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CloudSat Snow Observations: Ten years of flakesCloudSat Snow Observations: Ten years of flakes

Norman WoodNorman Wood

University of Wisconsin – MadisonUniversity of Wisconsin – Madison

Space Science and Engineering CenterSpace Science and Engineering Center

Int'l Workshop on Space-based Snowfall Measurements3 October 2016

Collaborators: Tristan L'EcuyerCollaborators: Tristan L'Ecuyer22, Andy Heymsfield, Andy Heymsfield33, Mark Kulie, Mark Kulie11, Claire, ClairePettersenPettersen11, Mark Smalley, Mark Smalley22

11University of Wisconsin – Madison, Space Science and Engineering Center;University of Wisconsin – Madison, Space Science and Engineering Center;22University of Wisconsin – Madison, Atmospheric and Oceanic Sciences;University of Wisconsin – Madison, Atmospheric and Oceanic Sciences;33National Center for Atmospheric Research, Boulder ColoradoNational Center for Atmospheric Research, Boulder Colorado

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CloudSat & 2C-SNOW-PROFILE (2CSP)CloudSat & 2C-SNOW-PROFILE (2CSP)

Reflectivity:

Estimated snowfall rates:

2CSP:● Bayesian: explicit a priori assumptions for PDFs of

● particle properties (mass,fallspeed, scattering)

● size distributions● Only when snow reaches surface● Phase based on reanalysis temps● Over all surface types● Surface snowfall estimated from lowest clutter-free bin

MilestonesMilestones::

Launch: 28 Apr 2006Launch: 28 Apr 2006

First measurements: 2 Jun 2006First measurements: 2 Jun 2006

Switch to 'daytime only': 1 Nov 2011Switch to 'daytime only': 1 Nov 2011

2CSP release: Feb 20132CSP release: Feb 2013

Stats:Stats:

Orbits released: ~47,000Orbits released: ~47,000

'Snowy' profiles: ~100e6'Snowy' profiles: ~100e6

'Snowy' radar bins: ~ 1000e6'Snowy' radar bins: ~ 1000e6

Snowflakes: ~2e21Snowflakes: ~2e21

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2CSP application examples2CSP application examples

● Long-term record: Accumulation assessmentsLong-term record: Accumulation assessments

● Repeatable ground track: Orographic precipitation studiesRepeatable ground track: Orographic precipitation studies

● Resolution and sensitivity: Mapping radar specs to observablesResolution and sensitivity: Mapping radar specs to observables

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2CSP → gridded2CSP → griddedaccumulationsaccumulations 2 degree grid, Epochs

1 thru 4 (~5 years):

Overpass thrusingle grid box

Samplecounts

Snow: 75.7 mm/y

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Comparisons versus multi-year observationsComparisons versus multi-year observations

● ~120 USCRN stations, plus int'l GCOS, coopobserver, daily synoptic summaries

● Global but little snowfall data outside NA

● snow depth measurement

2CSP:

GHCN: SNOTEL:

● Monitoring of remote mountain watersheds

● Precipitation storage gauge and snow pillow

● Undercatch correction

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Error sourcesError sources

2CSP - GHCN, fractional differences

Red: frequency offlag for shallowprecip, ground clutter

SamplingDifferences:

TerrainEffects (?): Clutter?

Orography?

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● Basic mechanism well understood butBasic mechanism well understood butdetailed observations are limiteddetailed observations are limited

● ground-based radar beam blockageground-based radar beam blockage

● sparse, (possibly) spatially-biasedsparse, (possibly) spatially-biasedobserving networkobserving network

● Impacts water resources, water-limitedImpacts water resources, water-limitedecosystems…ecosystems…

● What does CloudSat see?What does CloudSat see?

Orographic precipitationOrographic precipitationOrographic precipitationOrographic precipitation

M. Durand, Ohio State U.

Alpine Overpasses: Path C:

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Alpine cases:● clear signal of enhanced windward snowfall

● 2000 overpasses reduces to ~30 with snow, cross- mountain flow

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Mapping radar specs to observablesMapping radar specs to observables● Sensitivity → snow accumulation errors (W-band):

Snow: 75.7 mm/y

-1.0 mm/y (-1.3%) -6.8 mm/y (-9.0%) -46.8 mm/y (-61.8%)

-10 dBZ 0 dBZ 10 dBZ

CloudSat: -28 dBZ MDS2CSP: -15 dBZ for snowfall

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Mapping radar specs to observablesMapping radar specs to observables

Global

Antarctica

N. Midlatitudes

Southern Ocean

CloudSat: ~ 1.4 x 1.7 km

● Resolution → snow accumulation

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SummarySummary● Features to leverage:Features to leverage:

● Long-term record, but two-partLong-term record, but two-part(normal, then daytime only)(normal, then daytime only)

● Repeatability of ground trackRepeatability of ground track

● Resolution and sensitivityResolution and sensitivity

● CaveatsCaveats

● Phase distinctionPhase distinction

● Near-surface clutterNear-surface clutter

● Repeatability of ground trackRepeatability of ground track