Page 1© Crown copyright 2004 Recent progress in the development of Upper air Systems Catherine Gaffard Met Office Upper Air Team, University of Reading With contributions from J.Nash, T.Hewison, Richard Smout and T Oakley
Page 2© Crown copyright 2004 Introduction Upper air observations are required to improve climate and weather prediction Climate observations require “reference” quality, and improved reliability in new generation measurements Observations need to be provided at higher temporal and spatial resolution than in earlier networks for understanding processes for improved data assimilation - (1km grid, update every 15 minutes) Achievable by a mix of in situ measurements (Radiosondes, aircraft) and ground based remote sensing stations to complement satellite observations.
Page 3© Crown copyright 2004 Outline of talk Progress in radiosonde technology Progress in ground base remote sensing for operational use. Expected results from integration Conclusion
Page 4© Crown copyright 2004 Progress in radiosonde technology
Page 5© Crown copyright 2004 Temperature sensors Thermistor or thermocapacitor devices now have fast response, small radiation error. time response = Function of (density, speed of the flow, specific heat, size of sensor, shape of sensor) small and thin sensor will be fast radiation error = Function of (infrared and visible emissivity, total incoming flux in infrared and visible, surface of the sensor, sensor temperature) compensation by radiation correction scheme, however small aluminised coated sensor will have small radiation error thus small error in the correction.
Page 6© Crown copyright 2004 thermistor Modem radiosonde in Brazil,WMO test 2001 Modem radiosonde 2006 white paint coating, fine for short wave. but 0.8 emissivity in IR
Page 7© Crown copyright 2004 capacitor RS80 Vaisala temperature Sensor, 1.2mm diameter RS92 Vaisala temperature Sensor, 0.1mm diameter
Page 8© Crown copyright 2004 Mauritius comparison Temperature sensor evaluation. nearly all RS fall within ±0.20K bias (sip and 3 therm are <0.1K) Graw and Srs had a calibration problem Modem white coating induced strong radiative cooling (replaced now by aluminized coating) 10 years ago bias >1k were commonly observed in the stratosphere (above 25km) The reference is obtained by a careful editing of each flight rejecting data when conta- mination is identified. Night time
Page 9© Crown copyright 2004 std less than 0.1K for RS92 and 3 therm up to 35km, in general very good reproducibility for all sensors
Page 10© Crown copyright 2004 Evaporative cooling, well prevented by RS92 hydrophobic coating cloud top
Page 11© Crown copyright 2004 Geopotential height comparison GPS heights are very consistent with themselves. This seems to indicate that GPS heights are reliable. At 10hPa (31 km) in the tropics an error of 0.1hPa introduces an error of 70m in height
Page 12© Crown copyright 2004 Progress in humidity sensor The majority of modern radiosondes use thin film capacitors e.g. Vaisala(Finland), Meisei (Japan) Modem (France) and Graw (Germany), Sippican (USA), Intermet (USA) Carbon hygristor sensors are much larger than the thin film capacitors. These were distributed widely in the past by Sippican/VIZ [USA], being used by many national radiosonde designs. Sensors also now developed in China and India Gold-beater’s skin sensors have much slower response than the capacitors and hygristors but are still used in Russia and China [ to a limited extent]. Snow white is a chilled mirror hygrometer which measures dew and frost point.
Page 13© Crown copyright 2004 Vaisala RS80 - H Humicap, main UK sensor, thin film polymer, capacitance changes with relative humidity
Page 14© Crown copyright 2004 Sippican Carbon Hygristor, resistance very high at high relative humidity, low at low relative humidity
Page 15© Crown copyright 2004 Vaisala RS90 in 2000, No cover, heating pulses applied alternately to sensors to drive off contamination Sensors In Mauritius in 2005, bare circuit board near sensors aluminised to reduce heating of sensor surrounds, but may not yet be available In operational radiosondes
Page 16© Crown copyright 2004 Vertical structures are very similar in the middle troposphere
Page 17© Crown copyright 2004 Mauritius Intercomparison when temperature <-60C agreement between sensor often diverges
Page 18© Crown copyright 2004 RS 92 against reference very good agreement. Still some discrepancies at very low temperature
Page 19© Crown copyright 2004 Bias for day time larger than at night time (underestimation) Day night difference ~5% for RS92 in the lower troposphere
Page 20© Crown copyright 2004 World wide radiosonde network China is developing new generation of RS
Page 21© Crown copyright 2004 Progress in remote sensing technology
Page 22© Crown copyright 2004 Remote sensing technology may provide :- high time and space resolution data for model validation and initialisation (assimilation) automated unattended system for operational use complement to radiosonde (time evolution), AMDAR (aircraft), and satellite data Instruments considered here Microwave radiometer wind profiler GPS cloud radar, ceilometer
Page 23© Crown copyright 2004 Microwave radiometer : example of radiometer retrieved profile Integrated water vapour with optimum accuracy of ~0.7kg/m^2 (against rs) Integrated liquid water with optimum accuracy ~20g/m^2 (estimated error) temperature better than 1.5K (std) up to 3km (against rs) relative humidity accuracy 20% std (against rs) 12 channels around water vapour line and oxygen complex +IR channel automated unattended high time resolution low vertical resolution
Page 24© Crown copyright 2004 Wind profiler and VAD winds are assimilated in most of NWP centres weather radar VAD wind wind profiler network mixture of operational and research instruments
Page 25© Crown copyright 2004 Wind profiler used for AMMA (African Monsoon Multidisciplinary Analysis) 4 UHF ( 2 are permanently installed for airport security) 1 VHF
Page 26© Crown copyright 2004 example of diurnal cycle during dry season Bamako (march 2005) north easterly LLJ south easterly MLJ convective turbulence shear,friction turbulence
Page 27© Crown copyright 2004 FMCW radar ( affordable technology) Example of low stratus/fog evolution captured by the 78 GHZ cloud radar.
Page 28© Crown copyright 2004 GPS water vapour plot for Europe, showing current sites supplying data to E-GVAP hub in near real-time
Page 29© Crown copyright 2004 Actual GPS sensor site used to measure IWV in Africa
Page 30© Crown copyright 2004 Integrated ground base remote sensing station- expected results
Page 31© Crown copyright 2004 Integrated profiling systems wind profiler SNR+ ceilometer could be used with radiometer to get better vertical structure in the humidity profile RH retrieved by radiometer RH measured by hourly RS SNR measured by WP Refractive (potential) index gradient computed from RS
Page 32© Crown copyright 2004 convective scale: radiometer+ wind profiler vertical speed updraft seen by WP SNR (range corrected) from WP unstable before the updraft stable and lower RH in the updraft event last ~10min in the future it will be possible to assimilate such structure.
Page 33© Crown copyright 2004 cloud radar and ceilometer integration liquid content=Function (size and concentration) Cloud radar Zdb function of size( D^6)and concentration Ceilometer return, function of size(D^2) and concentration, The combination of the 2 allows an estimate of the water liquid profile for thin water cloud. Cloud base
Page 34© Crown copyright 2004 conclusion (radiosondes) Radiosondes are the only instrument that can give detailed profiler of humidity, temperature collocated with wind. It’s essential for climate reference that radiosonde biases are minimised and kept stable. New generation of radiosondes have much better design which minimise radiation error for temperature sensor. In the night, the absolute accuracy of the temperature sensor is reaching 0.1K with a very good reproducibility 0.1K. Climate monitoring with selected type of radiosonde could be envisaged using night temperature. China is developing new generation radiosondes.
Page 35© Crown copyright 2004 conclusion (radiosonde) There is no discrepancy between GPS height. Pressure sensor might become obsolete unless accuracy in both sensor can become such that their information could be used for non-hydrostatic model. For the humidity, in the middle troposphere,at night, the performance of sensors in Mauritius test was rather similar within ±5%. At higher level above 11km or when the temperature start to be lower than -60C, the agreement between all the radiosonde diverge. The best agreement with the snow white is obtained with RS92.
Page 36© Crown copyright 2004 conclusion ( remote sensing) The need for weather forecasting and understanding physical processes for climate prediction, requires data at high temporal and spatial resolution. This can only be achieved by a mixture of in situ and remote sensing. With the help of European funding, the development of a European network of wind profiler has facilitated the use of wind profiler and VAD wind. During AMMA, the deployment of wind profiler in Africa was successful, demonstrating the maturity of this remote sensing technique. Help from international funding will lead to sustainable development of wind profiler network, including training for technicians supporting the systems.
Page 37© Crown copyright 2004 conclusion ( remote sensing) With the evolution in the software and network architecture, GPS integrated water quantities are now available within 15 min. Integrated water quantities are now assimilated operational into NWP. This information is cheap and funding to help various regions to expand their actual networks is desirable. While having a limited vertical resolution, radiometers have the potential to be useful for high time resolution description of physical processes. FMCW cloud radars are becoming affordable as operational instruments. An integrated approach has the prospective to deliver better products than independently retrieved quantities.
Page 38© Crown copyright 2004 Conclusion : Future work The Met office is currently working on costed option of a new upper air network which can deliver the user needs for new generation of NWP. Several country in Europe including operational and research centre have expressed their interest for collaborative work to deliver an improved cost-effective European ground-based observing system design, providing essential atmospheric observations for both climate and weather from one integrated operational network for the decade
Page 39© Crown copyright 2004 Questions & Answers
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Page 41© Crown copyright c1c std less than 0.1K for rs92 and 3 therm up to 35km, in general very good reproducibility for all sensors
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Page 43© Crown copyright 2004 std larger at day time than at night time above 15km for all the sensors due to solar heating
Page 44© Crown copyright 2004 Wind Profiler UK Model Assimilation 7 sites Other NWP Centres DWD – 20 Sites Meteo France – 26 Sites (with restrictions) ECMWF – 13 Sites
Page 45© Crown copyright 2004 Weather Radar UK Model Assimilation 27 sites Other NWP Centres Only SMHI (local)