The Relation Between Ageostrophy and Boundary-Layer Structure in the Western-Pacific Trades (Wake Island) |
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| Authors: | Gad Levy Cole B McCANDLISH Dean Vickers |
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| Institution: | (1) College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR, 97331, U.S.A. |
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| Abstract: | Eight years (1980–1987) of Wake Island rawinsonde data are used to derive atmospheric boundary layer (ABL) depth, integrated boundary-layer moisture, and a measure of boundary-layer ageostrophy. The variability in these processes controls the accumulation of moisture and heat in the tradewind regions and their transport to regions of intense convection. Preliminary analyses using different methods reveal quasi-periodic signals in these data in the 30–60 days range. Cross correlation calculations in this intraseasonal range show that these ABL variables are coherent with each other and with the low-level flow. The integrated ABL variables and the ABL height exhibit local in-phase relationships. At higher frequencies, the analyses show intense diurnal variation of boundary-layer height but only a weak diurnal signal in integrated ABL properties. At the lower frequency range, the analyses show a significant reduction in the amplitude of the seasonal and intraseasonal variation in ageostrophy during the strong El-Niño event of 1982/1983. The results clearly establish a relationship between integrated water vapour and divergent ABL processes (Ekman pumping/suction) in which shallower (deeper) ABLs are associated with mass and moisture divergence (convergence) and higher (lower) sea-level pressure. A possible interpretation in terms of a remote dynamic response of the trade inversion and ABL processes to equatorial deep convection is suggested. |
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| Keywords: | Ageostrophy Intraseasonal variations Marine atmospheric boundary-layer structure Trade wind Western Pacific |
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