© Crown copyright Met Office Update on CAVIAR field experiments Stuart Newman NPL, 29 September 2010.

© Crown copyright Met Office

Update on CAVIAR field experimentsStuart Newman

NPL, 29 September 2010


Contents

This presentation covers the following areas

• Continuum coefficient estimates from ARIES in 1400-2000 cm-1 band

• Microwave retrievals as humidity constraint

• Can we use IASI satellite data over Swiss Alps mountainous terrain?


Continuum estimates from ARIES data


Field campaign summary:UK (Camborne), Switzerland (Jungfraujoch)

Flight Date Weather conditions Notes

B396 19.08.08 Persistent boundary layer cloud Partial NPL data

B397 22.08.08 Persistent boundary layer cloud Partial NPL data

B400 18.09.08 Good clear sky conditions Sonde chase, good flight

B466 16.07.09 Cloud at times over Jungfraujoch Partial NPL data

B467 19.07.09 Initially thin cirrus which cleared Good NPL data

B468 20.7.09 Good clear sky conditions FLASH sonde + MetOp overpass

B469 25.07.09 Cloud at times over Jungfraujoch Partial NPL data

B470 26.07.09 Some thin cirrus encroaching Good NPL data

B471 27.07.09 Excellent clear sky conditions MetOp overpass

B472 29.07.09 Excellent clear sky conditions ARIES failure

B473 01.08.09 Excellent clear sky conditions No TAFTS

B474 04.08.09 Partial cloud over Jungfraujoch Cancelled am flight, pm only


Accurate humidity profiles are crucial

Dropsondes are widely recognised as most accurate source of humidity data from the aircraft

However, for runs immediately after a profile descent (e.g. 35000 ft down to 15000 ft) FWVS may be more representative

Can compare sources of humidity data to estimate uncertainties


CAVIAR exampleB467 19-Jul-2009

• Initial run at high level for radiance measurements (here looking up)

• Spiral descent over Jungfraujoch observatory measuring in situ water vapour (rapid response FWVS probe used here)

• Subsequent run at lower level for radiance measurements (here looking up)

• Determine change in radiance due to water vapour in atmospheric path

• Derive continuum strength, compare to MT_CKD model in LBLRTM

If ARIES measures lower emission than LBLRTM/MT_CKD implies smaller continuum coefficient

If ARIES measures higher emission than LBLRTM/MT_CKD implies larger continuum coefficient


Combined resultsSelected data from flights B467-B474

Outliers at odds with laboratory measurements?


Microwave humidity retrievals


Humidity information from MARSS

• Microwave measurements from MARSS radiometer on FAAM aircraft are co-located with ARIES IR measurements

• In principle microwave observations at 183 GHz can be used to constrain water vapour profile above the aircraft

Microwave Airborne Radiometer Scanning System (MARSS)


Humidity information from MARSS

Three MARSS channels are sensitive to the water vapour profile

183 GHz line


Microwave retrieved humidity





• Tendency is for humidity to be reduced in retrievals where IWV is highest


Combined resultsSelected data from flights B467-B474

Outliers still at odds with laboratory measurements?


IASI satellite data over mountainous terrain


Can we use IASI data over Swiss Alps?

• IASI interferometer on MetOp polar-orbiting satellite covers a similar spectral range (645-2760 cm-1) to ARIES, so offers chance to intercompare measurements

• Flights on 20/7, 27/7 and 1/8/2009 coincided with MetOp overpasses

• However, IASI footprint is approx. 12 km diameter – over mountainous regions it is a challenge to represent the surface boundary and lower atmosphere properly…


Sensitivity to trace gases

• Increased CH4 concentration is needed to simulate spectrum in 1200-1400 cm-1 region


Model surface pressure

• Flight track• IASI footprints• Dropsonde• Jungfraujoch

• Use COSMO local area model to assign surface pressure to satellite footprints


Humidity profile from non-continuum IASI lines(assumes constant surface emissivity)

Use spectral information in weaker monomer lines to infer modified water vapour profile consistent with the measurement


Humidity profile from non-continuum IASI lines

Increase in humidity at lower levels, decrease higher up


Combined resultsIncluding satellite measurements


Summary

• Constraining humidity profiles for case studies remains the most difficult problem to solve

• Use of MARSS microwave data to retrieve humidity may be subject to error if microwave water vapour continuum is not adequately modelled

• Promising approach is to use monomer lines in ARIES and IASI spectra to retrieve humidity within instrument field of view (need to extend to more lines)

• The derived continuum coefficients in range 1400-2000 cm-1 still seem to be at odds with laboratory data – is this due to uncertainties in field data or is this real?


Questions and answers

© Crown copyright Met Office Update on CAVIAR field experiments Stuart Newman NPL, 29 September 2010.

Documents

humidity slide

aries data slide

iasi data

measurement slide

line slide

highest slide

sources of humidity

use of marss microwave