SATELLITE IMAGERY

other. An estimate of the effects of each must be made before a decision is reached. � When surface pressure falls occur near the center and in the forward quadrants of the high, the high will weaken. � When a cold high that is moving southward is being heated from below, it will weaken, unless the heating is compensated by intensification of the ridge aloft. The amount of intensification can be determined by correlating the contributions of height change at the 500-hPa level as progged and the change in thickness as advected. SATELLITE IMAGERY The AG2 TRAMAN, volume 1, provides a detailed discussion of satellite imagery analysis. It may be beneficial to review Unit 10 before you read this chapter. Satellite imagery provides the forecaster with an aid in forecasting the deepening of surface low- pressure systems. In the following series of illustrations, both visual and infrared imagery depicts the cloud features over a 60-hour period during the deepening of a low-pressure system. See figures 3-10 through 3-15. In figure 3-10, the visual pass at noon local time shows a large cloud mass with a low level vortex centered near A. A frontal band, B, extends to the southwest from the large cloud mass. The beginning of a dry tongue is evident. An interesting cloud band, C, which appears just north of the cloud mass, is of about the same brightness as the major cloud mass. The infrared scan for midnight, figure 3-11, shows the further development of the vortex with penetration of the dry tongue. Low-level circulation is not visible, but the brightness (temperature) distribution differs from the visual picture. The detail within the frontal band is apparent, with a bright cold line, DE, along the upstream edge of the band. In all probability, this is the cirrus generated by the convection near the polar jetstream. The cloud band, C, from the previous (daylight) picture is seen in the IR, and is composed of lower clouds than would be anticipated from the video. By the second noon (fig. 3-12), the vortex is clearly defined, but again the spiral arm of the frontal band is nearly saturated, with a few shadows to provide detail on cloud layering. The National Meteorological Center (NMC) operational surface analysis during this period shows that the cyclone has deepened. Figure 3-11.-Infrared, local midnight, first night. In figure 3-13, the pass for the second midnight shows the coldest temperatures form a hooked-shaped pattern with the highest cloudiness still equatorward of the vortex center at F. The granular gray-to-light- gray temperature within the dry tongue area, G, suggests cells that consist of cumulus formed from stratocumulus, and small white blobs indicating cumulus congestus. The visual pass for the third noon (fig. 3-14) shows the vortex to be tightly spiraled, indicating a mature system. The frontal band is narrower than it was 24 hours earlier, with some cloud shadows present to aid in determining the cloud structure. Surface analysis indicates that the lowest central pressure of the cyclone was reached approximately 6 hours prior to this picture. The final pass in this series (fig. 3-15) shows the coldest temperatures completely surround the vortex. The frontal band also shows the segmented nature of the active weather areas within the band. A typical vorticity 3-15