# Presentation: 647055

## HCl from EOS MLS on Aura: version 1.5 and preliminary version 2 data comparisons  L. Froidevaux1, Yibo Jiang1, A. Lambert1, N. J. Livesey1, W. G. Read1, J.W. Waters1                                     1 Jet Propulsion Laboratory, California Institute of Technologyand other contributors (for correlative data in particular)satellite and  balloon data teams

**HCl from EOS MLS on Aura: version 1.5 and preliminary version 2 data comparisons  ***L. Froidevaux**1**, Yibo Jiang**1**, A. Lambert**1**, N. J. Livesey**1**, W. G. Read**1**, J.W. Waters**1** ***                                    ****1**** *****Jet Propulsion Laboratory, California Institute of Technology******and other contributors (for correlative data in particular)******satellite and  balloon data teams***

##           Version 1.52 has small systematic difference (a few % in upper strat.) versus V1.51                                                       
            + somewhat poorer precision (by ~30%) and poorer vert. resolution
●  Version 2.1 has some other changes 
     -  Spectroscopy: not for HCl directly, but small linewidth changes to O3 (640 GHz) lines
     -  Changes in treatment of retrievals for temperature and tangent pressure                                                         
          > Different bands/channels & calib. adjustments  a few K cooler & changes in Ptan (~ 300m near 1 hPa)
          > Halve the retrieval’s vertical grid spacing (from 6 coefficients/decade in P to 12/decade - for P> 21 hPa)
      -  Changes in the treatment of vertical smoothing constraint   
 > Less constraint  better (~ 4 km) vertical resolution in upper stratosphere  (but noisier)

●  Changes in the retrieved standard HCl product (V2.1 versus V1.51)
      -  Precision (and observed scatter) are degraded (by ~factor of two)
     -  Systematic changes: < 5% for upper stratosphere, ~10 % for lower stratosphere
     -  However, MLS HCl at 147 hPa still not  deemed reliable enough (e.g., negative biases) 

-             + somewhat poorer precision (by ~30%) and poorer vert. resolution
- ●  **Version 2.1 has some other changes**
-      -  Spectroscopy: not for HCl directly, but small linewidth changes to O**3** (640 GHz) lines
-      -  Changes in treatment of retrievals for temperature and tangent pressure
-           > Different bands/channels & calib. adjustments  a few K cooler & changes in P**tan **(~ 300m near 1 hPa)
-           > Halve the retrieval’s vertical grid spacing (from 6 coefficients/decade in P to 12/decade - for P> 21 hPa)
-       -  Changes in the treatment of vertical smoothing constraint
-  > Less constraint  better (~ 4 km) vertical resolution in upper stratosphere  (but noisier)
- ●  **Changes in the retrieved standard HCl product (V2.1 versus V1.51)**
-       -  Precision (and observed scatter) are degraded (by ~factor of two)
-      -  Systematic changes: < 5% for upper stratosphere, ~10 % for lower stratosphere
-      -  However, MLS HCl at 147 hPa still not  deemed reliable enough (e.g., negative biases)

**MLS provisional version 2.1 data: HCl**

**O****3**

**37****HCl**

- ●  **Changes from version 1.5**
-      -  Starting in February 2006, signs of aging seen in
-          primary 640 GHz HCl band (B13)
-      -  Thought due to radiation hardness issues in a
-          particular batch of transistors
-      -  B13 off since Feb. 16; plan to turn it on infrequently
-         as consistency check (1 day at a time, on occasion)
-      -  HCl now comes from adjacent band (B14) covering
-          most of 35HCl line and isotopic 37HCl line

**35****HCl**

**Spectra**

## Changes in HCl from v1.51 to v1.52 (after Feb. 16, 2006) 

**Changes in HCl from v1.51 to v1.52 (after Feb. 16, 2006) **

- Small (but non-negligible) changes occurred when switching to Band 14 from Band 13
- Band 13 was turned off on Feb. 16, 2006 because of a rapid degradation in counts (after Jan. 2006)

**Global differences using v1.52 versus v1.51 retrievals**               (for Feb. 14, 2006)
- v1.52 values are:            ▪ 2 to 3% larger in upper strat. & lower mesosphere                                        ▪ 3 to 5 % smaller in lower strat. (except for 100 hPa, where values are ~10% larger than v1.51)
- Est. precision for v1.52 retrieval is poorer by 30-40%          in upper stratosphere

##      MLS provisional version 2.1 data: HCl 

- HCl differences (global averages)  from v1.51 to v2.1 are quite reproducible from day to day and over    more than         1 year
- - based on a few days that have been reprocessed with v2.1

- Note: because of the increased noise for single profiles (mainly in upper strat.), detection of small (5%) differences requires averaging of a number of profiles

##      MLS provisional version 2.1 data versus version 1.5 data: HCl                                                                                            

-  Based on 17 days of v2.1 MLS data                                    (made available on the AVDC)
- The HCl differences (V2.1 – V1.5) are fairly constant with latitude
-  mean values in tropics near 100 hPa are closer to zero, probably a good thing (given very low values expected and observed during CR-AVE)

## MLS HCl: brief review of status for v1.5 data

- see *Froidevaux et al., 2006* IEEE paper + Sep. 2005 Aura validation meeting
-   MLS v1.5 HCl has ~10 -15% positive bias versus HALOE
-       -  but HALOE values > other correlative data (ATMOS, balloon data) by a similar amount
-   MLS v1.5 HCl within ~ 5% of ACE-FTS values
-   Good tracking versus latitude (MLS vs HALOE and ACE)
-   Some differences in temporal changes (monthly means), MLS vs HALOE;                     	not obvious why, although sampling explains some of this.

## Changes to MLS HCl in v2.1: impact on comparisons 

**                          ****Satellite Data****:** MLS and HALOE HCl comparisons

- MLS/HALOE comparisons are not changed significantly, overall, compared to the systematic differences of ~10-15% (as expected from changes between V1.5 to V2.1)

- MLS vs HALOE (V19) coincident matches based on 17 days
- Top: MLS V1.5 data
- Bottom: MLS V2.1 data
- Left panels: average profiles (global)
- Right panels:                     dots: avg. difs. (+ prec.)  triangles: std. devs.

## Changes to MLS HCl in v2.1: impact on comparisons 

**                          ****Satellite Data****:** MLS and ACE HCl comparisons

- MLS vs ACE (V2.2) coincident matches based on 17 days
- Top: MLS V1.5 data
- Bottom: MLS V2.1 data
- Left panels: average profiles (global)
- Right panels:                     dots: avg. difs. (+ prec.)  triangles: std. devs.

- MLS/ACE comparisons (from a few days of data) still show good agreement                                                               - Now seem to obtain better agreement with ACE profiles in lower mes. (up to 0.3 hPa)                                                                                                                                                  - More days/statistics will give more robust results + can check diffs. vs latitude

## Changes to MLS HCl in v2.1: impact on comparisons 

- Balloon Data
- Changing HCl by ~ 5% will not result in an easily discernible change to a few balloon profile comparisons                                                                                                      - differences between balloon datasets can be > 5%                                                                - accuracy and single-profile precision for balloon and MLS datasets also > 5%

**Compare MLS versus   balloon HCl data**                                  (Fall 2005, Ft. Sumner)
-  Both data versions for MLS agree well with MkIV and SLS (avg.) profiles
-  Some of the currently archived (but not final) FIRS-2 profiles give significantly lower HCl values, in particular for Sep. 21 (night)  and P < 10-20 hPa, compared to the other profiles
-  at least partly explainable by profile shape assumptions and other factors (balloon sinking at night),... [per K. Jucks]

- Sep. 20 (daytime Aura overpass) Sep. 21 (nighttime Aura overpass)

## Changes to MLS HCl in v2.1: impact on comparisons 

**Balloon Data: September 2004, Ft. Sumner**

- The average results for 2004 versus the balloon data show agreement to within 10-15% with MLS           v2.1 data for 32 to 4.6 hPa, with larger variations at higher pressures.
- Several more flights would probably be needed to discern any clear biases                   (if such biases exist)                    between these datasets            - also, cannot get reliable results  (or extrapolation) for the uppermost stratosphere, most relevant to total chlorine

- MLS v2.1 results shown here (but dashed avg. in right panel is for MLS v1.5 data)

- Sep. 23/24: remote (MkIV: blue triangles, FIRS-2: cyan circles)                Sep. 17: in situ (ALIAS, purple boxes)

## Temporal changes in HCl (monthly near-global means) [~ 0.5 hPa, ~ 53 km]

- Abundances and decreases in HCl are as measured above for HALOE, MLS, ACE.
-   MLS frequent and repeatable coverage    a few pptv precision for 10° zonal means and decrease of ~ - 0.8% per year for first 18 months                                                     >  agrees with expectations from in situ ground data on total trop. chlorine (for ~5.5 yr time lag and ~0-2 year age spectrum)

- Can add V1.52 monthly means cautiously after adjustment for small (but non-negligible vs yearly decrease) shifts between v1.51 and v1.52 data.
- -  Global decrease continues.                          -  **Note:**  **Will need to reprocess the whole MLS mission (since Aug. 2004) to get best/consistent time series for analyses across Feb. 2006 time period.**

- V1.52 data

- V1.52 data with adjustement for                   mid-Feb. 2006 shift between MLS data versions  ~ 2% drop in 2 years

- V1.51 data

- Slope of                   expected decrease

## Summary and plans: MLS HCl validation 

**Validation comparisons are continuing – and within < 5-10% of v1.51 results**
- v1.52 for Feb. 16, 2006 and onward; use different band/channels (+ isotopic HCl line)
- v2.1 (and planned v2.2) retrievals also differ some  (T, Ptan, and spectroscopy for nearby O3 lines) + noisier (less smoothing constraint  better vertical resol. in upper stratosphere)
**            **MLS HCl still > HALOE;  < ~5% diff. vs ACE-FTS for most of 68 hPa - 0.5 hPa [17 days only]
**Validation paper for special issue**
*L. Froidevaux et al.* manuscript planned on HCl validation
-      >  Plan to mainly use v2.2 MLS data                                                                                                    >  Expand on satellite comparisons shown here; separate vs latitude and time of year,   	  update HALOE and ACE results (possibly use v1.5 data for some time series info.)         >  Add detailed error analysis (already done for upper stratosphere)                                                                                                                                           >  Include results/updates from balloon campaigns (Ft. Sumner 2004, 2005, - 2007??)
-      >  Add something on AVE, CR-AVE results                                                                                   (although nothing new on aircraft results shown here); to be discussed with CIMS team.
- Other related validation manuscript plans?                                                                                 > Please contact L.F.  if wish to coordinate and to avoid duplication (+ as a courtesy).
**Validation needs?**
- -  Campaigns: check high latitude winter balloon data (Kiruna 2007) for different conditions in the lower stratosphere (depleted HCl), although ‘one snapshot’ is not a stringent constraint
**Longer-term planning (mostly)**
-        -  Continue to look at MLS upper stratospheric data versus expected decreases
-         -  Continue consistency checks between MLS & ACE-FTS + more balloon data (08, 09?)
-         -  Add comparison to column IR data (HCl+ClONO**2**) [for > 2-3 yrs of MLS V2 data] + MW ClO