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G. J. Boer and K. Higuchi

Abstract

An analysis of variance of the 1000-500 mb thickness field is performed to investigate climatic variability from 1949 to 1975. The thickness field and its variance, averaged over the Northern Hemispheric cap from 25°N latitude to the pole, are obtained and the resulting time series are analyzed for their trends and interrelationships.

Analysis of the mean thickness and measures of transient eddy, standing eddy. and north-south variance shows a statistically significant linear trend in mean thickness and significant quadratic trend in standing eddy and north-south variance measures. No significant trend is found in transient eddy variance.

Correlation analysis of the time series shows a significant relationship between standing and transient eddy valances. No significant correlation between the mean thickness and the eddy terms nor between the north-south variance and the eddy terms is found.

The results of this study do not support the contention that the climate has become significantly more variable, nor do they support a connection between variability and either mean temperature or north-south variation of temperature.

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Munehisa K. Yamamoto, Fumie A. Furuzawa, Atsushi Higuchi, and Kenji Nakamura

Abstract

Tropical Rainfall Measuring Mission (TRMM) data during June–August 1998–2003 are used to investigate diurnal variations of rain and cloud systems over the tropics and midlatitudes. The peak time of the coldest minimum brightness temperature derived from the Visible and Infrared Scanner (VIRS) and the maximum rain rate derived from the Precipitation Radar (PR) and the TRMM Microwave Imager (TMI) are compared. Time distributions are generally consistent with previous studies. However, it is found that systematic shifts in peak time relative to each sensor appeared over land, notably over western North America, the Tibetan Plateau, and oceanic regions such as the Gulf of Mexico. The peak time shift among PR, TMI, and VIRS is a few hours.

The relationships among the amplitude of diurnal variation, convective frequency, storm height, and rain amount are further investigated and compared to the systematic peak time shifts. The regions where the systematic shift appears correspond to large amplitude of diurnal variation, high convective frequency, and high storm height. Over land and over ocean near the coast, the relationships are rather clear, but not over open ocean.

The sensors likely detect different stages in the evolution of convective precipitation, which would explain the time shift. The PR directly detects near-surface rain. The TMI observes deep convection and solid hydrometeors, sensing heavy rain during the mature stage. VIRS detects deep convective clouds in mature and decaying stages. The shift in peak time particularly between PR (TMI) and VIRS varies by region.

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M. A. Jenkins, W. C. Wong, K. Higuchi, and J. L. Knox

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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