Title: Northern European Possibilities for Ground Validation of Snowfall
1Northern European Possibilities for Ground
Validation of Snowfall
- Jarmo Koistinen
- FMI, Finland
- IPWG/GPM/GRP Workshop on Snowfall,
- Madison, October 2005
2- Most of Finland belongs to boreal forest climate
- 100-220 snow cover days/year
- Average snow depth in March 20-90 cm
3FMI weather radar network
8 C-band Dopplers Polar V, dBZ (dBT, W) archived
since 2000 Data availability 99.3 incl.
maintenance and telecommunications in 2004
4VVP wind profiles horizontal drifting of snow
5Cold Boreal Forest Climate
- Temperature and snow depth in Sodankylä
Months
Oct Nov Dec Jan Feb Mar Apr May
6Potential GV site for snow Sodankylä (the
northernmost radar, 67N)
Global CEOP validation site (Nr 29) Coordinated
Enhanced Observing Period (CEOP)
7Helsinki Testbed (HTB), 60N, 2005-2007-?A
coastal, mesoscale high latitude research and
development facility (WMO/WWRP endorsement tbd).
All other stations shown except Road
Weather. Average WS distance 9 km (FMI regular 50
km).
- IC lightning system CG lightning system
8HTB Precipitation Measurements -circles radar
20-60km (0-250 km) -dot manual obs -big diamond
FD12P -small diamond potential FD12P -triangle
autom snow depth -square weighing gauge - plan
2 POSS to be implemented http//testbed.fmi.fi
public realtime data during the campaigns (6
months during Aug 2005 Aug 2006, snow Nov,
Jan-Feb)
9Vaisala polarimetric radar at HTB, prototype
resultsRHI scans across a bright banddBZ
?HV LDR
10NORDRAD-composite (25 radars, operational)
11GEWEX Global Energy and Water Cycle
Experiment WCRP World Climate Research Program
12WCRP/GEWEX/BALTEX DBZC - Composites of radar
reflectivity
BALTRAD composite 2005-05-28 1415 UTC
- More than 30 radars in 11 countries BALTRAD
- Radar Data Centre at SMHI, Sweden (Daniel
Michelson) - Continuous operation since October 1, 1999
- Resolutions 2?2 km, 15 minutes, 0.4 dBZ
BALTEX Radar Data Center
13RR - 3 and 12-hour Gauge-adjusted Accumulated
Precipitation Gauges-only Accumulation
- 2?2 km horizontal resolution
- Every 3 and 12 hours
- 32-bit depth
- Wind corrected gauge observations
- 3-hour BALTRAD area
- 12-hour BALTEX Region (see example)
14Eumetnet OPERA ProgrammeThe aim of OPERA is to
harmonize European radar data and products,
raise their qualities, facilitate their
exchange, and support their application
- Opera runs projects on
- Quality information
- Radar data use
- New technologies
- Products to exchange
- New data formats
- BUFR software
- Radar data hub
15European Co-operation in the Field of Scientific
and Technical Research (COST)
16EUMETSAT Hydrology SAF
- SAF Satellite Application Facility under
EUMETSAT contract - HSAF lead by Servizio Meteorologico
dellAeronautica, Italy - Hydrology SAF
- Precipitation (Italy)
- Soil Moisture (Austria)
- Snow parameters (Finland)
- Mainly EUMETSAT operational satellites, but also
other (research) satellites are used, when
applicable
17Hydrology SAF
Satellites/instruments during development NOAA (
AVHRR) MetOp (AVHRR, ASCAT) Meteosat (SEVIRI
) EOS-Terra/Aqua (MODIS) DMSP (SSM/I,
SSMIS) EOS-Aqua (AMSR-E) QuickSCAT (SeaWinds)
- Products
- Snow recognition (SR)
- Snow effective coverage (SCA)
- Snow status (wet or dry)
- Snow Water Equivalent(SWE)
Satellites/instruments during operations MetOp (A
VHRR, ASCAT) Meteosat (SEVIRI) NPOESS (VIIRS,
CMIS) MW radiometers of the GPM constellation
18Hydrology SAF
19Helsinki University of Technology Modeling
polarimetric microwave scattering, e.g. snow,
sleet, boreal forest, insects, birds
20Growth of uncertainties in the Ground Reference
process of snowfall at ground
WMO inter- comparison
21 Work to improve quality(implemented)
- Absolute calibration is still an issue (at best
1-3 dB) - A relative calibration method based on comparing
precipitation accumulation in the overlapping
area of radar pairs. - Elevation angle calibration to better than 0.05
degrees (high latitude sun hits the operational
scans densely during rise and set). - Cold climate phenomena diagnosed applying pattern
recognition and fuzzy logics (in future applying
polarimetry) - Anomalous propagation common introducing strong
sea and ship clutter. - Migration of birds and insects.
22Antennas tuned mechanically
2312h accumulation of problems
Clutter Jamming Ships Stroboscope effect
24(No Transcript)
25But R(Z)-S(Ze) relations play only a minor role
3000 gauge/radar winter comparisons
- Variable-phase (R or S) method in solid line
- Z-R only in dashed line
- Snow cases in orange, all cases in grey
- Correct Z-R or Z-S is negligible compared to the
increasing bias as a function of range due to the
vertical profile of reflectivity!
Gauge/Radar
Range
26Reality Underestimation far from radarWHY?
Average 12 hourly gauge/radar ratio (dB), summer
Kuopio radar, 3 months winter accumulation (3 dB
colour steps), range 250 km
27Examples of measured reflectivity profiles
Snow,melting close to ground
Snow
28Overhanging snow (virga, Altostratus)
Snow, evaporation and residual clutter
1(2)
29Automatic real time classification of VPRs based
on radar and NWP data (556 471 profiles)
VPR. type (at ground)
30Snowfall measurements require 20 dBs more
sensitivity than those of rainfall
Cumulative probability distribution of snowfall
in 106 825 profiles (range 2-40 km)
MDS of GPM
31Reasonable boundary layer winds obtainable 90
of time in winter with sensitive radars (ice
crystals from the ground ?)
32Climatological profiles based on the measured 220
000 precipitation profiles
33Vertical profiles of reflectivity (VPR) in winter
introduce large biases (S) in the radar estimates
of surface precipitation
1(2)
34Example Bright band at ground
Radar bias i.e. VPR correction for 500 m PsCAPPI
and dry snow S(Ze)
1(2)
35Profile correction for 500 m PsCAPPI
Example A Snow Case
1(2)
36Yearly average ground reference bias for 500 m
PsCAPPI as a function of range
In snowfall sample size 106 000 VPRs
1(2)
37Improving reference data applying a spatially
continuous VPR correction
Corrected to ground level
Measured
24 h accumulated precipitation Nov 7, 2002, 14
UTC
1(2)
38Log(Gauge/Radar), note excellent VPR-effect
39Overhanging precipitation (OP)
40Remaining problem complete beam overshooting
in very shallow snowfall.
41GPM Blind Zone may mask shallow
precipitation Case Precipitation top height
March 2001 (snow). Note 0.3-1 km high snowfall
regular in Finland (difficult to diagnose from
VPRs).
Not known
1(2)
4224 h accumulated precipitation Dec 21, 2002, 21
UTC . VPR correction does not help at the edges
where complete beam overshooting occurs (shallow
snow).
No VPR correction
With VPR correction
1(2)
43Better accuracy with integrated data but in
proper order!
- Remove non-meteorological echoes and OP.
- Attenuation correction (sleet!).
- Blocking- VPR-correction intelligent
compositing gt Precipitation at ground - Time-space variable R(Z) / S(Ze) relations.
- Diagnose areas of total beam overshooting and POD
of snowfall detection. - Gauge-radar adjustment.