# Presentation: 890081

## HOCl from EOS MLS on Aura: version 1.5 and preliminary version 2 data comparisons with other measurements and modelsL. Froidevaux1, L.J. Kovalenko1, A. Lambert1, N. J. Livesey1, W. G. Read1,                      R.J. Salawitch1, R.A. Stachnik1, G.C. Toon1, J.W. Waters1, K.W. Jucks2        1Jet Propulsion Laboratory, California Institute of Technology        2 Harvard Smithsonian Center for Astrophysics

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## HOCl data from MLS

- ●  MLS measurement discontinuities affect HOCl
-     -  The 640 GHz radiometer bands 10 and 29                                                          	(mainly affecting ClO and HOCl retrievals, respectively)                                                                                           	were turned off for a while to better understand potential degradation issues
-               > off for 2006 April 8,9,10 and also for April 17 (19:52 UT) through May 17
-                no useful HOCl (or ClO) data for above periods [although L2 files exist]
-     -   These bands now seem likely to last for nominal mission lifetime (5 - 6 years)
-          and they have remained on since May 18, 2006.
- ●  MLS HOCl requires averaging (e.g. 10° zonal means for > 1 week) to get useful 	sensitivity (~ 10 pptv or less)
- ●  From last meeting: V1.5 MLS HOCl retrievals were not considered useful in the                           	lower stratosphere (pressure of ~20 hPa and larger)
-               -  but morphology in upper stratosphere seems reasonable, to first-order
-               -  lower priority product than others
- ●  Update given here for V2 results and expectations
-      	-  not many days have been reprocessed using V2.1 software

## •  HOCl global measurements from MIPAS (on ENVISAT) have recently been published [Von Clarmann et al., JGR, 2006]                                                                                 -  Difficult measurement in infrared emission, with contaminant species and “hard-to-see” spectrum – but reduced residuals when include HOCl in fits.                                                   -  MIPAS results are slightly larger than FIRS-2 measurements (older balloon data corrected for time difference and increase in chlorine)                                                                                                    -  MIPAS retrievals are significantly larger than MLS values, but qualitatively similar.  

- •  HOCl global measurements from MIPAS (on ENVISAT) have recently been published *[Von Clarmann et al., JGR, 2006]*                                                                                 -  Difficult measurement in infrared emission, with contaminant species and “hard-to-see” spectrum – but reduced residuals when include HOCl in fits.                                                   -  MIPAS results are slightly larger than FIRS-2 measurements (older balloon data corrected for time difference and increase in chlorine)                                                                                                    -  MIPAS retrievals are significantly larger than MLS values, but qualitatively similar.

-  MIPAS HOCl (2002 Sep./Oct.)         MLS (Sep. 2004)   [16-days]   MLS (Sep. 2005)

**DAY**

**NIGHT**

**DAY**

**DAY**

**NIGHT**

**NIGHT**

**DAY-NIGHT**

**DAY-NIGHT**

## MLS V2.1 versus MLS V1.5 data: HOCl 

-  Changes in HOCl are fairly systematic (but averaging of many profiles required)
-   Global average change shows a decrease by ~ 10 to 40% in the upper stratosphere
-   No significant improvements in the lower stratosphere (still see large oscillations in the profiles)

## MLS HOCl and balloon results 

- Results from balloon campaign data on HOCl for Sep. 2005 (Ft. Sumner)
-  MLS values for v2.1 should decrease roughly as shown on the left (10 deg. zonal means used for 16-day avg. in v1.5 data; crude adjustment shown for v2.1)
-   Day/night MLS differences are qualitatively similar to FIRS-2 results, but absolute values are lower for MLS (by ~ 30-50%), and in better agreement with SLS data

**PSS model (Kovalenko/Salawitch) constrained by MLS long-lived species**

- MkIV (dashed blue)                 is corrected (solid blue)                 for sunset to 1:30 p.m. diurnal change based on PSS model results

## •  HOCl photochemical equilibrium (simple model – for fun...)  

-  In daytime equilibrium, expect to see                                                                                    	[HOCl] (J1 + k2 [O])  = k1 [ClO] [HO2]
-        or    [HOCl] = k1 [ClO] [HO2] / (J1 + k2 [O])
-          where J1 = J(HOCl) ; photodissociation rate constant for HOCl  [s-1]
-          k’s are rate constants (formation and loss)
- -  We can estimate the daytime equilibrium abundance of HOCl if we have estimates
- for [ClO] , [HO2], [O], and the rate constant values (temperature-dependent) [ need T ]
-   As luck would have it... MLS measures ClO, HO2, and T                                                          (and even OH for small other loss term from OH + HOCl)                                                          and [O] can be obtained from equilibrium with ozone ( J2 [O3] = k4 [O][O2][M] )
- Use J1, J2 values from model values for daytime MLS solar zenith angle (Kovalenko/Salawitch) and k values from JPL recommendations                                                  (+ a few test cases discussed below for k1)

**MLS HOCl and balloon results: other (simple) model/data checks**** **

##    16-day HOCl averages (day and night) for MLS & SLIMCAT near Sep. 20, 2005      	solid: daytime    dashed: nighttime       black: MLS    orange: SLIMCAT 

-    16-day HOCl averages (day and night) for MLS & SLIMCAT near Sep. 20, 2005      	solid: daytime    dashed: nighttime**       black: MLS    ****orange: SLIMCAT**

**Equilibrium (daytime) model results for HOCl**
- - Main diffs. from SLIMCAT come from HO**2** (different than SLIMCAT), even if use day-night MLS HO**2**.

**-  SLIMCAT**                                       day, solid; night: dashed _[SLIMCAT values thanks to  I. MacKenzie,                       M. Chipperfield,                   R. Harwood  et al.]_

##  MkIV (sunset) (triangles)                        [older (but July archive) version of MkIV data shown here, lower values]

- 16-day zonal means (MLS V1.5)                                                             -  daytime (open circles)                            -  nighttime (closed circles)
-   **FIRS-2 balloon data                              day (open); night (closed) **
-  MkIV (sunset) (triangles)                        [older (but July archive) version of MkIV data shown here, lower values]
-   Equilibrium results: purple squares                                    >  thin:  k1 (ClO+HO2) [JPL, 2006]                      >  thick: faster k1 [JPL, 2000]                                   >  thickest: fastest k1 [Stimpfle et al., 1979]
**  ****PSS model (Kovalenko/Salawitch)                       for Sep. 20/05 (constrained by MLS long-lived species)**
** ****SLIMCAT**                                       day, solid; night: dashed
**  ****Orange boxes: Equilibrium model HOCl** **using SLIMCAT values for** ClO, HO2, O3, T  _**using equilibrium results seems OK**_

**Results:**                                                                                     > MLS V1.5 has oscillations for P of 10 hPa and larger;                   but has same general characteristics as FIRS-2                               - higher altitude peak for nighttime than daytime                    and lower night values than day.                                                    >  MLS values lower than FIRS-2 (by ~ 30 - 50%);                         MLS values (and SLS data, not shown here) agree better with slow (JPL 2006) k1, FIRS-2 (and MkIV) better with faster k1

## Summary and plans: MLS HOCl 

**Summary of validation results**
-       -  Can use MLS HOCl data (V1.5 and V2) for continued evaluations at pressures from
-           ~ 10 hPa to 2 hPa (revised vertical range)
-        -  MLS HOCl values are lower (by ~ 30-50%) than FIRS-2 data (and MIPAS data), but agree
-            better with SLS data for Sep. 2005 balloon campaign.
-        -  Sep. 2004 balloon campaign gives similar results (MLS versus FIRS-2); not updated here.
-        -  MLS day and night data (averages) show some similarities with FIRS-2  and models
-            > night profiles peak at higher altitude
-            > smaller daytime abundances than nighttime
-        -  Uncertainties in rate of formation for HOCl affect model results; the lower values (MLS, SLS)
-           agree better with lower (recommended) rate constant, the larger (FIRS-2) values agree better
-           with a higher rate constant – based on constrained simple daytime equilibrium model or
-           based on PSS model (from Salawitch/Kovalenko).
-      >  Main MLS issue: improve the lower stratospheric MLS HOCl data quality
-              -  However, this has lower priority than other potential improvements for MLS
-       >  Which HOCl rate of formation rate constant is correct (balloon data do not agree)?
-           -  Slower (recommended) k agrees better with SLS/MLS than with FIRS-2, MkIV (or MIPAS).
-            -  Sort out balloon differences (?)
**Validation paper?  **Maybe...
- Radiance averaging approach may give better results, as for BrO (but TBD)
- A brief report _may_ be worthwhile, but probably worth trying for further improvements
-       before this is done (possibly not before JGR special issue deadline...)