Detecting Surface Features in Water Vapor Channel Imagery (Part 3)

February 5th, 2007 |

GOES, MODIS water vapor images

The strong arctic outbreak of early February 2007 brought an unusually cold and dry air mass over the northcentral and northeastern US. Water vapor channel imagery from the GOES imager and sounder on 05 February 2007 (above) showed a surprising result once the map overlay was removed (Java animation) — the outlines of parts of the Great Lakes and the Northeast coasts were clearly evident on the imagery. This is somewhat anomalous, given that the water vapor channel imagery normally depicts features in the middle to upper troposphere.

GOES water vapor channel weighting functions calculated using rawinsonde data from Upton, New York at 00 UTC on 06 February 2007 (below) reveal that the GOES imager 6.5 µm water vapor channel (black plot) was detecting radiation from an atmospheric layer that peaked at an unusually low altitude (near 700 hPa), while the GOES sounder 7.4 µm water vapor channel (red plot) was detecting a significant amount of radiation from near the surface. This enabled a signal of the strong surface thermal contrast (very cold land surfaces adjacent to relatively warm bodies of water) to “bleed up” through what little water vapor was present in the atmospheric column, allowing us to see coastal outlines across the Great Lakes and Northeast US regions on the water vapor channel imagery.
Upton NY water vapor channel weighting functions

Migrating drift ice

February 5th, 2007 |

GOES-12 visible image

As a follow-up to the previous blog post, cold air and lake-effect snow continued across the Great Lakes region on 05 February 2007. GOES-12 visible imagery (above; Java animation) revealed a narrow filament of drift ice that was being pushed by strong winds eastward out of the northern portion of Green Bay (just north of Washington Island) and into Lake Michigan. An AWIPS image of the MODIS sea surface temperature (SST) product indicated that lake water temperatures had cooled to the 32º to 41º F (0º to +5º C) range off the coast of Wisconsin. Also, note how the motion of the lake-effect snow bands over Lake Superior (in northern portion of the images) changes during the day, as the boundary layer winds develop more of a westerly component. Finer detail in the drift ice structure in Green Bay and northern Lake Michigan can be seen on a 500-m resolution MODIS true color image (below); drift ice coverage was also increasing in southern Lake Michigan, from Milwaukee WI to Chicago IL to South Bend IN.

MODIS true color image