INFLUÊNCIA DE CIRCULAÇÕES LOCAIS EM ÁREAS DE APROVEITAMENTO DE POTENCIAL EÓLICO NA REGIÃO DO LAGO DE SOBRADINHO

In this work local circulation patterns are investigated for the year of 2010 in the Sobradinho Lake region, at the 25 m and 50 m levels. The hodographs illustrate the local wind variation in the four quadrants of the wind rose, in the majority of the months. The local time (LT) and magnitude of the maxima and minima intensities depend on the time of the year. A negative vertical shear in the local wind during the late night-early morning (night) is more evident in the period from May to September (October to February). The local wind, at times of maximum intensity, represents up to 60% of the observed wind speed and, in the remaining of the twenty four hours of the day, between 10 and 30%. This ratio decreases with height in the twelve months of 2010, and is more evident in the periods 4-6 LT and 17-20 LT, with exception of March and June, respectively. The local circulations may be associated with coupling between the land (lake) breeze and the catabatic (anabatic) winds during the late night-early morning (late afternoon-early night). The months of June, July and August show less variability in wind direction, favoring a better use of the wind turbines.

Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch

Atmospheric composition measurements at Jungfraujoch are affected intermittently by boundary-layer air which is brought to the station by processes including thermally driven (anabatic) mountain winds. Using observations of radon-222, and a new objective analysis method, we quantify the land-surface influence at Jungfraujoch hour by hour and detect the presence of anabatic winds on a daily basis. During 2010–2011, anabatic winds occurred on 40% of days, but only from April to September. Anabatic wind days were associated with warmer air temperatures over a large fraction of Europe and with a shift in air-mass properties, even when comparing days with a similar mean radon concentration. Excluding days with anabatic winds, however, did not lead to a better definition of the unperturbed aerosol background than a definition based on radon alone. This implies that a radon threshold reliably excludes local influences from both anabatic and non-anabatic vertical-transport processes.

Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch

Atmospheric composition measurements at Jungfraujoch are affected intermittently by thermally-driven (anabatic) mountain winds as well as by other vertical transport mechanisms. Using radon-222 observations, and a new analysis method, we quantify the land surface influence hour-by-hour and detect the presence of anabatic winds on a daily basis. During 2010–2011, anabatic winds occurred on roughly 40% of days, but only from April–September. Anabatic wind days were associated with warmer air temperatures over a large fraction of Europe and with a shift in airmass properties. Shifts were evident even when comparing the same radon concentrations, a proxy for land-surface influence. Aerosol washout, when quantified as a function of rain-rate using a radon normalisation technique, was also influenced by anabatic winds being more pronounced on non-anabatic days. Excluding the influence of anabatic winds, however, did not lead to a better definition of the unperturbed aerosol background than a definition based on radon alone, supporting the use of a radon threshold to identify periods with weak land-surface influence.

Summertime boundary layer winds over the Darwin–Hatherton glacial system, Antarctica: observed features and numerical analysis

Three temporary Automatic Weather Stations measured summertime surface layer climate over the Darwin–Hatherton Glacial system. These data were used to test a Polar optimized Weather Research and Forecasting model (Polar-WRF) simulation for December as a case study. Observations show differences in hourly averaged solar and net all-wave radiation between white ice and blue ice areas (BIAs). Although the down-welling solar radiation is higher over the white ice region, the net all-wave energy is higher over the BIA. Derived albedo for each surface type confirms that the blue ice areas have lower albedo. Also, the hourly averaged temperatures are higher at lower elevation stations, creating a gradient towards the Ross Ice Shelf. Analysis shows that there is a diurnal oscillation in strength and intensity of the katabatic wind. The two lower stations register a distinct reversal of wind direction in the early afternoon due to intrusion of an anabatic circulation. Anabatic winds are not prevalent further up the Darwin Glacier. A high-resolution Polar-WRF simulation as a case study shows good agreement with observations. The December 2008 case study is characterized by a strong south-westerly katabatic wind over Hatherton, whereas the flow over Lower Darwin was diurnally reversing. Polar-WRF shows that the katabatic front advanced and retreated periodically between Hatherton and Lower Darwin.