Wind run

Abstract: The aims of this paper are to investigate the characteristics of the sea breeze that is developing in Volos area, a medium sized coastal city in central Greece, and to study the influence of sea breeze on concentration levels of ozone and PM10, during the period 2001–2005. The identification of sea breeze days is based on a set of strict, objective criteria, which include the wind direction and its diurnal reversal, the wind direction difference between the surface winds and the winds in the free atmosphere and the thermal contrast between the sea and the land surface. The statistical analysis reveals that sea breeze is developing in 85.6% of days from May until July, with maximum frequency of occurrence 89% in June. Its most frequent onset and cessation time periods are 09:00–11:00 and 20:00–22:00 LST respectively and its usual duration is approximately 10 h. The average maximum strength is 2.6 m/s, usually between 14:00 and 17:00 LST, while the maximum observed value equals 5.9 m/s. Studying the variation of ozone and PM10 levels during the cold and the warm period of the year (October–April and May–September respectively), it is concluded that sea breeze development is associated with an increase of the concentration of both pollutants. This increase is more pronounced during the cold period and is attributed to unfavourable meteorological conditions. Copyright © 2008 Royal Meteorological Society

Abstract: In many regions of the world, increasing temperatures in recent decades are paradoxically associated with declining pan evaporation, but evidence is sparse for this trend from the southern hemisphere in general and sub-Saharan Africa in particular. In this study, we examined changes in pan evaporation and four other meteorological variables (rainfall, wind run, temperature and vapour pressure deficit) at 20 climate stations in the predominantly winter-rainfall Cape Floristic Region (CFR) of South Africa over the period 1974–2005. Our results show that pan evaporation has declined significantly at 16 climate stations at an average rate of 9.1 mm a − 2 while wind run has declined significantly at all climate stations by more than 25% over the study period. Annual rainfall has not changed significantly at any of the climate stations while maximum temperature has increased significantly at all but one climate station at an average rate of 0.03°C a. − 1 over the study period. The trends in vapour pressure deficit are mixed and no clear regional pattern is evident. Our results raise important questions about the predicted catastrophic impact that the projected changes in twenty-first century climates will have on the rich flora of the region. If evaporative demand has declined over the last 30 years in the Cape Floristic Region then it is possible that more water has become available for plant growth, infiltration and runoff despite the widespread increase in temperature. However, decreased pan evaporation and wind run combined with increased temperatures could potentially reduce transpiration and exacerbate heat stress of plants on increasingly frequent hot and windless days during the summer drought. Contrary to other predictions for the area, it is also likely that the changing conditions will decrease the frequency and/or intensity of fires which are an important component of the ecology of the fire-adapted CFR. Consideration of other factors besides changes in temperature and rainfall are essential in debates on the impact of climate change on the vegetation of this region.

Abstract: A model was derived to calculate interception loss from a forest canopy on the basis of thrice daily observations of air temperature and relative humidity, daily means of wind run, daily totals of precipitation and the number of rainy hours and of bright sunshine. The forest canopy was characterized by mean tree height, crown density and water storage capacity. The model was calibrated and tested on four separate data sets obtained during 1964, 1965, 1980 and 1981 in the pine forest of the lysimeter station near Castricum, the Netherlands. Model sensitivity was demonstrated for roughness length, the above canopy wind correction factor and relative humidity during rain. Simulated net precipitation explained at least 92 percent of the observed net precipitation, suggesting a good predictive model.