2nd INTERNATIONAL PRECIPITATION WORKING GROUP WORKSHOP

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2nd INTERNATIONAL PRECIPITATIONWORKING GROUP
WORKSHOP
SIMULATED SNOWFALL MEASUREMENTS FROM SATELLITE
OBSERVATIONS AT MICROWAVE FREQUENCIES ALBERTO
MUGNAI (CNR/ISAC, ROMA, ITALY)
MONTEREY, CALIFORNIA, USA 25-28
OCTOBER 2004
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References
Mugnai, A., S. Di Michele, E.A. Smith, F. Baordo,
P. Bauer, B. Bizzarri , P. Joe, C. Kidd, F.S.
Marzano, A. Tassa, J. Testud, and G.J. Tripoli,
2004 Snowfall measurements by the proposed
European GPM mission. Measuring Precipitation
from Space EURAINSAT and the Future (V.
Levizzani, P. Bauer, and F.J. Turk, Eds.), Kluwer
Academic Publ., in press. Mugnai, A., et al.,
2004 EGPM-Ice Final Report. Final Report of
ESA/ESTEC Contract on Modelling and Retrieval of
Light Rainfall and Solid (Ice and Snow)
Precipitation for the EGPM Mission, CNR-ISAC, in
preparation. ESA, 2004 EGPM European
Contribution to Global Precipitation Measurement.
The Six Candidate Earth Explorer Missions
Report for Mission Selection SP-1279 (5),
ESA/ESTEC, 66 pp.
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EGPM EUROPEAN CONTRIBUTION TOGLOBAL
PRECIPITATION MEASUREMENT (GPM)
EGPM mission goal is to retrieve precipitation
with emphasis on Europe and Canada. EGPM mission
is integral but distinct component of GPM
constellation

• Improve accuracy of global precipitation
  estimates with focus on snowfall and light rain
  unique feature within GPM
• Improve global and regional NWP and climate model
  forecasts
• Improve near-real-time monitoring of hazardous
  and flash-flood producing storms.

ESAs Earth Observation Programme Board (PB-EO)
has recently recommended that EGPM mission
should be furthered within ESA Earth Watch
framework.
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SIGNIFICANCE OF LIGHT RAINFALL AND SNOWFALL
Latitude / precipitation rate category
diagram derived from COADS Dataset
At high latitudes there is large fraction of
light and solid precipitation
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VIEWING GEOMETRY OF EGPM RADIOMETER RADAR
Radiometer Antenna Size _at_ 500 km 1.0 m Radar
Antenna Size _at_ 500 km 1.2 m
Radar Radiometer Calibration Intercalibration Ext
ension to high latitudes
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EGPM MICROWAVE RADIOMETER CHANNELS
() channel should provide contiguous and
concentric coverage along and across () NAST-M
channels (NPOESS Aircraft Sounder Testbed
Microwave) () channels should provide either
all H or all V polarization
Bauer, P., and A. Mugnai, 2003 Precipitation
profile retrievals using temperature-sounding
microwave observations. J. Geophys. Res., 108
(D23), 4730, doi10.1029/2003JD003572. Blackwell,
W.J., J.W. Barrett, F.W. Chen, R.V. Leslie, P.W.
Rosenkranz, M.J. Schwartz, and D.H. Staelin,
2001 NPOESS Aircraft Sounder Testbed-Microwave
(NAST-M) Instrument description and initial
flight results. IEEE Trans. Geosci. Remote
Sensing, 39, 2444-2453.
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EGPM NADIR-POINTING PRECIPITATION RADAR (NPR)
Requirements
NPR instantaneous footprints  
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CLOUD RESOLVING MODEL (CRM) SIMULATIONS

• University of Wisconsin Non-hydrostatic
  Modeling System (UW-NMS) / Tripoli (1992 , 2004)
• Three-dimensional, time-dependent, explicit,
  non-hydrostatic CRM
• Bulk microphysics scheme for six different
  hydrometeors
• Cloud droplets
• Rain drops
• Graupel particles
• Pristine ice crystals
• Snowflakes
• Ice aggregates
• All particles are assumed to be spherical
• Size distributions
• Cloud droplets pristine ice crystals
  monodispersed
• Other hydrometeors inverse exponential
  constant-slope / constant-intercept
• n(D) A exp (-BD)
• Density
• Ice crystals, graupel snowflakes constant
• Ice aggregates size-dependent

• UW-NMS Simulations
• January 2000 snowstorm that produced significant
  snowfall over east coast of United States.
• January 2003 frontal system that produced light
  snow over Baltic area (Gotland).
• October 2002 frontal system that produced
  light-to-medium rainfall over southern United
  Kingdom and English Channel.

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US EAST COST SNOW STORM (JANUARY 24-26,
2000)UW-NMS NESTED GRID CONFIGURATION
Inner Grid 468 x 468 km2 2.34 km res.
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UW-NMS US EAST COST SNOW STORM SIMULATIONCOLUMNA
R LWC/IWCS (06.00, JAN. 25, 2000)
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US EAST COST SNOW STORM RAIN / SNOW RATE
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MODEL SIMULATION OF EGPM RADIOMETER
OBSERVATIONSLOW WINDOW FREQUENCIES
US East Coast Snow Storm
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MODEL SIMULATION OF EGPM RADIOMETER
OBSERVATIONSHIGH WINDOW FREQUENCIES
US East Coast Snow Storm
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MODEL SIMULATION OF EGPM RADIOMETER
OBSERVATIONSO2 SOUNDING CHANNELS
US East Coast Snow Storm
Four corresponding channel pairs provide
information on ice amount from top to different
depths inside cloud and reduce sensitivity to
surface.
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CROSS SECTION A LIQUID/ICE WATER CONTENTS
L / O
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CROSS SECTION A TBS
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CROSS SECTION C TBS
US East Coast Snow Storm
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MODEL SIMULATION OF EGPM RADAR OBSERVATIONS
US East Coast Snow Storm
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SNOW RETRIEVAL
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SNOWFALL MEASUREMENTSUMMARY
Snowfall over land or snow cover has distinct
signatures at high-frequency window channels (89
and 150 GHz), as well as at selected
temperature-sounding channel pairs of two oxygen
bands near 50-54 and 118 GHz. In particular,
TB-depressions and relative behavior of 89-150
GHz and 54-118 GHz frequencies carry information
on whether snow is precipitating out or is still
aloft, on vertical depth of snow layer, on
snowfall rate, as well as on possible concomitant
presence of rain. Thus, snowfall over land can be
detected and measured by space-borne radiometer
employing such frequency combinations
emphasizing value of sounding channels because
they are significantly less sensitive to surface
emissivity properties than window
channels. Snowfall over ocean can be observed
through its scattering/emission signatures at all
frequencies. Often, retrieval problem is more
complex because oceanic snowfall melts into
liquid precipitation above sea surfaces with SST
gt 0 C. EGPM radar will allow detection of light
precipitation and precipitating ice aggregates
and will help interpretation/retrieval of
radiometric observations.
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GOTLAND SNOW RETRIEVAL (OVER LAND)
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UK FRONTAL SYSTEM SNOW RAIN RETRIEVAL
SEA / LAND
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LIGHT-TO-MODERATE RAINFALL MEASUREMENTCONCLUSIONS
Light-to-moderate rainfall over ocean can be
directly sensed by lower window channels (18.7
and 36.5 GHz), as well as by water vapor channel
at 23.8 GHz. Light-to-moderate rain over land is
indirectly observed through scattering of
radiation by ice particles aloft at
high-frequency window channels (89 and 150 GHz)
and at temperature-sounding channels of oxygen
line near 118 GHz (to lesser extent, at 36 GHz
and at temperature-sounding channels of oxygen
band near 50-54 GHz). Generally, variability of
surface emissivity obfuscates rain emission and
thus retrieval problem over land is more complex
than over ocean. However, additional information
provided by sounding channels reduces retrieval
uncertainty (reduces both bias and rms
errors). EGPM radar will allow detection of
light-to-moderate precipitation and will help
interpretation/retrieval of radiometric
observations.
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Backup Slides
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DISTRIBUTION OF RAINFALL
Rainfall Accumulation Occurrence
Cumulative distribution of rainfall accumulations
(solid) and occurrence (dashed) against rainfall
intensity derived from European radar (Europe)
and from TRMM (Tropics).
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DISTRIBUTION OF SNOWFALL
Snowfall Accumulation
Snow to Total Precipitation Ratio
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CONCEPTUAL SCHEME OF THE EGPM RADIOMETER SIMULATOR
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US EAST COST SNOW STORMSURFACE TEMPERATURE
COLUMNAR WATER VAPOR
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US EAST COST SNOW STORM UW-NMS
SIMULATEDCOLUMNAR LWC/IWCS (06.00, JAN. 25)
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MICROWAVE SNOW EMISSIVITY
Weng, F., and B. Yan A Microwave Snow Emissivity
Model Empirically derived from satellite
retrievals and ground-based measurements
Large variation with frequency depending on snow
type Large variation with snow type at high
frequencies.
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CROSS SECTION A ?JS (RAIN)
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CROSS SECTION A ?JS (SNOW)
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CROSS SECTION C SNOW EMISSIVITY WINDOW
FREQUENCIES
L / O
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CROSS SECT. C SNOW EMISSIVITY SOUNDING
FREQUENCIES
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GOTLAND LIGHT SNOW UW-NMS SIMULATIONCOLUMNAR
LWC/IWCS
B
A
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GOTLAND LIGHT SNOW UW-NMS SIMULATION SURFACE
TEMPERATURE COLUMNAR WATER VAPOUR
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GOTLAND LIGHT SNOW LOW WINDOW FREQUENCIES
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GOTLAND LIGHT SNOW HIGH WINDOW FREQUENCIES
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GOTLAND LIGHT SNOW O2 SOUNDING CHANNELS
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GOTLAND CROSS SECTIONS LIQUID/ICE WATER CONTENTS
A
B
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GOTLAND CROSS SECTIONS TBS (OVER LAND)
A
B
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UW-NMS UK FRONTAL SYSTEM SIMULATIONCOLUMNAR
LWC/IWCS
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UK FRONTAL SYSTEM SURFACE RAINFALL RATE
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UK FRONTAL SYSTEM SIMULATIONSURFACE TEMPERATURE
COLUMNAR WATER VAPOUR
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MODEL SIMULATION OF EGPM RADIOMETER
OBSERVATIONSLOW WINDOW FREQUENCIES
UK Frontal System
Over ocean all frequencies are sensitive to
rainfall Over land 36.5 GHz responds to
scattering by large ice amounts
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MODEL SIMULATION OF EGPM RADIOMETER
OBSERVATIONSHIGH WINDOW FREQUENCIES
UK Frontal System
Both over ocean and over land Both frequencies
respond very strongly to scattering from ice
particles aloft
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MODEL SIMULATION OF EGPM RADIOMETER
OBSERVATIONSO2 SOUNDING CHANNELS
UK Frontal System
The four corresponding channel pairs provide
information on ice amount from top to different
depths inside the cloud and reduce sensitivity to
surface.
TBs
The four channels sense clouds and precipitation
to different depths.
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CROSS SECTION LIQUID/ICE WATER CONTENTS
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UK FRONTAL SYSTEMCOLUMNAR RAIN LWC VS. COLUMNAR
SNOW IWC
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UK TBS