Impact of Radiosonde Measurement
Accuracy on Predicting Weather
Johanna Lentonen, Raisa Lehtinen, Petteri Survo, Mona Kurppa
Vaisala Oyj
VAISALA
WMO TECHNICAL CONFERENCE ON METEOROLOGICAL AND
ENVIRONMENTAL INSTRUMENTS AND METHODS OF OBSERVATION
Session 2B
Madrid, Spain, 7-30 September 2016
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Content
 Radiosonde and atmospheric profile
 Meteorological indices, sensitivity on measurement errors
 Overview of indices
 Statistical study, method
 Results
 Winter precipitation type, sensitivity on measurement errors
 Atmospheric profile and precipitation types
 Case study, method
 Results
 Summary
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Radiosonde and atmospheric profile
 Temperature, humidity and wind profile
from ground up to 35 km
 Radiosonde data is used for
 numerical weather prediction (NWP)
 weather forecasting
 research
 climatology
 validation (satellites, NWP, ground
based remote sensing)
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Radiosonde and atmospheric profile
 Accurate profiles with details are
challenging to measure consistently in all
atmospheric conditions
-> Do accuracy and details matter?
 Two areas covered in this study
 sensitivity of meteorological indices
 sensitivity of winter precipitation type
 Method: The results of the profiles
including artificially made small errors are
compared with the original ones
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Summary
Meteorological indices and treshold values
 Meteorological
indices help
forecasters make
faster conclusions
in situations
where convection
and severe
weather are likely
to appear in the
next few hours
INDEX
PURPOSE
UNIT
WEAK
BRN
Storm cell type
-
< 10 pulse type 10-50 multi-cells
convection
Deep moist
convection
(thunder)
Will convection
happen?
J/kg
USA: < 500
Europe:< 100
USA: 500-2000
USA:> 2000
Europe:100-1000 Europe:> 1000
J/kg
> -50
< -50
Downdraft
strength
Instability
J/kg
< 500
500 – 800
> 800
20 – 30
> 30
Instability and
°C (K) USA:> -2
thunder potential
Europe:> 0
USA: -2 … -4
Europe:0 … -2
USA: < -4
Europe: < -2
Instability
0 … -3 thunder
< -3 severe
thunder
Bulk Richardson
Number
CAPE
Convective Available
Potential Energy
CIN
Convective Inhibition
DCAPE
Downdraft CAPE
KI
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STRONG
> 50 supercells
K-index
LI
 7 indices included
in the study
°C (K) < 20
MODERATE
Lifted Index
SI
Showalter Index
°C (K) > 0 showers
VAISALA
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Meteorological indices - method of study
 Sounding data from two regions
 RS92 or RS41, total 56 soundings
 University of Wyoming archive (2015)
 Severe convective weather conditions
 Small artificial errors introduced
 Offsets ± 0.2ºC, - 2%RH, - 4%RH,+ 2%RH
 Original and modified profiles were
analyzed with RAOB 6.3 -> indices
 Indices were analyzed, using original
profiles as a reference
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Meteorological indices, results (1/3)
Relative change, all soundings
 Relative change caused by
humidity offsets, ± 2%RH, - 4%RH,
were bigger than the change
caused by the applied temperature
offset ± 0.2ºC
 Humidity offset of - 4%RH:
 CAPE relative change 29%. CAPE
most significant in absolute values.
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Summary
Meteorological indices, results (2/3)
CAPE and CIN, absolute change as function of original value, - 4%RH offset
• Significant shifts of - 500…- 250 J/kg in an interesting
CAPE range of 500-2000 J/Kg (dark blue dots)
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• Decreased CIN values (dark blue dots). Combination
can lead to a serious underestimation of convection.
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Meteorological indices, results (3/3)
Relative change, less evident thunderstrom potential, 15 soundings
 Less evident thunderstorm potential
-> sensitivity to measurement
errors increased significantly
 Humidity offset of - 4%RH:
 CAPE relative mean change 49%
 CIN mean change - 23.4 J/Kg,
compared to mean value - 72.9 J/Kg,
can also be considered significant
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Winter precipitation
Snow?
Rain?
Freezing rain?
Ice Pellets?
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Winter precipitation
 Precipitation type
is affected by
atmospheric
conditions
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Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Winter precipitation – case study
• February 5 2014, eastern Europe,
light freezing rain
• RS92 sounding used as a reference
• Modification 1: Artificial wet-bulb
• Modification 2: Offsets + 0.3ºC and - 4%RH
• Precipitation type estimated for each profile
based on the conditions in the significant
layers of the atmosphere
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VAISALA
Summary
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Summary
Winter Precipitation – case study, results
Sounding profile
Ice formation
Elevated warm layer
On the ground
Relative effect
FORECAST
OBSERVED WEATHER
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13
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Modified sounding:
wet-bulb error
Shallow layer
T < -10 °C
 Probable ice formation
Original sounding
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
‒ ‒ ‒
Shallow layer
T < -10 °C
 Probable ice formation
Tmax = 2.8 °C
 Partial melting of ice
 Rain more probable,
also sleet can occur
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
Reference
Ice pellets (more probable) or
freezing rain or mix
Light freezing rain
(more probable) or ice pellets
Tmax = 1.9 °C
 Partial melting of ice
 Solid and liquid can occur
Light freezing rain
Modified sounding:
ΔT = +0.3 °C, ΔRH = -4 %
Shallow layer T < -10 °C
 Less probable ice formation
due to lower humidity
Tmax > 3 °C
 Complete melting of ice
 Rain
Tsurface > 0 °C  No freezing on
the ground
+ + +
Light rain or no rain
VAISALA
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Summary
Winter Precipitation – case study, results
Sounding profile
Ice formation
Elevated warm layer
On the ground
Relative effect
FORECAST
OBSERVED WEATHER
Page
13
© Vaisala
Modified sounding:
wet-bulb error
Shallow layer
T < -10 °C
 Probable ice formation
Original sounding
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
‒ ‒ ‒
Shallow layer
T < -10 °C
 Probable ice formation
Tmax = 2.8 °C
 Partial melting of ice
 Rain more probable,
also sleet can occur
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
Reference
Ice pellets (more probable) or
freezing rain or mix
Light freezing rain
(more probable) or ice pellets
Tmax = 1.9 °C
 Partial melting of ice
 Solid and liquid can occur
Light freezing rain
Modified sounding:
ΔT = +0.3 °C, ΔRH = -4 %
Shallow layer T < -10 °C
 Less probable ice formation
due to lower humidity
Tmax > 3 °C
 Complete melting of ice
 Rain
Tsurface > 0 °C  No freezing on
the ground
+ + +
Light rain or no rain
VAISALA
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Summary
Winter Precipitation – case study, results
Sounding profile
Ice formation
Elevated warm layer
On the ground
Relative effect
FORECAST
OBSERVED WEATHER
Page
13
© Vaisala
Modified sounding:
wet-bulb error
Shallow layer
T < -10 °C
 Probable ice formation
Original sounding
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
‒ ‒ ‒
Shallow layer
T < -10 °C
 Probable ice formation
Tmax = 2.8 °C
 Partial melting of ice
 Rain more probable,
also sleet can occur
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
Reference
Ice pellets (more probable) or
freezing rain or mix
Light freezing rain
(more probable) or ice pellets
Tmax = 1.9 °C
 Partial melting of ice
 Solid and liquid can occur
Light freezing rain
Modified sounding:
ΔT = +0.3 °C, ΔRH = -4 %
Shallow layer T < -10 °C
 Less probable ice formation
due to lower humidity
Tmax > 3 °C
 Complete melting of ice
 Rain
Tsurface > 0 °C  No freezing on
the ground
+ + +
Light rain or no rain
VAISALA
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Summary
Winter Precipitation – case study, results
Sounding profile
Ice formation
Elevated warm layer
On the ground
Relative effect
FORECAST
OBSERVED WEATHER
Page
13
© Vaisala
Modified sounding:
wet-bulb error
Shallow layer
T < -10 °C
 Probable ice formation
Original sounding
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
‒ ‒ ‒
Shallow layer
T < -10 °C
 Probable ice formation
Tmax = 2.8 °C
 Partial melting of ice
 Rain more probable,
also sleet can occur
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
Reference
Ice pellets (more probable) or
freezing rain or mix
Light freezing rain
(more probable) or ice pellets
Tmax = 1.9 °C
 Partial melting of ice
 Solid and liquid can occur
Light freezing rain
Modified sounding:
ΔT = +0.3 °C, ΔRH = -4 %
Shallow layer T < -10 °C
 Less probable ice formation
due to lower humidity
Tmax > 3 °C
 Complete melting of ice
 Rain
Tsurface > 0 °C
 No freezing on the ground
+ + +
Light rain or no rain
VAISALA
Radiosonde and atmospheric profile
Meteorological indices - Method - Results
Winter precipitation type – Method - Results
Summary
Winter Precipitation – case study, results
Sounding profile
Ice formation
Elevated warm layer
On the ground
Relative effect
FORECAST
OBSERVED WEATHER
Page
13
© Vaisala
Modified sounding:
wet-bulb error
Shallow layer
T < -10 °C
 Probable ice formation
Original sounding
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
‒ ‒ ‒
Shallow layer
T < -10 °C
 Probable ice formation
Tmax = 2.8 °C
 Partial melting of ice
 Rain more probable,
also sleet can occur
Tsurface < 0 °C
 Rain will freeze on the ground
 Ice accumulation or sleet
Reference
Ice pellets (more probable) or
freezing rain or mix
Light freezing rain
(more probable) or ice pellets
Tmax = 1.9 °C
 Partial melting of ice
 Solid and liquid can occur
Light freezing rain
Modified sounding:
ΔT = +0.3 °C, ΔRH = -4 %
Shallow layer T < -10 °C
 Less probable ice formation
due to lower humidity
Tmax > 3 °C
 Complete melting of ice
 Rain
Tsurface > 0 °C
 No freezing on the ground
+ + +
Light rain or no rain
VAISALA
Radiosonde and atmospheric profile
Meteorological Indices - Method - Results
Winter Precipitation Type – Method - Results
Summary
 Radiosonde data is a central input to
numerical weather prediction and to
several other applications in
meteorology and climatology
 This study focused on the impact of
radiosonde measurement accuracy on
meteorological indices and on prediction
of winter precipitation type
 Small errors in the atmospheric profile
measurement have a considerable effect
in the studied atmospheric conditions
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Summary
19
THANK YOU FOR THE ATTENTION
VAISALA
WMO TECHNICAL CONFERENCE ON METEOROLOGICAL AND ENVIRONMENTAL INSTRUMENTS AND METHODS OF OBSERVATION, 2016