Middle and upper-atmospheric wave structures in the vicinity of a subtropical jet stream

April 4th, 2016 |

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with ECMWF model maximum wind isotachs [click to enlarge]

Suomi NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with ECMWF model maximum wind isotachs [click to enlarge]

A strong (120-knot) subtropical jet stream was moving eastward across the Gulf of Mexico during the 03 April – 04 April 2016 period. During the overnight hours between these 2 days, a Suomi NPP VIIRS Day/Night Band (0.7 µm) image at 0753 UTC (above) revealed a large packet of arc-shaped mesospheric airglow waves south of the axis of the jet stream (as indicated by isotachs of the maximum tropospheric wind speed from the ECMWF model). Note how there were no cloud features which corresponded to these waves in the 0753 UTC VIIRS Infrared Window (11.45 µm) image; since the Moon was in the waning Gibbous phase (at 13% of Full), there was very little lunar illumination of cloud features, so airglow — essentially the “night glow” emitted from a variety of high-altitude (80-105 km) gases (primarily the sodium layer) near the mesopause — was allowing these high-altitude waves to be detected using the sensitive Day/Night Band (reference: “Suomi satellite brings to light a unique frontier of nighttime environmental sensing capabilities”).

During the subsequent daytime hours on 04 April, more interesting (tropospheric) waves were seen in the vicinity of this subtropical jet stream — small packets of waves that were propagating westward, against the ambient flow –one over Florida/Georgia/South Carolina, and another over South Texas. Unfortunately, these features fall into the “What the heck is this?” blog category, so no coherent explanation of them can be offered at this time.

GOES-13 Water Vapor (6.5 µm) images, with ECMWF model maximum wind isotachs [click to play animation]

GOES-13 Water Vapor (6.5 µm) images, with ECMWF model maximum wind isotachs [click to play animation]

An interesting question from Shea Gibson:

Low-level “barrier jet” along the southeast coast of Greenland

December 29th, 2013 |
GOES-13 6.5 µm water vapor images with Metop ASCAT scatterometer winds and surface METARs and surface analyses (click to play animation)

GOES-13 6.5 µm water vapor images with Metop ASCAT scatterometer winds and surface METARs and surface analyses (click to play animation)

AWIPS images of GOES-13 6.5 µm water vapor channel data with available overpasses of Metop ASCAT surface scatterometer winds (above; click image to play animation) revealed the presence of a low-level “barrier jet” along the southeast coast of Greenland on 29 December 2013. Maximum ASCAT wind speeds were 58 knots at 12:16 UTC, 62 knots at 13:57 UTC, and 62 knots at 22:09 UTC. It is interesting to note that a secondary area of low pressure was seen rotating around the primary low, and appeared to be rapidly intensifying judging from the quick development of a “corkscrew” appearance on the water vapor imagery near the end of the animation. ASCAT winds along the northwestern periphery of this secondary low were as high as 53 knots at 22:09 UTC.

The cyclonic circulation around the quasi-stationary area of low pressure located east of Greenland encountered the abrupt rise in topography of the island (below), which caused an acceleration of the flow known as a “barrier jet”.

Topography of Greenland, with Metop ASCAT scatterometer winds and surface METAR reports and surface analysis

Topography of Greenland, with Metop ASCAT scatterometer winds and surface METAR reports and surface analysis

Pacific moisture plume and strong jet

October 3rd, 2008 |
AWIPS images of water vapor composite

AWIPS images of geostationary satellite water vapor channel data

AWIPS images of geostationary satellite water vapor channel data (above) showed a long moisture plume moving across the Pacific Ocean toward the west coast of the US on 02-03 October 2008. A comparison of GOES-11 water vapor channel data with POES (AMSU) and SSM/I Total Precipitable Water (TPW) products (below) revealed that TPW values were as high as 50-60 mm (2.0-2.4 inches) within this moisture plume. The MIMIC TPW product suggested that this moisture plume originated over the western Pacific Ocean, southeast of Japan.

AWIPS images of POES TPW products and GOES water vapor channel

AWIPS images of POES TPW products and GOES water vapor channel

This moisture plume was associated with a strong polar jet stream, as seen by an overlay of hourly MADIS atmospheric motion vectors on GOES water vapor channel imagery (below).

GOES water vapor images + MADIS winds

GOES water vapor images + MADIS winds

The 18 UTC GFS model fields were forecasting maximum winds in the core of the jet to reach 170 knots (below) — there were a few MADIS wind vectors with speeds of 177-181 knots around that time (and a MADIS wind vector with a speed of 191 knots was seen at 21 UTC).

GFS winds + MADIS winds

GFS winds + MADIS winds

Water vapor imagery: upper level vortices and jet streaks

September 13th, 2006 |

GOES-12 water vapor animation

A QuickTime animation of GOES-12 imager 6.5 micrometer (“water vapor channel”) imagery (above) reveals an interesting vortex associated with a cutoff upper-level low which was migrating eastward from Illinois to Ohio on 13 Sepember. Several pulses of convection can be seen developing along the periphery of the vortex. In addition, GOES-12 sounder total column ozone values were slightly elevated within the core of the vortex (~350 Dobson Units, compared to the background of ~300 DU), suggesting that some stratospheric air was also present.

Also of interest were the subtle indications that the structure of the jet stream (within the southeastern quadrant of the upper low circulation) was very complex — note the “streaky” appearance on the water vapor images across the Tennessee and Ohio River Valley regions, especially evident on the 1km resolution MODIS water vapor channel (below, upper right panel), but also apparent on the 10km resolution GOES-12 sounder water vapor channel (below, lower left panel). The relatively smooth NAM 300mb wind speeds simply indicated a broad jet streak core oriented SW-NE from Mississippi to Virginia, with a 500mb jet streak axis located farther to the northwest. The striated appearance of the water vapor imagery suggests that the broad jet core region may have been comprised of multiple jet streaks (likely existing at different altitudes).

The lower right panel below is the CRAS model forecast of the GOES water vapor channel, close to the time of the actual satellite images in the other 3 panels; while the CRAS model was unable to resolve the fine mesoscale structure associated with the multiple jet streak cores, it did offer a good prognosis of the “3-pronged structure” of the leading edge of the dry slot.
AWIPS water vapor channel comparison