Recent progress in the development of Upper air Systems

1. 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

2. 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.

3. Outline of talk • Progress in radiosonde technology • Progress in ground base remote sensing for operational use. • Expected results from integration • Conclusion

4. Progress in radiosonde technology

5. 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 .

6. thermistor white paint coating, fine for short wave. but 0.8 emissivity in IR Modem radiosonde 2006 Modem radiosonde in Brazil,WMO test 2001

7. capacitor RS80 Vaisala temperature Sensor, 1.2mm diameter RS92 Vaisala temperature Sensor, 0.1mm diameter

8. Mauritius comparison Temperature sensor evaluation. The reference is obtained by a careful editing of each flight rejecting data when conta- mination is identified. Night time -0.5 0.5 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)

9. 0.0 0.4 0.2 std less than 0.1K for RS92 and 3 therm up to 35km, in general very good reproducibility for all sensors

10. cloud top Evaporative cooling, well prevented by RS92 hydrophobic coating

11. 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

12. 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.

13. Vaisala RS80 - H Humicap, main UK sensor, 1996 -thin film polymer, capacitance changes with relative humidity Protective cap essential for cloudy conditions

14. Sippican Carbon Hygristor,resistance very high at high relative humidity, low at low relative humidity Hygristor mounted in a duct within the radiosonde body Sensor Length =65 mm Electrical contacts

15. Vaisala RS90 in 2000,No cover, heating pulses applied alternately to sensors to drive off contamination Sensors faces downward in flight faces upward in flight 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

16. Vertical structures are very similar in the middle troposphere

17. Mauritius Intercomparison when temperature <-60C agreement between sensor often diverges

18. RS 92 against reference very good agreement. Still some discrepancies at very low temperature

19. Bias for day time larger than at night time (underestimation) Day night difference ~5% for RS92 in the lower troposphere

20. World wide radiosonde network China is developing new generation of RS

21. Progress in remote sensing technology

22. 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

23. Microwave radiometer : example of radiometer retrieved profile temperature better than 1.5K (std) up to 3km (against rs) • 12 channels • around water • vapour line • and oxygen • complex • +IR channel • automated • unattended • high time • resolution • low vertical • resolution relative humidity accuracy 20%std(against rs) Integrated water vapour with optimum accuracy of ~0.7kg/m^2 (against rs) Integrated liquid water with optimum accuracy ~20g/m^2 (estimated error)

24. Wind profiler and VAD winds are assimilated in most of NWP centres wind profiler network mixture of operational and research instruments weatherradarVAD wind

25. Wind profiler used for AMMA(African Monsoon Multidisciplinary Analysis) 4 UHF ( 2 are permanently installed for airport security) 1 VHF

26. south easterly MLJ north easterly LLJ example of diurnal cycle during dry seasonBamako (march 2005) convective turbulence shear,friction turbulence

27. FMCW radar ( affordable technology) Example of low stratus/fog evolution captured by the 78 GHZ cloud radar.

28. GPS water vapour plot for Europe, showing current sites supplying data to E-GVAP hub in near real-time 12 17 37 18 32

29. Actual GPS sensor site used to measure IWV in Africa

30. Integrated ground base remote sensing station- expected results

31. Integrated profiling systems SNR measured by WP RH retrieved by radiometer Refractive (potential) index gradient computed from RS RH measured by hourly RS wind profiler SNR+ ceilometer could be used with radiometer to get better vertical structure in the humidity profile

32. convective scale: radiometer+ wind profiler 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. vertical speed updraft seen by WP

33. 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

34. 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 .

35. 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.

36. 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.

37. 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.

38. 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 2010-2020.

39. Questions & Answers

41. 1 c std less than 0.1K for rs92 and 3 therm up to 35km, in general very good reproducibility for all sensors

43. std larger at day time than at night time above 15km for all the sensors due to solar heating

44. Wind Profiler UK Model Assimilation 7 sites Other NWP Centres DWD – 20 Sites Meteo France – 26 Sites (with restrictions) ECMWF – 13 Sites

45. Weather Radar UK Model Assimilation 27 sites Other NWP Centres Only SMHI (local)