Transcript MEASUREMENT OF SOLID PRECIPITATION Challenges and opportunities TECO-2010 Helsinki, 30 August 2010 Rodica Nitu, Canada.

MEASUREMENT OF SOLID PRECIPITATION
Challenges and opportunities
TECO-2010
Helsinki,
30 August 2010
Rodica Nitu, Canada
CIMO Guide, Part I, Chapter 6:
Measurement of Precipitation
• The amount of precipitation measured:
less than the actual precipitation
reaching the ground by 30% or more.
Error terms:
• systematic wind-field
deformation above the gauge
orifice:
• Systematic losses vary by type of
precipitation.
• The systematic error of measurement
of solid precipitation: an order of
magnitude greater than for liquid
precipitation.
•
•
•
•
• The true amount of precipitation may
be estimated by adjusting for some or
all of the various error terms.
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– 2-10% for rain,
– 10-50%, for snow;
wetting losses;
evaporation losses: 0-4%;
blowing and drifting snow;
in- and out-splashing: 2%;
ToR CIMO XIV
Expert Team on Surface-based Instrument Intercomparisons
and Calibration Methods:
Assess the methods of measurement and observation of solid
precipitation, snowfall and snow depth at automatic unattended
stations used in cold climates (polar and alpine) :
Update metadata related to precipitation instrumentation;
Prepare national summaries of the methods, issues and challenges of
automated solid precipitation measurement;
Assess the need for an intercomparison of methods and equipment for
automated snowfall/snow depth/precipitation measurements;
– Document the needs of the WMO Technical Commissions and Programmes;
– Compile and ensure compatibility of measurement standards and requirements
of WMO Technical Commissions, for cold climate precipitation measurement;
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2008 Survey on the measurement and
observation of solid precipitation at AWS
• Focused on parameters specific to the measurement of solid
precipitation (total precipitation, snow depth, snowfall);
• Results: IOM Report #102, WMO/TDNo.1544
http://www.wmo.int/pages/prog/www/IMOP/publications-IOMseries.html;
•
•
•
•
54 WMO Members answered (46% of global land mass);
35 participants (28% of global landmass) monitor solid precipitation;
42% of stations report solid precipitation;
Measurements: primarily manual (>80%).
• Results in line with previous surveys; (Sevruk and Klemm, 1989;
Sevruk, 2002); over 200,000 gauges in use by NMHSs.
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Survey results:
Measurement of
Total Precipitation
Automatic
instruments
type WG
3.3%
Automatic
instruments
type TBG
14.9%
Other
automatic
instruments
0.2%
Tipping Bucket type gauges:14.9%
 28 models, 22 manufacturers;
 Sensitivity 0.1 to 0.5 mm;
 Some heated, some not;
 Windshields: 31% (30%, USA,
Japan + 1% elsewhere)
40%
30%
20%
10%
WG use, by principle of operation
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0.5
0%
0.1
Vibrating wire: 37%
50%
0.25
Single point electronic
load: 44%
60%
0.2
Strain Gauge 19%
% of total instruments in use
Weighing Gauges: 3.3%
 6 models, 6 manufacturers;
 capacity: 250-1000 mm;
 Some heated, some not;
 78% use single wind shields
(Alter, Tretyakov, Nipher);
Manual
measurements
81.7%
TB use, by sensitivity (mm)
Relative performance of selected gauges
Total Accumulation :
Dec 02, 08 – April 15, 09
CARE 2008 December 2 to 2009 April 15:
Instruments and Configurations
Shield
Instrument
Type
Heating
(Y/N)
If Yes, Type
Belfort Fisher&Porter
WG
No
Alter Shield
Vaisala VRG 101
WG
Yes
Double Alter
Shield
Geonor T200
WG
No
Alter Shield
Geonor T200 in DFIR: field
WG
No
Double Fence
reference
Geonor T200
WG
No
Alter Shield
OTT Pluvio 1, 1000 mm
WG
Yes
Tretyakov Shield
OTT Pluvio 1, 1000 mm
WG
Yes
Tretyakov Shield
OTT Pluvio 2, 750 mm
WG
No
No
Vaisala PWD22
Distrom
No
No
Vaisala 2G 13H
TBRG
Yes
No
All Weather 6021-B
TBRG
Yes
No
All Weather 6021-B
TBRG
Yes
No
CAE PMB22
Hydrological Services TB3
Hydrological Services TB3
TBRG
TBRG
TBRG
Yes
Yes
Yes
No
No
No
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Total accumulation (mm)
Heated TB Gauges
Be
lfo
Relative performance of gauges: Total
Accumulation : Dec 02, 08 – April 15, 09
WG double shield
Field reference: Geonor-DFIR
WG single shield
Field reference
WG no shield
Optical gauge
350
300
250
Heated TB Gauges
200
150
100
50
0
Total Precipitation:
snow vs rain
24-hour total precipitation accumulation (mm)
Jan 28-29, 2009
TB
3
T
Be
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rt
F&
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V
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W
D
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▪ Tmax = - 7.1 deg C
▪ Wind speed: up to 8 m/s;
eo
n
• Jan 28-29, 2009:
or
T2
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or
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FI
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V
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PM
B2
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12
10
8
6
4
2
0
24-hour Total Precipitation Accumulation (mm):
Feb 11-12, 2009
• Feb 11-12, 2009:
25
▪ Tmin = 6.8 deg C
▪ Wind speed: up to 10 m/s
20
15
10
5
eo
n
G or T
eo
no 200
G r_ D
eo F
V nor IR
ai
sa T2
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A 02
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Measurement of Snow on the Ground
and Snowfall
• Automatic measurement of snow on the ground (SoG):
•
•
•
•
7% of all sites (11 countries);
Point measurement;
One sensor per site;
Snowfall: differential of two consecutive SoG
measurements;
Sensor technologies:
– sonic ranging depth sensors (50 kHz pulse);
– phase variation of visible laser;
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Derived measurements: snowfall
• MSC Derivation of snowfall from snow on the ground
measurements:
– Working Hypothesis: a triple configuration of SR50’s, the
consensus of changes in snow depth measurements over time,
would yield a snowfall measurement with better accuracy.
– A Total Precipitation Gauge (Geonor) validates the SR50
reported changes in snow depth.
• Results
– Three sensors were found to be statistically better than two, and
two sensors, statistically better than one.
– Using a TPG as a precipitation verification check helps to reduce
false reports of snowfall.
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Current Development and Testing Work
Snow Depth Sensor
Surface for Snow
Depth Sensor
Precipitation Gauge
Present Weather
Sensor
Austria
Canada
Germany
France
Morocco
New Zealand
Sweden
United States
of America
Canada
Denmark
Lithuania
Slovakia
Sweden
Ukraine
United States of
America
Canada
Germany
Switzerland
United States of
America
Canada
Germany
Morocco
Portugal
Slovakia
Switzerland
United Kingdom
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Towards a solid precipitation
measurement intercomparison?
Proposed objectives for a WMO led intercomparison of
methods and instruments for automatic snowfall/snow
depth/precipitation measurements:
– evaluate the performance and configuration of instruments and methods
of observation of solid precipitation, in field conditions;
– multi-parameter algorithms to improve AWS precipitation data.
– development of adjustment procedures of systematic errors;
– WMO field reference standard using automatic gauges;
– Develop ability to support validation of satellite measurements;
– feedback to manufacturers.
– recommendations for consideration by CIMO.
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Thank you!
Questions?