Water vapor imagery from Monday 4 April 2011 over the Gulf of Alaska shows the development of what appears to be Kelvin-Helmholtz instability, an instability that occurs in regions of strong shear. In this case, the shear zone occurs within a gradient of moisture along the edge of a polar vortex, so the developing vortex deforms the water vapor field as detected by the GOES-11 Imager. The vertical circulation associated with the roll vortex can also change the detected moisture field: infer descent in the regions where the water vapor signal decreases with time, and ascent in regions where the water vapor signal increases with time. When these vortices are sampled by the GOES Sounder, it is common to see an enhanced ozone signal in the driest part of the developing vortex, suggesting the entrainment of dry stratospheric air into the vortex circulation.

The vortices have a signal only in the water vapor imagery. Visible imagery from AVHRR (here) show no evidence of wrapped-up vortices.

Note that the GOES-11 Imager was in eclipse between 0800 UTC and 1030 UTC and so no images were received then.

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GOES-11 0.65 µm visible channel images (click image to play animation)

McIDAS images of GOES-11 0.65 µm visible channel data (above; click image to play animation) showed a number of well-defined ship condensation trails (or “ship tracks”) propagating southward within the marine boundary layer stratocumulus cloud field over the eastern North Pacific Ocean on 31 March 2011.

A comparison of AWIPS images of 1-km resolution POES AVHRR 0.86 µm visible channel data and the corresponding 1-km resolution POES AVHRR Cloud Particle Effective Radius product (below) revealed that the ship tracks were composed of slightly smaller particles (lighter cyan color enhancement) than the surrounding stratocumulus clouds that they were embedded within. Note that many of the ship tracks could not be seen on the visible image within the more overcast stratocumulus cloud deck that covered the southern portion of the image — but their detection was possible using the Cloud Particle Effective Radius product.

POES AVHRR 0.63 µm visible and Cloud Particle Effective Radius product images

As can be seen below, the ship track features did not show up very well in 1-km resolution images of the POES AVHRR Cloud Type product (showing liquid type clouds, cyan color enhancement), the Cloud Top Temperature product (showing temperatures around +10º C, green color enhancement), or the Cloud Top Height product (showing cloud tops around 2-3 km, purple color enhancement).

POES AVHRR Cloud Type product

POES AVHRR Cloud Top Temperature product

POES AVHRR Cloud Top Height product

CIMSS participation in GOES-R Proving Ground activities includes making a variety of POES AVHRR images and products available for National Weather Service offices to add to their local AWIPS workstations.

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MODIS true color RGB images from 24, 27, 28, 29, and 30 March 2011

A series of MODIS true color Red/Green/Blue (RGB) images from 24 March, 27 March, 28 March, 29 March, and 30 March (above) showed that most of the northern 2/3 of Wisconsin had significant snow cover during this period (much of it due to the late winter storm of 22-23 March) — the  maximum snow depths across the state ranged from 24 inches on 24 March to 18 inches on 30 March.  Also note that there were also a few small brown-colored areas in far northwestern Wisconsin with no snow on the ground at this time.

This combination of deep snow late-season cover along with cloud-free skies due to persistent high pressure over the region allowed northern Wisconsin to record the coldest overnight low temperatures in Lower 48 states for 8 consecutive days at the end of March 2011:

• 24 March: -8ºF at Hayward
• 25 March: -12ºF at Tomahawk
• 26 March: -13ºF at Tomahawk
• 27 March: -12ºF at Tomahawk
• 28 March: -13º F at Tomahawk
• 29 March: -7ºF at Tomahawk
• 30 March: +1ºF at Tomahawk
• 31 March: +7ºF at Antigo

A comparison of AWIPS images of the MODIS 0.65 µm visible channel and the corresponding MODIS Land Surface temperature (LST) product (below) showed the effect that the deep snow cover was having across Wisconsin and Lower Michigan on 29 March. MODIS LST values ranged from the upper 20s to middle 30s F (green color enhancement) over the snow covered areas to the upper 60s to low 70s F (darker orange color enhancement) just to the south

MODIS visible image + MODIS Land Surface Temperature product (29 March)

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GOES-13 6.5 µm water vapor images (click image to play animation)

McIDAS images of 4-km resolution GOES-13 6.5 µm water vapor channel data (above; click image to play animation) showed a well-defined warm/dry “arc” feature (denoted by the brighter yellow color enhancement) just upwind of a large Mesoscale Convective System (MCS) that was moving eastward along the northern Gulf of Mexico and the adjacent Gulf Coast states on 30 March 2011. The MCS eventually produced a number of reports of damaging winds, large hail, and tornadoes across northern Florida. Also note that a subtle signature of what appeared to be gravity waves could be seen within portions of this warm/dry arc feature (especially in the southern portion, over the Gulf of Mexico).

AWIPS images of 1-km resolution MODIS 6.7 µm water vapor channel data (below) offered a more detailed view of the packet of gravity waves that was associated with the southern portion of the dry arc feature. This warm/dry arc seen on the water vapor imagery could have been a signature of a region of strong compensating subsidence along the rear edge of the intense deep convection.

MODIS 6.7 µm water vapor images

A number of pilot reports of moderate turbulence were co-located within this warm/dry arc feature seen on the water vapor imagery (below; click image to play animation), especially around 14 UTC, 16 UTC, and 17 UTC. There was also a report of severe turbulence along the northern portion of the arc feature as it moved over far southern Alabama at 17:35 UTC. This supports the idea that the warm/dry arc was likely a signature of strong subsidence in the wake of the MCS.

GOES-13 6.5 µm water vapor images + pilot reports of turbulence (click to play animation)

Note that a small patch of clouds developed along the southern portion of the warm/dry arc which contained the gravity waves over the Gulf of Mexico after about 18 UTC — additional information about this cloud patch could offer some clues as to the approximate altitude of the gravity waves. The POES AVHRR Cloud Type product (below) indicated that the cloud patch associated with the gravity wave was a cirrus feature (orange color enhancement).

POES AVHRR Cloud Type product

The corresponding POES AVHRR Cloud Top Height product (below) suggested that the tops of that cloud patch were generally in the 12-13 km range (darker green color enhancement). POES AVHRR cloud top temperatures were in the -55 to -65º C range with this feature.

POES AVHRR Cloud Top Height product

All of the above satellite evidence suggests that the gravity waves seen on the water vapor imagery were not surface-based, but were located at a higher altitude within the middle troposphere. In fact, the GOES-13 water vapor weighting functions calculated using rawinsonde data from Lake Charles, Louisiana (upstream of the MCS) and Tampa, Florida (downstream of the MCS) both peaked around 450 hPa (below), which tells us that the thermal energy being sampled by the water vapor channel in non-cloudy air was originating from within a high-altitude layer.

Lake Charles, Louisiana water vapor weighting function plot

Tampa, Florida water vapor weigting function plot

CIMSS participation in GOES-R Proving Ground activities includes making a variety of  MODIS and POES AVHRR images and products available for National Weather Service offices to add to their local AWIPS workstations.

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