Precipitation at Ocean Weather Station “P"

M. A. Jenkins Department of Earth and Atmospheric Sciences, York University, North York, Ontario, Canada

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W. C. Wong Department of Earth and Atmospheric Sciences, York University, North York, Ontario, Canada

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K. Higuchi Climate Diagnostics Research Group, Atmospheric Environment Service, Downsview, Ontario, Canada

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J. L. Knox Toronto, Ontario, Canada

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Abstract

This paper examines the 27-yr record of precipitation measurements at Ocean Weather Station “P” (50°N, 145°W). The credibility of the rainfall observations is assessed, and the testing of certain extraordinary features of the fall and winter seasonal precipitation time series is outlined. Using the portion of the record established to be close to “ground truth” (1954–1967), the authors have statistically related present weather observations to seasonal precipitation amounts at Ocean Weather Station “P.” With this approach, the authors have reproduced the first half (1954–1967) and predicted the second half (1969–1980) of the precipitation time series to compare to observations. Precipitation is physically estimated by determining the vertical moisture convergence at Ocean Weather Station “P” and comparing the relative consistency of the moisture convergence time series to the contemporaneous seasonal rate of measured precipitation. The analysis suggests that the Ocean Weather Station “P” record of measured precipitation is a substantial improvement over previous estimates of precipitation in the northeast Pacific for the period between 1954 and 1967, but that the second half of the record, particularly during the early 1970s, remains questionable. Reliable rainfall estimates along with measurements for the 27-yr record are given to aid studies dealing with energy balance calculations and the verification of oceanic precipitation generated by global climate models.

Abstract

This paper examines the 27-yr record of precipitation measurements at Ocean Weather Station “P” (50°N, 145°W). The credibility of the rainfall observations is assessed, and the testing of certain extraordinary features of the fall and winter seasonal precipitation time series is outlined. Using the portion of the record established to be close to “ground truth” (1954–1967), the authors have statistically related present weather observations to seasonal precipitation amounts at Ocean Weather Station “P.” With this approach, the authors have reproduced the first half (1954–1967) and predicted the second half (1969–1980) of the precipitation time series to compare to observations. Precipitation is physically estimated by determining the vertical moisture convergence at Ocean Weather Station “P” and comparing the relative consistency of the moisture convergence time series to the contemporaneous seasonal rate of measured precipitation. The analysis suggests that the Ocean Weather Station “P” record of measured precipitation is a substantial improvement over previous estimates of precipitation in the northeast Pacific for the period between 1954 and 1967, but that the second half of the record, particularly during the early 1970s, remains questionable. Reliable rainfall estimates along with measurements for the 27-yr record are given to aid studies dealing with energy balance calculations and the verification of oceanic precipitation generated by global climate models.

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