A marked mesoscale pressure-induced wind variation

Garratt and Physick (1983) presented observations which show a strong correlation between low-level wind behaviour and the passage of mesoscale pressure systems. They numerically simulated the wind observations by specifying a time sequence of perturbation pressure gradients and then solving the vertically integrated momentum equation. Here a similar procedure was used for computing the low-level wind field associated with the passage of a squall line over Lake Huron on August 22, 1971. The results from the numerical model agree reasonably well with observations.     

Estimation of the Probability of Exceedance of Contaminant Concentrations

Several alternative probability distributions for estimating the probability of exceedance of contaminant concentrations are examined for their appropriateness for developing inputs to risk assessments. The rationale is provided for using the log Pearson Type III distribution, a three-parameter model, for estimation of the exceedance probabilities.     

Turbulence above Lake Ontario: Velocity and scalar statistics

Measurements of the fluctuations of wind, temperature and humidity were made with an instrumented aircraft at altitudes from 30 to 300m above Lake Ontario. The variations of the standard deviations of these fluctuations are examined. By applying Monin-Obukhov similarity theory based on local fluxes, it is shown that the vertical velocity, temperature and humidity fluctuations scale with the local Monin-Obukhov length. In the limit of free convection, 1/3 and –1/3 power laws are approached with constants of 1.2, 1.2, and 0.8 for vertical velocity, temperature and humidity, respectively. The von Karman scale lengths increase with height but were much larger than those found by Taylor et al. (1970).     

An intercomparison of two rawinsonde systems

Abstract

An intercomparison of the Väisälä MicroCora system used in the Automated Shipboard Aerological Program (ASAP) and the Atmospheric Environment Service upper‐air system (GMD/ADRES) was conducted in May‐June 1983. Thirty‐three paired ascents were made. The ASAP system dry‐bulb temperatures averaged 0.3°C warmer. For the lowest 100 mb, the dew‐point temperature difference (ASAP ‐ GMD/ADRES) was near ‐1°C whereas for the 780–500 mb layer, the difference was 1°C. The wind component mean differences averaged were small but with a 4 m s^?1 standard deviation.     

Identification of changes in heavy rainfall events in Ontario,Canada

To assess whether changes in the frequency of heavy rainfall events are occurring over time, annual maximum records from 21 rainfall gauges in Ontario are examined using frequency analysis methods. Relative RMSE and related boxplots are used to characterize assessment for selecting distributions; the Gumbel distribution is verified as one of the most suitable distributions to provide accurate quantile estimates. Records were divided into two time periods, and tested using the Mann-Kendall test and lag-1 autocorrelations to ensure that data in each period are identically distributed. The confidence intervals of design rainfalls for each return period (2, 5, 10, and 25-year) are derived by using resampling method, and compared at 90 % confidence levels. The changes in heavy rainfall intensities are tested at gauges across the Province of Ontario. Several significant decreases in heavy rainfall intensities are identified in central and southern Ontario. Increases in heavy rainfall intensities are identified in gauges at Sioux Lookout and Belleville. The sensitivity analysis of changes identified with respect to the year of splitting indicates changes are occurring during the 1980s and 1990s.     

黑潮海域海洋异常加热对后期北半球大气环流影响的分析

计算了黑潮海域海洋异常加热与后期1—12个月北半球大气环流的时滞相关，分析了二者的相关关系。结果表明，海洋异常加热对后期半年到一年北半球大气环流场有重要影响。当黑潮海域海洋异常多加热时，后期半球范围内大气环流的经向度将趋减小，反之则趋加强。在分析相关场演变的基础上，讨论了上述时滞关系的可能物理过程，指出黑潮海域海洋异常加热对后期下游大气环流型的影响，是通过改变中纬大气与高纬极地大气之间温度和位势高度梯度，进而影响后期下游大气环流型来实现的。     

Estimation of the Pacific Ocean meridional heat flux at 35°N

Abstract

The meridional heat flux in the North Pacific Ocean at 35°N is estimated primarily using hydrographic section data, following the method of Bryan (1962) and Bennett (1978). The meridional heat flux in the Kuroshio, computed using the Worthington and Kawai section across the current, was 1.76 PW (positive northward), with over 80% of the flux occurring in the upper 400 m. The large‐scale baroclinic heat flux across the rest of the section (145°? to North America) was —1.0 PW for the indopac (1976) section and —0.5 PW for the IOS‐72 section. The fluxes across the sections were also concentrated in the upper ocean with the upper 300 m accounting for over 75% of the flux. The mean horizontal barotropic gyre circulation results in little (0.1 PW) net heat flux because the northward‐moving water is only about 0.5°C warmer than the southward‐moving water. The contributions due to Ekman heat flux (—0.16 PW) and flow through the Japan Sea (0.13 PW) are also relatively small. The eddy heat flux is quite uncertain, but estimated to be about 0.3 PW. The total meridional heat flux, for the 1976 section, is calculated to be about 1.0 PW. The total is very dependent on the baroclinic heat flux in the highly variable Kuroshio region. The northward heat flux found in this study is more consistent with large‐scale atmospheric estimates and with Bryden et al. ‘s (1990) estimate for 24°? in the Pacific.