Cumulonimbus Research Articles

АКТИВНЫЕ ВОЗДЕЙСТВИЯ НА ОБЛАКА С ЦЕЛЬЮ УЛУЧШЕНИЯ УСЛОВИЙ ПОГОДЫ В МЕГАПОЛИСАХ

Some results of activities on improving weather conditions (weather protection) in megacities by cloud seeding are presented. The main tasks of the activities were to dissipate clouds and reduce or stop precipitation in the protected area during political, cultural, and sport events. In accordance to the methodological guidelines, four seeding methods are recommended depending on synoptic conditions: the dissipation of stratiform cloudiness; the initiation of premature precipitation on the windward side of the protected area by cloud seeding to form the precipitation “shadow”; the intense seeding (“overseeding”) of precipitation-forming clouds moving toward the protected area to reduce the efficiency of precipitation formation in them; the dissipation of deep cumulonimbus clouds by the dynamic method. To perform weather protection operations, up to 12 aircraft equipped with measuring equipment necessary for seeding, the “ground-air-ground” data communication system, and cloud seeding means were used. Liquid nitrogen, solid carbon dioxide, silver iodide, and coarse powder were used as reagents for cloud seeding. Ground-based automated weather radar systems were used to control aviation operations and to monitor the results of the seeding. The results of more than 100 large-scale operations on the creation of favorable weather conditions performed in various regions of Russia and neighboring countries indicate the efficiency of the methods and technical means of cloud seeding developed in the USSR and Russia for the artificial precipitation control.

Identification of the Puting Beliung Event by Utilizing the Interpretations of Radar Products and Himawari-8 Weather Satellite (Case Study: Puting Beliung Incident, November 22, 2018 in Jakarta)

<em>Indonesia was shocked again by a Puting beliung or tornado-like incident on November 22, 2018, in the Jakarta area. This incident caused many losses. In this regard, a study was conducted to observe the reflectivity products to identifiy the hook echo or bow echo patterns, and the velocity products for mesocyclone patterns as the characteristic of the Puting Beliung used radar product. The study required the Cengkareng C-Band raw data radar that was processed to produce CMAX, VCUT, and CAPPI (V) at 0.5 km, 1.0 km, and 1.5 km elevations overlay by HWIND. The CMAX and VCUT radar products are used to identify the cloud structure that caused Puting Beliung, by observed the highest reflectivity of the Puting Beliung-producing clouds. Then the CAPPI product overlay by HWIND is used to identify the movement of the wind which is suspected to be the beginning of the formation of a Puting Beliung at that location which is characterized by the presence of a mesocyclone pattern in the form of wind components and radial velocity. It was suspected that there was a wind rotating in the Central Jakarta area which indicated a Puting Beliung in the area. The analysis of this radar interpretation was then validated using satellite imagery to detect the cumulonimbus clouds forming the Puting Beliung. From this research, it is known that the Puting Beliung occurred around 08.12 UTC. The growth of cyclone-producing clouds occurred rapidly with a reflectivity value between 35 - 45 dBZ and wind speed up to 35 knots. Analysis of satellite imagery showed a significant decrease in cloud peak temperature so that the formation of convective clouds in the form of Cumulonimbus clouds indicates the phenomenon of the Puting Beliung. However, in this case study the Puting Beliung phenomenon is indicated as seen from the mesocyclone pattern of the rotating radial velocity component, and not from the hook echo or bow echo pattern.</em>

Properties, Changes, and Controls of Deep‐Convecting Clouds in Radiative‐Convective Equilibrium

AbstractChanges in tropical high clouds associated with deep convection with warming are one of the largest sources of uncertainty in climate feedbacks. Here, we leverage an ensemble of models of many types in an idealized configuration to investigate how and why high clouds change the way they do. We find that deep‐convecting anvils, independent of how cloud fraction is defined, increase in height, increase slightly in temperature, and (generally) decrease in cloud fraction with warming sea surface temperature (SST). The controls on anvil height and temperature have well established physical reasoning, but the response of anvil cloud fraction to warming is more variable across studies and not as well understood. We test a previously published hypothesis for control of anvil coverage and find that, at least to first order, it is highly controlled by radiatively‐driven divergence, in which, with warming, anvil clouds occur in a more stable environment requiring less divergence to balance radiative cooling and, therefore, decreasing cloud coverage. We also find mid‐level clouds robustly decrease in coverage with warming SST and can be represented by a diagnostic scaling which attributes the robust decrease in mid‐level clouds to the rapid increase in the overall convective heating of the clouds compared to the much slower increase in the integrated radiative cooling rate. The robust response of deep‐convective clouds to warming and support for the underlying physical mechanisms across the spectrum of models, with both explicit and parameterized convection, increases confidence in their contribution to climate feedbacks.

Interpretation of black box for short-term predictions of pre-monsoon cumulonimbus cloud events over Kolkata

Interpretation of black box for short-term predictions of pre-monsoon cumulonimbus cloud events over Kolkata

Developing Cumulonimbus cloud and shower

Developing Cumulonimbus cloud and shower

ОПАСНЫЕ АТМОСФЕРНЫЕ ЯВЛЕНИЯ КОНВЕКТИВНОГО ХАРАКТЕРА В РОССИИ: НАБЛЮДАЕМЫЕ ИЗМЕНЕНИЯ ПО РАЗЛИЧНЫМ ДАННЫМ

Changes in the frequency and intensity of atmospheric severe convective events, including heavy rainfall, thunderstorm, hailstorm, squall, and tornado, in the Russian regions during the warm season are analyzed using different independent sources of information. Based on observations at Russian weather stations in 1966-2020, the frequency of thunderstorm, hailstorm, and strong wind, the contribution of extreme showers to total precipitation, and the cumulonimbus cloud fraction are estimated. Based on satellite data, the frequency and intensity of tornado and squall events that caused windthrows for 1986-2021 and the height of the top of deep convective clouds for 2002-2021 are also evaluated. The ERA5 reanalysis data are used to analyze the frequency of conditions favorable for the development of moderate and intense severe convective events in 1979-2020. The results indicate a general intensification of severe convective events in most Russian regions, except for a number of regions in the south of the European part of Russia. The frequency of moderate hazards has a decreasing trend, and the frequency of the most intense severe hazards has an increasing trend. It is reasonable to take the results into account when developing plans for the adaptation of Russian regions and industries to climate change.

Process‐Level Assessment of the Iris Effect Over Tropical Oceans

AbstractThe iris hypothesis suggests a cloud feedback mechanism that a reduction in the tropical anvil cloud fraction (CF) in a warmer climate may act to mitigate the warming by enhanced outgoing longwave radiation. Two different physical processes, one involving precipitation efficiency and the other focusing on upper‐tropospheric stability, have been argued in the literature to be responsible for the iris effect. In this study, A‐Train observations and reanalysis data are analyzed to assess these two processes. Major findings are as follows: (a) the anvil CF changes evidently with upper‐tropospheric stability as expected from the stability iris theory, (b) precipitation efficiency is unlikely to have control on the anvil CF but is related to mid‐ and low‐level CFs, and (c) the day and nighttime cloud radiative effects are expected to largely cancel out when integrated over a diurnal cycle, suggesting a neutral cloud feedback.

ENTICE Satellite Orbital Simulator to Study Ice Clouds

AbstractClouds play a significant role in the Earth's energy balance and hydrologic cycle through their effects on radiation and precipitation, and therefore are crucial for life on Earth. Earth's NexT‐generation ICE mission (ENTICE) is proposed to measure diurnally resolved global vertical profiles of cloud ice particle size, ice water content, and in‐cloud humidity and temperature combining a 94 GHz cloud radar and multi‐frequency sub‐millimeter (sub‐mm) microwave radiometers from space. The scientific objective of ENTICE is to identify the important processes by which anvil clouds evolve and interact with ambient thermodynamic conditions to advance our fundamental understanding of clouds and reduce uncertainties in cloud climate feedback. Whether such a science objective could be achieved depends on the orbital sampling characteristics of the mission. In this study, ENTICE sampling statistics are simulated with more than 1 billion (109) profiles and using five different scanning methods in a 400 km altitude precession orbit with an inclination of 65°: nadir, forward pointing, side scanning, and conical scanning for the radiometers, and nadir pointing for the radar. These statistics can then be used to help with future mission planning efforts. Using the GEOS‐5 model atmosphere (produced by nature‐run at 7‐km and 30‐min resolution), the simulator calculates sampling statistics related to cloud types and overpass times with enhancement from radar. The wide swath of ENTICE radiometers by conical and side scanning methods ensures ample high cloud samples (1.3 × 109 samples) gathered by ENTICE over its 2‐year mission for different types of clouds with sufficient sampling over the diurnal cycles. Sampling differences between radar and radiometers at nadir shows the combination of radar and radiometers will allow for measurements of cloud vertical profiles. Therefore, our results show that the designed orbit sampling of ENTICE is sufficient to fulfill the mission science goals.

Hallett‐Mossop Rime Splintering Dims Cumulus Clouds Over the Southern Ocean: New Insight From Nudged Global Storm‐Resolving Simulations

AbstractIn clouds containing both liquid and ice with temperatures between −3°C and −8°C, liquid droplets collide with large ice crystals, freeze, and shatter, producing a plethora of small ice splinters. This process, known as Hallett‐Mossop rime splintering, and other forms of secondary ice production, can cause clouds to reflect less sunlight and to have shorter lifetimes. We show its impact on Southern Ocean shallow cumuli using a novel suite of five global storm‐resolving simulations, which partition the Earth's atmosphere into 2–4 km wide columns. We evaluate simulated clouds and radiation over the Southern Ocean with aircraft observations from the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES), and satellite observations from Clouds and the Earth's Radiant Energy System (CERES) and Himawari. Simulations with large concentrations of ice crystals in boundary layer clouds, which agree better with SOCRATES observations, have reduced mixed‐phase cumulus cloud cover and weaker shortwave cloud radiative effects (CREs) that are less biased compared with CERES. Using a pair of simulations differing only in their treatment of Hallett‐Mossop rime splintering, we show that including this process increases ice crystal concentrations in cumulus clouds and weakens shortwave CREs over the Southern Ocean by 10 W m−2. We also demonstrate the key role that global storm‐resolving models can play in detangling the effects of clouds on Earth's climate across scales, making it possible to trace the impact of changes in individual cumulus cloud anvils (10 km2) on the radiative budget of the massive Southern Ocean basin (107 km2).

Diurnal Differences in Tropical Maritime Anvil Cloud Evolution

AbstractSatellite observations of tropical maritime convection indicate an afternoon maximum in anvil cloud fraction that cannot be explained by the diurnal cycle of deep convection peaking at night. We use idealized cloud-resolving model simulations of single anvil cloud evolution pathways, initialized at different times of the day, to show that tropical anvil clouds formed during the day are more widespread and longer lasting than those formed at night. This diurnal difference is caused by shortwave radiative heating, which lofts and spreads anvil clouds via a mesoscale circulation that is largely absent at night, when a different, longwave-driven circulation dominates. The nighttime circulation entrains dry environmental air that erodes cloud top and shortens anvil lifetime. Increased ice nucleation in more turbulent nighttime conditions supported by the longwave cloud-top cooling and cloud-base heating dipole cannot compensate for the effect of diurnal shortwave radiative heating. Radiative–convective equilibrium simulations with a realistic diurnal cycle of insolation confirm the crucial role of shortwave heating in lofting and sustaining anvil clouds. The shortwave-driven mesoscale ascent leads to daytime anvils with larger ice crystal size, number concentration, and water content at cloud top than their nighttime counterparts.Significance StatementDeep convective activity and rainfall peak at night over the tropical oceans. However, anvil clouds that originate from the tops of deep convective clouds reach their largest extent in the afternoon hours. We study the underlying physical mechanisms that lead to this discrepancy by simulating the evolution of anvil clouds with a high-resolution model. We find that the absorption of sunlight by ice crystals lofts and spreads the daytime anvil clouds over a larger area, increasing their lifetime, changing their properties, and thus influencing their impact on climate. Our findings show that it is important not only to simulate the correct onset of deep convection but also to correctly represent anvil cloud evolution for skillful simulations of the tropical energy balance.

On the Resolution‐Dependence of Anvil Cloud Fraction and Precipitation Efficiency in Radiative‐Convective Equilibrium

AbstractTropical anvil clouds are an important player in Earth's climate and climate sensitivity, but simulations of anvil clouds are uncertain. Here we identify and investigate one source of uncertainty by demonstrating a marked increase of anvil cloud fraction with resolution in cloud‐resolving simulations of radiative‐convective equilibrium. This increase in cloud fraction can be traced back to the resolution dependence of horizontal mixing between clear and cloudy air. A mixing timescale is diagnosed for each simulation using the cloud fraction theory of Seeley, Jeevanjee, Langhans, and Romps (2019) (https://doi.org/10.1029/2018GL080747) and is found to scale linearly with grid spacing, as expected from a simple scaling law. Thus mixing becomes more efficient with increasing resolution, generating more evaporation in middle and lower tropospheric updrafts. This decreases their precipitation efficiency (PE), thereby increasing their overall mass flux, leading to greater detrainment at the anvil level and hence higher anvil cloud fraction. The decrease in PE also yields a marked increase in relative humidity with resolution.

Simulation of Rapid Intensification of Super Typhoon Lekima (2019). Part II: The Critical Role of Cloud-Radiation Interaction of Asymmetric Convection

In this study, super typhoon Lekima (2019) with an atypical rapid intensification (RI) episode is investigated by conducting a pair of experiments. In the control experiment, the model reproduces reasonably well the evolution characteristics of convective activity and intensity changes. That is, active downshear-left convection moved counterclockwise to the upshear flank. In the sensitivity experiment without the cloud-radiation feedback (CRF), the simulation fails to capture the observed upshear deep convection and the RI process. Our analyses suggest that the cloud–radiation interaction acts as positive feedback between the tilting-induced convective asymmetry (TCA) and outflow channel. On the one hand, the radiative process will induce upper (lower) cooling (warming) above (within) the cloud anvil of the outflow layer. This thermodynamical pattern locally destabilizes the upper troposphere and is conducive to enhance the deep convection. On the other hand, the enhanced deep convection provides the energy source to promote the upper divergent flows. The stronger divergent flow acts efficiently to block the vertical wind shear (VWS) and leads to a stronger outflow channel. This CRF assists in the development of a thicker and more radially extensive outflow than that CRF-off simulation. This study further confirms the outflow blocking effect, which gains insights on the evolution of upshear-left asymmetric convection and its role in the atypical RI event.

The Acoustic Nature of “Storm Nose”, “Supercell” Vortices and Tornadoes

The process of cumulonimbus cloud Cb calvus formation in the middle latitudes of real atmosphere is analyzed in this work. Its transformation from initial lifecycle stage to “maturity” undergoes due to the formation of the waveguide called “aerial acoustic channel” in the troposphere near the level of temperature minimum that is close to 2 km altitude. This “aerial acoustic channel” can be considered as analog of “deep sound channel” that corresponds to the minimal sound speed level. Tropospheric “channel” related to the thermal inversion zone is almost unlimited horizontally. Synchronous generation of two compression waves (ascending one above Cb and descending one inside Cb) is caused by Cb calvus dome ascension. The first one can provoke the aerodynamic draft previously unexplained. The second one results in the growth of its “storm nose” and in the axial and peripheral descending mechanisms in Cb. The penetration of Cb into stratosphere results in the destruction of dynamic balance around Cb top and hence in its unloading in the descending decompression wave. Here the air cools down to the “dew point” in the place of conjugation with parental cloud – due to Snellius law it results in the formation of aerosol “vortex” as condensation front; this “vortex” has calculated value of its generatrix against vertical. Due to D. Snow’s criterion, this vortex forms either “supercell” vortex or tornado vortex.

Intraseasonal variability and possible causes of large-scale and convective precipitations over the Gangetic plain of India

The occurrence of Indian summer monsoon rainfall (ISMR) during June to September, especially over the eastern Gangetic plain of India, is the lifeline for densely residing people. The intraseasonal and interannual variability in ISMR provokes drought and flood conditions and largely affects agriculture practices. Owing to its importance, several studies on the variability of ISMR over the meteorological subdivisions, namely West Bengal (WB), Jharkhand (JH), Bihar (BR), East Uttar Pradesh (EUP), and West Uttar Pradesh (WUP), respectively, have been conducted; however, the contribution of large-scale precipitation (LSP) and convective precipitation (CP) in ISMR needs to discuss. The LSP is precipitated out from the stratus or nimbostratus clouds, while CP occurs from the cumulus and cumulonimbus clouds, and both of them coexist in ISMR during summer monsoon months. The objective of this paper is to analyze and discuss the climatological characteristics and possible causes of occurrence of LSP and CP over the meteorological subdivisions. For this purpose, the data of LSP, CP, zonal, meridional (u and v components) wind, and relative humidity (rh) at the spatial resolution of 0.25° × 0.25° for the period of 1980–2019 are taken from the European Centre for Medium-Range Weather Forecasts (ECMWF). The outgoing longwave radiation (OLR) data at a surface resolution of 1° × 1° for the same periods are obtained from the National Centre for Environmental Information (of NOAA). The observed rainfall data of the India Meteorological Department at the same resolution and period is considered and compared with ECMWF Reanalysis (ERA5) data. The spatial and temporal distribution of both types of precipitation is analyzed, and their linkage with OLR, zonal winds, and rh at pressure levels of 1000 hPa, 850 hPa, and 700 hPa (in lower troposphere) is examined. The daily climatological values of CP (LSP) are relatively higher (lower) in each meteorological subdivision. The associated lower values of OLR are noticed over the Gangetic West Bengal, Jharkhand, and Bihar, while higher values of OLR are seen over the East and West UP. From the pressure levels of 1000 to 700 hPa, the change in the zonal wind, i.e., easterly to westerly and vice versa, and occurrence of a large amount of rh (>80%) may be possibly initiated moist convective activity for more precipitating out CP over the Gangetic West Bengal, Jharkhand, and Bihar in comparison to East and West Uttar Pradesh.

The Interaction between African Easterly Waves and Different Types of Deep Convection and Its Influence on Atlantic Tropical Cyclones

This study revisited the association of African easterly waves (AEWs) to Atlantic tropical cyclone (TC) development using weather states (WSs) from the International Satellite Cloud Climatology Project, National Hurricane Center best track hurricane data (HURDAT2), and reanalysis products. The WS data are used as a proxy for two different types of deep convection. This study covers July–October 1984–2009. Statistical analysis based on HURDAT2 and objectively tracked AEWs has shown that a small fraction (~20%) of the AEWs that propagate from Africa serve as TC precursors. About 80% of the AEWs from the continent were non-developing. As in the past work, our study showed an important difference between developing and non-developing AEWs. Composites based on developing AEWs revealed well-organized large scale deep convection (one type, composed of mesoscale systems and thick anvil clouds) is tightly coupled to the AEW trough, while scattered, less well-organized deep convection (second type, isolated cumulonimbus and cumulus congestus clouds) dominated a large area downstream of the developing AEW trough. Developing AEWs propagate westwards while strengthening. In contrast, non-developing AEWs showed that the peak well-organized deep convection is located either behind (to the east of) or far ahead (to the west) of the AEW trough (peaks values are not in close proximity). Moreover, well-organized deep convections associated with non-developing AEWs were weaker than those associated with developing AEWs. The results indicated that convective activity ahead of the non-developing AEWs is weak. Positive relative humidity (RH) anomalies dominate the area around AEWs and downstream over the main TC development region. In contrast, negative RH dominated the main TC development region ahead of non-developing AEWs, suggesting an unfavorable environment downstream of the AEWs. The results also showed that developing AEWs maintained stronger features in the lower and middle troposphere, while non-developing AEWs exhibited weaker structures, in agreement with past work.

Weatherscapes

Due to the complex interplay of various meteorological phenomena, simulating weather is a challenging and open research problem. In this contribution, we propose a novel physics-based model that enables simulating weather at interactive rates. By considering atmosphere and pedosphere we can define the hydrologic cycle - and consequently weather - in unprecedented detail. Specifically, our model captures different warm and cold clouds, such as mammatus, hole-punch, multi-layer, and cumulonimbus clouds as well as their dynamic transitions. We also model different precipitation types, such as rain, snow, and graupel by introducing a comprehensive microphysics scheme. The Wegener-Bergeron-Findeisen process is incorporated into our Kessler-type microphysics formulation covering ice crystal growth occurring in mixed-phase clouds. Moreover, we model the water run-off from the ground surface, the infiltration into the soil, and its subsequent evaporation back to the atmosphere. We account for daily temperature changes, as well as heat transfer between pedosphere and atmosphere leading to a complex feedback loop. Our framework enables us to interactively explore various complex weather phenomena. Our results are assessed visually and validated by simulating weatherscapes for various setups covering different precipitation events and environments, by showcasing the hydrologic cycle, and by reproducing common effects such as Foehn winds. We also provide quantitative evaluations creating high-precipitation cumulonimbus clouds by prescribing atmospheric conditions based on infrared satellite observations. With our model we can generate dynamic 3D scenes of weatherscapes with high visual fidelity and even nowcast real weather conditions as simulations by streaming weather data into our framework.

ИСПОЛЬЗОВАНИЕ СПУТНИКОВЫХ ДАННЫХ О КОНВЕКТИВНОЙ ОБЛАЧНОСТИ ДЛЯ АНАЛИЗА ЛЕТНЫХ ПРОИСШЕСТВИЙ И ИХ ПРЕДУПРЕЖДЕНИЯ

Conditions are discussed of three well-known flight accidents in which deep convection has been observed (the crash of aircraft getting into the cloud system of a mesoscale convective complex; another crash in attempt to land in an area of embedded convection at the atmospheric front; ice-crystal icing of engines in an anvil cloud). In all the cases, convective clouds were clearly seen at the satellite images. The accidents could have been possibly avoided if this information, or the nowcasting results which take into account the satellite data, had been available in time to flight controllers and pilots. The state-of-art is analyzed of deep convection forecasting basing on satellite data assimilation into numerical models. A significant advancement is noted in nowcasting and very-short-range forecasting, along with some special problems of model result verification by means of their comparison against the satellite data.

Using Radiative Convective Equilibrium to Explore Clouds and Climate in the Community Atmosphere Model

AbstractCharacteristics of, and fundamental differences between, the radiative‐convective equilibrium (RCE) climate states following the Radiative‐Convective Equilibrium Model Intercomparison Project (RCEMIP) protocols in the Community Atmosphere Model version 5 (CAM5) and version 6 (CAM6) are presented. This paper explores the characteristics of clouds, moisture, precipitation and circulation in the RCE state, as well as the tropical response to surface warming, in CAM5 and CAM6 with different parameterizations. Overall, CAM5 simulates higher precipitation rates that result in larger global average precipitation, despite lower outgoing longwave radiation compared to CAM6. Differences in the structure of clouds, particularly the amount and vertical location of cloud liquid, exist between the CAM versions and can, in part, be related to distinct representations of shallow convection and boundary layer processes. Both CAM5 and CAM6 simulate similar peaks in cloud fraction, relative humidity, and cloud ice, linked to the usage of a similar deep convection parameterization. These anvil clouds rise and decrease in extent in response to surface warming. More generally, extreme precipitation, aggregation of convection, and climate sensitivity increase with warming in both CAM5 and CAM6. This analysis provides a benchmark for future studies that explore clouds, convection, and climate in CAM with the RCEMIP protocols now available in the Community Earth System Model. These results are discussed within the context of realistic climate simulations using CAM5 and CAM6, highlighting the usefulness of a hierarchical modeling approach to understanding model and parameterization sensitivities to inform model development efforts.

Ground-based measurements of microwave brightness temperature and electric field fluctuations for clouds with a different level of electrical activity

Simultaneous measurements of the brightness temperature and short-period electric field fluctuations were carried out to reveal possible connections between the electrification rate and turbulence intensity in clouds. The measurements were conducted in Nizhny Novgorod, Russia (56°19′37″N 44°00′27″E) in 2013 and 2018. The 8 mm radiometer was used to measure the brightness temperature of thermal radiation, and the vertical component of the atmospheric electric field were carried out using an electrostatic fluxmeter. With the use of meteorological data and electric field measurements the state of analyzed events has been classified into 4 types: cloudless atmosphere and high-level clouds (Cs), cumulus clouds (Cu), cumulonimbus clouds without lightning that cause strong electrical field disturbances near the ground surface (Cb), cumulonimbus thunderstorm clouds with lightning discharges (Cb+). Detailed statistical characteristics of brightness temperature fluctuations and short-period electric field fluctuations are obtained for the first time for the indicated types of events.It is shown that measured spectral densities of the atmosphere brightness temperature and electric field fluctuations correspond well enough in the considered frequency range to the results of presented theoretical consideration. Precipitation particles in clouds can be considered herewith as passive scalar, and the movement of inhomogeneities in the particle density can be described by Kolmogorov theory. Since electric charges are located on the precipitation with small droplet and ice particles, an increase in the inhomogeneities of the water content means likely an increase in the inhomogeneities of the electric charge. For thunderclouds the estimates of the relative fluctuations of liquid water content give values of the order of tens of percent. There is a tendency towards a relative increase in brightness temperature fluctuations at high frequencies in the band around f ≈ 10−2 Hz (and possibly higher than fmax ≈ 0.05 Hz) for the sequence of cloud types Cu, Cb, Cb+.

Vertical Structure of Ice Clouds and Vertical Air Motion from Vertically Pointing Cloud Radar Measurements

The vertical structure of ice clouds and vertical air motion (Vair) were investigated using vertically pointing Ka-band cloud radar. The distributions of reflectivity (Z), Doppler velocity (VD), and spectrum width (SW) were analyzed for three ice cloud types, namely, cirrus, anvil, and stratiform clouds. The radar parameters of the cirrus clouds showed narrower distributions than those of the stratiform and anvil clouds. In the vertical structures, the rapid growth of Z and VD occurred in the layer between 8 and 12 km (roughly a layer of −40 °C to −20 °C) for all ice clouds. The prominent feature in the stratiform clouds was an elongated “S” shape in the VD near 7–7.5 km (at approximately −16 °C to −13 °C) due to a significant decrease in an absolute value of VD. The mean terminal fall velocity (Vt) and Vair in the ice clouds were estimated using pre-determined Vt–Z relationships (Vt = aZb) and the observed VD. Although the cirrus clouds demonstrated wide distributions in coefficients a and exponents b depending on cloud heights, they showed a smaller change in Z and Vt values compared to that of the other cloud types. The anvil clouds had a larger exponent than that of the stratiform clouds, indicating that the ice particle density of anvil clouds increases at a faster rate compared with the density of stratiform clouds for the same Z increment. The significant positive Vair appeared at the top of all ice clouds in range up to 0.5 m s−1, and the anvil clouds showed the deepest layer of upward motion. The stratiform and anvil clouds showed a dramatic increase in vertical air motion in the layer of 6–8 km as shown by the rapid decrease of VD. This likely caused increase of supersaturation above. A periodic positive Vair linked with a significant reduction in VD appeared at the height of 7–8 km (approximately −15 °C) dominantly in the stratiform clouds. This layer exhibited a bi-modal power spectrum produced by pre-existing larger ice particles and newly formed numerous smaller ice particles. This result raised a question on the origins of smaller ice particles such as new nucleation due to increased supersaturation by upward motion below or the seeder-feeder effect. In addition, the retrieved Vair with high-resolution data well represented a Kelvin-Helmholtz wave development.