Assessment of one year of Medspiration L4 fields

J. Tournadre, J.F. Piollé and E. Autret

• Since January 2006 we have stabilized the OA configuration of the Medspiration L4 processing– Daily, 2km resolution, night-time data only– NAR17-18, Seviri, AATSR, AMSRE, TMI, AVHRR

17-18 Gac and LAc

• More than one year of homogeneous data are now available

• Analysis of this data setL2P and L4 processinggeophysical applications

L4 works even if not perfectly

• Strong Mistral event at the beginning of August 2006 cooled down the French Riviera by

more than 5K!!

SST

SST

Qscat wind

Which L2P do we use??

• L4 = OA of L2P

Area covered Number of days sampled /year

AMSRE

AATSR

SEVIRI

NAR17

NAR18

SEVIRI has the largest temporal and spatial coverage and constitutes the base of the L4 analysis even if the number of samples /day is 10 times smaller than the AVHRR ones.

How do these L2P data feeding the L4 OA compare to each other?

Difference between collated and L4 SST for April 2006

•NAR17 (AVHRR17) no bias (first choice in data selection after AATSR)

•Large biases for NAR18

•Strong regional biases for SEVIRI

•AATSR strong local biases (not enough samples)

•Strong temporal and spatial variability of inter-sensor biases

•For July 2006 from –0.5 to 0.5K

•Especially strong in upwelling regions.

• The regional biases are partially due to the SST local variability

SST RMS in 0.5° boxes Feb

SST RMS in 0.5° boxes Aug

Related to strong surface SST gradients

Strong temporal variability of the inter-sensor biases

Comparison of collated data with NAR17 collated

• Most of the problems we encountered during this year of operation are related to large biases between sensors (sometimes more than 1.5K)

• These biases are highly variable in time and space.• Improvement of the L4 fields can only come from an

improvement of the intercalibration of sensors.

What can we do with the L4 products?

Annual variation of SST for 3 location

Near Atlantic

Gulf of Lions

Eastern Med

SST RMS in 0.5°boxe

SST

Mistral event

Seasonal Cycle in the Med

• Amplitude• Day of

maximum SST

Max at end of summer

Max at early August

Max at early september

Weak cycle Strong cycle Medium cycle

• Mean change of SST over the meddspiration zone• Western Bassin an central bassin

cooling

heating

Mistral

Detail of the Mistral event which seems to condition the SST evolution in at least the

western and central med basins

Intense heating in the Gulf of Lions July

Intense cooling in the Gulf of Lions July

Low winds

Mistral

• L4 : good data base to study the evolution and variability of SST at fine temporal and spatial scale

• More studies needed and more validation

• Spectral analysis of Western, Central and Eastern Med. Basins. Daily spectra

• Both for validation and geophysical studies purposes

Both short scale ans seasonnal variations

Latitudinal zonal

10km Seviri spectral peak

Mean spectral behaviour of SST in the 3 basins

Different spectral slopes

Difference of slope

Westen basin zonal spectra

•Seasonal variation

•Short period variations associated with weather patern

spectra Spectra anomalies

Spectral slope

Change associated to Mistral event

Temporal spectra Western (black) and Central (green) basins

10 days 3 days

Western

Central

A look at the diurnal cycle?Seviri –L4 every3 hours

DC=Max -Min

DWGradSSTSST/t

Wind

DC

SST/t

Number of days with DW greater than

0.5, 1 and 2K

Perspective

• Still work to do to improve the L4 products• Mainly in the inter-calibration of L2P SST• SSES can certainly improve but not

everything. Dynamical inter-calibration method necessary

• More validation work to be conducted• As it is L4 fields gives a very easy to use data

base to better study/understand the dynamics of the Mediterranean Sea.