GOES-13: Data during eclipse period

August 31st, 2006

One of the important changes made to the GOES-N/O/P series of satellites is the addition of increased onboard battery capacity to enable the satellites to continue to provide imager and sounder data during the Spring and Fall season “eclipse periods”. During these eclipse periods (which can last 1-3 hours), the GOES satellites are in the Earth’s shadow, so their solar panels cannot provide power to all of the satellite instrument payloads.

Below is a comparison of GOES-12 and GOES-13 10.7 micrometer IR (“IR window”) data, showing convective rain bands associated with Tropical Storm Ernesto. At 04:02 UTC (below, left), one of the rain bands (with cloud top temperatures of -60 to -70 C, denoted by the red to black color enhancement) is moving inland across southeastern Georgia with light rain begining along the coast at Brunswick. However, no GOES-12 images are available between 04:15 UTC (below, right) and 06:15 UTC, a period when this particular convection was exhibiting a trend of cooling cloud top temperatures. A QuickTime animation (22 images, 5.2 MB file size) shows that GOES-13 IR data was available during this ~2 hour eclipse period, allowing the cloud top temperature trends of these convective rain bands to be monitored continuously.
GOES-12/GOES-13 IR imagesGOES-12/GOES-13 IR images

Tropical Depression Ernesto

August 30th, 2006

Tropcal Storm Ernesto moved inland over southern Florida this morning, and was downgraded to a Tropical Depression. The AWIPS image below shows a MODIS vs. GOES comparison of the longwave IR (“IR Window”) and shortwave IR channels around 16 UTC. Note on the 1-km resolution MODIS IR Window channel (upper left panel) the much larger circular-shaped area of colder cloud top temperatures (-75 to -80 C, gray to white enhancement) over Florida, compared to the 4-km resolution GOES-12 IR Window channel (upper right panel). Also of interest is a signature of slightly warmer cloud top temperatures (darker grey enhancement) over that same region on the MODIS shortwave IR (lower left panel) – no such signature was yet evident on the corresponding GOES-12 shortwave IR at that time (lower right panel):
AWIPS MODIS/GOES IR comparison

This signature on the shortwave IR channel is due to the dominance of smaller cloud particles within the storm tops of the active convection (similar to what is sometimes observed with “overshooting tops” associated with severe convection) — these smaller, more numerous ice particles exhibit a larger shortwave IR albedo, which is manifest as slightly warmer shortwave IR brightness temperatures (due to enhanced solar reflectance). GOES-10 Super Rapid Scan Operations (SRSO) imagery at 1-minute intervals (IR Window | Shortwave IR | Visible) indicated that this particular burst of convection was beginning to rapidly intensify around 16 UTC; this “small ice particle signature” did eventually become obvious on the GOES-10 shortwave IR imagery, but not until around 16:11 UTC.

GOES-10 1-minute interval imagery

August 29th, 2006

The GOES-10 satellite has been placed into Super Rapid Scan Operations (SRSO) mode while the satellite is being re-positioned to support Southern Hemisphere operations this Fall. While in SRSO, the imagery is available at 1-minute intervals for certain portions of each hour (see the SSEC Rapid Scan GOES-10 Visible Imagery and GOES-10 1 minute Data sites). This frequent imaging schedule lets us view the evolution of cloud features on a much shorter time scale than the normal 15-minute image interval allows. On this particular day, some interesting boundary layer roll clouds developed in the Oklahoma panhandle region (this is often a signature of strong warm air advection within the lower troposphere); some organized convection is then seen to develop near the western (upstream) edge of these cloud features. A QuickTime animation (154 images; 11 MB file size) shows these visible images at 1-minute intervals from 19:01 to 22:41 UTC.
GOES-10 visible image

Water vapor channel interpretation

August 28th, 2006

Today’s GOES-12 6.5 micrometer “water vapor channel” imagery shows a rather strong moisture gradient in the southcentral US, oriented along a cold frontal boundary. In the color enhancement applied to the AWIPS water vapor image below, dry air is denoted by the orange to yellow shades, while increasing moisture is indicated by the blue to white shades (thick clouds are enhanced with the white to green colors). In particular, note the sharp water vapor gradient between the dry atmosphere at Amarillo TX (KAMA) and the moist atmosphere at Fort Worth TX (KFWD):
AWIPS water vapor image
The water vapor channel shows us the distribution of moisture features in the middle to upper troposphere, but the actual altitude of the dry or moist layers that are being detected by the water vapor channel can vary quite a bit depending on the temperature/moisture profile of the atmosphere. To assess the altitude and depth of the layer from which the radiation is originating, we can calculate the water vapor weighting function based upon the temperature and moisture profile for that region. The CIMSS GOES Realtime Weighting Functions website allows you to select a particular rawinsonde location and then view the GOES weighting functions for a few of the imager and sounder channels (including the imager water vapor channel and the 3 sounder water vapor channels). Note that in the dry air at Amarillo TX (below, left) the altitude of the peaks of the various imager and sounder water vapor channel weighting function plots is significantly lower than those in the moist atmosphere just 310 miles (500 km) to the southeast at Fort Worth TX (below, right):
Amarillo TX weighting functionsFt. Worth TX weighting functions