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UDC aal.~6.l:aal.~.21~4)((084.1)PICTURE OF THE MONTHOrographic Fibrous Plumes Over New EnglandJOHN H. CONOVER-Air Force Cambridge Research Laboratories, Bedford, Mass.ABSTRACT-The enhancement of cirrus cloudiness by oro- Their high emissivity suggests cloud condensation ingraphic effects along the periphery of a large-scale thin liquid form, which quickly freezes to form long icecrystalcirrus cloud system is illustrated. From radiometric meas- plumes. These crystals may have seeded a

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David M. Schultz, Derek S. Arndt, David J. Stensrud, and Jay W. Hanna

circulation of the HCRs likely encompassed the depth of the surface mixed layer. In addition, the clouds composing the bands at the top of the planetary boundary layer developed within the favored growth zone for dendritic ice crystals between −12° and −18°C (e.g., Fukuta and Takahashi (1999) , and references therein). Longwave infrared (channel 4) satellite imagery confirms that the cloud-top temperatures of the bands ranged from near −20°C when first revealed from underneath the large

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seeding whichlead to relatively large amounts of snowfall. This idea isfurther supported by the fact that little or no precipita-tion occurred east of the stratus, even though the middleand high clouds persisted as the vorticity center movedsoutheastward away from the low clouds. Bergeron (1949)made a study that may apply to this situation. He showedthat when orographhdy produced clouds are naturallyseeded with ice crystals from a higher cloud, a significantincrease in precipitation amount results

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appears thin' in the video picture, and someof it is not readily identifiable as cirrus. Comparisons ofITOS simultaneous video and infrared data indicate thatcirrus clouds which can be identified in video data canalways be identified in IR imagery. Cirrus is often moreobvious in the infrared than in the video because the IRsensor produces a greater contrast between the cold(white) cirrus cloud and its warmer (darker) background.In the video, there is lower contrast between the re-flectivity of ice

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