Biondi, Riccardo

Neubert, Torsten

Nielsen, Johannes

Syndergaard, Stig

Water vapour transport to the upper troposphere (UT) and lower stratosphere (LS) by deep convective storms affects the radiation balance of the atmosphere and has been proposed as an important component of climate change. The aim of the work presented here is to understand if the GPS Radio Occultation (RO) technique will be useful for characterisation of this process. In the last 25 years, several instruments have become available to study atmospheric water vapour, and many studies show the increase of water vapour in the UT during this period. It is also well known that deep convection from storms increases the relative humidity in the tropics. In this way, Tropical Cyclones (TCs) should play an important role since they lead to deep convective activity. TCs increase the water vapour content of the UT, the integrated water vapour in the vicinity of the storm, they warm the mid troposphere and they cool the tropopause layers. The GPS radio occultation technique is useful for studying severe weather phenomena because the GPS signals penetrate through clouds and allow measurements of atmospheric profiles related to temperature, pressure, and water vapour with high vertical resolution. The assessment presented here is based on an analysis of data from COSMIC satellites. GPS data were analyzed in relation to TC positions for the period 1996-2008 when GPS-MET, SAC-C CHAMP and COSMIC acquisitions where available, identifying several hundred ROs that coincide with TC positions. Whereas no evident variation at the tropopause is seen in the standard RO data products like water vapour pressure and temperature profiles, the GPS signal bending angle profile shows a TC signature in the upper troposphere. The presentation is focused on two particular TCs, the hurricane Bertha, which formed in the Atlantic Basin during July 2008 and reached a maximum intensity of Category 3 and the typhoon Hondo, formed in the south Indian basin during February 2008 with maximum intensity of Category 4. Using measurements from a variety of earth observation satellites (A-Train constellation) and from aircraft together with the best track information, we reconstructed the characteristics of the two TCs and compared them to ROs from COSMIC. Our results suggest that the bending angle of a GPS radio occultation signal contains interesting information on the atmosphere because it consistently shows a pronounced signature at the tropopause above TCs. Parameters such as the temperature and refractivity profiles from the COSMIC mission often show a variation at the same altitudes as the bending angle, but the signature is less pronounced and sometimes not evident. Perturbations to the bending angle are generally caused by temperature or water vapour gradients. The water vapour profile derived from COSMIC data do not show enhancements above TCs at the tropopause, however, the data are model dependent as ECMWF is used in their derivation. Comparisons with A-Train data, on the other hand, show some agreement between RO bending angle profiles and the water vapour mixing ratio profiles in the UT/LS. We are currently investigating to what extent the bending angle signature at the tropopause heights could be caused by the presence of enhanced water vapour content

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Downloaded from orbit.dtu.dk on: Dec 17, 2017COSMIC Radio Occultation technique for measurement of the tropopause duringtropical cyclonesBiondi, Riccardo; Neubert, Torsten; Syndergaard, Stig; Nielsen, JohannesPublication date:2009Link back to DTU OrbitCitation (APA):Biondi, R., Neubert, T., Syndergaard, S., & Nielsen, J. (2009). COSMIC Radio Occultation technique formeasurement of the tropopause during tropical cyclones. Poster session presented at Fourth FORMOSAT-3/COSMIC Data Users Workshop, Boulder (CO) - USA, .190 200 210 220 230 240 250 260 270 280 290 3002468101214161820Temperature [K]Altitude above msl [km]  Bertha´s temperatureAnnual mean value-20 -10 0 10 20 30 402468101214161820Percentage anomaly [%]Altitude above msl [km]  COSMIC Radio Occultation technique for measurement of the tropopause during Tropical cyclones Riccardo Biondi1, Torsten Neubert1, Stig Syndergaard2 and Johannes Nielsen2 1DTU Space, Danish Space Institute, 2Danish Meteorological InstituteWater vapour transport to the upper troposphere (UT) and lower stratosphere (LS) by deep convective storms affects the radiation balance of the atmosphere and has been proposed as an important component of climate change. The aim of the work presented here is to understand if the GPS Radio Occultation (RO) technique will be useful for characterisation of this process.   180 W  120 W   60 W    0     60 E  120 E  180 E  60 S  45 S  30 S  15 S   0    15 N  30 N  45 N  60 N GPS phase & amplitude -> Bending angleAbel inversion -> RefractivityN=77.6*P/T+3.73*105*pw /T2N refractivity, T temperature, P pressure, pw water vapour pressureECMWF model -> Temperature, Pressure, Water VapourBertha 2008 Hondo 2008 Bending angle profile shows a clear TC signature in the UT/LS Temperature and refractivity profiles from the COSMIC mission often show a variation at the same altitudes as the bending angle, but the signature is less pronounced and sometimes not evident The water vapour anomalies from COSMIC agree largely with those of ECMWF, which can be explained by the fact that the ECMWF model is used in the derivation of the water vapour profilesPeriod 1996-2008, area 400 km, time window 3 hMore than 500 coincidences, more than 100 Tropical Cyclones~ 71% from COSMICGoal & MethodsCase selectionBertha 2008Hondo 2008ComparisonsConclusionsBending angle, refractivity, temperature, Pressure, Water VapourUT/LSTropical DepressionTropical StormTropical CycloneMaximum categoryExtra-Tropical CycloneGPS Radio Occultation3rd July20th JulyCategory 32nd February29th FebruaryCategory 4-20 -10 0 10 20 30 40 50 602468101214161820Percentage anomlay [%]Altitude above msl [km]  TC season mean anomalyNo TC season mean anomalyBertha´s anomaly- 20 0-20 -10 0 10 20 30 4002468101214161820Percentage anomaly [%]  UT/LSUT/LSUT/LSBertha´s anomalyTC season monthly meanNo TC season monthly meanThe bending angle of a GPS radio occultation signal contains interesting information on the atmosphere around the tropopause above the tropical cyclone. Temperature and refractivity profiles often show a variation at the same altitudes as the bending angle, but the signature is less pronounced and sometimes not evident. The water vapour anomalies from COSMIC agree largely with those of ECMWF, which can be explained by the fact that the ECMWF model is used in the derivation of the water vapour profiles.WarmerAll the TC tracks were compared with GPS/MET, CHAMP, SAC-C and COSMIC ROs. More than 70% of coincidences are coming from COSMIC project. We finally selected two different TCs, Bertha 2008 and Hondo 2008, with completely different characteristics.Analysis of Hondo profiles, confirms the same trends that we have found in Bertha. During Bertha all the ROs analysed were in TC status, during Hondo they are mostly during tropical depression status. The bending angle anomaly during tropical depression status is usually smaller in amplitude in the UT/LS and the peak is extended up to 25 km of altitude.   The temperature profiles show the TCs warm core and the cold peak reached in the UT/LS. This behaviour is confirmed from ECMWF, AIRS and MLS temperature profile. In the UT/LS the water vapour comparisons with ECMWF show that the model largely influences the mixing ratio profile but the MLS mixing ratio anomaly has a behaviour in agreement with the bending angle anomaly.08/07/2008 Bertha Cat 3 (maximum strength)12/07/2008 Bertha Cat 1-20 0 20 40 60 80 100 120 140 160 1802468101214161820Percentage anomaly [%]Altitude above msl [km]  Bending angleRefractivityTemperatureWV Mixing RatioWV Mixing Ratio ECMWF-10 -5 0 5 10 15 20 25 302468101214161820Percentage anomaly [%]Altitude above msl [km]  Bending angleRefractivityTemperatureUT/LSUT/LS UT/LS-20 0 20 40 60 80 100 120 1402468101214161820Percentage anomaly [%]Altitude above msl [km]  Bending angleRefractivityTemperatureWV Mixing RatioWV Mixing Ratio ECMWF-10 -5 0 5 10 15 20 25 302468101214161820Percentage anomaly [%]Altitude above msl [km]  Bending angleRefractivityTemperature180 200 220 240 260 280 3002468101214161820Temperature [K]Altitude above msl [km]  Hondo´s temperatureAnnual mean valueUT/LSUT/LS UT/LSColder Warmer05/02/2008 Hondo Cat 1 27/02/2008 Hondo tropical depression -20 -10 0 10 20 30 40 50 6002468101214161820Percentage anomaly [%]Altitude above msl [km]-20 -10 0 10 20 30 40 502468101214161820Percentage anomaly [%]Altitude above msl [km]  RefractivityBending angle-20 -10 0 10 20 30 40 50 602468101214161820Percentage anomaly [%]Altitude above msl [km]TC COSMIC CALIPSO MLS AIRS08/07 00.00 08/07 02.0108/07 12.00 08/07 14.19 08/07 16.50 08/07 13.30 08/07 17.0510/07 06.00 10/07 05.34 10/07 05.58 10/07 02.00 10/07 06.1110/07 06.00 10/07 04.36 10/07 05.58 10/07 02.00 10/07 06.1111/07 18.00 11/07 17.21 11/07 13.30 11/07 17.4712/07 12.00 12/07 12.37 12/07 16.5312/07 12.00 12/07 12.47 12/07 16.5313/07 12.00 13/07 17.09 13/07 13.30 13/07 17.3518/07 00.00 18/07 02.44 18/07 05.1719/07 00.00 19/07 02.07 19/07 05.59190 200 210 220 230 240 250 260810121416182022  Temperature [K]Altitude above msl [km]196 198 200 202 204 206 208 2101414.51515.51616.51717.518  190 200 210 220 230 240 250 260810121416182022Temperature [K]Altitude above msl [km]  198 200 202 204 206 208 2101414.51515.51616.51717.518  ECMWFCOSMICAnnual averageAIRSCALIPSOMLS-25 -20 -15 -10 -5 0 5 10 15 20 25810121416182022Percentage [%]Altitude above msl [km]  WV Mix Ratio MLSBending Angle-25 -20 -15 -10 -5 0 5 10 15 20 25810121416182022Percentage [%]Altitude above msl [km]  WV Mix Ratio MLSBending AngleBertha´s anomalyTC season monthly meanNo TC season monthly meanContactsRiccardo Biondi DTU Space email: ribi@space.dtu.dkBertha´s mean values Bertha´s mean values Bertha´s mean valuesHondo´s mean values Hondo´s mean values Hondo´s mean valuesColderBertha´s track correspondences180 200 220 240 260 280 30002468101214161820Temperature [K]Altitude above msl [km]  Annual mean valueHondo´s temperature-50 0 50 100 150 200 250 3002468101214161820Percentage anomaly [%]Altitude above msl [km]  WV Mix Ratio ECMWFRefractivityWV Mix RatioBending angleBertha´s anomalyTC season monthly meanNo TC season monthly mean-20 -10 0 10 20 30 40 50 6002468101214161820Percentage anomaly [%]Altitude above msl [km]  RefractivityBending angle-50 0 50 100 150 200 250 300 350 400 450 50002468101214161820Percentage anomaly [%]Altitude above msl [km]  WV Mix Ratio ECMWFRefractivityWV Mix RatioBending angle180 200 220 240 260 280 3002468101214161820Temperature [K]Altitude above msl [km]  Annual mean valueHondo´s temperature20 40 60 80Percentage anomaly [%]  WV Mixing Ratio ECMW FTemperature Pressure RefractivityWV Mixing Ratio Bending AngleUT/LSAnomaly = (TCvalue -Annualvalue )/Annualvalue

COSMIC Radio Occultation technique for measurement of the tropopause during tropical cyclones

http://orbit.dtu.dk/ws/files/4625483/Poster_COSMIC09.pdf

COSMIC Radio Occultation technique for measurement of the tropopause during tropical cyclones

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