Search results for "Overcast"
showing 9 items of 9 documents
Towards a More Sustainable City: The Role of the Daylight Factor in Evaluating the Energy Requirements of Buildings
2018
The Daylight factor is the reference parameter used in Energy Standard EN15193:2008 to assess daylight contribution in the energy performance of buildings. But its efficacy in putting in relation buildings energy performance, daylight availability and visual tasks is now a subject of discussion in literature. In fact, the daylight factor is a static indicator independent from building geometry and environmental parameters. From the energy point of view, it has still to be assessed if it can ensure when the switch of artificial light is needed, representing therefore the most disadvantageous outdoor illuminance conditions. The goal of this study is demonstrating if the daylight factor calcul…
Influence of cloudiness over the values of erythemal radiation in Valencia, Spain
2009
The influence of cloudiness over experimental UV erythemal radiation (UVER) has been studied. This influence has been analysed considering total cloudiness and low clouds. The measurements of cloudiness correspond to the daily values registered at 13:00 GMT at the Meteorological Centre of Valencia, which is part of the State Agency of Meteorology of Spain (AEMET). The UVER measurements were made using a YES UVB-1 radiometer located on the roof terrace of the Physics Faculty at the Burjassot Campus, Valencia (latitude 39.508° , longitude − 0.418° , 60 m above sea level). First, a statistical analysis of cloudiness at 13:00 GMT in Valencia was carried out, confirming that the situation is mai…
Further examination of the thermodynamic modification of the inflow layer of tropical cyclones by vertical wind shear
2013
Recent work has developed a new framework for the impact of vertical wind shear on the intensity evolution of tropical cyclones. A focus of this framework is on the frustration of the tropical cyclone's power machine by shear-induced, persistent downdrafts that flush relatively cool and dry (lower equivalent potential temperature, &theta;<sub>e</sub>) air into the storm's inflow layer. These previous results have been based on idealised numerical experiments for which we have deliberately chosen a simple set of physical parameterisations. Before efforts are undertaken to test the proposed framework with real atmospheric data, we assess here the robustness of our previous res…
High gas-phase mixing ratios of formic and acetic acid in the High Arctic
2018
Abstract. Formic and acetic acid are ubiquitous and abundant in the Earth's atmosphere and are important contributors to cloud water acidity, especially in remote regions. Their global sources are not well understood, as evidenced by the inability of models to reproduce the magnitude of measured mixing ratios, particularly at high northern latitudes. The scarcity of measurements at those latitudes is also a hindrance to understanding these acids and their sources. Here, we present ground-based gas-phase measurements of formic acid (FA) and acetic acid (AA) in the Canadian Arctic collected at 0.5 Hz with a high-resolution chemical ionization time-of-flight mass spectrometer using the iodide …
Relationship between the effective cloud optical depth and different atmospheric transmission factors
2015
This study examines the sensitivity of cloud optical depth (COD) for overcast conditions to radiation transmission using data collected in Valencia, Spain. These relationships are provided as simple empirical functions, therefore avoiding the need to apply complex model minimisation schemes to obtain COD. Comparisons are presented between COD obtained by a minimization method and several radiation transmission factors comprising a clearness index (kt), a modified version (kt'), a cloud modification factor (CMF) and its modified version (CMF'). Additionally, a statistical model of COD proposed by J.C. Barnard and C.N. Long (2004) is tested with our data. Statistical relationships between COD…
Effective cloud optical depth and enhancement effects for broken liquid water clouds in Valencia (Spain)
2017
Partly cloudy skies with liquid water clouds have been analysed, founding that it is essential to distinguish data if the Sun is obstructed or not by clouds. Both cases can be separated considering simultaneously the Cloud Modification Factor (CMF) and the clearness index (kt). For partly cloudy skies and the Sun obstructed the effective cloud optical depth (τ) has been obtained by the minimization method for overcast skies. This method was previously developed by the authors but, in this case, taking into account partial cloud cover. This study has been conducted for the years 2011–2015 with the multiple scattering model SBDART and irradiance measurements for the UV Erythemal Radiation (UV…
Correlation between relative sunshine and state of the sky
1981
Abstract It is possible to construct a sunshine map referring to a large zone, lacking in a widespread network of recording stations, correlating the relative sunshine with the “state of the sky”, defined by the monthly mean number of the clear, mixed and overcast days, whose data are more largely available. In the correlation here proposed climatological and meteorological factors are introduced in order to express the helioclimatic characteristics of every location. The application to Italy, using the data of the period 1973–1977 provided by the 31 stations of ITAV, has suggested the classification of these stations in seven “helioclimatic groups” characterized by different values of the …
Effective cloud optical depth for overcast conditions determined with a UV radiometers
2014
Using a sky camera, episodes characterized by overcast low clouds in the Valencia region of Spain have been selected for analysis. One year of cloud optical depth data have been produced by inverting UV erythemal irradiance measured with a UVB-1 radiometer from Yankee Environmental Systems using the LibRadtran radiative transfer model. Measurement uncertainties, aerosol single scattering albedo and cloud properties are, in order of decreasing importance, the most important factors influencing the accuracy of cloud optical depth retrieval when using UV erythemal radiometers. Statistics for cloud optical depth show a highly skewed frequency distribution best described by a gamma distribution …
Reproducing cloud microphysical and irradiance measurements using three 3D cloud generators
2007
Using three cloud generators, three-dimensional (3D) cloud fields are reproduced from microphysical cloud data measured in situ by aircraft. The generated cloud fields are used as input to a 3D radiative transfer model to calculate the corresponding fields of downward and upward irradiance, which are then compared with airborne and ground-based radiation measurements. One overcast stratocumulus scene and one broken cumulus scene were selected from the European INSPECTRO field experiment, which was held in Norwich, UK, in September 2002. With these data, the characteristics of the three different cloud reproduction techniques are assessed. Besides vertical profiles and histograms of measured…