Satellite detection of wet ground surfaces

October 13th, 2012 |
Suomi NPP VIIRS 11.45 µm IR, MODIS 11.0 µm IR, and POES AVHRR 12.0 µm IR images

Suomi NPP VIIRS 11.45 µm IR, MODIS 11.0 µm IR, and POES AVHRR 12.0 µm IR images

Much of the central US had been experiencing prolonged severe to exceptional drought conditions during the latter half of 2012, leaving the soil surfaces very dry. A sequence of Suomi NPP VIIRS 11.45 µm IR, MODIS 11.0 µm IR, and POES AVHRR 12.0 µm IR images (above) showed snapshots of a number of large mesoscale convective systems that were moving northeastward from New Mexico and Texas across Kansas and Nebraska during the pre-dawn hours on 13 October 2012 — and these storms produced much-needed widespread rainfall, with some locations receiving 1-2 inches (including 1.97 inches at Clayton, New Mexico and 2.30 inches at Sublette, Kansas).

A night-time MODIS 11.0 µm – 3.7 µm IR difference “fog/stratus product” image (below) showed swaths of low clouds over the wet ground surfaces across parts of northeastern New Mexico and the Texas and Oklahoma panhandle regions, immediately in the wake of the passing convective cells.

MODIS 11.0 µm - 3.7 µm IR difference "fog/stratus product"

MODIS 11.0 µm – 3.7 µm IR difference “fog/stratus product”

During the following afternoon, the swaths of wet ground appeared notably cooler (lighter gray color enhancement) on Suomi NPP 11.45 µm IR imagery (below), since the surrounding dry soil surfaces were able to heat up much more quickly.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

The MODIS Land Surface Temperature (LST) product (below) showed that LST values over the moist soil areas were generally in the 60s and 70s F (lighter orange color enhancement), compared to the much warmer LST values in the 80s and low 90s F (darker red color enhancement) over the adjacent dry soil surfaces.

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and Land Surface Temperature product images

MODIS 0.65 µm visible channel, 11.0 µm IR channel, and Land Surface Temperature product images

 

Convective bursts associated with Invest 97L (Tropical Storm Patty)

October 10th, 2012 |
Suomi NPP VIIRS 11.45 µm and GOES-14 10.7 µm IR images

Suomi NPP VIIRS 11.45 µm and GOES-14 10.7 µm IR images

A night-time (just after 07 UTC) comparison of AWIPS images of 375-meter resolution (mapped onto a 1-km AWIPS grid) Suomi NPP VIIRS 11.45 µm IR and 4-km resolution GOES-14 10.7 µm IR channel data (above) showed deep convection associated with tropical cyclone Invest 97L located to the east of the Bahamas on 10 October 2012. Cloud top IR brightness temperatures were as cold as -87 C on the VIIRS images, compared to -80 C on the GOES image. Also note the parallax shift on the GOES image, with features appearing to be located farther to the north and west due to the geostationary satellite viewing angle.

About 90 minutes later, a similar comparison of 1-km resolution POES AVHRR 12.0 µm IR and 4-km resolution GOES-14 10.7 µm IR channel data (below) again showed a significant difference in the coldest cloud top IR brightness temperatures seen (-89 C on AVHRR vs -79 C on GOES). Note the appearance of cloud-top gravity waves propagating along the southeastern quadrant of the convective cluster on the VIIRS and AVHRR IR images.

POES AVHRR 12.0 µm IR and GOES-14 10.7 µm IR images

POES AVHRR 12.0 µm IR and GOES-14 10.7 µm IR images

During the afternoon hours, a comparison of 1-km resolution MODIS 12.0 µm IR and 4-km resolution GOES-14 10.7 µm IR data (below) showed an even larger difference between the coldest cloud top IR brightness temperatures (-92 C on MODIS, -79 C on GOES).

Suomi NPP VIIRS 11.45 µm IR and GOES-14 10.7 µm IR images

Suomi NPP VIIRS 11.45 µm IR and GOES-14 10.7 µm IR images

An animation of GOES-14 10.7 µm IR channel images with an overlay of ASCAT surface scatterometer winds at 14:12 UTC from the CIMSS Tropical Cyclones site (below) suggested that much of these deep convective bursts were occurring to the southeast of the low-level circulation center.

GOES-14 10.7 µm IR images with ASCAT surface scatterometer winds

GOES-14 10.7 µm IR images with ASCAT surface scatterometer winds

===== 11 October Update =====

Invest 97L was classified as Tropical Storm Patty by the National Hurricane Center on 11 October. A comparison of Suomi NPP VIIRS 0.64 µ visible channel and 11.45 µm IR channel images (below) showed that the deep convection persisted, with IR cloud top temperatures as cold as -90º C (violet color enhancement).

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

===== 12 October Update =====

Suomi NPP VIIRS 0.8 µm Day/Night Band, 3.74 µm shortwave IR, and 11.45 µm IR images

Suomi NPP VIIRS 0.8 µm Day/Night Band, 3.74 µm shortwave IR, and 11.45 µm IR images

Due to persistent southwesterly wind shear, the low-level circulation center of Tropical Storm Patty became increasingly decoupled from the deep convection. The night-time circular signature of the low-level circulation center can be seen on 06:25 UTC (2:25 AM local time) Suomi NPP VIIRS 0.8 µm Day/Night Band and 3.74 µm shortwave IR images (above). Subsequent daytime GOES-14 visible images on 12 October 2012 showed the low-level circulation center became completely exposed (below).

GOES-14 0.63 µm visible channel images

GOES-14 0.63 µm visible channel images

Snow cover across southern Manitoba, northeastern North Dakota and northwestern Minnesota

October 6th, 2012 |
Suomi NPP VIIRS 0.64 µm visible image + VIIRS false-color Red/Green/Blue (RGB) image

Suomi NPP VIIRS 0.64 µm visible image + VIIRS false-color Red/Green/Blue (RGB) image

The first significant winter storm of the season over the north-central US and south-central Canada produced snowfall amounts as high as 14 inches over northwestern Minnesota and 4 inches over northeastern North Dakota on 04 October 2012. It is interesting to note that this snow event occurred 2 days after that same region was impacted by significant wildfire activity ahead of an advancing cold front.

The snow cover that remained on 06 October 2012 could be seen in an AWIPS comparison of a Suomi NPP VIIRS 0.64 µm visible channel image and the corresponding false-color Red/Green/Blue (RGB) image created using the 1.61 µm “snow/ice” channel (above), where the snow on the ground was enhanced with a brigher pink color. Note the lack of development of cumulus clouds over the deeper snow cover in northwestern Minnesota, where boundary layer stability was maintained by the lack of surface heating over the high-albedo snow surfaces.

A comparison of the MODIS 0.65 µm visible channel image with the corresponding MODIS Land Surface Temperature (LST) product (below) showed that LST values over the areas of deeper snow cover in northwestern Minnesota were only in the upper 20s to low 30s F (darker green color enhancement), while LST values just to the west over bare ground in far eastern North Dakota LST values were in the upper 40s to low 50s F (lighter green to yellow color enhancement). Surace air tempertures were alo recoverng more rapidly at nearby stations with no snow cover.

MODIS 0.65 µm visible image + MODIS Land Surface Temperature product

MODIS 0.65 µm visible image + MODIS Land Surface Temperature product

GOES-14 0.63 µm visible channel images (below; click image to play animation) showed the rapid melting of snow cover in areas wherre the snow depth was only on the order of 1-2 inches on the morning of 06 October.

GOES-14 0.63 µm visible channel images (click image to animate)

GOES-14 0.63 µm visible channel images (click image to animate)

On the following night, the deep snow cover remaining across northwestern Minnesota could be seen (via illumination by moonlight) in a Suomi NPP VIIRS 0.7 µm Day/Night Band (DNB) image at 07:58 UTC (2:58 AM local time). The corresponding VIIRS fog/stratus product image confirmed that this bright area on the DNB image was not a low cloud or fog feature; however, there there were some thin cirrus features over the area at the time, which showed up as darker black on the fog/stratus product image and brighter white to cyan to blue colors on the 11.45 µm IR image.

Suomi NPP VIIRS 0.7 µm Day/Night Band, Fog/stratus product, and 11.45 µm IR images

Suomi NPP VIIRS 0.7 µm Day/Night Band, Fog/stratus product, and 11.45 µm IR images

Ship tracks in the East Pacific Ocean, and valley fog in British Columbia

October 6th, 2012 |
Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel images

A comparison of AWIPS images of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel data at 11:32 UTC (4:32 AM local time) on 06 October 2012 (above) demonstrated the value of using the Day/Night Band as “visible imagery at night” to aid in the detection of features such as ship tracks that were difficult to identify in the IR image. Snow cover in the higher terrain of western British Columbia cuould also be seen, appearing as brighter white areas on the Day/Night Band image.

Additional ship tracks could be identified within the marine boundary layer stratus clouds by examining the coresponding Suomi NPP VIIRS IR brightness temperature difference “Fog/stratus product” image (below) — as well as numerous fingers of valley fog across interior British Columbia.

Suomi NPP VIIRS 0.7 µm Day/Night Band and Fog/stratus product images

Suomi NPP VIIRS 0.7 µm Day/Night Band and Fog/stratus product images