Sensing warming terrain with water vapor imagery

February 14th, 2012 |
GOES-15 6.5 µm water vapor channel images (click image to play animation)

GOES-15 6.5 µm water vapor channel images (click image to play animation)

GOES water vapor imagery tells you how moist or how dry the middle to upper troposphere is, right? Well, in general, yes — but it’s important to remember that the water vapor imagery actually displays the temperature of a layer of moisture that is emitting radiation. This layer of moisture emitting the radiation that is sensed by the water vapor detectors is usually located within the middle to upper troposphere, but if the atmosphere is quite dry (and/or quite cold), the water vapor channel can actually “see” further down through the troposphere and sense thermal radiation that is emitted from the surface.

On 14 February 2012, GOES-15 6.5 µm water vapor channel images (above; click image to play animation) centered on the Big Island of Hawaii showed how the two highest topographical features  (Mauna Kea and Mauna Loa) initially appeared cooler (darker blue color enhancement) than the rest of the island prior to sunrise, but then quickly warmed (exhibiting brighter yellow colors) during the morning hours as sunlight warmed the surface.

GOES-15 0.63 µm visible channel images (below; click image to play animation) showed that the peaks of Mauna Kea and Mauna Loa were cloud-free during this period.

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

While there was a band of higher moisture associated with the ITCZ well south of Hawaii, and another band of moisture along a cold frontal boundary well northwest of Hawaii, the atmosphere over Hawaii itself was fairly dry — MIMIC Total Precipitable Water values (below) generally in the 20-25 mm range over the islands (animation).

MIMIC Total Precipitable Water product + surface analysis

MIMIC Total Precipitable Water product + surface analysis

In this case, the middle to upper troposphere over the Hawaii region was quite dry, which had the effect of shifting the altitude of the water vapor channel weighting function (below) to an altitude low enough to enable some thermal radiation emitted from the higher terrain on Hawaii to “bleed up” through what little water vapor was present aloft and be detected on the GOES-15 water vapor channel imagery.

GOES-15 water vapor channel weighting function (using Hilo HI rawinsonde data)

GOES-15 water vapor channel weighting function (using Hilo HI rawinsonde data)

 

Tropical Cyclone Giovanna (12S)

February 13th, 2012 |
Meteosat-7 10.8 µm IR images

Meteosat-7 10.8 µm IR images

 

EUMETSAT Meteosat-7 10.8 µm IR images from the CIMSS Tropical Cyclones site (above) showed the formation of a well-defined eye as Tropical Cyclone Giovanna (12S) intensified from a Category 3 to a Category 4 storm over the Indian Ocean late in the day on 12 February 2012.

Tropical Cyclone Giovanna maintained a Category 4 intensity as it approached the island nation of Madagascar on 13 February, with the diameter of the eye contracting somewhat on IR imagery as Giovanna was undergoing an eyewall replacement cycle (below).

Meteosat-7 10.8 µm IR images

Meteosat-7 10.8 µm IR images

A few hours prior to landfall, a timely overpass of the EUMETSAT Metop-A satellite allowed a nice view of the surface wind structure using ASCAT scatterometer winds (below).

Meteosat-7 10.8 µm IR images + MetOp-A ASCAT scatterometer surface winds

Meteosat-7 10.8 µm IR images + MetOp-A ASCAT scatterometer surface winds

As the tropical cyclone approached the eastern coast of Madagascar, the erosion of the eastern semicircle of the inner eyewall of Giovanna could be seen in the MIMIC-TC product (below).

MIMIC-TC microwave product

MIMIC-TC microwave product

Large mesoscale convective system over Argentina

February 7th, 2012 |
GOES-12 10.7 µm IR channel images (click image to play animation)

GOES-12 10.7 µm IR channel images (click image to play animation)

McIDAS images of 4-km resolution GOES-12 10.7 µm IR channel data (above; click image to play animation) showed the development of a very large mesoscale convective system (MCS) over Argentina on 07 February 2012. A number of smaller, discrete thunderstorms initially began to develop around 14:45 UTC, which then eventually merged into a large MCS having large areas which exhibited cloud top IR brightness temperatures of -80 C and colder (purple color enhancement). Multiple “enhanced-v” storm top signatures could be seen at various times, which is a satellite signature of thunderstorms that are capable of producing either tornadoes, large hail, or damaging winds.

Much more detail in the cloud top IR brightness temperature structure can be seen in a 375-meter resolution Suomi NPP VIIRS 11.45 µm image at 18:21 UTC (below). The coldest VIIRS IR brightness temperatures sensed was -96 C (darker violet color enhancement) — much colder than the -77 C seen on the corresponding 18:15 UTC GOES-12 IR image. The black striping seen along the right side of the image is an artifact of the side-to-side scan strategy of the VIIRS instrument; software to remove these artifacts and create a smoother-looking image is under development.

Suomi NPP VIIRS 11.45 µm IR image

Suomi NPP VIIRS 11.45 µm IR image

Large outbreak of Saharan dust over the eastern Atlantic Ocean

February 7th, 2012 |
EUMETSAT Meteosat-9 0.635 µm visible channel images (click image to play animation)

EUMETSAT Meteosat-9 0.635 µm visible channel images (click image to play animation)

McIDAS images of EUMETSAT Metosat-9 0.635 µm visible channel images (above; click image to play animation) showed a very large outbreak of airborne Saharan dust streaming off the continent of Africa and moving west-southwestward out over the adjacent waters of the eastern Atlantic Ocean on 07 February 2012. In addition, a pair of long von Karman vortex streets can be seen moving southwestward from the Cape Verde islands.

While the viewing angle was more extreme, the Saharan dust could also be seen on GOES-13 0.63 µm visible channel images (below).

GOES-13 0.63 µm visible channel images + surface reports

GOES-13 0.63 µm visible channel images + surface reports

The emergence of this Saharan dust over water can be seen to occur around 00:00 UTC on 06 February on the Meteosat-9 Saharan Air Layer tracking product (below).

EUMETSAT Meteosat-9 Saharan Air Layer tracking product

EUMETSAT Meteosat-9 Saharan Air Layer tracking product