Drifting ice in Green Bay

December 27th, 2009 |
GOES-14 and GOES-12 visible images

GOES-14 and GOES-12 visible images

McIDAS images of GOES-14 and GOES-12 visible channel data (above) showed that a large portion of the land-fast ice in the southern half of Green Bay began to break away and drift slowly northeastward on 27 December 2009. Unlike a similar case seen on 11 March 2009 with strong surface winds, the southwesterly winds on this particular day were quite light (generally 10 knots or less at inland stations over northeastern Wisconsin) — however, winds were gusting to 13-18 knots farther to the northeast at coastal sites with an upwind exposure to the bay.

As part of its ongoing NOAA Science Test, the GOES-14 satellite had been placed into Rapid Scan Operations (RSO) mode, supplying imagery as frequently as every 5 minutes. The more frequent RSO imaging (along with the improved GOES-14 Image Navigation and Registration) allowed the motion of the drifting ice to be more accurately visualized compared to the 15-minute interval GOES-12 imagery with poorer image navigation.

250-meter resolution MODIS true color images from the SSEC MODIS Today site (below) showed a more detailed view of the motion of the ice between the overpass of the Terra satellite at 17:10 UTC and the Aqua satellite at 18:55 UTC.

MODIS true color images

MODIS true color images

Stratospheric intrusion vortices over the Pacific Northwest

December 27th, 2009 |
GOES-14 6.5 µm water vapor images

GOES-14 6.5 µm water vapor images

McIDAS images of the GOES-14 6.5 µm water vapor channel data (above; also available as a QuickTime animation) revealed that a pair of stratospheric intrusion vortices developed over the Pacific Northwest region of the US on 26 December27 December 2009. The spin-up of these vortices occurred within the pronounced dry band that had formed along the western periphery of the large central US Christmas Blizzard. As a part of its ongoing NOAA Science Test, the GOES-14 satellite had been placed into Rapid Scan Operations (RSO) mode, providing imagery as frequently as every 5 minutes.

There have been cases where turbulence aloft has been associated with these types of stratospheric intrusion vortices — and in this instance, AWIPS images of the GOES-West/GOES-East composite water vapor channels with overlays of pilot reports (below) did indeed show a few reports of moderate turbulence between 26,000 feet and 40,000 feet above ground level in the vicinity of the vortices.

GOES water vapor images + pilot reports of turbulence

GOES water vapor images + pilot reports of turbulence

As the trailing vortex began to pass over Vancouver Island around 12 UTC on 27 December (water vapor image), a north-to-south oriented vertical cross section of NAM80 model fields (below) showed how the dynamic tropopause (taken to be the PV1.5 potential vorticity surface) was being pulled downward to around the 450 hPa pressure level. The GOES Sounder Total Column Ozone product also showed a slight increase in ozone values — to around 350 Dobson Units — associated with the stronger (trailing) stratospheric intrusion vortex.

NAM80 vertical cross section

NAM80 vertical cross section