Profiles Of Liquid Water Content Research Articles

Crocus test results for snowpack modeling in two snow climates with respect to avalanche forecasting

Overall results comparing field observations and Crocus simulations during the winters 1993–94 and 1994–95 in two different climate zones are presented. We present information on: snow depth, snow-temperature profiles, density profiles, liquid-water content profiles and grain metamorphism. Snow profiles illustrating the typical behavior of the model are presented and are shown to illustrate the sensitivity of Crocus to different mountain climates. Heat-exchange simulation, together with qualitative analysis of meteorological data, give promising results for surface-hoar prediction.

Crocus test results for snowpack modeling in two snow climates with respect to avalanche forecasting

Overall results comparing field observations andCrocussimulations during the winters 1993–94 and 1994–95 in two different climate zones are presented. We present information on: snow depth, snow-temperature profiles, density profiles, liquid-water content profiles and grain metamorphism. Snow profiles illustrating the typical behavior of the model are presented and are shown to illustrate the sensitivity ofCrocusto different mountain climates. Heat-exchange simulation, together with qualitative analysis of meteorological data, give promising results for surface-hoar prediction.

The potential of times series of C-Band SAR data to monitor dry and shallow snow cover

A study was conducted to assess the potential of C-band synthetic aperture radar (SAR) data to determine the snow water equivalent (SWE). A multitemporal (three winters) SAR data set was obtained using the Convair-580 from the Canada Centre for Remote Sensing (CCRS) over a watershed in the Appalachian Mountains in Southern Quebec, Canada. The SAR data were relatively calibrated using extended targets (coniferous stands). Extensive ground measurements were done simultaneously to each of the seven flights, in order to measure the snow cover characteristics (depth, density, SWE, liquid water content, temperature, and dielectric profiles) as well as the soil characteristics (moisture, temperature). To estimate the SWE of a given snowpack, a model which links the scattering coefficient to the physical parameters of the snow cover and the underlying soil has been developed. The model is based on the ratio of the scattering coefficient of a field covered by snow to the scattering coefficient of a field without snow. The analysis has revealed that volume scattering from a shallow dry snow cover (SWE<20 cm) is undetectable. The backscattering power is dominated by soil surface scattering, the latter varying with the decrease of liquid water content in the surface layer with decreasing soil temperature below 0/spl deg/C. Then, the scattering ratio decreases proportionally to the dielectric constant of the soil in winter. Furthermore, a unique relationship for three acquisition dates has been found between the thermal resistance, R, of the snow pack and the backscattering power ratio. Then, the spatial distribution of the power ratio should depict the spatial distribution of R, given spatially uniform climatological conditions over the study area. Since linear relationships between SWE and R have been observed, it should be possible to estimate the SWE of shallow dry snow cover with C-band SAR data using few ground truthing data in an open area when the soil is frozen.

Stratiform and Convective Classification of Rainfall Using SSM/I 85-GHz Brightness Temperature Observations

Abstract A better understanding of global climate calls for more accurate estimates of liquid and ice water content profiles of precipitating clouds and their associated latent heating profiles. Convective and stratiform precipitation regimes have different latent heating and therefore impact the earth’s climate differently. Classification of clouds over oceans has traditionally been part of more general rainfall retrieval schemes. These schemes are based on individual or combined visible and infrared, and microwave satellite observations. However, none of these schemes report validations of their cloud classification with independent ground observations. The objective of this study is to develop a scheme to classify convective and stratiform precipitating clouds using satellite brightness temperature observations. The proposed scheme probabilistically relates a quantity called variability index (VI) to the stratiform fractional precipitation coverage over the satellite field of view (FOV). The VI for a s...

Microphysics of Marine Stratocumulus Clouds with Two Drizzle Modes

Abstract This observational study looks at the distribution of some cloud microphysical properties measured from the University of Washington's aircraft in mostly unbroken stratocumulus (Sc) clouds in the vicinity of the Azores Islands during ASTEX. The average behavior of the Sc includes the presence of two drizzle modes. In 85% of the Sc the amount of drizzle LWC (liquid water content in droplets with radius r > 20 µm) is less than 0.01 g m−3, while in the rest, drizzle LWC is much larger than 0.01 g m−3. The microphysics of light-drizzle Sc approach classical conditions, because measured and adiabatic LWC profiles are similar, and droplet spectral dispersions decrease with height. The lognormal function fits approximately measured droplet spectra of light-drizzle Sc. Standard deviations of these spectra remain about constant with height, vary over a small range, and average 1.74-µm radius. Drizzle LWC > 0.01 g m−3 is found on the average in Sc with spectra that have effective radii re &ge 16 µm. This h...

Retrieval of Vertical Profiles of Liquid Water and Ice Content in Mixed Clouds from Doppler Radar and Microwave Radiometer Measurements

Abstract A new method to retrieve vertical profiles of liquid water content Mw(z), ice water content Mi(z), and ice particle size distribution Ni(D, z), (where D is the ice particle size and z the vertical coordinate) in mixed nonprecipitating clouds using the observations of a zenith-viewing Doppler radar and of a microwave radiometer is proposed. In this method, the profile of the vertical air velocity deduced from Doppler radar measurements is used to describe the rate of production by the updrafts of water. vapor in excess of saturation with respect to ice. Using a Zi − Mi power-law relation with an unknown linear parameter (let αi, be this parameter) and initially assuming that Zw is negligible with respect to Zi, (where Zw and Zi are the radar reflectivity factors of liquid water and ice particles respectively), the measured radar reflectivity factor profile Zm (≈ Zi) is inverted to estimate Ni(D, z). From Ni(D, z), the profile of the rate of water vapor that can be consumed by pure deposition on ic...

Simulation of summer snowmelt on the Greenland ice sheet using a one‐dimensional model

A one‐dimensional heat and mass balance model of a snowpack over frozen soil was modified for use in glacial environments. The model solves a set of governing equations for the energy and mass balances of the snow, subject to observed meteorological conditions at the upper boundary and the assumption of a steady state at the lower boundary. The initial state of the snowpack is defined by the temperature, density and grain size profiles at the beginning of the simulation period. The data used to test the model on the Greenland ice sheet are a subset of the meteorological and surface data collected during the 1990 summer field season by the Swiss Federal Institute of Technology (ETH) Greenland Expedition. The site was located near the equilibrium line elevation on the west slope of the ice sheet. The relatively large amount of snowmelt experienced at this site during the summer of 1990 provides a robust test of the snowmelt model. Both the simulated height and mass of the snowpack agree well with the observations. The evolution of profiles of temperature, density and liquid water content also conform to our expectations of the physical changes taking place in the snowpack during melt. Results from the present model are also compared to those from a similar model and differences between the models are discussed.

Cloud physics studies with 8 mm wavelength radar

Results from recent cloud experiments with an 8 mm wavelength Doppler radar demonstrate that millimeter wavelength radar can provide important new information about nonprecipitating and lightly precipitating clouds. Millimeter wave radar can be used to document small-scale spatial structure of cirrus and marine stratus clouds. Its data can be used to estimate profiles of ice content, particle size and concentration in cirrus clouds and profiles of liquid water content and turbulence in marine stratus clouds. New results with mm wave radar suggest that plate-like crystals may be distinguishable from aggregates with polarization techniques. Quantitative information about cirrus cloud ice crystal fallspeeds, and therefore ice mass flux, can also be produced with newly developed techniques that exploit the sensitivity and velocity precision of such radars. The good sensitivity to cloud particles, the immunity from ground clutter contamination, and the good spatial resolution of millimeter wavelength radar make it an excellent instrument for documenting quantitative microphysical and dynamical properties of non-precipitating and lightly precipitating clouds.

冬季南西諸島海域における層状雲の雲物理学的性質

Microphysical properties of stratiform clouds were observed over the Southwest Islands Area as a part of intensive field observations of Western North-Pacific Cloud-Radiation Experiments (WENPEX). The observation was made under the weak outbreak of cold airmass in January 1991. The observed clouds were mainly stratocumulus clouds, whose cloud depths were about 0.5 to 1.2 Km. A strong temperature inversion was always observed near the cloud tops, above which there was a stable dry layer. The air temperature near cloud tops reached values lower than 0°C for some clouds (minimum temperature: -5°C). The clouds consisted mainly of cloud droplets and they were non-precipitating clouds. The clouds showed considerable horizontal inhomogeneity and vertical changes. The number concentration of cloud droplets in the central parts of clouds showed a tendency to be constant with height. The mean concentration reached approximately 500 to 800 cm -3 as a result of a high CCN concentration. Mean droplet radius rose from about 3 μm near cloud base to 7 μm near cloud top. The vertical profiles of liquid water content (LWC) indicated that the values increased with height as a result of an increase in droplet size rather than concentration. The peak LWC reached about 1.0 g/m 3 in the thick clouds. The envelope of maximum LWC was generally smaller than the adiabatic values. Effective radius changed from about 3 μm near cloud base to 6 μm near cloud top. The characteristics of the stratocumulus clouds over the Southwest Islands Area in Japan is discussed from the microphysical standpoint, as compared with the stratiform clouds observed in geographically different areas.

Remote sensing of liquid water content with combined radar-radiometer system

Field observation of liquid water content (LWC) in precipitating clouds with a combined Radar-Radiometer System were made and are compared with in-situ measurements. The deduced LWC profiles for different evolution stages of precipitating cloud are also given. It is shown that the LWC measurements with the combined system are obviously better than that with single radar only. The main errors of the combined method are analyzed. These results will be valuable to the future operational application of LWC measurements with combined active-passive microwave (MW) remote sensing.

Solving the inverse problem for soil moisture and temperature profiles by sequential assimilation of multifrequency remotely sensed observations

An algorithm is developed to solve the inverse problem for the retrieval of the soil moisture and temperature profiles based on remotely sensed observations of multispectral irradiance. A model of coherent wave radiative transfer and a model of coupled heat and moisture diffusion in porous media are combined in order to estimate the liquid volumetric water content and temperature profiles in a soil column using low-frequency passive microwave and infrared emitted radiation observations and without the use of empirical relations. The central purpose of this mainly theoretical paper is to pose the inverse problem and present the physics-based algorithm as the solution. The algorithm is tested on a basic synthetic example in order to ascertain that the retrieval is feasible. Additional work in the future is necessary and planned in order to test the algorithm with field observations, extend it to include vegetation, and refine it for detail in the specification of heterogeneity in soil types and boundary conditions. >

Physical Characteristics of Arctic Stratus Clouds

Observations of the physical properties of Arctic status clouds (ASC) over the Beaufort Sea area were made by the NCAR Electra aircraft during June 1980. The cloud morphology and microstructure observed during these experiments are described here. Arctic stratus clouds were formed under various meteorological conditions, but not when the axis of the Beaufort Sea ridge was zonal and the airflow into the region was continental. The mean drop diameter in clouds observed under all conditions remained near 10 μm, while the mean liquid water content (LWC) was characteristic of the air mass forming the clouds and essentially determined by the mean drop concentration. Clouds showed considerable horizontal homogeneity but significant vertical changes occurred within them. The vertical profiles of LWC show that the values generally increased with height, as a result of an increase in droplet size rather than concentration. The drop size distribution near the base was monomodal, characteristic of condensation on a nucleus spectrum, but changed to a bimodal distribution near the top of the cloud.

A field study of nocturnal stratocumulus: I. Mean structure and budgets

AbstractObservations of anticyclonic stratocumulus obtained with ground‐based and balloon‐borne equipment during the night of 19/20 November 1976 at Cardington, Bedford, UK, are described in relation to the synoptic situation.The mean structure of the atmosphere from ground to about 300m above cloud top is discussed. Of particular interest are the large temperature and humidity ‘jumps’ observed within a layer 1‐10m thick at cloud top, and the thermally stable surface layer about 200m thick in the presence of an overcast sky and surface wind speed of 3–4 ms−1. The mean liquid water content profile is accounted for in terms of turbulence theory, but the cause of observed large variations in total cloud water content is not identified.The locally steady conditions allowed estimates to be made of the local budgets of heat and water for the boundary layer (cloud top to ground) as a whole. In particular, the shape of the temperature inversion above cloud top allowed a quantitative estimate of cloud top entrainment rate to be made.Although the local water budget appears to be in approximate balance, only about one‐third of the radiative loss from cloud top is accounted for locally. It is not possible to account for this deficit in terms of the observations; it is suggested it could result in a downstream mean cooling of the boundary layer of about 0.5K per 100km.The observed dispersal of cloud downstream cannot be explained by the local budget deficit (which would tend to increase cloud). It is estimated that a local subsidence rate of 2–4cms−1 through the cloud would be required to disperse it on the observed time scale. Potential sources of evidence for this are discussed.

Some thermodynamical and microphysical aspects of monsoon clouds

The thermodynamical and microphysical characteristics of monsoon clouds in the Poona, Bombay and Rihand regions were investigated using extensive aircraft in-cloud observations. The number of clouds sampled at Poona, Bombay and Rihand is 2199, 169 and 104 respectively.The temperatures inside the cloud are colder than its environment at Poona and Rihand. The maximum difference is about 3°C at the cloud base level and the difference decreased with height. At Bombay the difference is less than 1°C and at some levels the temperatures inside the cloud are warmer than its environment.The lapse rates of temperatures inside the cloud are slightly less than those in the immediate environment of the cloud. The environmental lapse rates are nearly equal to the saturated adiabatic value.The positive increments in liquid water content (LWC) are associated with the increments in temperature inside the cloud. Similarly positive increments in temperatures inside the cloud are associated with the increments in temperature of its immediate environment at the same level or the layer immediately above.The maximum cloud lengths observed at Poona and Bombay respectively are 14 and 3 km. The horizontal cross-section of LWC showed a maximum number of 13 peaks in clouds at Poona while only 7 peaks were observed at Bombay. The location of maximum LWC in the horizontal cross-section is more or less at the centre of the cloud. The LWC profile showed an increase with height from the base of the cloud at Poona and Bombay. There is no marked variation of LWC with height at Rihand.The total droplet concentration at different altitudes at Poona and Bombay is in the range 28–82 cm−3. The size distribution of cloud droplets experienced a broadening effect with increase in height from the cloud base at Poona. The broadening effect at Bombay is not as marked as that at Poona.

Window region infrared radiation transfer through clouds and the sensitivity of cloud parameters to radiative effects

The effects due to the passage of i.r. radiation through clouds are predominantly due to the window region spectrum (between 8 and 13 μm). An approximation scheme is used to identify those parameters in the cloud model that determine the heating and cooling effects and the sensitivity of these effects to the variations in the parameters. The results show that the anomalously large heating/cooling effects predicted by the exact calculations are actually a consequence of the choice of a homogeneous liquid water content profile and that an adjustment in this profile results in a lessening of these effects. The radiative effects are also found to be dependent on the size distribution in a nontrivial fashion. In particular, it is found that the use of bimodal distributions, a characteristic feature of clouds with entrainment, results in a lowering of the heating and cooling effects, even with a homogeneous vertical profile, to values more realistic than those obtained with monomodal distributions.

Computer Modeling of Hailstone Growth in Feeder Clouds

The growth of hailstones is studied using a one-dimensional non-steady-state model of a growing feeder cloud. Conditions within the mature cloud are assumed to be adiabatic. Vertical velocity and liquid water content profiles change at a predetermined rate, beginning with small values and gradually increasing to values that can be expected in a mature thunderstorm. Hailstone growth equations used in the model are developed in terms of the well-known dry- and wet-growth regimes and include terms that account for growth in a mixture of supercooled cloud droplets and ice crystals. Hailstone embryos in the form of liquid cloud droplets are introduced into the model at various heights and times, and the subsequent trajectories are analyzed. Different versions of the model that incorporate changes in updraft magnitude and shape are tested. Results show that the model produces hailstones, radii ranging from near zero to 1.3 cm in 40 min or less, from 20 to 50 μ radius embryos introduced under a variety of updraft conditions, at many places in the life of the feeder cloud model.