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Global Criteria for Tracing the Improvements of Radiosondes over the Last Decades P. Jeannet 1) , C. A. Bower 2) , B. Calpini 1) 1) MeteoSwiss, Payerne 2) US NWS, Silver Spring. TECO-2006, WMO, Geneva, 05.12.2006. Task, action, deliverables 2004: WMO-CIMO ET on UASI-1. - PowerPoint PPT Presentation

Text of TECO-2006, WMO, Geneva, 05.12.2006

Titel der PräsentationFederal Department of Home Affairs FDHA Federal Office of Meteorology and Climatology MeteoSwiss
TECO-2006, WMO, Geneva, 05.12.2006
Global Criteria for Tracing the Improvements of Radiosondes over the Last Decades
P. Jeannet1), C. A. Bower2), B. Calpini1)
1) MeteoSwiss, Payerne
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Task, action, deliverables
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
Dans le cadre de l’action COST720 ...
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Preliminary analysis
WMO international radiosonde comparisons,
ECMWF model values,
(3) elaborating first a general CIMO questionnaire to the NMHSs, or
(4) extracting numbers from the scientific literature.
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
First WMO radiosonde comparisons:
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
WMO Radiosonde Comparison (Phase VI) at Vacaos, Mauritius, 2005
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
using the previous IOM reports
Candidate criteria: priority to a short list
Temperature:
+ standard deviation
Geopotential height
+ standard deviation
+ standard deviation
(tropospheric values only) + standard deviation
(Wind)
Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Criteria (temperature and geopotential)
Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
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.
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
using the previous IOM reports
Value
Fig. Number of IOM report
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
using the previous IOM reports
All individual values of the previous slide, without any additional information
Graph is „anonymous“
Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
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 thus…not 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’ types…and additionally different data post processing (correction of the radiation error on temperature, etc.)
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for geopotential altitude
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for geopotential altitude
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for temperature
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for temperature
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for temperature
Results of process analyses would bring explanations related to these improvements
(Fig. from J. Nash)
Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for pressure
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for pressure
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
Results for humidity
(see Mauritius report)
Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
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.
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Tracing the Improvements of Radiosondes TECO-2006 P. Jeannet et al.
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.
Pressure bias at 100 hPa, day and night times
-4
-3
-2
-1
0
1
2
3
4
Pressure difference (hPa)
UK 1984 Phase I USA 1985 Phase II URSS 1989 Phase III
Japan 1993 Phase IV Brazil 2001 Phase V Mauritius 2005 Phase VI (only GPS)
Std. Dev. Envelope
0
0.5
1
1.5
2
2.5
3
Std. dev. of differences (hPa)
UK 1984 Phase I USA 1985 Phase II
URSS 1989 Phase III Japan 1993 Phase IV
Brazil 2001 Phase V Mauritius 2005 Phase VI (only GPS)
Mean Envelope
-4
-3
-2
-1
0
1
2
3
4
5
Temperature difference (Degree C)
UK 1984 Phase I USA 1985 Phase II URSS 1989 Phase III
Japan 1993 Phase IV Brazil 2001 Phase V Mauritius 2005 Phase VI
Std. Dev. Envelope
Phase Synthetic Result
I, 1984 At high relative humidity the standard devia tion of all five designs is typically 2.5%
RH, increasing to 6% RH for humidity below about 50% RH (measurements were only
analyzed between surface and 500 hPa).
II, 1985 Based on a repeatability of 2% RH for the carbon hygristor, the repeatability appear s to
be 4-6% for the capacitive sensor, and 10% for the LiCl hygristor (measurements were
only analyzed between surface and 400 hPa) .
I + II The carbon hygristor sensor has a typical reproducibility of about 3.5 % RH, but a poor
resolution at RH below 20 %. The thin film capacitance sensor measures too low near
saturation in low level clouds, but is considered more reliable than the carbon hygristors
at the dry end of the humidity scale. Goldbeater’s skin, hair and Lithium Chloride
sensors have more limited capabilities than the carbon resistor and thin film capacitor
sensors.
III, 1989 The thin film capacitor sensor had a better time response at lower pressure than the
other sensors. However, it did not prove the same reliability under pressure significa ntly
lower than 200 hPa.
IV, 1993 Large humidity differences were observed in the low humidity range, according to the
type of sensor (capacitive film or carbon hygristor).
1995 None of the sensors reported identical humidity profiles. A final, and very important
conclusion is that it is doubtful that the sensor measurements can be accepted at
temperatures lower then -40
o
C.
V, 2001 In the troposphere up to around 8000 m, where the mixing ratio is large, the radiosonde
measurements presented a low disper sion. At higher altitudes the measurements were
highly dispersed.
VI, 2005 Estimating a suitable working reference is most difficult for relative humidity.
At night the two most reliable relative hum idity sensors agreed on average within ±2
percent relative humidity from the surface to 14 km ( -70
o
relative humidity encountered in the intercomparison. This performance represents a
large improvement over any relative humidity sensing system in previous WMO
Radiosonde intercomparison s.
Large systematic biases in relative humidity measurements occurred in nighttime
measurements as well as in daytime measurements. At temperatures higher than -40°C,
maximum bias from the chosen reference at night was + 10 %. In the daytime, many
radiosonde types had systematic biases in the range -10 to -20 % relative humidity for
temperatures lower than -40 °C. Standard deviations of the differences between
different relative humidity sensors were usually relatively small (less than 5 per cent) at
temperatures higher than -40°C, so the random errors in relative humidity were usually
much smaller than the large systematic biases. This suggests that many of the large
systematic biases could be resolved by improved sensor mounting and exposure, plus
improved estimation/measurement of the relative humidity sensor temperature.
Temperature bias at 10 hPa, day
-4
-3
-2
-1
0
1
2
3
4
Temperature difference (Degree C)
UK 1984 Phase I USA 1985 Phase II URSS 1989 Phase III
Japan 1993 Phase IV Brazil 2001 Phase V Mauritius 2005 Phase VI
Geopotential height bias at 10 hPa (night and day for all Phases)
-2000
-1500
-1000
-500
0
500
1000
1500
2000
Geopotential height difference (m)
UK 1984 Phase I USA 1985 Phase II (versus radar) URSS 1989 Phase III
Japan 1993 Phase IV Brazil 2001 Phase V (versus GPS) Mauritius 2005 Phase VI (only GPS)
Std. Dev. Envelope Span
(night and day time results for all Phases)
0
200
400
600
800
1000
1200
1400
1600
1800
Std. dev. of differences (m)
UK 1984 Phase I USA 1985 Phase II (versus radar)
URSS 1989 Phase III Japan 1993 Phase IV
Brazil 2001 Phase V (versus GPS) Mauritius 2005 Phase VI (only GPS)
Mean Envelope
differences
around
night/day time
The 10 hPa level is the highest standard level in the
TEMP messages.
mperature
higher data sample is found
around
G
differences
around
Recent
major
differences
around
time
The 100 hPa level is the primary level used in the
quality control of
with numerical model outputs.
differences
around
essure range.
The 100 hPa level is proposed as it is a primary
pressure
level
monitoring
between
unique range proposed in the left column
: between
-
-
performance.
humidity ranges, a further selection in 3 classes should
be made: e.g. below 25%, 25%

demonstrating the range of systematic errors
in RS80 temperature sensor from 1984 to 2003
Temperature differences of Vaisala RS80 [link radiosonde]
at night from the working reference ,
WMO Radiosonde Comparisons + PREFRS
calibration facilities was faulty
positive offset at low temperatures
for some batches of radiosondes
Increase in error with
in Degree Celsius
Phase -UK 1984
Table used: I:4dII: 5.5 (1400UTC)III: 5.10IV: 2.2a, 2.2.cppt NashFig. 9.13
Type of reading AnalogicAnalogicDigitalDigitalAnalogicAnalogic
0
0.5
1
1.5
2
2.5
3
1980 1985 1990 1995 2000 2005
Std. dev. of differences (Degree C)
UK 1984 Phase I USA 1985 Phase II URSS 1989 Phase III
Japan 1993 Phase IV Brazil 2001 Phase V Mauritius 2005 Phase VI
Mean Envelope

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