Hurricane Fred

September 9th, 2009 |

Meteosat-9 IR images

Meteosat-9 IR images

Meteosat-9 IR images from the CIMSS Tropical Cyclones site (above) showed that Hurricane Fred began to exhibit a well-defined eye as it rapidly intensified to a Category 3 storm on 09 September 2009. As noted in the National Hurricane Center discussion:


IT IS QUITE UNUSUAL TO HAVE SUCH A POWERFUL SYSTEM SO FAR EAST IN
THE BASIN AND FRED IS ONLY THE THIRD MAJOR HURRICANE NOTED EAST OF
35W IN THE TROPICAL ATLANTIC OCEAN...AND THE STRONGEST HURRICANE SO
FAR SOUTH AND EAST IN OUR DATA RECORD.  THIS TYPE OF SYSTEM...
HOWEVER...WOULD HAVE BEEN VERY DIFFICULT TO ACCURATELY OBSERVE
BEFORE SATELLITE PICTURES BEGAN IN THE 1960S.

Terra MODIS visible image

Terra MODIS visible image

At 12:50 UTC, a “transverse banding” structure was seen on the cold cloud tops surrounding the western periphery of the eyewall region on the  Terra MODIS visible image (above) and the 11.0 µm Terra MODIS IR image (below). MODIS IR brightness temperatures were as cold as -74º C within the transverse bands.

Terra MODIS 11.0 µm IR image

Terra MODIS 11.0 µm IR image

Fred was not expected to undergo much more in the way of intensification, since the cyclone was moving toward increasing values of environmental wind shear and warmer sea surface temperatures (below).

Meteosat-9 IR image with CIMSS wind shear analysis

Meteosat-9 IR image with CIMSS wind shear analysis

Hurricane Fred forecast track + Sea Surface Temperature analysis

Hurricane Fred forecast track + Sea Surface Temperature analysis

MODIS false color images showing the Station Fire burn scar

September 8th, 2009 |
250-meter resolution MODIS false color images

250-meter resolution MODIS false color images

A sequence of daily 250-meter resolution MODIS false color images from the SSEC MODIS Today site (above; also available as a QuickTime animation) shows the rapidly increasing size of the burn scar associated with the Station Fire north of Los Angeles during the 28 August – 07 September 2009 period. The fire burn scar appears as the large darker red feature (which is seen to grow very quickly to the north and east on 30-31 August), while the hottest actively burning fires appear as smaller clusters of  pink to white along the periphery of the burn scar. Thick smoke partially obscured the burn scar area on 01 September, while large pyrocumulus clouds were seen to form over the eastern portion of the fire activity on 02 September.

As of the morning of 08 September, the Station Fire had burned over 160,000 acres, making it the largest fire in Los Angeles County history (and the 9th largest fire in California history).

GOES-14 vs GOES-12 visible channel

September 1st, 2009 |
GOES-12 visible image

GOES-12 visible image

GOES-14 visible image

GOES-14 visible image

A comparison of enhanced visible channel images from GOES-12 and GOES-14 at 13:15 UTC on 01 September 2009 is shown above — both images have been remapped to a Mercator projection over the state of Wisconsin. The obvious “meteorological” phenomenon is the early morning fog in the Mississippi, Wisconsin, and Kickapoo River basins, in addition to numerous other valleys and river basins feeding into the Mississippi River.
There are a couple of significant differences to note between the 2 visible images. First of all, the fog is a bit brighter and a little more extensive in the GOES-14 image compared to the GOES-12 image. This is primarily due to the relative age of the visible sensors (which noticeably degrades with time). The second major difference is the relative contrast of lakes, rivers, vegetation, and land usage. GOES-12 has slightly  more  contrast between  land and lakes (and/or other bodies of water) than GOES-14.

On the other hand, GOES-14 is able to discern urban centers more readily than GOES-12, as well as variations in vegetation type. Examples of this are around the large metropolitan region of southeastern Wisconsin and northeastern Illinois (i.e. Milwaukee to Chicago). Also, both the Baraboo Range (located just to the northwest of Madison) and the “Military Ridge” (which runs east to west from Madison to Prairie du Chien) stand out more boldly in the GOES-14 image compared to the GOES-12 image (AWIPS topography image). This difference is primarily due to the slight variation in the spectral width of the two visible bands on the GOES-12 and GOES-14 Imager instruments. A comparison of the visible channel spectral response function for GOES-12 and GOES-14 (below) shows that the sharper cutoff for wavelengths beyond 0.7µm on the GOES-14 visible channel makes it less sensitive to the signal from the mature corn crops, allowing greater contrast between the thick vegetation of the agricultural fields and the more sparsely vegetated cities, towns, and highway corridors.

Spectral response functions for GOES-12 and GOES-14

Spectral response functions for GOES-12 and GOES-14

A time series of GOES-12 visible images (below) illustrates how the cumulus cloud field developed during the morning hours as solar heating increased — convective clouds were seen to develop right over the Baraboo Range and the Military Ridge (AWIPS topography image). At 15:15 UTC and 15:32 UTC, effect of the terrain on cumulus initiation was quite evident, while more “ridge-line cumulus” developed and filled the region by 16:00 UTC and later.

GOES-12 visible image time series

GOES-12 visible image time series

Re-mapped GOES-12 and GOES-14 visible images at 15:45 UTC are shown below, after cumulus development had progressed.

GOES-12 visible image

GOES-12 visible image

GOES-14 visible image

GOES-14 visible image