CHEMICAL ASSIMILATION OF GOMOS NOy DATA

COST workshop, ESTEC, 11-13 March 2003

Slimane Bekki, M. Marchand, A. Hauchecorne, J-L Bertaux IPSL (UPMC/CNRS)

GOMOS MEASUREMENTS

UV-visible-Near IR spectrometer (stellar occultations) -> 400 profiles/day all around the globe of : O3, NO2, NO3, H2O, aerosols and T from upper tropos./lower strat. to the mesosphere

Retrieval of NO2 and NO3 adversely affected by scintillation (most acute for stars setting obliquely through the atmosphere) -> new retrieval DOAS algorithm

Validation of the Self-consistency of GOMOS NO3,NO2, and O3 Data Using Chemical Data Assimilation

Night-time chemistry: NO2 + O3 -> NO3 + O2 NO3 + NO2 + M -> N2O5 + M N205 + M -> NO3 + NO2 + M

No validation measurements for GOMOS NO3 dataHowever, simultaneous measurements of 03 and NO2 strongly coupled chemically to NO3 -> self-consistency test

NO2

NO3

O3

N2O5

Analyzed NO3=f{O3, NO2, k(T),density} -> GOMOS NO3 GOMOS ECMWF

APPROACH

1/ GOMOS measurements : O3 , NO2 NO3

2/ Variational assimilation in a photochemical model

3/ Analysis : O3 , NO2 , NO3

4/ Comparison

GOMOS measurements: Star Beta Carinae (S029) °January 03: vertical star setting (little scintillation) °December 02: oblique star setting (strong scintillation) -> Test DOAS retrieval

Example of case study:

On 31th, January 2003 at 7h40 UTAt a position of 16.23° latitude and 214.6° longitude.

Time evolution of the analyzed O3 (a), analyzed NO2 (b), analyzed NO3 (b)along the trajectory.

GOMOS NO3 measurements as a function of analyzed NO3

(a)For all the cases (= 465) (b) For cases when NO2 Error < 30% (= 296)

NO3 error measurements are indicatedwith vertical lines.

December (oblique star setting) January (vertical star setting)

GOMOS NO3 measurements as a function of analyzed NO3(averaged over isentropic levels)

[735, 900, 990, 1100, 1210, 1350, 1510,1670, 1830, 1960 K]

(a)For all the cases (= 465) (b) For cases when Error of NO2 < 30% (= 296)

CONCLUSIONS

° Validation of GOMOS NO3, NO2, and O3 data: chemically consistent

° Validation of the model chemistry

Analyzed NO3=f{O3, NO2, k(T),density} -> GOMOS NO3 GOMOS ECMWF

° Validation of the new DOAS retrieval system (no differences between vertical and oblique star setting occultations)

Example of a case study

NO2

O3

NO3

NO3 GOMOS data

NO3 Analysis

Slope = 0.884

330 points, many superposed

NO3

NO2

O3

O3 GOMOS data

O3 Analysis

NO2 GOMOS data

NO2 Analysis

NO3 GOMOS data

NO3 Analysis

AVERAGING OVER THETA LEVELS

no large bias in GOMOS NO3 data GOMOS O3, NO2, NO3 data self consistent chemically. night-time NO2 and NO3 chemistry is well understood