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NRL Monterey, Marine Meteorology Division
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NRL Monterey, Marine Meteorology Division
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| Fig 1. DMSP Very High Resolution (VHR) Visible Image |
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| Fig. 1 is a VHR depiction of weather effects around the island of Luzon in
the Philippine Island area during the northeast monsoon. The example was
originally published in the Navy Tactical Applications Guide (NTAG) before
the advent of scatterometer data (Fett and Bohan, 1977). A distinct dry
toned (black) clear area, in the lee of the island, is indicative of
easterly to northeasterly flow over the region. On the windward (eastern)
portion of the island moist air is lifted, clouds form, and rain removes
moisture from the air. Thus, the air in the immediate lee of the island
is much drier than the air on the windward side and also dryer than the
air which flows around the periphery of the island or low lying channels.
The DMSP visible sensor is very responsive to changes in aerosol sizes. In the dark-toned area, aerosol size is smaller and, as a result, visibilities should be good. To the northwest a light-toned region is indicative of larger aerosol sizes where visibility at low-levels would be anticipated to be reduced. The edge of the light-toned region also likely indicates the position where wind speeds suddenly increase in value. The stronger winds in this region are anticipated due to the unrestricted movement of air from northeast to southwest through the Luzon Strait. Significant changes in low-level refractivity can also be anticipated because of these changes in low-level moisture content. |
| Fig. 2. Scatterometer Data During a Period of the Northeast Monsoon |
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| Fig. 2 is scatterometer data over the WESTPAC region acquired on 2 February 2001 at 0000Z. These data provide near real time wind estimates for speeds up to 60 kt based on radar return from Bragg scattering off of the ocean's surface. Note the very high wind speeds through the Luzon Channel Between Luzon and Taiwan. The sheltering effect of Luzon to northeasterly flow is clearly shown in this image. Of special interest is the sharp increase of wind speed shown by the radar data in approximately the position of the gray shade change shown by the DMSP data of Fig. 1 in the upper left portion of the image. Although almost a quarter of a century separates these images the effects of nature are shown to be remarkably consistent. |
| Fig. 3. |
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| Fig. 3 is a GOES image taken two days prior to the scatterometer data of
Fig. 2 above. Northeast monsoon effects are apparent on this date and
reveal the intense drying effect caused by this flow in the lee of the
island of Luzon. Not so apparent is the wind shear line one would
anticipate just northwest of the northern tip of Luzon. REFERENCES: Fett, R. W. and W. A. Bohan, 1977, Navy Tactical Applications Guide, Vol 1, Techniques and Applications of Image Analysis, Naval Research Laboratory, Monterey, CA., pp176. |
Author: Bob Fett Last Updated: Mon Dec 9 10:42:14 2002 Produced by: The Composer (Ver: 1.1.2 ) |
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