Menyhart L.,Festetics u. |
Anda A.,Festetics u. |
Nagy Z.,Hungarian Meteorological Service
Idojaras | Year: 2014
Pyranometers are fundamental instruments widely used for measuring global irradiance. When operating weather stations without continuous manning, pyranometer may tilt from horizontal position. Error caused by inclination of a few degrees was calculated for the annual, daily, and instantaneous global radiations. Global irradiance incident on both horizontal and tilted surfaces were calculated from the direct beam, diffuse and ground-reflected irradiances. These components were measured by accurately leveled and regularly supervised instruments. The second purpose of this paper was to determine the minimum tilt angle that is detectable by calculating certain quantities. To detect the east-west inclination, the sum of the global radiation before and after the solar noon was compared. To detect the north-south inclination, it was tested whether the global irradiance measured at a fixed solar elevation with a horizontal and a tilt pyranometer is stochastically equal. Our findings show that tilt angle of 1° in east-west direction is already detectable. Tilting to the direction at an angle of 15° from the northsouth is the most difficult to detect. Here 3° is the smallest detectable tilt angle. © 2014, Quarterly Journal of the Hungarian Meteorological Service. All rights reserved.
Anda A.,Festetics u. |
Nagy K.,West transdanubian Water Inspectorate |
Soos G.,Festetics u. |
Kucserka T.,Festetics u.
Idojaras | Year: 2015
The aim of the study was to estimate long term évapotranspiration (ET) of Kis-Balaton wetland through the investigation of Lake Fenéki. Data set was processed using the West-transdanubian Water Inspectorate methodology. Potential evapotranspiration (PET) was calculated using Hungarian empirical models (Antal and Dunay), while Lake Fertô formula was applied evaluating the ET that includes the impacts of vegetation. Calculated PET values of the wider (adjacent) environment of Lake Fenéki (Zalaegerszeg, Nagykanizsa, and Keszthely meteorological stations) differed significantly and further variation was observed in PET, when measured meteorological elements on Lake Fenéki were applied. PET increment, as a result of linear trend fitted to the 43-year long data (Keszthely station) was 3-4 mm year-1. Relation between PET calculated from the data of Keszthely station and for Lake Fenéki was strong, so PET of Lake Fenéki can be originated from the data of Keszthely station. Calculated ET was not significantly different due to the likely similar input data in ET calculation model of Hungarian Meteorological Service (OMSZ). 43-year annual mean ET for Lake Fenéki was 809±88 mm. This ET was 84% of calculated PET. Analyzing the nine dry-warm seasons, average annual ET exceeded the long term average (874.7±37.6 mm) with 78 mm. The average ET of the remaining 34 wet-cold seasons totalled 796.6±89.4 mm. Empirical formulas cannot be replaced, according to monthly ET comparisons, by using "A" class pan estimating the ET of aquatic habitats. Seasonal pattern of monthly ET time series for Lake Fenéki was analyzed using autoregressive integrated moving averages (ARIMA) modeling technique. After first differencing, the transformed series was stationary and found to be governed by moving average process of order 1. © 2015, Hungarian Meteorological Service. All rights reserved.