Page 1© Crown copyright 2004 Review of Progress in the Development of Operational Upper Air Technology May 2005.

© Crown copyright 2004 Introduction to Wind Profilers in the UK John Nash, Upper Air Team Manager Observing Methods Technology Centre, Technology and Applied Science Met Office, Exeter, UK john.nash@metoffice.gov.uk

© Crown copyright 2004 Introduction Progress will be reviewed for four different types of upper air system  Radiosondes – giving very detailed vertical profiles of temperature, relative humidity and wind  Wind profilers and Doppler weather radars, able to provide continuous monitoring of upper wind given suitable conditions  Microwave radiometers, able to provide continuous monitoring of temperature, water vapour and cloud properties in the lower troposphere, but with certain limits on vertical resolution  GPS measurements of integrated water vapour, able to provide continuous monitoring of integrated water vapour from a large number of sites.

© Crown copyright 2004 General comments (1)  Groundbased remote sensing offers the chance of measurements at very high temporal resolution, but for temperature and humidity poorer vertical resolution than radiosondes  Is ground based remote sensing developed with research interests in mind or are the systems being moved towards operational applications?  Do operational meteorologists hinder development by lack of consistency in suitable specifications for systems, e.g. Should the customer provide the detailed techcnical specification for his solution, or just the required accuracy of the system ouptut + certain basic technical requirements?  Is the failure to produce many skilled upper air instrument specialists within the NMHS services hindering progress, with poor guidance being provided to manufacturers?

© Crown copyright 2004 General comments (2)  Operational upper wind and temperature measurements from large commercial aircraft are of similar quality to some radiosonde systems. Relative humidity measurements are starting to become available in the US, see following talk by J. Stickland.  However, radiosonde and ground –based vertical soundings do have a viable future, since there are clearly areas in every upper air network where aircraft will never provide enough operational measurements.  The question of a viable market size for instrument manufacturers [ e.g. for wind profilers] and the impact on unit costs of drastically reducing the number of radiosondes in use should not be ignored by network planners.

© Crown copyright 2004 Progress with radiosondes [as indicated by WMO High quality radiosonde test, Mauritius]  Small temperature sensors with rapid time constants of response allow daytime solar heating errors to be reduced to less than 1.5 deg C at 10 hPa, on many radiosondes.  At night, temperatures of the best radiosondes agree to within 0.3 deg C, as long as aluminized sensors are used to ensure minimal coupling to the infrared radiation fields.  Many relative humidity sensors now provide consistent results in both wet and dry conditions, with reasonably good agreement in vertical humidity structure down to temperatures of -70 deg C.  Most relative humidity sensors have a day-night bias of at least 5 per cent at high humidity in the tropics, and this problem has yet to be tackled properly.

© Crown copyright 2004 Progress with radiosondes continued  Code correlating winds have good accuracy with low amounts of missing wind data  Radiosonde transmitters are narrow band and much more stable than in earlier generations, so WMO cannot be criticised for wasting spectrum by ITU  This has a by-product in that it is much easier to perform comparison testing with large numbers of radiosondes than in earlier years.  Height assignment errors at pressures lower than 100 hPa from pressure sensor errors can be eliminated by using GPS height measurements

© Crown copyright 2004 Current problems [1]  The rapid change over to the new radiosondes is causing problems to many Members. Customers are reluctant to pay the price associated with upgrade. On the other hand manufacturers need to change techniques, e.g. soldering, and must use modern manufacturing technology to minimise production costs.  The customer cannot be expected to pay for endless upgrades, particularly when equipment was purchased as perfectly adequate only a few years ago.  The solution requires serious negotiation between the two parties, or external help from those with the necessary technical background.

© Crown copyright 2004 Countries that wish to manufacture their own radiosondes  The radiosondes from these countries generally lag behind the measurement quality of the commercially available radiosondes  Better methods need to be devised by CIMO to encourage progress with the new designs currently being prepared for introduction.

© Crown copyright 2004 Some questions?  Should wind profilers cost as much as weather radars or do they need to be significantly cheaper?  Do wind profilers need to be as accurate as the best radiosondes or can larger random errors be tolerated?  How do users and manufacturers work together to keep costs down?  Are existing wind profilers positioned in the most beneficial localities?

© Crown copyright 2004 Microwave radiometer  In the last three years the cost of multichannel microwave radiometers has begun to drop from about €400,000 towards €130,000. In the very long term, this technology may become very much cheaper than this…  The radiometers can provide temperature and relative humidity profile in the lower troposphere, with much less vertical resolution than a radiosonde, but with continuous monitoring.  The radiometers have now been improved with blowers to allow operation in light rain and drizzle. Integrated water vapour measurements are of good quality apart from in heavier rain.  Scan rates of the radiometers have improved so that sampling is now more appropriate for measuring cloud properties such as total liquid water content plus profiles of liquid water,  In the UK, the radiometers have been very reliable in deployment needing little maintenance intervention.

© Crown copyright 2004 Radiometrics MP3000 Microwave Radiometer  7 Channels: 51-59 GHz  O 2 band - temp. profile  5 Channels: 22-30 GHz  H 2 O line - humidity, cloud  Infrared Radiometer  Pressure, temp., RH sensors  Dew Blower & Rain Sensor  Automatic Calibration black body, noise diode  Zenith and Elevation Scans  Zenith, ±60°, ±70°, ±75°  Observation Cycle: 1 min Radiometrics MP3000 Microwave Radiometer at Camborne

© Crown copyright 2004 Radiometer Physics HATPRO  Filter bank Design – Fast!  22-29 GHz – humidity/cloud  51-58 GHz – temperature  Beamwidth: 3.5  at 22 GHz  Radiometric noise: 0.3-0.4 K rms at 1.0 s integration  Absolute system stability: 1.0K  Thermal stability: < 0.02 K  Rain sensor and shutter (including a dew-blower)  Integrated PC on-board  GPS clock  Pressure, humidity, temperature sensors  Optional IR-radiometer  Frequency extension possible by tandem operation  “Low cost”! Radiometer Physics’ HATPRO Humidity And Temperature PROfiler

© Crown copyright 2004 Calibration Differences MP3000-HATPRO Average Differences between MP3000-Modelled sondes and MP3000-HATPRO in clear skies during HATPRO trial 10/11/04-3/1/05, Camborne (12 cases) Error bars indicate standard errors of averages. Estimate of HATPRO - Modelled radiosondes

© Crown copyright 2004 Microwave radiometers will probably be used in conjunction with other sensing systems in future.  The COST 720 Integrated profiling project expects a combination of :- microwave radiometer laser ceilometer surface measurements cloud radar to provide estimates of cloud structure/liquid water content + temperature and relative humidity profiles. Use with wind profiler/ and or weather radar signals is also to be investigated

© Crown copyright 2004 GPS water vapour  Needs GPS antenna installed on stable mount with good horizon and minimal multipath reflections, i.e. GPS cannot be readily reflected into the antenna from nearby surfaces, see next slide  GPS receiver must process signals at two frequencies to allow compensation for signal delays in the ionosphere, see following slide  Receiver needs realtime communications to a central processing centre  In order to compute integrated water vapour amount it is essential to measure atmospsheric pressure at the antenna height, and it is helpful

© Crown copyright 2004 How to afford a detailed network with spacing between sensors less than 70 km??  Installation of receiver + purchase of receiver costs about £15,000, so it is too expensive for the Met Office to install a widespread network  All wind profilers in the UK have a collocated GPS sensor since the combination of wind + water vapour measurement at high temporal resolution is much more useful than water vapour on its own  UK network has now increased to more than 70 sites, because of a memorandum of understanding with the UK national mapping Agency [Ordnance Survey], where the Met Office hosts some of the Ordnance Survey sensors at some automatic weather station sites. In return Ordnance Survey allow access to the data from all their sites in the UKas collected at the HQ in Southhampton.

© Crown copyright 2004  The capability of the GPS network across the British Isles is illustrated by hourly measurements associated with a warm and then a cold front crossing the British Isles in April 2005  These measurements were delivered to users 45 minutes after the end of the sample period. Processing was performed at Nottingham University on a system to be reinstalled at the Met Office in May 2005.  The plots are contoured at 2 kg.m -2 intervals, with 21 kg.m -2 corresponding to saturation with respect to water in the warm sector and 17 kg.m -2 to saturation in the colder air.  Random error in the water vapour measurements is expected to be about 1 kg.m -2 corresponding to an average random error in relative humidity of between 5 and 6 per cent at these temperatures

© Crown copyright 2004 Summary about GPS water vapour  GPS water vapour measurements are not yet handed over to full time operations in any national network.  Whilst improved forecast capability is found using data from pre- operational real time networks in the USA and Europe, evidence of benefit has not always been so strong that all countries performing research are willing to invest in the costs of an operational network.  Costs can clearly be reduced by cooperating with other agencies deploying GPS sensors, e.g. for geodesy, surveying, seismology, tide gauges, marine navigation and other transport and tracking applications.  This system will work well in tropical countries, but probably requires centralised regional processing and measurement distribution to be established through some cooperative program.

Page 1© Crown copyright 2004 Review of Progress in the Development of Operational Upper Air Technology May 2005.

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Page 1© Crown copyright 2004 Review of Progress in the Development of Operational Upper Air Technology May 2005.

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