Project Ahupua'a: Solar Meteorological Field Measurements on the Island of Hawaii, Summer 1978. 5. Southern Flank of Mauna Loa

摘要

Between 12-21 June 1978, four instrumented vans were deployed in a nearly linear transect above Na'alehu, along the steep southeastern slope of Mauna Loa. The transect, traversing a pronounced rainfall and insolation gradient, was designed to monitor sunlight and other meteorological variables related to solar energy. Surprisingly, many locations here receive more insolation during winter than during summer. Stronger than normal trade wind conditions prevailed during the period. A minor distrubance moved eastward to the north of the Island of Hawaii on 20 June, weakened the trade winds for nearly 24 h, and offered the opportunity to examine the development of island-generated circulations unhindered by the large scale flow. The amount of insolation recieved at the transect stations was less than the long-term mean. Persistent cloudiness attenuated insolation. Orographic cloud limited morning insolation while a sea breeze-anabatic cloud depleted afternoon insolation. Peak sunlight values were recorded during the mid-morning transition. This pattern occurred on all nine trade wind days. On 20 June, no orographic cloud formed and maximum values of insolation were received at three of the four transect sites. Strong gusty surface winds recorded along the transect may have been associated with a low level jet stream with Mauna Loa acting as a western boundary to the trade wind current. All transect stations experienced nocturnal wind pulses. Wind speed fluctuations, occasionally exceeding 5 m s exp -1 , occurred with pronounced changes in wind direction. Increasing winds veered toward the prevailing trade wind direction, decreasing winds backed. Low level jet stream instabilities were a likely cause of these fluctuations. (ERA citation 08:017746)