December 28th, 2011 | Scott Bachmeier
EUMETSAT Meteosat-9 High Resolution Visible (HRV) images
EUMETSAT Meteosat-9 High Resolution Visible (HRV) images (above) showed the classic signature of a “warm seclusion“: a nearly cloud free eye-like structure at the center of the circulation. Surface station wind barbs (in knots) are also plotted in cyan on the images.
A similar eye-like appearance was seen on Meteosat-9 water vapor channel images (below) as the mature cyclone moved just north of the British Isles on 28 December 2011.
EUMETSAT Meteosat-9 water vapor channel images
Hurricane force wind gusts were observed at Tiree, Scotland (station identifier EGPU), with a peak gust of 69 knots (79 mph) at 14:20 UTC (below).
Tiree, Scotland (EGPU) surface reports
Surface analyses from the NWS/NCEP Ocean Prediction Center (below) showed the intensification and evolution of the cyclone during the day.
Ocean Prediction Center surface analyses
Warm seclusions are also sometimes observed with intense cyclones along the East Coast of the US, as in this 20 December 2009 case.
December 28th, 2011 | Scott Bachmeier
MTSAT-1R 10.8 Âµm IR channel images
MTSAT-1R 10.8 Âµm IR channel images from the CIMSS Tropical Cyclones site (above) showed Category 1 Tropical Storm Thane (06B) in the Bay of Bengal, moving toward the east coast of India on 28 December 2011.
Contours of 850-200 hPa satellite-derived deep layer wind shear overlaid on MTSAT-1R 6.75 Âµm water vapor channel images (below) indicated that Thane was in an environment of low wind shear, which favored some intensification prior to making landfall.
MTSAT-1R 6.75 Âµm water vapor channel images + Deep layer wind shear
It is interesting to note that the MIMIC Total Precipitable Water product (below) showed the northern counterclockwise circulation of Tropical Storm Thane and the southern clockwise circulation of Tropical Storm Four (04S) — each drawing moisture from the Inter-Tropical Convergence Zone (ITCZ).
MIMIC Total Precipitable Water product
===== 30 December Update =====
Tropical Storm 04 S intensified in a similar low wind shear environment, becoming Tropical Cyclone Benilde in the South Indian Ocean. Benilde was forecast to intensify, with wind gusts up to 140 knots. Meteosat-7 visible/shortwave IR images with an overlay of ASCAT scatterometer surface winds (below) showed the structure of Benilde.
Meteosat-7 visble/shortwave IR imagery + ASCAT surface winds
December 26th, 2011 | Scott Bachmeier
GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 Âµm water vapor channel images (click image to play animation)
Strong winds aloft associated with a cyclonically-curved jet streak over the Northern Rocky Mountains were responsible for a number of mountain waves and lee “banner clouds” over parts of Wyoming and Montana on 25 December – 26 December 2011. A side-by-side comparison of GOES-15 (GOES-West) and GOES-13 (GOES-East) 6.5 Âµm water vapor channel images (above; click image to play animation) revealed some interesting differences in the appearance of these mountain waves. Note that the images are displayed in the native projection of their respective satellites.
A comparison of the GOES-15 and GOES-13 imager 6.5 Âµm water vapor channel weighting functions (below) showed that the satellite viewing angles (or satellite zenith angles) were very close — 56.41 degrees for GOES-15, and 59.95 degrees for GOES-13 — and the weighting function profiles were nearly identical. However, the fact that GOES-15 was viewing the region from the west allowed it to better resolve the warm/dry signatures (yellow color enhancement) of the most pronounced sinking regions associated with some of the stronger mountain waves. These warm/dry subsidence signatures were possibly masked by the high-altitude lee banner clouds when viewed from the east with GOES-13.
GOES-15 vs GOES-13 water vapor channel weighting function profiles
At 00:40 UTC there was one pilot report of brief moderate turbulence at an altitude of 37,000 feet near the Wind River Range in west-central Wyoming (below). Only a lee banner cloud was evident on the GOES water vapor imagery at that particular time, but a few hours later the warm/dry signature of strong mountain wave subsidence started to become more distinct over that location.
GOES-13 6.5 Âµm water vapor channel image + pilot report of turbulence
Had higher spatial resolution water vapor imagery been available closer to the 00:40 UTC time of the turbulence encounter, perhaps a more distinct mountain wave signature might have been apparent. For example, a comparison of 1-km resolution MODIS 6.7 Âµm and 4-km resolution GOES-13 6.5 Âµm water vapor images at 05:01 UTC (below) demonstrated the advantage of improved spatial resolution water vapor imagery for identifying subtle mountain wave signatures across the region.
MODIS 6.7 Âµm and GOES-13 6.5 Âµm water vapor channel images
December 25th, 2011 | Scott Bachmeier
NOAA-18 AVHRR false color Red/Green/Blue (RGB) image
On 25 December 2011 a new all-time record high temperature of +9.9Â° F (-12.3Â° C) was set at the Amundsen-Scott South Pole Station — the previous all-time record high was +7.5Â° F (-13.6Â° C) on 27 December 1978. A NOAA-18 AVHRR false color Red/Green/Blue (RGB) image (above) displayed a variety of low cloud and high cloud features across the region at 11:17 UTC. Station identifier NZSP marks the location of the Amundsen-Scott station; the edge of the Ross Ice Shelf is at the top of the image.
A listing of available NZSP surface reports is shown below — the maximum temperature actually occurred at 02:50 UTC (15:50 local time). Note that there was also snow (S), light snow grains (SG-), or ice crystals (IC) being reported during much of the day that experienced the record high temperature!
NZSP surface reports
NOAA-18 AVHRR 3.7 Âµm shortwave IR image
A NOAA-18 AVHRR 3.7 Âµm shortwave IR image (above) depicted a number of patches of low altitude clouds composed of supercooled water droplets — these low cloud features appeared darker (warmer) since the shortwave IR channel is also sensitiveÂ to the reflection of solar radiation off the cloud tops.
On the other hand, the corresponding NOAA-18 AVHRR 10.8 Âµm IR image (below) showed that there were high altitude cirrus clouds (cyan to dark blue color enhancement) in the vicinity of station NZSP. These high cirrus clouds could have been contributing to a “seeder-feeder effect” to help produce the periods of light precipitation that were observed on that day.
NOAA-18 AVHRR 10.8 Âµm IR image
A EUMETSAT MetOp-A false color Red/Green/Blue (RGB) image (below; courtesy of Dave Santek, SSEC) showed the cloud features over the South Pole region at 02:52 UTC (very close to the time of the record high temperture).
MetOp-A false color Red/Green/Blue (RGB) image
For additional satellite images and information on this event, see the Antarctic Meteorological Research Center “On the Ice” blog and The Antarctic Sun.