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VIIRS view of Invest 97S at night

Posted On: April 10, 2012 - By: Curtis Seaman


On 5 April 2012, the Joint Typhoon Warning Center was watching an area of the Mozambique Channel for possible development of a tropical cyclone. This area was named Invest 97S. As 6 April 2012 was a full moon, this is a good case to test the capabilities of low-light visible imagery channels for detection of tropical cyclone development at night.

The Operational Linescan System (OLS) aboard the Defense Meteorological Satellite Program (DMSP) satellite F-18 has a low-light visible channel (that inspired the development of the Day-Night Band (DNB) for VIIRS). The image below is from this channel on F-18, taken at 17:22 UTC, 5 April 2012 (courtesy the Naval Research Laboratory).

DMSP OLS low-light visible image of Invest 97S, taken at 17:22 UTC, 5 April 2012

DMSP OLS low-light visible image of Invest 97S, taken at 17:22 UTC, 5 April 2012. Image courtesy Naval Research Laboratory.

The landmass on the right of the image is Madagascar with Mozambique on the left side of the image. A low-level circulation is visible in the clouds just off the coast of Madagascar in the center of the image.

Suomi-NPP passed over the area at 23:02 UTC. The images below are taken from the VIIRS DNB, which is a low-light visible channel (centered at 0.7 µm) with higher radiometric resolution, a higher signal-to-noise ratio and higher spatial resolution. The second image is a zoomed-in version of the first.

VIIRS DNB image of Invest 97S taken at 23:02 UTC, 5 April 2012

VIIRS DNB image of Invest 97S taken at 23:02 UTC, 5 April 2012. Image courtesy Dan Lindsey and Steve Miller.

Zoomed-in image of Invest 97S from the VIIRS DNB taken at 23:02 UTC, 5 April 2012

Zoomed-in image of Invest 97S from the VIIRS DNB taken at 23:02 UTC, 5 April 2012. Image courtesy Dan Lindsey and Steve Miller.

In the nearly six hours that elapsed between the DMSP OLS image and the VIIRS DNB image, you can see that the line of deeper convection to the southwest of the circulation center has moved further south away from the center of the circulation and outflow from these storms has cleared out the low level clouds from where the storms used to be.

Compare these images with the high-resolution infrared window channel (11.45 µm), I-5, from VIIRS, seen below.

VIIRS channel I-5 image of Invest 97S, taken at 23:02 UTC, 5 April 2012

VIIRS channel I-5 image of Invest 97S, taken at 23:02 UTC, 5 April 2012.

The low level circulation is difficult to distinguish, given that there is no significant temperature contrast between the low level clouds and the background (ocean) surface. The deeper convective clouds are easy to spot in I-5, however.

The information provided by the VIIRS DNB near full moon events would be a great help to tropical cyclone forecasting in cases such as this where, typically, only IR data is available at night. Assuming latency issues with VIIRS can be solved, of course.

In the end, Invest 97S failed to develop into a tropical cyclone, which spared Madagascar and Mozambique – both of which had been affected by the cyclones Giovanna and Funso earlier this year.


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