Results 1 - 10 of 562
Results 1 - 10 of 562. Search took: 0.024 seconds
|Sort by: date | relevance|
[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] Accurately calibrating a neutron probe for the field measurement of soil water content is not a simple task. The most straightforward calibration technique is done in the field by determining the volumetric soil water content of soil cores taken around the access tube and relating it to the instrument reading. Although the sampling procedure is time-consuming and sometimes arduous, it is probably the most accurate method currently in use. Plastic cylinders of different outside diameters have been found to be valuable intermediate standards for transferring the field calibration from one neutron probe to another when the detector type, source strength, and geometry are similar. This new technique will greatly facilitate the calibration of any number of neutron probes in many different soils. (author)
[en] This work presents the computational evaluation of a new model for relative humidity sensor based on the principle of intermodal interference using a square-section no-core tapered optical fiber compared to a classical cylindrical tapered optical fiber sensor. Attempting at a new application of this type of sensor, simulations were carried out in the range of up to 60% of relative humidity, the main interest range of the pharmaceutical industry. Several materials were used in its modeling and an analysis was developed in its constructive dimensions, in order to verify the influence of each of them on the sensor performance.
[en] The purpose of this paper is to develop and document a position on Relative Humidity (RH) requirements in the WSCF Laboratories. A current survey of equipment vendors for Organic, Inorganic and Radiochemical laboratories indicate that 25% - 80% relative humidity may meet the environmental requirements for safe operation and protection of all the laboratory equipment
[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] We performed experimental studies of the effect of humidity on the dynamics of electrostatically driven granular materials. Both conducting and dielectric particles undergo a phase transition from an immobile state (granular solid) to a fluidized state (granular gas) with increasing applied field. Spontaneous precipitation of solid clusters from the gas phase occurs as the external driving is decreased. The clustering dynamics in conducting particles is primarily controlled by screening of the electric field but is aided by cohesion due to humidity. It is shown that humidity effects dominate the clustering process with dielectric particles
[en] In this article an optical psychrometer, in which temperature measurements are performed by means of two fiber Bragg grating sensors used as dry-bulb and wet-bulb thermometers, is introduced. The adopted design exploits both the high accuracy of psychrometric-based relative humidity measurements with acknowledged advantages of wavelength-encoded fiber optic sensing. Important metrological issues that have been addressed in the experimental work include calibration of the fiber Bragg grating temperature sensors, evaluation of response time, sensitivity, hysteresis, linearity, and accuracy. The calibration results give confidence that, with the current experimental setup, measurement of temperature can be done with an uncertainty of ±0.2 deg. C and a resolution of 0.1 deg. C. A detailed uncertainty analysis is also presented in the article to investigate the effects produced by different sources of error on the combined standard uncertainty uc(U) of the relative humidity measurement, which has been estimated to be roughly within ±2% in the range close to saturation
[en] The results of old and new measurements of salt nuclei are reviewed in order to estimate the effects of particle size and of environmental humidity or temperature on the size distribution of potential cloud condensation nuclei. Several possible improvements of the sampling and evaluation technique are discussed