| Popis: |
The objective of this study is to determine the air mass advection eastward from the North American continent as a function of season, latitude and altitude. The eastern coastline of the continent has been subdivided into eight climatologicall y distinct and homogeneous segments on the basis of air stream and synoptic disturbance analysis. Mean resultant wind vectors and standard deviations have been derived for the 1000, 850, 700 and 500 mb levels from published analyses of upper air and surface winds in the period 1946–1964. Probablity wind roses were calculated assuming a bivariate normal distribution of wind vectors, and offshore and onshore air mass advection has been calculated for each season, coastal segment and layer. Offshore advection exhibits a broad maximum between 33 and 52°N, while onshore flow reaches a sharp maximum between 43 and 47°N because of the orientation of this segment. Offshore advection increases by a factor of approximately two for each successively higher layer, and the ratio of onshore to offshore flow decreases from 0.7 to 0.2 between the surface and layer 4. Winter air mass advection is ~ 1.8 times that in summer. Despite uncertainties introduced by the available wind data and the assumption of a normal distribution, the approach is considered to provide air mass advection values with an estimated uncertainty of about 25%. The results are expected to be useful for improved continental pollutant outflows and budgets. |
