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[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] 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] 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)
[en] This study explores change of precipitation and temperature using the Mann–Kendall test and the spatiotemporal variation of dryness/wetness using the standardized precipitation evapotranspiration index and empirical orthogonal function (EOF) analysis on 1-month time scales in Zhejiang Province, China, over 1971–2015. The results show that monthly precipitation had significant decreasing trends during April, May, September, and October, and significant increasing trends during November and December. Monthly temperatures had significant increasing trends in each month. Increasing temperature significantly increased drought events and intensity. There were consistent spatial patterns of dryness/wetness in Zhejiang. There were dryness trends in April, May, and September, a wetness trend in August, and no dryness/wetness pattern change in other months. The second EOF modes showed that dryness/wetness patterns were anti-phase between northern and southern Zhejiang during April–October. The third EOF modes showed that patterns were anti-phase between eastern and western Zhejiang in August and September.
[en] An automatic weather station (AWS) was installed on the Greenland Summit (72.30 degree N, 38.00 degree W, 3,210 m) in May 1987. The AWS unit operated for two years until May 1989 when it was moved to Fresh Air Site (72.82 degree N, 38.82 degree W, 3,185 m), an air sampling site, where it is still operating. The AWS data were transmitted to the ARGOS data collection system on the NOAA polar-orbiting satellites. The AWS unit measures wind speed and direction, air temperature, and the relative humidity at a nominal height of 3 m, air pressure at the height of the electronics enclosure, and the vertical air temperature difference between 3.0 and 0.5 m. The latent and sensible heat from the snow surface to the air were estimated using the wind speed, vertical air temperature difference, and the relative humidity. The data are compared with those from two earlier stations, Eismitte (70.90 degree N, 40.70 degree W, 3,000 m) from September 1930 through August 1931 (Wegener's expedition) and Station Centrale (70.92 degree N, 40.64 degree W, 2,993 m) from September 1949 through August 1951 (Victor's expedition). The winds observed at Cathy Site were quite similar to those observed at the two previous stations. Also, the large fluctuations in temperature observed during the winter months at the two historic stations were observed at Cathy Site. The transition from positive to negative values for the sensible and latent heat flux occurred in October
[en] Heat and mass transfer processes in a cross flow liquid desiccant dehumidifier, in which wet durable honeycomb paper constitutes the packing material, is investigated in this paper. The device is expected to be used in hot and humid areas to control the indoor humidity environment. A mathematical model, able to determine the heat and mass transfer between the air and the falling film of liquid desiccant, is developed, and the analysis on Nusselt and Sherwood numbers at the liquid-air interface is performed considering the solution of 40% H2O/CaCl2. Also obtained is the theoretical Nusselt number under assumed conditions and the relevant analysis, as well as the comparison between the two results
[en] The objective of this paper is to evaluate the potential error in estimating the net radiation and reference evapotranspiration resulting from errors in the measurement or estimation of weather parameters. A methodology for estimating the net radiation using hourly weather variables measured at a typical agrometeorological station (e.g., solar radiation, temperature and relative humidity) is presented. Then the error propagation analysis is made for net radiation and for reference evapotranspiration. Data from the Raimat weather station, which is located in the Catalonia region of Spain, are used to illustrate the error relationships. The results show that temperature, relative humidity and cloud cover errors have little effect on the net radiation or reference evapotranspiration. A 5°C error in estimating surface temperature leads to errors as big as 30 W m−2 at high temperature. A 4% solar radiation (Rs) error can cause a net radiation error as big as 26 W m−2 when Rs ≈ 1000 W m−2. However, the error is less when cloud cover is calculated as a function of the solar radiation. The absolute error in reference evapotranspiration (ETo) equals the product of the net radiation error and the radiation term weighting factor [W = Δ(Δ1+γ)] in the ETo equation. Therefore, the ETo error varies between 65 and 85% of the Rn error as air temperature increases from about 20° to 40°C. (author)