Results 1 - 10 of 1158
Results 1 - 10 of 1158. Search took: 0.021 seconds
|Sort by: date | relevance|
[en] Regimes in moist stratified flows over simply shaped 3D mountains have been studied in numerical simulations made with a mesoscale meteorological model. One of the aims that this work intends to examine is the possible existence of multiple solutions, searching for different solutions depending on the path followed by the system in the parameter space. Results from three different sets of experiments are discussed here. In the first set of simulations, the height of the mountain has been progressively changed in time. In the second group of experiments, the humidity of the air flowing over the obstacle has been increased in time by adding a source term to the equation of evolution of moisture. The case of advection of moist air towards an obstacle, initially embedded in dry air, has been studied as a third type of flow. A dependence on the past history of the flow seems to characterize some types of system evolution, leading to different flow regimes over the obstacle. The experiments indicate that this result is mainly a consequence of changes of state of water, associated with the presence of humidity in the atmosphere. These effects are emphasized in the case of an elliptical mountain, with its longer axis perpendicular to the main flow. In the three different sets of experiments presented here, evident differences with simulations where flow parameters are kept constant from the beginning persist in the flow regimes, also for periods of time much longer than the characteristic time of evolution towards stationary solutions
[en] In 1989, within the framework of the Etude de precipitations par satellite (EPSAT) operation, an isotopic study of precipitation and its atmospheric context (temperature and humidity) was performed along the Guinean monsoon trajectory between Cotonou and Agades. The dewatering process which progressively affects the air masses over the continent is stopped at the sub-Sahelian latitude. Precipitations and their surrounding environment are therefore the reflection of new conditions of humidity linked to a large contribution of recycled vapour. (author)
[en] During the Pyrenees Experiment (PYREX) in October and November 1990 in radiosonde network was in operation with enhanced spatial and temporal resolution. This atlas contains standardized output from a three-dimensional, objective analysis scheme which is used to interpolate from the observed significant levels to a regular grid centred over the Pyrenees. For each of the 68 release times during ten intensive observation periods 12 horizontal charts are displayed on one page. These charts contain temperature, relative humidity or potential vorticity, and horizontal wind (vectors and isotachs) in four levels. The atlas is considered as basic material for more detailed studies at or between selected release times. (orig.)
[de]Waehrend des Pyrenaeen Experiments (PYREX) wurde im Oktober und November 1990 ein Radiosondennetz mit erhoehter raeumlicher und zeitlicher Aufloesung betrieben. Dieser Atlas enthaelt standardisierte Ergebnisse eines drei-dimensionalen, objektiven Analysenschemas, mit dessen Hilfe von den Beobachtungen an allen signifikanten Punkten auf ein regulaeres, ueber den Pyrenaeen zentriertes Gitter interpoliert wurde. Fuer jeden der 68 Aufstiegstermine innerhalb der zehn intensiven Beobachtungsphasen sind 12 horizontale Karten auf einer Seite zusammengefasst. Diese enthalten Temperatur, relative Feuchte oder potentielle Vorticity, sowie den Horizontalwind (Vektoren und Isotachen) in vier Niveaus. Der Atlas stellt Grundlagenmaterial bereit fuer eingehendere Studien zu oder zwischen einzelnen Aufstiegsterminen. (orig.)
[en] Cirrus clouds are ubiquitous in the upper troposphere and still constitute one of the largest uncertainties in climate predictions. Our paper evaluates cloud-resolving model (CRM) and cloud system-resolving model (CSRM) simulations of a midlatitude cirrus case with comprehensive observations collected under the auspices of the Atmospheric Radiation Measurements (ARM) program and with spaceborne observations from the National Aeronautics and Space Administration A-train satellites. The CRM simulations are driven with periodic boundary conditions and ARM forcing data, whereas the CSRM simulations are driven by the ERA-Interim product. Vertical profiles of temperature, relative humidity, and wind speeds are reasonably well simulated by the CSRM and CRM, but there are remaining biases in the temperature, wind speeds, and relative humidity, which can be mitigated through nudging the model simulations toward the observed radiosonde profiles. Simulated vertical velocities are underestimated in all simulations except in the CRM simulations with grid spacings of 500 m or finer, which suggests that turbulent vertical air motions in cirrus clouds need to be parameterized in general circulation models and in CSRM simulations with horizontal grid spacings on the order of 1 km. The simulated ice water content and ice number concentrations agree with the observations in the CSRM but are underestimated in the CRM simulations. The underestimation of ice number concentrations is consistent with the overestimation of radar reflectivity in the CRM simulations and suggests that the model produces too many large ice particles especially toward the cloud base. Simulated cloud profiles are rather insensitive to perturbations in the initial conditions or the dimensionality of the model domain, but the treatment of the forcing data has a considerable effect on the outcome of the model simulations. Despite considerable progress in observations and microphysical parameterizations, simulating the microphysical, macrophysical, and radiative properties of cirrus remains challenging. Comparing model simulations with observations from multiple instruments and observational platforms is important for revealing model deficiencies and for providing rigorous benchmarks. But, there still is considerable need for reducing observational uncertainties and providing better observations especially for relative humidity and for the size distribution and chemical composition of aerosols in the upper troposphere.
[en] Soil moisture (SM) feedback on climate variables especially temperature is an important aspect in land-atmosphere coupling. Based on the Global Land Data Assimilation System (GLDAS) V2.0 SM data and the gridded observational temperature data, we statistically analyze the thermal feedback of SM over North China (NC). The results show that SM exerts a decreasing trend under the background of evident warming over NC, inducing a decadal enhancement of SM feedbacks on the local temperature and extreme hot events. The SM feedback contributes 6% of the total air temperature variation during 1961–2012, while it reaches 36% after the regional warming during 1994–2012. Such SM affecting temperature is mainly reflected in its feedback on daily maximum temperature, which is also intensified during the warm period. The decadal intensification is also found in the feedback of SM on hot extremes. Further analyses show that the abnormal changes of the latent and sensible heat fluxes caused by the SM anomaly are the main reasons that affect the thermal conditions. Besides, the rising Bowen ratio indicates that upward thermal transfer on the land surface is enhanced in recent years, which suggests that the atmosphere is more sensible to the abnormal heating on the ground. This consequently translates into the decadal intensification of the local thermal feedback of SM in summer over NC.
[en] To know the importance of different climate variables on reference crop evapotranspiration (ETo), a step-by-step sensitivity analysis of ETo to single, two, and multi-climate variables (C) was conducted. ETo in north, south, and entire Xinjiang Province, China, over 1961–2013 was estimated using the Penman-Monteith equation. Trends in the involved six Cs (i.e., minimum temperature—Tmin, average temperature—Tave, maximum temperature—Tmax, wind speed at 2 m—U2, sunshine hour—n, and relative humidity—RH) were detected by the modified Mann-Kendall test. Nineteen scenarios of changed Cs were preset to obtain recalculated ETo values considering the actual trend in each C and the Pearson’s correlation relationship between ETo and Cs. The results showed that ETo was mostly sensitive to Tmax, U2, and n. Sensitivity of ETo to the two overlapped changes of Tmin and Tmax caused larger increases in ETo than Tmax and Tave, Tave and Tmax, Tmax and (−n), Tmax and RH, Tmax and (−U2), and Tmin and Tave, but the overlapped changes (−U2) and (−n) caused larger decreases in ETo than the other two C scenarios. The simultaneously increased Tmax, Tmin, Tave, and RH plus decreased U2 and n had caused the actual decreases in ETo in Xinjiang. In general, the effects of decreased U2 and n on decreasing ETo compensated the effects of increased Tmax on decreasing ETo in Xinjiang.
[en] The hydrology division of the Forstliche Versuchs- und Forschungsanstalt of Bavaria is the responsible operator of forest climate stations, with which it fulfills the following basic tasks: - securing of climate data relevant to growth and vitality which are representative of all major Bavarian forest areas, - measurement of soil humidity in region-typical forest sites as a parameter of forest site prospection and for the application of forest-hydrological models, - establishment of the deposition of pollutants and nutrients to forest ecosystems, - verification of the quality of soil leachates under forest sites, - preparing of budgets of substance cycles in forest ecosystems, - monitoring of biological processes in forest ecosystems as an instrument of precautionary environmental care. Furthermore, these basic data are prepared for use in ecosystemal research approachers in cooperation with other scientific disciplines. (orig.)
[de]Das Sachgebiet Hydrologie der Bayerischen Forstlichen Versuchs- und Forschungsanstalt ist verantwortlicher Betreiber der Waldklimastationen und hat hierbei folgende grundlegende Aufgaben zu erfuellen: - Gewinnung von wachstums-und vitalitaetsrelevanten Klimadaten, repraesentativ fuer alle groesseren Waldgebiete Bayerns, - Messung der Bodenfeuchte auf gebietstypischen Waldstandorten als Grundlage fuer die forstliche Standorterkundung und zur Anwendung forsthydrologischer Modelle, - Ermittlung der Eintraege von Schad-und Naehrstoffen in Waldoekosysteme, - Erfassung der Qualitaet des Bodensickerwassers unter Waldbestaenden, - Bilanzierung der Stoffkreislaeufe in Waldoekosystemen, - Ueberwachung der Lebensablaeufe im Waldoekosystem als Instrument zur Umweltvorsorge. Daneben erfolgt eine Aufbereitung dieser zentralen Basisdaten zur Verwendung in oekosystemaren Forschungsansaetzen in Zusammenarbeit mit anderen Forschungsdisziplinen. (orig.)
[en] This paper presents a study of feasibility of different existing methodologies linked to field's data acquisition from remote meteorological stations. The data transmission serves to collect field's meteorological information, such as temperature, humidity and radiation. In our study the experimental data is registered in a weather station located about 100 km from University of Almeria. Various existing techniques are studied, especially Radio, GSM (global system of mobile communication) and GPRS (general packet radio service). In the result of these studies has been designed a system of field's data acquisition (herein referred as Meteologger) which we are going to present in this paper. The system is based on an ATmega 16 microcontroller, which scans 8 sensors together at any programmable intervals. This paper presents the study of the mentioned project, application and some main characteristics of the prototype system and its program. We attempt to implement the system, and subsequently present the performance of tests regarding the mentioned system. To verify its functioning some comparison of this measurement system with two others commercial data-acquisition system (Campbell and Hobo H8) has been carried out
[en] An increase of the 2 m temperature over Europe is expected within the current century. In order to consider health impacts, it is important to evaluate the combined effect of temperature and humidity on the human body. To achieve this, projections of a basic index—the humidex—representative of the perceived temperature, under different scenarios and periods, have been investigated. The simultaneous occurrence of observed extreme temperature events and perceived extreme temperature events is seldom found within the present climate, reinforcing the importance of investigating the combination of the two fields. A set of 10 km resolution regional climate simulations, provided within the EURO-CORDEX multi-model effort, demonstrates an ability in representing moderate to extreme events of perceived temperature over the present climate, and to be useful as a tool for quantifying future changes in geographical patterns of exposed areas over Europe. Following the RCP8.5 emission scenario, an expansion of the area subject to dangerous conditions is suggested from the middle of the current century, reaching 60 °N. The most significant increase of perceived extreme temperature conditions is found comparing the 2066–2095 projections to the 1976–2005 period; bearing in mind that changes in relative humidity may either amplify or offset the health effects of temperature, a less pronounced projected reduction of relative humidity in the north-eastern part of Europe, associated with extreme humidex events, makes northern Europe the most prone region to an increase of moderate to extreme values of perceived temperature. This is in agreement with a pronounced projected specific humidity increase. (letter)