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TECO-2006, WMO, Geneva, 05.12.2006

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Title: Titel der Pr sentation Author: Holderegger Christian Last modified by: Etudiant Jeannet Created Date: 3/16/2006 8:40:30 AM Document presentation format – PowerPoint PPT presentation

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Title: TECO-2006, WMO, Geneva, 05.12.2006


1
Global Criteria for Tracing the Improvements of
Radiosondes over the Last Decades P. Jeannet1),
C. A. Bower2), B. Calpini1) 1) MeteoSwiss,
Payerne 2) US NWS, Silver Spring
  • TECO-2006, WMO, Geneva, 05.12.2006

2
Task, action, deliverables 2004 WMO-CIMO ET on
UASI-1
  • Task develop performance measures to demonstrate
    the continuous improvement in the quality of
    upper-air observations.
  • Action elaborate global criteria for tracing the
    improvements, based on previous intercomparisons
    and recent radiosonde development, and including
    remote sensing
  • Deliverables IOM report on global criteria for
    tracing the improvements of radiosondes

3
Preliminary analysis
  • Following methods were considered
  • (1) using the previous IOM reports on the
    WMO international radiosonde comparisons,
  • (2) comparing radiosonde measurements with
    ECMWF model values,
  • (3) elaborating first a general CIMO
    questionnaire to the NMHSs, or
  • (4) extracting numbers from the scientific
    literature.

4
First WMO radiosonde comparisonsWMO World
Comparison of Radiosondes at Payerne,
Switzerland 1950 and 1956
5
WMO Radiosonde Comparison (Phase I) at Beaufort
Park, U.K., 1984.
6
WMO Radiosonde Comparison (Phase VI) at Vacaos,
Mauritius, 2005
7
using the previous IOM reports
  • Candidate criteria priority to a short list
  • Temperature
  • Mean difference _at_10hPa or 30 hPa DAY/NIGHT time
    standard deviation
  • Geopotential height
  • Mean difference _at_10hPa or 30 hPa DAY/NIGHT time
    standard deviation
  • Mean difference _at_100hPa DAY/NIGHT time
    standard deviation
  • Humidity
  • Mean difference in the temperature range -35 to
    -45C, (tropospheric values only) standard
    deviation
  • (Wind)

8
Criteria (temperature and geopotential)
9
using the previous IOM reports
  • Candidate criteria are based on differences
    between simultaneous measurements obtained with
    different types of radiosondes launched under the
    same balloon (50-100 launches during an
    intercomparison)
  • The first WMO radiosonde comparisons defined 15
    pressure categories in the comparison of
    simultaneous measurements. The 10 hPa category
    considered all measurements between 8.4 and 11.9
    hPa, as defined by the link sondes. The 30 hPa
    category was more exactly centred at 32 hPa (24.5
    41.5). The 100 hPa category range was 84 119
    hPa. This ensured that the statistics were
    relying on a sufficient number of time-paired
    measurements. In the more recent radiosonde
    comparisons, 2 km wide altitude categories were
    introduced instead of the previous ones.
  • This method represents a valuable tool for
    comparison over the last two decades.
  • Examples (Excel file and graph) systematic
    temperature differences _at_10 hPa, _at_ day time

10
using the previous IOM reports
Systematic temperature differences at 10 hPa, day
time, in degree Celsius. All individual values
extracted from the IOM reports without any
modification
Value
Fig. Number of IOM report
11
using the previous IOM reports
All individual values of the previous slide,
without any additional information Graph is
anonymous
12
using the previous IOM reports
  • Results presented in somewhat different forms
  • final reports Brazil and Mauritius !
  • Some intercomparisons addressing a given class
    of parameters and thusnot presenting all the
    necessary results.
  • Brazil 2001 relative humidity measurements in
    the tropics and performance of the GPS sondes.
  • No true reference sonde, but link radiosondes
    thus only relative numbers can be extracted, but
    they are still somewhat related to absolute
    accuracy
  • Different sondes typesand additionally
    different data post processing (correction of the
    radiation error on temperature, etc.)

13
Results for geopotential altitude
Bias of the geopotential altitude around 10 hPa
(simultaneous measurements)
14
Results for geopotential altitude
Estimated random errors of the geopotential
altitude around 10 hPa (simultaneous
measurements)
15
Results for temperature
Bias of the temperature around 10 hPa
(simultaneous measurements ) night/day time
16
Results for temperature
Standard deviation of the temperature around 10
hPa (simultaneous measurements)
17
Results for temperature
  • Results of process analyses would bring
    explanations related to these improvements (Fig.
    from J. Nash)

18
Results for pressure
Bias of the pressure around 100 hPa (simultaneous
measurements)
19
Results for pressure
Estimated random errors of the pressure
measurements around 100 hPa (simultaneous
measurements)
20
Results for humidity (see Mauritius report)
21
Conclusions radiosonde improvements over the
last 20 years
  • Geopotential height around 31 km (10 hPa) the
    largest improvements (one order of magnitude) due
    to GPS
  • Temperature an improvement by a factor of 3
    around 31 km.
  • Pressure large improvements, GPS technology is
    a way of improving the pressure measurement
    accuracy in the stratosphere
  • Humidity most challenging parameter, strong
    deficiencies in the past, the Mauritius
    intercomparison documents a large improvement
    over any hygristor in the past.
  • Wind not studied, but large improvement due to
    GPS.

22
Final remarks
  • The proposed criteria can be extracted from the
    IOM reports, as well as from other/further
    radiosondes intercomparisons.
  • They rely on comparisons of simultaneous
    (time-paired) measurements.
  • This method provides valuable results, but also
    suffers from some limitations despite the fact
    that the WMO intercomparisons are very carefully
    organized.
  • Remote sensing was not introduced in this study.
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