極軌道衛星NOAAに搭載されているSplit Windowで算定された雲型別雲量の昼と夜でのちがい

Abstract

Split window measurements aboard the NOAA polar orbiting satellites have been used to study cloud cover change between day and night over the western Pacific. The split window technique can discriminate optically thin cirrus type clouds (ice clouds) from optically thick cumulus type clouds. In this study, cirrus and cumulus type clouds are each divided into two classes depending on cloud brightness temperatures (TBB). Cirrus are classified as either warm or cold type, while cumulus type are divided into cumulonimbus type and low-level cumulus/stratocumulus type. From the comparison with ISCCP analysis, mean optical thickness of warm cirrus, cold cirrus, cumulus/stratocumulus and cumulonimbus type clouds were found to be 2.2, 7.4, 15.3 and 33.7, respectively.The diurnal change in cloud cover of the above cloud types is studied for typhoon cases as individual convective systems and for an area of 20 degrees latitude by 30 degrees longitude over the western tropical Pacific. Cumulonimbus type clouds, warm cirrus type clouds and low-level cumulus/stratocumulus type clouds show tendencies toward higher cloud cover at night (about 2:30 local time). Cold cirrus type clouds show a tendency toward more cloud cover during the day (about 14:30 local time).