GOES-10: Southern Hemisphere Coverage

December 21st, 2006 |

GOES-10 Sounder coverage (animated GIF)

GOES-10 (which is currently located at approximately 60 degrees West longitude) imager and sounder data are currently being ingested by the SSEC Data Center in support of the Earth Observation Partnership of the Americas (EOPA) project. The animated GIF of GOES-10 sounder coverage (above; Java animation) shows the 4 separate sectors that are scanned at 60 minute intervals. Examples of all 19 channels on the GOES-10 sounder are shown for sector 1, sector 2, sector 3 and sector 4. Of particular interest is the warm signature of the Andes Mountains in the sector 4 images, which is evident on the water vapor (channel 10) and CO2 absorption bands (channels 3,4,5) as well as the other IR channels.

An animated GIF of GOES-10 imager IR window channel images (below) shows the larger areal coverage and improved temporal resolution of the GOES-10 imager (Java animation), which has 1 visible and 4 IR channels. These GOES-10 imager and sounder images are shown in their native satellite projections (no remapping has been done).
GOES-10 imager IR window (animated GIF)

Detecting Surface Features in Water Vapor Channel Imagery (Part 2)

December 18th, 2006 |

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

Another example of detection of surface features on “water vapor channel” imagery was apparent on 18 December 2006. In this particular case, the “surface” was the high terrain of the Absaroka Range, Wind River Range, and Big Horn Mountains in Wyoming (all of which reach altitudes in excess of 13,000 feet / 4000 m), making it easier to sense radiation from the ground using the 6.5µm/6.7µm water vapor channel. Since this channel is essentially an InfraRed (IR) channel, the cold temperature signature of the snow-covered mountain features (morning temperatures were as cold as -30 F / -34 C at Old Faithful in Yellowstone Park, where 22 inches / 56 cm of snow were on the ground) was very obvious against the warmer background temperature of the surrounding bare ground at lower elevations. Very little water vapor was present within the atmospheric column, so the water vapor channel weighting function (calculated using the Riverton, Wyoming rawinsonde profile) for both GOES-11 and GOES-12 peaked at an altitude just below 500 hPa (very near the altitude of the aforementioned mountain features).

A Java animation of GOES-11, GOES-12 and GOES-13 water vapor imagery shows that the mountain features become more apparent as a drier pocket of air passed over the region. Due to the higher spatial resolution (4km) of the spectrally-wider 6.5µm water vapor channel on both GOES-12 and GOES-13, the mountain features are resolved with greater clarity compared to the 8km resolution 6.7µm channel on GOES-11. In addition, since the mid-tropospheric winds across that region were fairly light (and generally parallel to the orientation of the terrain), there were no “mountain wave” signatures to the lee of these mountain ranges.

Dissipation of Fog

December 15th, 2006 |

The long nights of winter can be ideal for the formation of fog. Clear, calm conditions are conducive to strong radiational cooling, and if the cooling occurs over a moist surface, cooling to the dewpoint is likely and fog may be a result. Once fog has formed over a location, when will it lift? In large part that depends on the distance to the fog edge, as radiation fog will frequently erode from the outside in. Consider this example from December 15.

Fog image with isobars and plotted visibility

Visibilities are plotted and mean sea level pressure values (both from 1300 UTC) are contoured on this visible image from 1332 UTC on 15 December 2006. Very low visibilities (in statute miles) correspond to the region of fog and low clouds in central North Carolina. The sounding from Greensboro from 1200 UTC that morning (click on the thumbnail below) confirms that the saturated layer is confined to the surface and was likely a result of strong raditional cooling in the absence of any strong winds (as evidenced by the weak pressure gradient and the surface winds in the Greensboro sounding). The region of fog is centered on the Pee Dee River valley east of Charlotte.

GSO rawinsonde
What happens during the day? A thin layer of fog will dissipate as it mixes with the dryer air above it. For that to happen, mixing in the vertical that is driven by insolation must begin. Insolation underneath a dense fog is very minimal, but as you approach the edge of a region of fog, the fog thins and insolation increases, allowing more vertical mixing that entrains dry air above the fog into the fogbank, hastening evaporation. Because of that, isolated radiation fog banks such as this erode from the outside in.

Note in the visible image loop from 1332 UTC to 1815 UTC below (at 15-minute intervals, with some gaps) that this fog bank initially expands to the east. It is likely that regions east of the fog bank continued cooling to their dewpoint after sunrise. Cooling to the dewpoint at night was inhibited by the presence of upper level cirrus associated with a jet streak propagating up the East Coast.

The development of this fog at night was detectable using the method described here.
Loop of Fog Erosion

GOES-13: Images at 30-Second Intervals

December 12th, 2006 |

GOES-13 visible images (QuickTime animation)
On 12 December 2006 (Day 6 of the GOES-13 post-launch NOAA Science Test), the GOES-13 satellite was placed into Super Rapid Scan Operations (SRSO) mode, providing images at 30-second intervals for the entire day. A 200-image QuickTime animation of visible imagery (above) shows the development of convection along an advancing cold frontal boundary during the late morning into the early afternoon hours; isolated severe thunderstorm warnings were issued for counties in eastern Mississippi (however, no reports of severe weather were received from these particular storms). Previous GOES satellites have provided 30-second interval imagery during special test periods (for example, GOES-8 in 1996), but such SRSO test periods were much shorter (about 10 minutes total duration).

A QuickTime animation of GOES-13 10.7µm IR images (below) reveals fairly cold cloud top temperatures (around -55 to -60 C, orange to red enhancement), but no “enhanced-v” signature was observed. A few cloud to ground (CG) lightning strikes were seen in the vicinity of the strongest convection, but flash rates were quite low (GOES-12, MODIS IR images with CG strikes).
GOES-13 IR images (QuickTime animation)