SCIAMACHY long-term validation

M. Weber, S. Mieruch, A. Rozanov, C. von Savigny,

W. Chehade, R. Bauer, and H. Bovensmann

Institut für Umweltphysik, Universität Bremen

ENVIVAL-LIFE Annual Meeting, Bremen, 6-7 Dec 2010

Topics

Validation of scientific SCIA retrievals:

Total ozoneozone limb profilesNO2 limb profiles

Total ozone

Merged WFDOAS total ozone (´GSG´) data set (1995-2010): www.iup.uni-bremen.de/gome/wfdoas

Used in WMO assessment 2010

Weber and Steinbrecht, 2010

GOME SCIAMACHY GOME2

record ozone hole

1990s cold Arcticwinters

split ozone hole

QBO

SCIAMACHY TO3 validation GSG merged data set

WMO requirements for trend detection: <1%/decade

GOME1 (1995-present)Loss of global coverage after June

2003Very good agreement with ground

data until now (mean bias < 1%)

SCIAMACHY (2002-present)Good agreement with GOME at

start of record

Instrumental trend of -4% per decade

GOME2 (2007-present)Bias of -1% w.r.t. GOME1 GOME (3 month

avg.)

SCIAMACHY

GOME minus Brewers daily mean <60° lat.

Dobsons

Brewers

Merged WFDOAS total ozone data set (1995-2009)

Merged WFDOAS data record with GOME1 as reference data set:

GOME1 (July 1995- May 2003)

SCIAMACHY bias and trend corrected (June 2003 – March 2007)

GOME2 bias corrected (April 2007 – present)

deseasonalised

Weber and Steinbrecht, 2010

Other GOME/SCIA/GOME2 merged data records

Similar approach for ESA/EUMETSAT operational data products (Loyola et al. 2009) GSG data are also part of the NIWA assimilated data record (Bodeker et al., 2005) Data assimilation approach combining all available satellites and different

algorithms covering 30 years (van der A et al., ACP, 2010)

Loyola et al., 2009

Conclusion total ozone

Good agreement with groundbased Brewers and Dobsons

But: significant -4%/decade trend wrt GOME1 and ground dataNot a retrieval issue (all algorithms are affected)

Most likely level-1 issue

m-factor corrections (level 1 V5) only partially helps

Trend correction wrt to GOME1 merged GOME1/SCIA/GOME2 data setZonal means are in good agreement with SBUV/TOMS/OMI merged and ground data

Used in WMO 2010 assessment

SCIAMACHY limb ozone data set

SCIAMACHY limb ozone profiles 2002-present (Sonkaew et al., 2009) Version 2.1 Altitude coverage: 10-70 km Vertical resolution: 4 km

Relevance of data set: WMO asessment 2010 ESA climate change initiative ´ozone

ecv´ (2010-2013) merged limb/occ. ozone profiles

(Ubr, KIT, FMI/LATMOS) from ENVISAT and ESA-Third Party missions (ODIN/ACE)

SPARC ozone profile initiative trend quality ozone profile data

sets

1980 1985 1990 1995 2000 2005 2010

-505

-505

-505

35

to 4

5 k

m o

zone

ano

ma

ly [%

]

-505

-20-15-10

-505

F 10.7cm

Lidar, W ave, S AG E, H A LO E, SB U V , G O M O S, SC IA , all

H ohenpeissenberg/Bern(48°N)

H aute P rovence(44°N ,6°E)

Table M ounta in(35°N ,118°W )

H awaii (20°N ,156°W )

Lauder (45°S,170°E)

-ESC(4 yr, 2w d, 0B r)

Steinbrecht et al. 2009, WMO, 2010; Weber and Steinbrecht 2010

Long-term validation of SCIA O3 profiles

Comparison of monthly mean zonal means with SAGE II, HALOE, SABER, MLS, ACE-FTS

Direct comparison of zonal means (all profiles)

all profiles

Long-term validation of SCIA O3 profiles

Comparison of monthly mean zonal means with SAGE II, HALOE, SABER, MLS, ACE-FTS

Comparisons of collocated profiles only (<400 km)

Results of all & collocated profile comparisons are similar, some fine details are different

collocated profiles

Long-term validation of SCIA O3 profiles

SCIA overestimates in the UTLS (e.g. <20 km in the tropics)General good agreement with solar occulation (HALOE, SAGE, ACE-

FTS) to better than 10%Larger differences wrt MLS (above 30 km) and SABER (extratropics)

all profiles

collocated profiles

Long-term validation of SCIA O3 profiles

SCIA overestimates in the UTLS (e.g. <20 km in the tropics)General good agreement with solar occulation (HALOE, SAGE, ACE-

FTS) to better than 10%Larger differences wrt MLS (above 30 km) and SABER (extratropics)

sss

Long-term validation of SCIA O3 profiles

larger differences with MLS and SABER are significant (MLS bias confirmed by Considine et al., 2008)

small oscillation in the difference profile to solar occultation profiles are statistically significant residual tangent pointing problem most pronounced in the tropics (under investigation)

Question: Are the differences between SCIA and other instruments real?Make a χ2-test null

hypothesis check (von Clarmann 2006) using only random errors (error covariance of other instruments are unknown

SCIAMACHY tangent height offset

50oN– 70oN: ~7 m/year

Retrieved from SCIAMACHY occultation measurements comparing the predicted and observed position of the Sun.

Retrieved from SCIAMACHY limb measurements in UV spectral range using the “TRUE” algorithm (von Savigny et al., 2005).

Tropics: ~21 m/year

SCIA instrumental O3 trends

Trend analysis (incl. Seasonal cycle, QBO, autocorrelation)Siginificant negative trends at

around 37 km (~-1%/decade)

larger trends than SABER

Most likely related to the residual tangent height problem

Conclusion O3 limb profiles

Excellent agreement with solar occulation data (< 10%) from 20 to 50 km

Strong overestimation below 20 km in the tropicscloud interference (ca. 90% of all data)

Some statistically significant oscillatory structure in the mean difference profilesTangent height issue?

Negative trend of 1%/decade at about 37 km, larger than SABER‘s trend (~-0.4%/decade)Tangent height issue

NO2 limb profile validation

NO2 limb retrieval V3.1

Spectral range 420-470 nm

Vertical range 11-40 km

vertical resolution: 3-5 km

Retrieval grid: 1 km

Comparisons to SAGE II, HALOE, and ACE-FTS

Max. time difference: 8h

Max. distance: 500 km

Similar PV at 475 K (Bracher et al. 2004)

Difference in tropopasue height less than 2 km abpove 8 km altitude

SAGE II, HALOE, and ACE-FTS measurements are scaled to SCIAMACHY SZA using a 2D photo-chemical model (Bracher et al., 2005)

Comparison to SAGE II (2003-2004)

Good agreement at northern high latitudes above 20 km (<10%)

Increasing differences (up to 30% near 40 km) at low and soutrhern latitudes

Comparison to HALOE (2003-2004)

Good agreement at northern high latitudes above 20 km (<10%)

Increasing differences (up to 30% near 40 km) at middle and tropical latitudes

Similar results für SAGE II,HALOE, and ACE-FTS

Comparison to ACE-FTS (2004-2005)

Good agreement at northern latitudes (<10%)

Increasing differences (up to 30% near 40 km) at low and soutrhern latitudes

Similar results für SAGE II,HALOE, and ACE-FTS

Summary: NO2 limb profile

60°N – 90°N altitude range all measurements agree mostly within 10% above 20 km. Below, SAGE II shows nearly the same results as SCIAMACHY, HALOE is lower and ACE- FTS is higher than SCIAMACHY

30°N – 60°N altitude all measurements agree mostly within 10% above 20-24 km (depending on the reference instrument). Below, SAGE II and ACE- FTS are higher and HALOE is lower than SCIAMACHY

SCIAMACHY in most cases 10-15% higher than other satellites

High bias of SCIAMACHY is believed to be due to too low NO2 scaling factor resulting from the photochemical model

for small solar zenith angles (confirmed by comparisons with the photo-chemical model of Chris McLinden)

Results show a better agreement than for the previous retrieval version (V3.0) reported by Bracher et al., 2005 (comparison was done only for 55N-69N latitude range).