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Contributions of GPS Data to
Severe Weather Forecasting in
California
Seth I. Gutman

NOAA Earth
System Research Laboratory

Boulder, CO USA 80305
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Outline

• Background
• What is GPS Meteorology?
• The storm of 4-5 January 2008
• Advances in monitoring and prediction
• Other applications
• Conclusions

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Acknowledgements
1 NOAA Earth System Research Laboratory, Boulder,
CO 80305 USA 2 Cooperative Institute for Research
in Environmental Sciences, University of Colorado
Boulder, CO 80305 USA
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Background

• When GPS was designed for the U.S. military, the
  use of GNSS for atmospheric remote sensing was
  probably the last application on their minds.
• Its also reasonable to assume that the
  techniques developed by geodesists to estimate
  atmospherically induced signal delays as nuisance
  parameters and (2) remove them to improve survey
  accuracy, were not developed to improve weather
  forecasts.
• So the recognition that ground based GNSS
  observations could be used to study the
  atmosphere can rightfully be called
  serendipitous.
• This is how GPS Meteorology works and how NOAA is
  using it to improve its severe weather forecasts
  and warnings in California.

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Background

• Water vapor is one of the most important
  components of the Earths atmosphere.
• It is the source of clouds and precipitation, and
  an ingredient in most major weather events.
• PW moves rapidly through the atmosphere,
  redistributing energy (latent heat) through
  evaporation and condensation.
• One of the most valuable attributes of GNSS is
  its ability to provide accurate water vapor
  estimates under all weather conditions, including
  thick cloud cover and precipitation.

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Background

• Water vapor also plays a critical role in the
  global climate system
• It is by far the most plentiful greenhouse gas
• It absorbs and radiates energy from the sun
• It affects the formation of clouds and aerosols
  and the chemistry of the lower atmosphere
• So understanding monitoring water vapor, and
  the effects it has on atmospheric radiation and
  circulation, is vital to the diagnosis and
  prognosis of long-term changes in climate
  including droughts severe weather.

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Overview of GPS Meteorology

• GPS Signal in Troposphere
• Refractivity associated with changes in T,P,WV in
  neutral atmosphere.
• Signal delays are unrelated to frequency below 30
  GHz.
• Delays must be modeled using assumptions about
  the structure and length-scale variability of
  these parameters.

• GPS Signal in Ionosphere
  
• Refractivity associated with changes in electron
  plasma density or TEC between 50 and 400 km AGL.
• Signal delays in dispersive media are inversely
  proportional to frequency.
• Ionospheric delays are estimated (or removed)
  using dual frequency receivers.

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GPS Water Vapor Measurements
January 01, 2008 to January 14, 2008 (08001 to
08014) Point Loma, CA (PLO5)La Jolla, CA
(SIO3)San Diego, CA (NKXB)
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Major West Coast Storm 4-5 January 2008

• Blizzard warning
• Heavy snow warning
• Winter storm warning
• Flash flood watch
• Flood warnings
• Coastal flood watch
• Coastal flood warning
• Gale warning
• Heavy surf warning
• High wind warning
• many others.

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What Happened

• An exceptionally strong Extratropical Cyclone (a
  low pressure system) traversed much of the
  Pacific Ocean before the first main wave arrived
  late on January 3.
• The storm entrained moisture (water vapor) from
  the subtropics in a long narrow region called an
  Atmospheric River.
• The storm (actually a series of three storms)
  impacted the Pacific Coast from British Columbia
  to northern Mexico.

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What Happened

• Atmospheric rivers (ARs) are formed as part of
  the "warm conveyor belt", a hemispheric cycle by
  which the cold dry air of the Arctic flows
  southward, and warm humid air from the tropics is
  forced northward.
• This "conveyor belt" plays a key role in the
  formation of Pacific storms.
• Modeling studies suggest that more than 90 of
  the total water vapor transported from the
  equator toward the poles are concentrated in
  these rivers.

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What Do ARs Look Like?
Atmospheric rivers (ARs) represent the business
end of west coast winter storms.
Due to lack of observations, ARs are poorly
defined, monitored, and forecast.
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The storm at time of major impact
Note that major impacts were focused gt500 miles
south of the Low pressure center in this
storm. This differs significantly from
hurricanes, but the impacts are enormous and
spread over a large area
L
Many major impacts are associated with the
landfall of the atmospheric river element of
the storm, the precise characteristics of which
are not currently monitored operationally
offshore or onshore.
Atmospheric river

• GOES IR image of major West Coast storm
• Time 0030 UTC 5 January 2008
• Low pressure center is off WA coast

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Three experimental observing sites monitored AR
conditions upon land-fall
L
BBY
PPB
GLA
Distance from BBY to GLA 500 km, i.e. the
average width of an atmospheric river
Bodega Bay (BBY 12 m MSL) Cazadero (Mountain
site 475 m MSL)
Pt. Piedras Blancas (PPB 11 m MSL) Three Peaks
(Mountain site 1021 m MSL)
Goleta (GLA 3 m MSL) San Marcos Pass (Mountain
site 701 m MSL)
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Typical AR Monitoring Site Bodega Bay (BBY) Radar
Wind Profiler (1)
Surface Met Sensors (2) GPS
Receiver and Antenna (3)
(1)
(2) (3)
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GPS Water Vapor Measurements
January 01, 2008 to January 07, 2008 (08001 to
08007) Bodega Bay, CA (BBY5)
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Observations at Bodega Bay (upslope orientation
230 deg) Max AR bulk flux 115 units (total) 100
units (upslope component) Time of max AR flux
1500-1600 UTC 4 January 2008 Max wind in
controlling layer (hourly avg) 39.4 m s-1 194
deg Max IPW 31.1 mm Max hourly rain rate 0.8 in
h-1 (20 mm h-1) Storm total rainfall at nearby
mountain site 10.39 in (264 mm)
Wind speed, direction return signal power from
wind profiler Upslope wind speed and IPW from
wind profiler and GPS IPW flux and rain rate
from profiler, GPS rain gauge
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Observations 48-h forecasts
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Conclusions

• A new forecast model moisture flux verification
  tool has been developed by NOAAs Earth System
  Research Laboratory.
• The tool combines observations and NWP model
  output to maintain situational awareness and
  evaluate weather model performance.
• Plans are being made to transition the observing
  systems and moisture flux tool from NOAA Research
  into National Weather Service operations.

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Contact Information Seth I. Gutman, Physical
Scientist
NOAA Earth System Research Laboratory (ESRL)
325 Broadway R/GSD7

Boulder, CO 80305-3328 Phone [phone]

FAX [phone] Email
Seth.I.Gutman_at_noaa.gov
Web http//gpsmet_test.fsl.noaa.gov
.
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Thanks for your Attention!
Any Questions?