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Spatial variability of surface irradiance measurements at the Manus ARM site
Author(s) -
Riihimaki Laura D.,
Long Charles N.
Publication year - 2014
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2013jd021187
Subject(s) - environmental science , orographic lift , atmospheric sciences , irradiance , climatology , shortwave , cloud cover , wind direction , prevailing winds , rainband , sunrise , meteorology , wind speed , radiative transfer , geology , geography , precipitation , physics , tropical cyclone , cloud computing , quantum mechanics , computer science , operating system
The location of the Atmospheric Radiation Measurement (ARM) site on Manus island was chosen because it is very close to the coast, in a flat, near–sea level area of the island, hopefully minimizing the impact of local island effects on the meteorology of the measurements. In this study, we confirm that the Manus site is indeed less impacted by the island meteorology than slightly inland by comparing over a year of broadband surface irradiance and ceilometer measurements and derived quantities at the standard Manus site and a second location 7 km away as part of the ARM Madden Julian Oscillation Investigation Experiment (AMIE)‐Manus campaign. The two sites show statistically similar distributions of irradiance and other derived quantities for all wind directions except easterly winds, when the inland site is downwind from the standard Manus site. Under easterly wind conditions, which occur 17% of the time, there is a higher occurrence of cloudiness at the downwind site likely due to land heating and orographic effects. This increased cloudiness is caused by scattered clouds often with bases around 700 m in altitude. While the central Manus site consistently measures a frequency of occurrence of low clouds (cloud base height less than 1200 m) about 25% of the time regardless of wind direction, the AMIE site has higher frequencies of low clouds (38%) when winds are from the east. This increase in low, locally produced clouds causes an additional −20W/m 2 shortwave surface cloud radiative effect at the AMIE site than the Manus site.