S IMULATED S NOWFALL M EASUREMENTS FROM S ATELLITE O BSERVATIONS AT M ICROWAVE F REQUENCIES A LBERTO...

SIMULATED SNOWFALL MEASUREMENTS

FROM SATELLITE OBSERVATIONS

AT MICROWAVE FREQUENCIES

ALBERTO MUGNAI(CNR/ISAC, ROMA, ITALY)

2nd INTERNATIONAL PRECIPITATIONWORKING GROUP WORKSHOP

MONTEREY, CALIFORNIA, USA – 25-28 OCTOBER 2004

2

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.

3EGPM – EUROPEAN CONTRIBUTION TOGLOBAL PRECIPITATION MEASUREMENT (GPM)

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.

EGPM mission goal is to retrieve precipitation with emphasis on Europe and Canada.

EGPM mission is integral – but distinct component of GPM constellation

ESA’s 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

At high latitudes there is large fraction of light and solid precipitation

Latitude / precipitation rate category diagramderived from COADS Dataset

5

satellite orbit

swath width

flight direction

Radiometer FOV

fore-view

aft-view

45° flight direction

fore-view

aft-view view from the top

Radar FOV

VIEWING GEOMETRY OF EGPM RADIOMETER & RADAR

Radiometer Antenna Size @ 500 km: 1.0 mRadar Antenna Size @ 500 km: 1.2 m

Radar:

Radiometer Calibration

Intercalibration

Extension to high latitudes

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EGPM MICROWAVE RADIOMETER CHANNELS

36.5

Footprint[km x km]

Polarization

26 x 26 H + V

26 x 26 H or V

13.4 x 13.4 H + V

5.5 x 5.5 H + V

Frequency[GHz]

18.7

23.8

89.0(*)

150.0(*)

5.5 x 5.5 H + V

Window

Footprint[km x km]

Polarization

13.4 x 13.4

H or V(***)

13.4 x 13.4

H or V(***)

13.4 x 13.4

H or V(***)

13.4 x 13.4

H or V(***)

13.4 x 13.4

H or V(***)

13.4 x 13.4

H or V(***)

13.4 x 13.4

H or V(***)

Frequency[GHz]

50.3(**)51.8(**)52.8(**)53.8(**)

118.75 ± 8.5(~**)

118.75 ± 4.2(~**)

118.75 ± 2.3(~**)

118.75 ± 1.2(~**)

13.4 x 13.4

H or V(***)

Temperature-Sounding

(*) 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, doi:10.1029/2003JD003572.

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)

NPR instantaneous footprints

Parameter Mission Requirement

Sensitivity to precipitation 0.1 mm/hour

Fundamental integration length < 5 km

Footprint diameter < 5 km

Vertical resolution < 250 m

Vertical range - 3 to 15 km

Requirements

8

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 Simulations1) January 2000 snowstorm that produced significant snowfall over east coast of

United States.2) January 2003 frontal system that produced light snow over Baltic area (Gotland).3) October 2002 frontal system that produced light-to-medium rainfall over southern

United Kingdom and English Channel.

9US EAST COST SNOW STORM (JANUARY 24-26, 2000):UW-NMS NESTED GRID CONFIGURATION

Inner Grid:468 x 468 km2

2.34 km res.

10UW-NMS US EAST COST SNOW STORM SIMULATION:COLUMNAR LWC/IWC’S (06.00, JAN. 25, 2000)

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US EAST COST SNOW STORM : RAIN / SNOW RATE

12MODEL SIMULATION OF EGPM RADIOMETER OBSERVATIONS:LOW WINDOW FREQUENCIES

US East Coast Snow StormB

rig

thn

ess

Tem

per

atu

re (

TB

)

Over ocean: all sensitive to rainfall Over land: 36.5 GHz responds to scattering by large snow amounts

Co

lum

nar

Wat

er C

on

ten

t (C

WC

)

13MODEL SIMULATION OF EGPM RADIOMETER OBSERVATIONS:HIGH WINDOW FREQUENCIES

US East Coast Snow Storm

Bri

gth

nes

s T

emp

erat

ure

Over ocean: both highly sensitive to scattering by ice particles aloftOver land: both respond very strongly to scattering from snow

Co

lum

nar

Wat

er C

on

ten

t

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TB’s

Four channels sense clouds and precipitation to different depths.

Co

lum

n W

ater

Co

nte

nt

MODEL SIMULATION OF EGPM RADIOMETER OBSERVATIONS:O2 SOUNDING CHANNELS


Four corresponding channel pairs provide information on ice amount from top to different depths inside cloud and reduce sensitivity to surface.

15CROSS SECTION A : LIQUID/ICE WATER CONTENTS

L / O

16

CROSS SECTION A : TB’S

17

CROSS SECTION C: TB’SC

olu

mn

ar W

ater

Co

nte

nt

Dis

tan

ce


18

Co

lum

n W

ater

Co

nte

nt

MODEL SIMULATION OF EGPM RADAR OBSERVATIONS


0 dBZ5 dBZ

16 dBZ

Five (5) dBZ sensitivity of EGPM radar will allow detection of light precipitation at surface and of full precipitation profile.

19

SNOW RETRIEVAL

Average retrieval accuracy of the near-ground (up to 500 m) snow equivalent LWC

(“true” average model value = 0.7841 gm-3)

20SNOWFALL 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 > 0 °C.

EGPM radar will allow detection of light precipitation and precipitating ice aggregates and will help interpretation/retrieval of radiometric observations.

21

GOTLAND : SNOW RETRIEVAL (OVER LAND)

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UK FRONTAL SYSTEM : SNOW + RAIN RETRIEVAL

SEA / LAND

23LIGHT-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.

24

Backup Slides

25

DISTRIBUTION OF RAINFALL

Cumulative distribution of rainfall accumulations (solid) and occurrence (dashed)against rainfall intensity derived from European radar (Europe) and from TRMM

(Tropics).

Rainfall Accumulation & Occurrence

26

DISTRIBUTION OF SNOWFALL

Snow to Total Precipitation Ratio

Snowfall Accumulation

27

CONCEPTUAL SCHEME OF THE EGPM RADIOMETER SIMULATOR

28US EAST COST SNOW STORM:SURFACE TEMPERATURE & COLUMNAR WATER VAPOR

29US EAST COST SNOW STORM: UW-NMS SIMULATEDCOLUMNAR LWC/IWC’S (06.00, JAN. 25)

30

MICROWAVE SNOW EMISSIVITY

Weng, F., and B. Yan: A Microwave Snow Emissivity ModelEmpirically derived from satellite retrievals and ground-based measurements

Large variation with frequency depending on snow type;Large variation with snow type at high frequencies.

31CROSS SECTION A :ΔJ’S (RAIN)

32CROSS SECTION A :ΔJ’S (SNOW)

33CROSS SECTION C : SNOW EMISSIVITY & WINDOW FREQUENCIES

L / O

34CROSS SECT. C : SNOW EMISSIVITY & SOUNDING FREQUENCIES

35GOTLAND LIGHT SNOW UW-NMS SIMULATIONCOLUMNAR LWC/IWC’S

A

B

36GOTLAND LIGHT SNOW UW-NMS SIMULATION SURFACE TEMPERATURE & COLUMNAR WATER VAPOUR

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GOTLAND LIGHT SNOW : LOW WINDOW FREQUENCIES

38

GOTLAND LIGHT SNOW : HIGH WINDOW FREQUENCIES

39

GOTLAND LIGHT SNOW : O2 SOUNDING CHANNELS

40

GOTLAND CROSS SECTIONS : LIQUID/ICE WATER CONTENTS

A B

41

GOTLAND CROSS SECTIONS : TB’S (OVER LAND)A B

42UW-NMS UK FRONTAL SYSTEM SIMULATIONCOLUMNAR LWC/IWC’S

43

UK FRONTAL SYSTEM : SURFACE RAINFALL RATE

44UK FRONTAL SYSTEM SIMULATIONSURFACE TEMPERATURE & COLUMNAR WATER VAPOUR

45MODEL SIMULATION OF EGPM RADIOMETER OBSERVATIONS:LOW WINDOW FREQUENCIES

Co

lum

na

r W

ate

r C

on

ten

t (C

WC

)B

rig

thn

es

s T

em

pe

ratu

re (

TB

)

Over ocean: all frequencies are sensitive to rainfall Over land: 36.5 GHz responds to scattering by large ice amounts

UK Frontal System

46MODEL SIMULATION OF EGPM RADIOMETER OBSERVATIONS:HIGH WINDOW FREQUENCIES

Both over ocean and over land:Both frequencies respond very strongly to scattering from ice particles aloft

Co

lum

na

r W

ate

r C

on

ten

t (C

WC

)

Bri

gth

ne

ss

Te

mp

era

ture

(T

B)

UK Frontal System

47

Co

lum

na

r W

ate

r C

on

ten

t (C

WC

)

MODEL SIMULATION OF EGPM RADIOMETER OBSERVATIONS:O2 SOUNDING CHANNELS

The four channels sense clouds and precipitation to different depths.

TB’sThe four corresponding channel pairs provide information on ice amount from

top to different depths inside the cloud and reduce sensitivity to surface.

UK Frontal System

48

CROSS SECTION : LIQUID/ICE WATER CONTENTS

49UK FRONTAL SYSTEMCOLUMNAR RAIN LWC VS. COLUMNAR SNOW IWC

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UK TB’SSEA / LAND

S IMULATED S NOWFALL M EASUREMENTS FROM S ATELLITE O BSERVATIONS AT M ICROWAVE F REQUENCIES A LBERTO...

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