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

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

2 © Crown copyright Met Office Contents This presentation covers the following areas Continuum coefficient estimates from ARIES in cm -1 band Microwave retrievals as humidity constraint Can we use IASI satellite data over Swiss Alps mountainous terrain?

3 © Crown copyright Met Office Continuum estimates from ARIES data

4 © Crown copyright Met Office Field campaign summary: UK (Camborne), Switzerland (Jungfraujoch) FlightDateWeather conditionsNotes B Persistent boundary layer cloudPartial NPL data B Persistent boundary layer cloudPartial NPL data B Good clear sky conditionsSonde chase, good flight B Cloud at times over JungfraujochPartial NPL data B Initially thin cirrus which clearedGood NPL data B Good clear sky conditionsFLASH sonde + MetOp overpass B Cloud at times over JungfraujochPartial NPL data B Some thin cirrus encroachingGood NPL data B Excellent clear sky conditionsMetOp overpass B Excellent clear sky conditionsARIES failure B Excellent clear sky conditionsNo TAFTS B Partial cloud over JungfraujochCancelled am flight, pm only

5 © Crown copyright Met Office 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 ft down to ft) FWVS may be more representative Can compare sources of humidity data to estimate uncertainties

6 © Crown copyright Met Office CAVIAR example B 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

7 © Crown copyright Met Office Combined results Selected data from flights B467-B474 Outliers at odds with laboratory measurements?

8 © Crown copyright Met Office Microwave humidity retrievals

9 © Crown copyright Met Office 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)

10 © Crown copyright Met Office Humidity information from MARSS Three MARSS channels are sensitive to the water vapour profile 183 GHz line

11 © Crown copyright Met Office Microwave retrieved humidity

12 © Crown copyright Met Office Microwave retrieved humidity

13 © Crown copyright Met Office Microwave retrieved humidity Tendency is for humidity to be reduced in retrievals where IWV is highest

14 © Crown copyright Met Office Combined results Selected data from flights B467-B474 Outliers still at odds with laboratory measurements?

15 © Crown copyright Met Office IASI satellite data over mountainous terrain

16 © Crown copyright Met Office Can we use IASI data over Swiss Alps? IASI interferometer on MetOp polar-orbiting satellite covers a similar spectral range ( 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…

17 © Crown copyright Met Office Sensitivity to trace gases Increased CH 4 concentration is needed to simulate spectrum in cm -1 region

18 © Crown copyright Met Office Model surface pressure Flight track IASI footprints Dropsonde Jungfraujoch Use COSMO local area model to assign surface pressure to satellite footprints

19 © Crown copyright Met Office 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

20 © Crown copyright Met Office Humidity profile from non-continuum IASI lines Increase in humidity at lower levels, decrease higher up

21 © Crown copyright Met Office Combined results Including satellite measurements

22 © Crown copyright Met Office 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 cm -1 still seem to be at odds with laboratory data – is this due to uncertainties in field data or is this real?

23 © Crown copyright Met Office Questions and answers


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