TS 15 The Great Salt Lake System ASLO 2005 Aquatic Sciences Meeting Climatology and Variability of Satellite-derived Temperature of the Great Salt Lake Erik T. Crosman Erik T. Crosman John D. Horel John D. Horel University of Utah University of Utah NOAA Cooperative Institute for Regional Prediction

Why Study the Temperature of the Great Salt Lake?  Scientific research related to the impacts of changes in the physical state of the GSL has increased in recent years (Gwynn 2002)  Lake level, areal extent, salinity and surface temperature respond to regional climate variations  Lake temperature has been examined for selected case studies and short field programs based on in situ and remote observations (Baskin 1998; Zastrow and Ridd 2002; Rich 2002)  The contrast in temperature between the surface of the Great Salt Lake and surrounding land surfaces combined with the areal extent of the Lake affects local weather and climate (lake breezes, lake-effect snowstorms, etc.)  Hypothesis: Variability in lake areal extent and temperature on daily to interannual time scales leads to variations in local weather and climate  Goal- Document the spatial and temporal variations of lake surface temperature in order to assess: –the sensitivity of the lake to regional climate forcing –The sensitivity of local weather and climate to changes in lake surface temperature  Method- Use satellite data to document spatial and temporal variations in lake surface temperature 1981-present

TS 15 The Great Salt Lake System ASLO 2005 Aquatic Sciences Meeting

TS 15 The Great Salt Lake System ASLO 2005 Aquatic Sciences Meeting Lake-breeze Fronts vs. Lake Surface Elevation

Methodology  Advanced Very High Resolution Radiometer (AVHRR) images from 5 spectral channels at 1.1 km resolution from NOAA polar orbiting satellites 1981-present  Three visible channels used for daytime cloud identification and two infrared channels used for cloud identification and temperature  Infrared data calibrated and converted to brightness temperature using an inverse Planck function  Linear and nonlinear split-window techniques used to correct for the effects of atmospheric water vapor to produce sea/lake surface temperature estimates  Lake temperature retrievals measure “skin” temperature of infinitesimally thin surface layer  Accuracy of AVHRR sea surface temperature retrievals approximately +/- 0.5 C based on comparison to ocean buoys  Skin temperature measurements may be significantly different than subsurface temperature when the lake is thermally stratified  Variations in satellite orbital path affect accuracy of image registration that can be compensated for

TS 15 The Great Salt Lake System ASLO 2005 Aquatic Sciences Meeting Best possible lake temp image

TS 15 The Great Salt Lake System ASLO 2005 Aquatic Sciences Meeting Cloud Masking Procedure  Based on CLAVR-1 and CLAVR-x cloud detection, designed to detect clouds in AVHRR data  Cloud masks based on differences between cloud and lake reflectance and infrared emission  Uniformity tests too restrictive, not applied to the Great Salt Lake

Example of Cloud Masking Upper left: Visible satellite image Upper right: Infrared channel difference test Lower right: Reflectance ratio test

Cloud Masked Lake Temperature Cloud Masked Lake Temperature Channel 4 Brightness Temperature Cloud Masked Lake Surface Temperature

Spatial Variability of Surface Temperature Spatial Variability of Surface Temperature -- Further understanding of lake surface temperature spatial variability -- What effects does lake level, local wind forcing, (mixing and Ekman pumping) have on lake temperature variations? What impact does spatial variations in lake temperature have on local wind circulations? -- What impact does spatial variations in lake temperature have on local wind circulations?

TS 15 The Great Salt Lake System ASLO 2005 Aquatic Sciences Meeting Satellite-derived and in situ measurements Satellite-derived and in situ measurements Satellite-derived annual temperature cycle South arm temperature cycle at various depths (J.W. Gwynn, Utah Geological Survey Initial validation shows general agreement (+/- 1-2 C) between post-processed 4- km satellite temperature retrievals and available in situ data Seasonality of diurnal signal related to thermal stratification?

Variability Variability -- Understand lake temperature variability on time scales ranging from days to years -- Create a 25-year spatially and temporally high-resolution climatology of lake temperature -- Climate signal? -- Relationship to lake depth?

TS 15 The Great Salt Lake System ASLO 2005 Aquatic Sciences Meeting Current and past lake temperature data