Study of the possibility of stimulating precipitation from warm convective clouds by hygroscopic particles from numerical simulation

We present the results of numerical simulation of the action of hygroscopic particles on a convective cloud for obtaining additional precipitation. The correspondence of vertical profiles of cloud parameters to those actually observed under natural atmospheric conditions is achieved within a one-dimensional numerical model by parametrization of the process of heat and moisture entrainment into the upward air flow forming the cloud. The model describes in detail microphysical processes in a cloud with the use of the kinetic equation for the size distribution of cloud droplets. The processes of forming precipitation in convective clouds with a vertical thickness of 3–4 km during their natural development and during the introduction of hygroscopic particles are analyzed using numerical calculations. It is shown that it is actually possible to obtain additional precipitation from convective clouds of continental type under the action of hygroscopic particles with sizes of 1–1.5 μm. The results of calculating the intensity and total amount of precipitation as functions of the vertical thickness of a cloud and the parameters of particles introduced into it are presented. The conditions necessary for obtaining the maximum positive effect are elucidated.     

Formation of cloud microstructure during hygroscopic seeding

The evolution of cloud microstructure initiated by hygroscopic seeding is studied on the basis of numerical simulation of cloud formation in the initial stage of condensation. The influence of both physicochemical properties of atmospheric aerosol and atmospheric conditions controlling the cloud type on the microstructure of a developing cloud (without hygroscopic seeding) is analyzed. It is shown that cloud seeding with additional particles whose sizes exceed the characteristic size of atmospheric condensation nuclei leads to a decrease in the concentration of cloud droplets and an increase in their sizes. This result of cloud seeding represents a positive effect for stimulation of precipitation from convective clouds. It is shown that this positive effect is achieved if there are some relationships between the parameters characterizing the hygroscopic particles and the atmospheric conditions. In particular, the maximum effect of action can be achieved at some optimal concentration of seeded particles. The decrease in the concentration of cloud droplets because of hygroscopic seeding is compared to the results of numerical simulations performed by other authors with allowance for coagulation processes in clouds. It is shown that this decrease can serve as an estimate for the effectiveness of hygroscopic seeding as a means for artificial intensification of precipitation from convective clouds.     

Efficiency of stimulating precipitation from convective clouds using salt powders

Comparative estimates of the efficiency of hygroscopic reagents for the seeding of convective clouds to obtain additional precipitation are performed based on numerical simulation. It is shown that the use of polydisperse salt powders has many benefits over other known hygroscopic reagents. The effect of seeding with salt powders manifests itself at mass concentrations of hygroscopic particles an order of magnitude less than when pyrotechnic flares are used. With salt-powder seeding, it is possible to obtain precipitation from warm convective clouds of moderate thickness from which precipitation does not typically fall. In this case the effect of “reseeding” of clouds, which can be observed in seeding with hygroscopic reagents having narrow size distributions of particles, does not reveal itself.     

Numerical simulation of the action on a warm convective cloud by hygroscopic particles

A one-dimensional numerical model of a warm convective cloud is presented. This model is used to study the effectiveness of the action on the cloud by hygroscopic particles with the aim of intensifying precipitation. The numerical simulation takes into account the processes of condensation, coagulation, and sedimentation of cloud droplets and makes it possible to obtain spatiotemporal characteristics of cloud development. A system of differential equations describing time variations in the temperature, pressure, and watervapor supersaturation during the adiabatic rise of a continuous air flow is solved. The evolution of the size distribution of cloud droplets is described by a kinetic equation. A continuous acting source of droplets with the size distribution calculated with consideration for condensation properties and dispersion characteristics of condensation nuclei (natural and additionally introduced during the action) is specified at the cloud-base level. The cloud top is formed owing to the evaporation of droplets in the barrier atmospheric layer over the cloud. The influence of changes in the barrier-layer height on the structure of cloud parameters and precipitation-formation processes is analyzed. The introduction of additional hygroscopic particles into a cloud is shown to act as a trigger mechanism initiating the processes of coagulation and sedimentation in the cloud medium. In this case, a positive effect of action by fine particles can be achieved if a certain reserve of sufficiently large droplets is present in the cloud. The results of calculating the dependence of the action effect on the height of the barrier layer, restricting cloud development, are presented.     

Modeling the convective cloudiness and its impact on the atmospheric gaseous composition

A combined three-dimensional numerical model of convective cloudiness with detailed microphysics and a model of the transport of atmospheric trace gases with gas- and aqueous-phase chemistry were developed. We consider the main physical mechanisms responsible for the formation of midsized droplet clouds and the transport of gases with differing solubility therein. Test numerical calculations were performed to investigate the sensitivity of the cloud model to variations in input parameters, as well as the variability of the ion composition of cloud drops with regard to their size distribution. The results of numerical calculations are presented with a preliminary analysis.     

A comparison of summer precipitation structures over the South China Sea and the East China Sea based on tropical rainfall measurementmission

The three-dimensional structures of summer precipitation over the South China Sea （SCS） and the East China Sea （ECS） are investigated based on tropical rainfall measurement mission （TRMM）. The primary results are as follows. First, both the convective and stratiform precipitation rates in the SCS are much higher than those of the ECS. The contribution of the convective cloud precipitation to the surface precipitation is primarily over the SCS and the ECS with a proportion of about 70%, but the contribution of convective cloud precipitation is slightly larger in the SCS than the ECS. The contribution of stratus precipitation is slightly larger in the ECS than that in the SCS. Second, the content of cloud particles and precipitation particles in the ECS in June was greater than that in the SCS, while in July and August, the content of cloud and precipitation particles in the ECS was less than that in the SCS. Third, the latent heat profile of the ECS is quite different from that of the SCS. In June, the peak values of evaporation and condensation latent heating rates in the ECS are greater than those in the SCS. In July and August, however, the peak values of evaporation and condensation latent heating rates in the ECS are about 0.05°/h less than those in the SCS.     

Experimental investigations of the effect of cloud-medium modification by salt powders

The results of experimental investigations into the action of polydispersion salt powders on model cloud media are presented. The results of experiments show a considerable positive effect of the modification of convective clouds by salt powders in order to obtain additional precipitation. The introduction of polydispersion salt powder into a forming cloud medium leads to the appearance of large cloud droplets and to the droplet-spectrum broadening. This result is a positive factor for the stimulation of coagulation processes and further precipitation formation. No “overseeding” phenomenon (when, instead of the enlargement of droplets, their sizes decrease and the concentration of cloud droplets increases) is observed at rather high mass concentrations of the introduced powder.     

Electricity of the convective atmospheric boundary layer: Field observations and numerical simulation

The electric state of the middle-latitude convective atmospheric boundary layer (ABL) is investigated during a point in time when it is not disturbed by clouds, precipitation, mist, or industrial aerosols. A numerical model is developed that estimates the electroaerodynamic state of the convective ABL. The model is parameterized using results of field observations and laboratory experiments. According to the model, vertical profiles of atmospheric electric field strength, space charge density, electric conductivity, and atmospheric electric current density are calculated in the horizontally homogeneous approximation with a high space-time resolution.     

Radar estimation of water content in cumulonimbus clouds

The method and results of radar researches of vertically and volumetric integrated water content in powerful cumulonimbus (Cb) clouds obtained for the first time are considered. It is established that in hailstorms of Northern Caucasus vertically integrated liquid (VIL) water content varies in limits from 8 up to 50 kg/m², in shower clouds—from 0.5 up to 12 kg/m², in Nimbostratus (Ns) clouds—it is usual less than 0.5 kg/m² and in clouds with a drizzle—less than 0.05 kg/m². The main water content of hailstorms in a stage of development is concentrated in their supercooled layer, in a maturity stage—in a layer from the ground up to height 8–10 km and in a stage of dissipation—in a ground layer. The ratio of VIL of the supercooled and warm parts of cloud allows estimating hail dangers of clouds and stage of their development. It is shown that the volume of hailstorms varies in limits from 10³ up to 5 × 10⁴ km³ and their volumetric integrated mass (VIM) of water content — from 10⁵ up to 6 × 10⁶ tons. The volume of hail localization seldom exceeds 5–25% from total cloud volume, but its contribution to VIM achieves 30–60%. Speed of precipitation formation in powerful hailstorms achieves 1 × 10⁴−5 × 10⁵ tons/min and the same order of value has speed of recession of VIM in their stage of dissipation.     

Convective cloud fields in the Atlantic sector of the Arctic: Satellite and ground-based observations

Convective cloudiness in the Atlantic sector of the Arctic is considered as an atmospheric spatially self-organized convective field. Convective cloud development is usually studied as a local process reflecting the convective instability of the turbulent planetary boundary layer over a heated surface. The convective cloudiness has a different dynamical structure in high latitudes. Cloud development follows cold-air outbreaks into the areas with a relatively warm surface. As a result, the physical and morphological characteristics of clouds, such as the type of convective cloud, and their geographical localization are interrelated. It has been shown that marginal sea ice and coastal zones are the most frequently occupied by Cu hum, Cu med convective clouds, which are organized in convective rolls. Simultaneously, the open water marine areas are occupied by Cu cong, Cb, which are organized in convective cells. An intercomparison of cloud statistics using satellite data ISCCP and ground-based observations has revealed an inconsistency in the cloudiness trends in these data sources: convective cloudiness decreases in ISCCP data and increases in the groundbased observation data. In general, according to the stated hypothesis, the retreat of the sea-ice boundary may lead to an increase in the amount of convective clouds.     

On the use of poorly soluble hygroscopic substances for modification of warm clouds and fogs

From analysis of the relationships between the equilibrium state of condensation nuclei and the relative humidity, a conclusion is made concerning the preferred use of poorly soluble substances for the generation of artificial condensation nuclei (ACN) designed for modification of warm clouds and fogs with the purpose of their dissipation and precipitation formation. The advantage of poorly soluble substances over commonly used soluble salts is that the finely dispersed part of the spectrum of the poorly soluble ACN does not deliquesce and so is not involved in the formation of cloud droplets. For experimental testing of the conclusions, preference was given to cement, whose main soluble substance is calcium oxide with a solubility of about 1 g/l. The spectrum of dispersed cement particles was measured and compared with the spectra of pyrotechnic flares widely used for modification at present. The process of formation of the cloud droplet spectra was simulated in the aerosol chamber of the Institute of Experimental Meteorology by decreasing the preliminarily generated excess pressure. It was found in these experiments that, compared to the spectra of particles formed on background condensation nuclei, the introduction of dispersed cement leads to the broadening of spectra and to a decrease in the concentration of droplets. Even at the early stage of condensation, droplets with radii of ∼20 μm appear. In this case, no “overseeding” phenomenon is observed, which, for soluble substances, manifests itself in an increase in the concentration of cloud droplets with a large ACN concentration. These effects indicate that, according to the existing concepts about the mechanism of warm-cloud modification with hygroscopic substances, the introduction of poorly soluble ACN (in particular, dispersed cement) below the base of cumulus clouds should stimulate coagulation processes and accelerate rain-formation processes. Considerations are given that the introduction of poorly soluble ACN into the already existing cumulus or stratocumulus clouds or fogs should also result in the acceleration of precipitation-formation processes or cloud dispersal. Comparison of cement powder with the well-known means of warm-cloud and fog modification is carried out. Original Russian Text ? N.P. Romanov, A.S. Drofa, N.S. Kim, A.V. Savchenko, G.F. Yaskevich, 2006, published in Izvestiya AN. Fizika Atmosfery i Okeana, 2006, Vol. 42, No. 1, pp. 80–91.     

A quasitropical cyclone over the Black Sea: Observations and numerical simulation

A long-living mesoscale cyclone observed over the Black Sea in September 2005 was characterized by a high wind velocity (25 m/sec) and induced an abnormal lowering of the sea-surface temperature (by more than 10°C). We performed the numerical simulation of this cyclone by using the MM5 model and the data of global operative analysis. The evolution of the cyclone and its structure similar to the structure of a tropical cyclone are reproduced. The primary azimuthal and secondary radial circulations, the clear-sky eye with warm core at medium levels, and the eyewall with strong air updraft and intense convection and precipitation are well visible. The fluxes of sensible and latent heat on the sea surface played the key role in the initiation and development of this cyclone. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 41–55, May–June, 2008.     

One-dimensional nonstationary model of vertical exchange in the Black Sea with regard for the mechanism of winter convection in the surface layer

We construct a one-dimensional nonstationary isopycnic model of vertical exchange in the Black Sea with regard for the processes of draining and transformation of waters of the Sea of Marmara (or “plume”), vertical diffusion, and the action of winter convection in the upper layer. It is assumed that mixing in the basin is local in space and time and that the winter wind action remains constant from year to year in the analyzed version of the model. The temperature of the upper mixed layer introduced to simulate the winter conditions is regarded as the principal external variable factor. Within the framework of the accepted restrictions, the model enables us to study the annual and interannual variability of the thermohaline characteristics and hydrochemical parameters in the water column of the sea. As an example, we perform the numerical analysis of the periodic action of external thermal conditions on the characteristics of the system with a period of six years. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 3–21, September–October, 2006.     

Investigation of the characteristics of surge phenomena in the Sea of Azov

We present the results of numerical simulation of currents and sea level for the Sea of Azov. In calculations, we use a three-dimensional nonlinear mathematical model taking into account the tangential wind stresses. We present the results of numerical analysis of the fields of currents and the amplitudes of oscillations of the sea level at the coastal stations as functions of the maximum velocity and the period of constant action of the west wind. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 12–25, January–February, 2008.     

Development of a Subcloud Layer over the Sea during a Cold Air Invasion

Evaporation and vertical moisture and heat transfer from the underlying surface are the basis of cloud formation. The situation when the coming relatively cold stably stratified air moves over a warm ocean is a typical problem in the development of a turbulent convective layer. The problem of cloud formation is also of scientific and practical interest. This paper considers the problems of the formation of a turbulent convective layer over a warmer ocean and the vertical distribution of relative humidity. The results of the theoretical model are compared with the data of observations of the development of the turbulent convective layer at low latitudes (in the Indian Ocean) and at higher latitudes (in autumn over Lake Michigan). Approximate equations describe well the dynamics of temperature and humidity of the layer as a function of the difference between the temperatures of the approaching and near-surface air layers. The theoretical results are compared with the data on measurements of the condensation heights obtained at the Novosibirsk Tolmachevo Airport. Some discrepancy between them is due to the unsteadiness measurement and the approximations adopted in the theoretical model.     

Assimilation of climatic data in a model of circulation of waters in the Black Sea with regard for the space and time behavior of the variances and cross-covariance functions of forecast errors

We propose an improvement of the algorithm of joint assimilation of the data on climatic temperature, salinity, and altimetric sea level in a model of circulation. Unlike the previous works, the variances of the forecast errors of temperature and salinity and the cross-covariance functions of of the forecast errors of salinity-level and temperature-level depend on the dynamics of waters. It is shown that the structure of the fields of cross-covariance functions in the upper mixed layer is formed by the vertical turbulent diffusion of the variances of forecast errors of temperature and salinity. At greater depths, these statistical characteristics are mainly determined by the vertical advection. We compared the results of calculations with and without taking into account the dynamics of the statistical characteristics. The analysis of the influence of the dynamics of these characteristics makes it possible to reconstruct the mutually adapted climatic fields of temperature, salinity, and horizontal and vertical current velocities in the Black Sea with the assimilation of data in the numerical model in each time step. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 18–31, July–August, 2008.     

Reconstruction of the space and time variability of thermohaline fields in the Sevastopol Bay

The aim of the present work is to reconstruct the space and time variability of the three-dimensional fields of currents, temperature, salinity, and density in the Sevastopol Bay under the influence of the actual external factors in 1999. For this purpose, we use a version of the numerical multilayer model on the σ-coordinates. A vast array of the data of observations accumulated as a result of regular monitoring of the Sevastopol Bay contains, in particular, the data on the sea-surface temperature measured with six-hour intervals (at the hydrometeorological station located near the center of the bay) and almost monthly vertical profiles of temperature and salinity obtained at seven hydrological stations. The comparison of the numerical results with the data of observations enables us to conclude that, in general, the model fairly correctly describes the space structure and rearrangements of the fields of temperature and salinity. Among the most important distinctions, we can mention the fact that the fresh river water penetrating into the bay is mixed with seawater faster than predicted by the model. We also discuss the causes of these distinctions. Translated from Morskoi Gidrofizicheskii Zhurnal, No. 5, pp. 23–39, September–October, 2008.     

Seasonal Variations and Transformations of Climatic Currents with Depth on the Basis of Assimilation of New Climatic Data on Temperature and Salinity in a Model of the Black Sea

The seasonal climatic circulation of the sea reconstructed on the basis of assimilation of new arrays of many-year average hydrological data in a model is analyzed. Five layers are discovered in the structure of climatic currents in the sea in depth: the surface Ekman layer (∼ 10 m), a layer with small vertical gradients of the kinetic energy (∼ 10–60 m), a layer with relatively high vertical gradients of the kinetic energy (∼ 60–150 m), a layer with gradual decrease in the kinetic energy and intensification (from 250–350 m) of the east cyclonic gyre and Batumi anticyclonic eddy (∼ 150–1000 m), and an abyssal layer characterized by an almost barotropic velocity (∼ 1000–2000 m). The specific features of the seasonal evolution of currents at these depths are investigated. It is shown that the key role in the formation of deep-water circulation of the sea is played by the south east flow, east cyclonic gyre, and Batumi anticyclonic eddy. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 6, pp. 28–45, November–December, 2005.     

Modeling of Circulation and Propagation of Contaminating Impurities in the Balaklava Bay

The Princeton Ocean Model is adapted to the water area of the Balaklava Bay for the numerical analysis of circulation. The calculations are performed with the help of the diagnostic method by using the data of the hydrological survey carried out in the bay in August 1992. We study the structure of the surface and bottom currents in the analyzed period as well as the vertical circulation of waters and the circulation averaged over the depth. The obtained three-dimensional fields of currents are used for the numerical analysis of the process of propagation of passive contaminating impurities from the sources located on the coasts of the Balaklava Bay. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 49–61, May–June, 2005.