1. 1 Modern Observing Systems Used in NWP Mohan Ramamurthy Department of Atmospheric Sciences University of Illinois at Urbana- Champaign E-mail: mohan@uiuc.edu COMET Faculty Course on NWP June 7, 1999

2. 2 Acknowledgement Tom Schlatter NOAA Forecast Systems Laboratory A significant part of this presentation is based on Tom’s talk at the COMAP Symposium on Numerical Weather Prediction on 17 May 1999

3. 3 Observing Systems & NWP Modern observing systems (in-situ and remote sensing instruments) Quality control Objective analysis and initialization Four-dimensional data assimilation Data sensitivity/impact Observing system experiments Sampling strategies: Adaptive (targeted) observations

4. 4 Data Assimilation

5. 5 OUTLINE How does this talk relate to NWP? What observations are only recently being assimilated into operational U.S. models? What you need to know about automated aircraft reports and profiler data with regard to NWP The North American Atmospheric Observing System (NAOS) program - What problems does it tackle?

6. 6 How does this talk relate to NWP? Observations feed prediction models. For short forecasts, accuracy of initial state is more of an issue than realism of model. Observations used to gauge accuracy of evolving forecast, to formulate the nowcast (30-90 minute extrapolation). ACARS and profiler observations, separately and together, have led to improvements in tropospheric predictions of temperature and wind. New products from these sources can also help you improve your nowcast. NAOS strives to put logic behind the proliferation of observing systems. What observing strategies are best for NWP? Targeted observations: put them where they make the most difference in downstream forecast accuracy.

7. 7 “ Traditional” Observations used to initialize Operational NWP Models  Surface observations (ASOS, Synop, etc)  Surface ship observations  Upper-air radiosondes  Upper-air wind observations  Buoy data from ocean platforms  Bogus observations (e.g., Hurricanes)  AIREP/AMDARAircraft observations  SATEMTemperature soundings from POES  TOVSTemperature soundings from POES  SATOBCloud motion winds

8. 8 What observations are only recently being assimilated into operational U.S. models? Note: Listed data sources are being assimilated into at least one of these three NCEP models: AVN/MRF, Eta, and RUC-2. VAD winds from WSR-88D Raw radiances from NOAA satellites Precipitable water vapor estimates from satellites Scatterometer data (to infer winds at sea surface) ACARS en route and ascent/descent data Boundary-layer profilers Radio Acoustic Sounding System Cloud-drift winds from GOES

9. 9 Coming Soon raw radiances from GOES satellite radial winds from WSR-88D water vapor drift winds from GOES precipitable water vapor estimates from GPS receivers on the ground This lecture focuses on those observation sources highlighted in red.

10. 10 Hourly Data for MAPS/RUC-2 (Source: Stan Benjamin, FSL) Yellow items new for RUC-2

11. 11 Hourly Data for MAPS/RUC-2, continued Yellow items new for RUC-2 Real-time observation counts at http://maps.fsl.noaa.gov for RUC-2 and 40-km MAPS

12. 12 ACARS Aircraft Addressing and Reporting System Digital data link system transmitted via VHF radio, allowing airlines to communicate with aircraft in their fleet “email for airplanes” - each aircraft has a unique address Nearly 50,000 observations/day –About 16,000 observations between 0500 and 1400 UTC

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15. 15 Distribution of ACARS Data on 1/10/99

16. 16 Nominal contribution of different airlines to the total daily number of ACARS reports American11% Delta 23% Federal Express 4% Northwest 7% United26% United Parcel Service29% (for 17 June 1998)

17. 17 Number of ACARS Ascents/Descents during a one week period: 26 July-2 August, 1998

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19. 19 Eta model 3D VAR Data Sensitivity Source: CIMSS

20. 20 What is new with ACARS? More reports More airlines participating in data collection Increasing percentage of ascent / descent reports Web page available to WFOs Water Vapor Sensing System

21. 21 Water Vapor Sensing System (WVSS) A water vapor sensor installed on commercial aircraft that delivers relative humidity values along with wind and temperature as part of the ACARS/MDCRS report.

22. 22 WVSS Probe Source: Rex Fleming

23. 23 Progress As of January 1999, 104 aircraft-weeks of WVSS reports (~190,000) had been collected. Two different aircraft obtained the measurements. With careful calibration, the WVSS delivers good humidity information under a wide variety of conditions, including in the high troposphere. Errors range from ~4% in mid-troposphere at low Mach numbers to ~17% in the high, cold troposphere at high Mach numbers. 5 UPS aircraft now equipped with WVSS NOAA owns 60 total systems; within ~12 months, about half should be installed on UPS and the other half on American jets.

24. 24 Problems UPS has been very slow to add new sensors to its fleet. Other airlines have expressed interest but have not yet agreed to install the sensors on their aircraft. Some airlines prefer a single probe for temperature and humidity rather than two separate probes, as is the case now. This is prompting a redesign of the WVSS and requires new FAA approval--a lengthy process.

25. 25 NOAA Profiler Network

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27. 27 What’s new in atmospheric profiling? Potential of 6-min data Potential to infer vertical gradient of mixing ratio Loss of frequency allocation for NOAA Network Boundary-layer profiler data and RASS data available on the Web Processing GPS signals to obtain total precipitable water

28. 28 The Radio Acoustic Sounding System (RASS) Operates in conjunction with a wind profiling radar Sound waves emitted upward from the ground When the acoustic frequency of the sound waves is just right, the profiler can sense the velocity of the sound waves as a function of height. The speed of sound c is related to the virtual temperature T v through c = (  RT v ) 1/2 where  is the ratio of specific heat at constant pressure to that at constant volume for dry air, and R is the gas constant for dry air. T v = (c / 20.047) 2 when c is in m s -1 and T v is in degrees K.

29. 29 RASS & 915 MHz BLP RASS Signal

30. 30 RASS Example: Warm Front

31. 31 Boundary Layer Profilers Small, low-cost UHF Doppler radars Fixed as well as portable Resolution: 60 - 400 m AGL Range: Winds up to about 3 km AGL As of now ~ 65 BLPs Operated by ~30 agencies in different ways! Most provide hourly winds, some every 10 minutes

32. 32 Boundary Layer Profiler Network

33. 33 GPS Integrated Precipitable Water Measurement A new method for measuring water vapor. Radio signals propagating through the atmosphere are refracted (bent and delayed) by the ionosphere and the neutral troposphere. The ionospheric effect can be removed via dual frequency signal. GPS detects water vapor due to the delay of the signal from the satellite to the receiver. Water vapor degrades GPS positioning accuracy. However, if the position of a receiver is known, the receiver can then detect the errors in the GPS signal and determine with great precision the water vapor content in the atmosphere. GPS receivers can be ground based or LEO satellite based. Several IPWV networks of GPS receivers now exist.

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35. 35 A ground GPS receiver at a NOAA/ERL Profiler site

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37. 37 Thunderstorm

38. 38 NOAA GPS-IPW Demonstration Network SEAW HKLO NDSK DQUA WSMN GDAC VCIO HVLK HBRK PRCO WES2 AOML KYW1 EKY1 MOB1 ENG1 GAL1 ARP3 NDBC PLTC JTNT PATT CCV3 WNFL SIO3 TCUN MNP1 SHK1 900 km LMNO CHA1 FMC2 WLCI SYCN OPERATING NOAA (FSL & NGS) GPS-IPW SITES OPERATING DGPS SITES w/ GSOS EXPLANATION SCHEDULED FSL GPS-IPW SITES CENA TLKA GNAA

39. 39 GPS/MET: Satellite-based Receivers A constellation of GPS/MET LEO satellites needed to make impact on NWP Currently 125 (limit 500) proof-of-concept soundings made with MicroLab-1 receiver Use 24 GPS Occulting Satellites (20,231 km) with LEO micro-satellites (885 km) UCAR/COSMIC planning to deploy 8 LEO satellites by 2002 Use double-differencing method ~4000 GPS/MET soundings/day will be obtained

40. 40 Advantages of GPS/MET data High accuracy High vertical resolution Full global coverage (distribution scattered) All weather – unaffected by clouds, aerosols, precipitation Requires no first guess No instrument drift Independent of radiosonde calibration Complementary to ground and space nadir viewing instruments

41. 41 DOT NDGPS (SCHEDULED)66 USCG DGPS (INSTALLED)11 USCG DGPS (PENDIING)54 USCG LORAN (TENTATIVE)20

42. 42 Addition of Calibrated GOES-8 TPW Improves the Spatial Resolution of GPS-only IPW Data. 5 NOV 1997 1500 UTC NCAR_IPWPPT

43. 43 Web Address For comprehensive information about: NOAA Network Profilers and RASS Boundary-layer profilers Surface-based estimates of total precipitable water vapor from GPS Go to: http://www-dd.fsl.noaa.gov/profiler.html

44. 44 Introduction to NAOS NAOS - North American Atmospheric Observing System Program to make recommendations on the configuration of the upper air observing systems over North America and adjacent water areas NAOS Council has representatives from 15 agencies in U.S., Canada, and Mexico to identify issues, set priorities, coordinate work of the program, and seek financial support NAOS Test and Evaluation Working Group –Assesses potential effects of proposed observing systems and configurations on the overall efficacy of forecasting services. –Assessments involve tests of hypotheses concerning the sensitivity of forecast accuracy to specific mixes of observing systems. –Assessments must also consider utility of data to field forecasters, who use them subjectively, and to the climate community.

45. 45 Hypothesis 1 It will be possible to reduce the number of rawinsondes in the U.S. network without noticeably reducing forecast accuracy provided that the sites removed have substitute observing systems already in place. Test in two steps: Identify rawinsonde sites close to busy hub airports. At these sites withhold rawinsonde and all potential substitute observations for the periods covered by the sensitivity test. Compare forecasts generated from reduced data set with operational forecasts. Restore all substitute observations but continue to withhold rawinsondes. Compare these forecasts with operational forecasts.

46. 46 Selection criteria for matching raob sites and hub airports 1) Average number of ascents or descents per day (fewer on weekends) 2) Distance from the airport to the raob site 3) Expected similarity in climate between the airport and raob site 4) Average number of points in aircraft "slant” sounding 5) Impact of deletions on overall uniformity of rawinsonde distribution 6) Don't touch GCOS sites.

47. 47 Match-ups RaobAirport# Ascents and Descents / week Salem ORPortland~100 Oakland CASan Francisco>500 Desert Rock NVLas Vegas>100 Salt Lake City UTSalt Lake City50-80 Santa Teresa NMWhite Sandsprofiler Denver CODIA~500 Fort Worth TXDallas/Fort Worth~ 80 Topeka KSKansas City(MCI)40-70 Chanhaussen MNMinneapolis (MSP)~ 20 Buffalo NYToronto25-30 Peachtree City GAAtlanta~ 50 Slidell LANew Orleans~ 75 Miami FLMiami (MIA)~ 65 Upton NYNew York City (JFK)>150

48. 48 Test Status for Hypothesis 1 May 1999 NASA has donated computer time on its 32- processor Cray J-90. Wintertime tests (late Dec 97 until mid-Feb 98) have been completed on the J-90 computer with NCEP’s global spectral model (MRF) and Eta model. No statistically significant degradation noticed so far in the tests with the above two models. Individual short-range forecasts may be different. Tests with the RUC-2 model are in progress.