October « 2008 « CIMSS Satellite Blog

Mountain waves in Colorado and New Mexico

October 10th, 2008

GOES-11, GOES-12, GOES-13 water vapor images

Strong southwesterly winds over the southern and central Rocky Mountains led to the development of mountain waves downwind of the higher terrain in Colorado and New Mexico on 10 October 2008. A distinct mountain wave signature was seen on 6.7 µm water vapor channel imagery from GOES-11 and 6.5 µm water vapor channel imagery from GOES-13 and GOES-12 (above). Note the improved appearance of the mountain waves on the 4-km resolution GOES-13 and GOES-12 imagery (compared to the 8-km resolution GOES-11 imagery). These mountain waves were also easier to identify and track using GOES-13, due to the more direct viewing angle of GOES-13 (positioned at 105º W longitude) and also the fact that GOES-13 was able to operate and supply imagery through the eclipse period (when the satellite was in the Earth’s shadow, and the solar panels could not supply power to the spacecraft).

AWIPS images of GOES-12 and MODIS water vapor channel data

AWIPS images of the GOES-12 and MODIS water vapor channel data (above) showed further improvement in mountain wave identification using 1-km resolution data from MODIS. Mountain waves on water vapor imagery have long been recognized as a signature of potential clear air turbulence, and there were indeed a few pilot reports of light to moderate turbulence over eastern Colorado and New Mexico (below).

AWIPS image of GOES-12 water vapor channel data + pilot reports

Posted in Aviation, GOES-11, GOES-12, GOES-13, MODIS | Comments Off

Of large eyes and midget tropical cyclones

October 8th, 2008

GOES-13 visible images (Hurricane Norbert)

GOES-13 visible imagery (above) revealed the rather large eye of Hurricane Norbert on 08 October 2008 — Norbert was a Category 4 storm at that time, and the eye appeared to be about 30-35 nautical miles in diameter. Hurricane Norbert underwent a period of rapid intensification during the pre-dawn hours on 08 October, which was clearly seen on a plot of the Advanced Dvorak Technique intensity estimate (below) from the CIMSS Tropical Cyclones site.

CIMSS Advanced Dvorak Technique

To illustrate the diversity of tropical cyclone spatial scales, it is interesting to compare the large eye of Hurricane Norbert (in the eastern Pacific Ocean) with the small cluster of deep convection around the core of Tropical Storm Marco (2 days earlier in the Gulf of Mexico) — Marco is not much larger than the eye of Norbert! The visible and IR images shown below are from the same satellite (GOES-13) at the same time of day (20:00 UTC), displayed with the same magnification (zoomed in to an effective 0.5 km resolution). According to the National Hurricane Center discussions, Tropical Storm Marco may have been one of the smallest tropical cyclones on record, with tropical storm force winds only extending about 10 nautical miles away from the center.

GOES-13 visible images (Hurricane Norbert and Tropical Storm Marco)

GOES-13 IR images (Hurricane Norbert and Tropical Storm Marco)

Posted in GOES-13, Tropical cyclones | Comments Off

River valley fog in the Northeast US

October 7th, 2008

AWIPS images of GOES and MODIS fog/stratus product

AWIPS images of the GOES-12 and MODIS fog/stratus product around 07:30 UTC or 3:30 AM local time (above) told two very different stories regarding the formation of river valley fog across parts of the Northeast US on 07 October 2008. In general, there was a surprising amount of disagreement between to two images: the 4-km resolution GOES-12 fog/stratus product suggested that fog was forming over places like the Finger Lakes region of New York and the Lake Champlain region along the Vermont/New York border, while the 1-km resolution MODIS fog/stratus product indicated significant areas of river valley fog across parts of northern Pennsylvania into southern New York.

A closer view (below) helps to illustrate the problem of fog/stratus product verification — there was a lack of reporting stations in the actual areas where river valley fog was forming.

AWIPS images of GOES and MODIS fog/stratus product

A 1-km resolution NOAA-15 AVHRR fog/stratus product (below) from a few hours later (11:10 UTC or 7:10 AM local time) indicated that the fingers of river valley fog across northern Pennsylvania and southern New York had increased in the hours leading up to sunrise.

NOAA-15 fog/stratus product

Post-sunrise GOES-12 and GOES-13 visible images (below) revealed the widespread coverage of river valley fog across the Pennsylvania/New York border region, which dissipated rather quickly by 15:00 UTC or 11 AM local time.