INTERPRETATION
DISCUSSION
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Regional and Mesoscale Meteorology Team Cooperative Institute for Research in the Atmosphere (CIRA) Colorado State University Fort Collins, Colorado |
March 20, 2000
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Figure 1 |
xxxx | This satellite imagery discussion is focused
on spiral moisture patterns of cyclones as seen in the water vapor imagery
(6.7 microns) and their utility in diagnosing the state of the associated
surface low. This topic is discussed in the NOAA Technical Report
NESDIS 57 titled 'Water Vapor Imagery, Interpretation and Applications
to Weather Analysis and Forecasting' by Roger Weldon and Susan Holms, April
1991. These spirals are formed by the cyclonic rotation of relatively
dry air around an upper-level low. An example of such a spiral is
located over central NE as shown in Figure 1.
Click on image to enlarge |
| Weldon and Holms suggested that the presence of a spiral pattern in the water vapor imagery may develop after the formation of the associated surface low. The authors also suggested that some surface lows began filling (central pressured increased) before the formation of the spiral in the 6.7 micron imagery. Thus, the upper-level lows were not good indicators of the surface low pressure gradients (a measure of intensity) nor did it indicate the minimum pressures during the development of the surface lows. The authors did find, however, that for all cases studied the presence of a spiral (one or more revolutions of the dry air about the upper-level low center) indicated that the surface lows had stopped deepening and were usually filling. Thus, spirals in the 6.7 micron imagery may be used to indicate surface lows that are not likely to deepen further. |
| On March 8, 2000 a spiral in the water vapor imagery developed in New Mexico and traveled toward the northeast. At that time a surface low developed and moved along a similar path. The loop of images presented on this page are 12-km resolution 6.7 micron images from GOES-10. On each image the time and minimum pressure are written. While the surface pressure decreased (18 UTC - 00 UTC) the upper-level low was forming. During that time that upper-level low did not display a well formed spiral in the 6.7 micron images. By 14 UTC a well defined spiral was present in the 6.7 micron image. At that time the pressure of the surface low had been at its minimum (994 mb) for nearly 5 hours. At 17 UTC the surface low minimum pressure began to increase (i.e., the surface low began to fill). In this example the behavior of the upper-level low and the associated spiral in the 6.7 micron images appears to support the results presented in Weldon and Holms (1991). | 
Click on image to start loop |