Tropical Invest 97L in the western Atlantic Ocean

September 29th, 2014
GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

GOES-13 0.63 µm visible channel images with METAR surface reports (click to play animation)

Tropical Invest 97L formed near Bermuda during the pre-dawn hours on 29 September 2014. After sunrise, AWIPS II images of GOES-13 0.63 µm visible channel data (above; click image to play animation) revealed a well-defined low-level circulation spinning just to the west of Bermuda. It is interesting to note that at 12:55 UTC a waterspout was reported 4 km to the east of the Bermuda International Airport (station identifier TXKF), associated with a band of deep convection that was moving northward (below).

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

GOES-13 0.63 µm visible channel image with Bermuda METAR observation

An overpass of a Metop satellite at 14:38 UTC provided a good view of the surface wind field with data from the ASCAT scatterometer instrument (below). There was one wind vector with a speed around 30 knots (green) just to the east of the center of circulation.

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

GOES-13 0.63 µm visible channel image with Metop ASCAT scatterometer surface winds

A comparison of Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images at 15:25 UTC (below) showed that the coldest cloud-top IR brightness temperatures of -55º C (orange color enhancement) were located to the north of the circulation center.

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Terra MODIS 0.65 µm visible channel and 11.0 µm IR channel images

Co-registration Issues on GOES-13

September 29th, 2014

Previous posts on this blog (and elsewhere) have detailed the co-registration misalignment that exists between the 3.9 µm and 10.7 µm channels on the GOES-13 Imager. Because of this diurnally-varying co-registration error, a 3.9 µm pixel may be offset to the right or left of a 10.7 µm pixel; if this occurs near a pronounced temperature gradient (such as along a lakeshore), a false brightness temperature difference signal can ensue.

Brightness Temperature Difference (10.7 µm - 3.9 µm), 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

Brightness Temperature Difference (10.7 µm – 3.9 µm), 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

Consider, for example, the toggle above from 26 September 2014. A strong brightness temperature difference exists at 1825 UTC along the shorelines of Lakes Michigan, Huron and Erie; it is gone five minutes later, at 1830 UTC. There is no discernible change in the visible image over the same 5-minute interval (Link).

GOES-13 Imagery (0.63µm , top, 10.7µm , middle and 3.9µm micron, bottom) at 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

GOES-13 Imagery (0.63µm , top, 10.7µm , middle and 3.9µm micron, bottom) at 1825 and 1830 UTC, 26 September 2014 (click to enlarge)

NESDIS operations alters the GVAR signal just before 1830 UTC (when the 3.9 µm imagery is shifted one pixel to the West) and at 0630 UTC (when the 3.9 µm imagery is shifted one pixel to the East) to mitigate the effects of the diurnally-varying co-registrations differences between the 3.9 µm and 10.7 µm channels. The imagery above shows the visible and two infrared (10.7 µm and 3.9 µm) channels at 1825 and 1830 UTC (GOES-13 was in Rapid Scan Operations mode at this time). The 3.9 µm imagery shows a one-pixel westward shift that is especially evident if you look at the unchanging navigation along the eastern shore of Lake Michigan. (1825 UTC imagery: Visible, 3.9µm and 10.7µm; 1830 UTC imagery: Visible, 3.9µm and 10.7µm) A similar link between 1815 and 1830 UTC on 25 September shows the same shift in the shortwave IR. A toggle between 0615 and 0630 UTC on 29 September shows the eastward shift in the 3.9 µm imagery that occurs then.

NOAA/NESDIS continues to monitor this co-registration issue.

GOES Cloud Top Cooling Rate product used for SPC Mesoscale Discussion

September 17th, 2014
Storm Prediction Center Mesoscale Discussion #1724

Storm Prediction Center Mesoscale Discussion #1724

Using the GOES-R Cloud Top Cooling Rate product (applied to GOES-13 data), the Storm Prediction Center issued a Mesoscale Discussion (above) highlighting the risk of strong thunderstorms producing hail and/or strong wind gusts over parts of the Georgia/South Carolina border region on 17 September 2014. According to the SPC storm reports, there was hail up to 1.0 inch in diameter in addition to some tree and power line damage in southern South Carolina.

AWIPS II image combinations of the Cloud Top Cooling (CTC) rate product (colors) and the GOES-13 10.7 µm IR channel gray-scale images  (below; click image to play animation) showed that CTC rate values for the storm north of Augusta, Georgia (KAGS) at 19:00 UTC were as high as -16º C per 15 minutes; at 19:15 UTC, the CTC rate value for that storm was as high as -39º C per 15 minutes. The first Severe Thunderstorm Warning for this storm was later issued at 19:34 UTC.

Cloud Top Cooling Rate (colors) and GOES-13 10.7 µm IR (grayscale) images [click to play animation]

Cloud Top Cooling Rate (colors) and GOES-13 10.7 µm IR (grayscale) images [click to play animation]

GOES-13 10.7 µm IR channel images (below; click image to play animation) showed the rapidly cooling cloud-top IR brightness temperatures associated with these thunderstorms as they moved southeastward and intensified: the coldest value for the aforementioned thunderstorm was -40º C at 19:00 UTC, dropping to -62º C by 20:45 UTC.

GOES-13 10.7 µm IR channel images [click to play animation]

GOES-13 10.7 µm IR channel images [click to play animation]

About an hour later, another Severe Thunderstorm Warning was issued at 20:30 UTC for a storm near and south of Orangeburg, South Carolina (KOGB).

NASA Global Hawk flight to study Tropical Storm Dolly

September 2nd, 2014
NASA Global Hawk flight path, with Cloud Height, Tropical Overshooting Tops, and Lightning data (click to play animation)

NASA Global Hawk flight path, with Cloud Height, Tropical Overshooting Tops, and Lightning data (click to play animation)

The NASA Global Hawk aircraft are once again being used to study tropical cyclones during the 2014 season. As part of CIMSS participation in GOES-R Proving Ground activities, a Global Hawk flight path tool was developed to display important parameters such as ACHA Cloud Top Height, Tropical Overshooting Tops, and lightning (above; click image to play animation). Global Hawk pilots use this product to navigate the aircraft around locations of potential turbulence.

GOES-13 0.63 µm visible channel images (click to play animation)

GOES-13 0.63 µm visible channel images (click to play animation)

To support the Global Hawk investigation of Tropical Storm Dolly on 02 September 2014, the GOES-13 satellite was placed into Rapid Scan Operations (RSO) mode to provide images at 5-7 minute intervals. GOES-13 0.63 µm visible channel images (above; click to play animation) and 10.7 µm IR channel images (below; click to play animation) are shown which cover the 3-hour period of the Global Hawk flight segment shown above. There is evidence of overshooting tops seen in the visible imagery, with cloud-top IR brightness temperatures of -80º C and colder (purple color enhancement).

GOES-13 10.7 µm IR channel images (click to play animation)

GOES-13 10.7 µm IR channel images (click to play animation)