert M. Pickett, Thomas J. Pongetti, Changsub Shim, Qinbin Li, and Stanley P. Sander
*Jet Propulsion Laboratory, California Institute of Technology*
- Ross Cheung and Yuk L. Yung
*Division of Geological and Planetary Sciences, California Institute of Technology*
- Timothy Canty, Ross J. Salawitch
*Department of Atmospheric & Oceanic Science / Department of Chemistry & Biochemistry, University of Maryland, College Park*

**JPL**

**JPL**

## Introduction

**Introduction**

- TMF - Fourier Transform Ultra-Violet Spectrometer
- Total OH column abundance

- Aura – Microwave Limb Sounder
- Partial OH column

-  Earlier OH validation studies show good agreement between MLS and other observations/models in Sep.*[Pickett et al, 2006]*
-  This work is the first comparison of space- and ground-based OH measurements over seasonal / inter-annual time scale.
-  MLS measures OH down to ~ 21.5 hPa, which covers near 90% of the total OH abundance in the atmosphere.
-  To compare data from MLS and TMF, OH residual in the lower atmosphere is estimated with GEOS-Chem.

*[Cageao et al, 2001]*

## TMF OH column retrieval

- 8
- 6
- 4
- 2

- Removal of solar Fraunhofer lines by matching and ratioing E and W spectra
- Solar background correction by FFT smoothing
- Nano-window  fit for each OH line
- Weighted average OH abundance based on SNR *[Cheung et al, 2007]*

**TMF OH column retrieval**

- OH Abundance (1013)

- P1(1)
- P1(2)
- Q1(2)
- Q1(3)
- P1(3)

## OH residual in lower atmosphere

**OH residual in lower atmosphere**

- Estimation based on GEOS-Chem 2003 monthly mean OH profiles and OH diurnal variation from observations/model

*[Salawitch et al, 1994]*

- GEOS-Chem monthly mean results are compare with field observations and results from 1-D HOx model for four seasons.
- To justify the interpolation from monthly mean, a newer version GEOS-Chem with hourly time resolution is applied to calculated OH at satellite overpass time during selected months. The majority of the calculated results agree with the interpolated results within 30%.
- The uncertainty in this estimation contributes less than 4% to the total OH column.

## Overview of the measurements

**Overview of the measurements**

## Linear correlation of OH columns

**Linear correlation of OH columns**
**MLS + GEOS-Chem vs. TMF**

| Linear Fit |  | Slope | Intercept (1013) | R |
| --- | --- | --- | --- | --- |
| No error
Weighted | Fit through 0 | 1.0650.005 | 0 | 0.854 |
|  | Fit with unity slope | 1 | 0.40 0.03 | 0.854 |
|  | Standard fit | 0.673 0.029 | 2.20 0.16 | 0.854 |

| Linear Fit |  | Slope | Intercept (1013) | R |
| --- | --- | --- | --- | --- |
| No error
Weighted | Fit through 0 | 1.0650.005 | 0 | 0.854 |
|  | Fit with unity slope | 1 | 0.40 0.03 | 0.854 |
|  | Standard fit | 0.673 0.029 | 2.20 0.16 | 0.854 |
| Standard fit with y errors weighted |  | 0.686 0.019 | 2.09 0.10 | 0.850 |

## Linear correlation of OH columns

**Linear correlation of OH columns**
**MLS + GEOS-Chem vs. TMF**

| Linear Fit |  | Slope | Intercept (1013) | R |
| --- | --- | --- | --- | --- |
| No error
Weighted | Fit through 0 | 1.0650.005 | 0 | 0.854 |
|  | Fit with unity slope | 1 | 0.40 0.03 | 0.854 |
|  | Standard fit | 0.673 0.029 | 2.20 0.16 | 0.854 |
| Standard fit with y errors weighted |  | 0.686 0.019 | 2.09 0.10 | 0.850 |

## Linear correlation of OH columns

**Linear correlation of OH columns**
**MLS + GEOS-Chem vs. TMF**

| Linear Fit |  | Slope | Intercept (1013) | R |
| --- | --- | --- | --- | --- |
| No error
Weighted | Fit through 0 | 1.0650.005 | 0 | 0.854 |
|  | Fit with unity slope | 1 | 0.40 0.03 | 0.854 |
|  | Standard fit | 0.673 0.029 | 2.20 0.16 | 0.854 |
| Standard fit with y errors weighted |  | 0.686 0.019 | 2.09 0.10 | 0.850 |
| Orthogonal fit with x and y errors weighted |  | 0.835 0.185 | 1.308 0.003 | 0.855 |

## Seasonal histograms 

**Seasonal histograms **

## SZA histograms / T-tests 

**SZA histograms / T-tests **

## Summary

**Summary**

-  This is the first seasonal and inter-annual comparison of OH measurements from space and the ground-level.
-  In general, the total OH columns from MLS + GEOS-Chem and TMF agree, especially during high OH seasons (small SZAs). A linear correlation through zero shows a remarkable agreement within 6.5%.
-  Detailed statistical investigations, however, show differences during low OH seasons (large SZAs), suggesting a weaker seasonal variation in MLS measurements than TMF measurements and a possible offset.
-  The summer time data are too sparse, which may bias the linear fit. More data during summer will be available as the MLS reprocessing goes.
-  Further investigations, with focus on data at large SZAs, are required to understand the disagreement between these measurements.

## Acknowledgements

**Acknowledgements**

-  We appreciate the help from Alyn Lambert in the orthogonal linear fit with x and y errors.

* **Cageao, R.P., J.F. Blavier, J.P. McGuire, et al., High-resolution Fourier-transform ultraviolet-visible spectrometer for the measurement of atmospheric trace species: Application to OH, Appl. Opt., 40, 2024 – 2030*
* **Cheung, R., K.F. Li, S. Wang, et al., An improved method for retrieving hydroxyl radical (OH) abundances from ultraviolet spectra, to be submitted to Appl. Opt., 2007*
* **Pickett, H.M., B.J. Drouin, T. Canty, et al., Validation of Aura MLS HOx measurements with remote-sensing balloon instruments, Geophys. Res. Lett., 33, L01808, 2006*
* **Rohrer, F. and H. Berresheim, Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation. Nature, 442, doi:10.1038, 2006*
* **Salawitch, R.J., S.C. Wofsy, P.O. Wennberg, et al., The diurnal variation of hydrogen, nitrogen, and chlorine radicals: implications for the heterogeneous production of HNO2, Geophys. Res. Lett., 21(23), 2551 – 2554, 1994*
* **Wennberg, P.O., T.F. Hanisco, L. Jaegle, et al., Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere, Science, 279(49), dio:10.1126, 1998*

**References**