# Presentation: 051917

## Validation of OH and HO2 from MLS using balloon and ground-based observations 

**T. Canty****1****, H. M. Pickett****1****, R. J. Salawitch****1****, B. J. Drouin****1****, K. W. Jucks****2****, **
**R.P. Cageao****1****, S. Sander****1****, L. J. Kovalenko****1****, K. Minschwaner****3****, **
**G.E. Nedoluha****4****, N. J. Livesey****1****, W.G. Read****1****, **
**J. W. Waters****1****, and W. A. Traub****1**
- 1Jet Propulsion Laboratory, Caltech, Pasadena CA
- 2Harvard-Smithsonian Center for Astrophysics, Cambridge MA
- 3New Mexico Inst. of Mining &Technology, Socorro, NM
- 4Naval Research Laboratory, Washington, DC
- Tim.Canty@jpl.nasa.gov

**Validation of OH and HO****2**** from MLS using balloon and ground-based observations**** **

## Sept 23, 2004

**Ft Sumner,NM (34.5oN, 104oW)**
**BOH: OH Profile; OH Column ******** balloon**
**FIRS-2:OH,HO****2****,O****3****,H****2****O,N****2****O Profiles;**
**Columns ******** balloon**

**Table Mtn., CA (34.4****o****N, 117.7****oW)**
**FTUVS: OH Total Column**

**Socorro, NM (34oN, 107oW)**
**PEPSIOS: OH Total Column**

- Aura overpass of Ft. Sumner, NM on Sept 23, 2004 at 13:34 LST provided an opportunity to validate Microwave Limb Sounder (MLS) observations of HOx (OH+HO2)

## Observations and Model

_**Photochemical Steady State Model**_
- 	• Constrained by MLS observations of O3,H2O, Cly, NOy, N2O, and temp.
- 	• JPL 2002 kinetics
-  	• Reproduces solar variability, improved	Lyman-

_**Balloon Observations**_
**Balloon OH (BOH):** Limb viewing thermal emission instrument similar to THz module on MLS, OH only
**Far Infrared Spectrometer (FIRS-2):** thermal emission far-infrared Fourier transform spectrometer

_**Satellite**_
**Microwave Limb Sounder (MLS): **Heterodyne detection of OH thermal emission near 2.5 THz (119 **m)

## Profiles

**Model constrained by:**
-  MLS observations(grey shaded region)
-  FIRS-2 observations (dashed line)
- Measured profiles (25-40 km) agree
- within a standard deviation of:
- 	20% for OH
- 	18% for HO2
- Differences between observations/model:
-  	< 25% for OH
- 	< 17% for HO2*
-    * Pickett et al, *GRL*, submitted, 2005

- MLS 15 day zonal mean(24oN-44oN)

- BOH
- FIRS-2

## Column Observations

_**Tropospheric OH**_
- Contribution of tropospheric OH to the total column is based on Wennberg et al., GRL, 26, 1999.  Temporal variation based on Hanisco et al., JGR, 107, 2002.

_**Ground-based**_
**Fourier-Transform Ultraviolet Spectrometer (FTUVS): **Compares doppler-shifted East/West solar limb spectra
**Poly Etalon Pressure-Scanned Interferometric Optical Spectrometer (PEPSIOS): **Differential absorption measurement using Fabry-Perot interferometers** **

## Total Column

- Balloon and satellite columns
- augmented by model calculations.
- For high sun conditions, model higher
- than FTUVS, lower than PEPSIOS,
- similar to results reported by
- Canty et al., 2000, Mills et al., 2002

-  Anomalous “Dip” near noon is not reproduced by the model
-  Is the dip in HOx caused by by changes in water and/or solar irradiance?

## OH Chemistry

- H2O + O(1D)  2OH
- OH  [H2OO(1D)]1/2

**No anomalous signal from ground based ultraviolet radiometer observations at 305 and 320 nm from Socorro, NM.**
**Dip most likely caused by chemical processes**

- OH is primarily dependant upon H2O and J(O3)

## Changes in H2O

- Changes in H2O

- Water Vapor Millimeter-wave Spectrometer (WVMS)
- observations from Table Mtn., CA:
-    • indicate decrease in H2O at time of “dip”
-    • improved agreement between measured/modeled
-        OH profiles
-    • slightly better agreement between model OH
-        column and observations

## Seasonal OH

-  Model constrained by MLS observations on both days.
-  Model shows good agreement with observations near equinox
-  Noontime dip present in both days

## Seasonal OH

-  MLS OH profiles very similar on both days
-  Oscillation in MLS HO2, present on both days, may be a
-      retrieval artifact

## Seasonal OH

-  Model consistently higher than observations near solstice for
-      high sun conditions
-  Good agreement between FTUVS/MLS on June 15, 2004

## December OH

** ****FTUVS time series from Dec 3 to Dec 23 indicates deceasing OH column abundances**
** ****MLS OH largely unchanged over this period**

## December OH

**k****OH+O**** : Smith and Stewart****, **
**J. Chem. Soc. Faraday.Trans. 1994**

- • Change in O+OH kinetics gives
-     excellent agreement with MLS OH
-  Accounts for ~ 50% of difference between
-    model and FTUVS on Dec 23.
-  Much worse agreement between model and
-     FTUVS on Dec 03

## Conclusions

-  Good agreement between MLS, BOH, and FIRS-2 OH and
-      MLS and FIRS-2 HO2 between 25-40 km.*
-  H2O constraints from WVMS only partially explain noon time changes
-      in OH column for Sept 23, 2004
-  Changes in O+OH kinetics, that yield excellent agreement between model
-      and MLS OH, do not explain differences between model and FTUVS
-  MLS OH provides important constraints on our understanding of HOx
-      chemistry
-        *See Pickett et al*., GRL* 2005 (soon to be published) for more info

## “HOx Dilemma”

- HOx Dilemma:  Model overpredicts OH at
- Secondary peak (70km) and underpredicts OH
- at primary peak (40km) (*Conway et al., GRL,* 27, 2000)

- Previous studies modified the rates of O+OH,
- O+HO2, and/or OH+HO2 to bring measured
- and modeled mesospheric OH in agreement
- (*Summers et al., Science *277, 1997)*.*
- These changes increased the discrepancy in the
- stratosphere
- MLS observations of OH do not support these
- attempts to rectify model/measurement
- discrepancies.