Snow Cover: Current Capabilities, Gaps and Issues Canadian Perspective

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Snow Cover Current Capabilities, Gaps and
Issues (Canadian Perspective)

• Anne Walker
• Climate Research Branch, Meteorological Service
  of Canada
• IGOS-Cryosphere Theme Workshop, Kananaskis,
  Alberta, Canada, March 2-4, 2005

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Importance of Snow Cover

• Largest areal extent of any component of the
  cryosphere (mean max. extent of 47 x 106 km2)
• High spatial and temporal variability in
  properties
• Impacts both global/regional energy and water
  cycles
• high reflectance, thermal insulation, storage of
  water
• Key variables
• extent (areal coverage), depth, water equivalent
  (water content), wet/dry state, grain size
• Snowfall/solid precipitation
• Information requirements
• indicator of climate variability and change
• Input/validation of models NWP, hydrological,
  climate
• Environmental monitoring/prediction flood
  forecasting, severe weather (blowing snow), soil
  moisture/drought, forest fire risk, wildlife
• Economic hydropower production/management,
  agriculture, tourism

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CliC Requirements for Observations and Monitoring

• Validation of coupled climate models (gridded
  hemispheric-global datasets from observations)
• Improved understanding of processes and improved
  model parameterizations (detailed field datasets)
• Monitoring variability and change (long-term,
  homogeneous data series)
• Diagnostic studies of climate-cryosphere
  interactions (combination of re-analyses, data
  and modelling)

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Canadian Science Issues Related to Snow Observing
Systems

• Quantifying the spatial and temporal variability
  in snow properties (water resource planning,
  GCM/RCM evaluation, input to NWP)
• Quantifying the spatial and temporal variability
  of liquid and solid precipitation (essential
  input to climate and hydrological models,
  operational decision making)
• Improved understanding of snow interception,
  sublimation and redistribution (improved
  representation of snow in climate and
  hydrological models)

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Snow In Situ Observing Networks in Canada

• temperature and precipitation network (MSC)
• hourly/synoptic meteorological observations
  (MSC)
• snow on ground (depth) network (MSC)
• snow course observations (Provinces, MSC, hydro
  companies)

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Current MSC Snow Depth Network
Network biased to coastal locations in Arctic
Significant data sparse areas
Network biased to low elevations in cordillera
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Active Synoptic Stations
All active Synoptic Stations north of 50 N as of
29 Oct 2001 (WMO Publication No. 9 Volume A).
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MSC networks are under pressure
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Satellite Remote Sensing

• alternative information source for remote areas
  where conventional data are sparse or unavailable
• 20-30 yr data record for satellite-derived
  cryospheric information (sea ice, snow cover)
• high repeat coverage of large regions (daily)
• diurnal trends from multiple daytime passes
• consistent spatial info. across coverage
• gridded information for input/validation of
  models (climate, land surface process, hydrology,
  etc.)
• requires development of retrieval techniques
  (algorithms) to derive information on snow cover
  properties ? research

MODIS image - composite
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Snow Remote Sensing/Satellite Capabilities

• Snow Extent Areal Coverage
• optical (visible/infrared) AVHRR, Landsat,
  MODIS
• 30m to 1 km spatial information
• long history of standard snow products (NOAA snow
  charts back to 1960s)
• dependent on solar illumination, limited by cloud
  cover

Global Daily Snow Cover from MODIS (Red snow,
Blue clouds)
NOAA daily IMS snow chart
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Snow Remote Sensing/Satellite Capabilities

• Snow Depth/Snow Water Equivalent
• passive microwave only proven satellite
  technique for SWE retrieval
• historical record back to 1978 (SMMR, SSM/I)
  available in consistent 25 km grid format
• requires regionally-tuned algorithms to take into
  account landscape effects, variation in physical
  properties ? validation a challenge!
• On-going research into SWE retrieval from active
  microwave (SAR) offers higher spatial
  resolution capability

Global SWE map from AMSR-E (limited validation)
SSM/I SWE map for Canadian prairie
region (produced by MSC weekly for 15 years)
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Climate Research Applications of Passive
Microwave SWE

• Availability of SMMR and SSM/I in consistent
  gridded format (EASE-Grid) ? 25 winter seasons
  (1978/79 2002/03)
• Investigation of spatial and temporal variations
  in snow cover in relation to climate/atmospheric
  circulation
• Evaluation of climate model snow cover outputs
  GCM, RCM

Pentad winter season (DJF) SWE anomalies produced
using passive microwave satellite data time
series. Dashed line denotes transition from SMMR
to SSM/I.
Merging Conventional (1915-1992) and Passive
Microwave (1978 2002) Time Series
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Summary of Measurement Capabilities
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Issues Related to Snow Observing Systems

• 1. Decline in in situ capabilities
• decreasing networks
• effects of automation
• loss of manual measurements (e.g. snow survey),
  poor understanding of automated sensors
• solid precipitation measurement
• 2. Development/validation of satellite remote
  sensing capabilities
• validation of current snow retrieval products
  (esp. SWE)
• support of new satellite systems (e.g. E-GPM/CGPM
  for solid precipitation)
• support of algorithm development research
• 3. Data gaps in northern latitudes (gt 60 N)
• sparse in situ measurements
• challenge to validate satellite retrievals
• 4. Development of techniques to merge in situ
  measurements and satellite retrievals
• 5. Canadian GCOS Cryosphere Plan detailed
  summary of cryospheric data requirements and
  issues