Cyclonic Vorticity Research Articles

Evolution of the Mid-tropospheric Vortex during the Formation of Super Typhoon Megi (2010)

As a follow-up of a previously published article on the contribution of tropical waves, this study explores the evolution of the mid-tropospheric mesoscale cyclonic vortex (MV) during the formation of Typhoon Megi (2010) with a successful cloud-resolving simulation. It is found that the formation and intensification of the MV were related to the deep convection and subsequent stratiform precipitation, while the weakening of the MV was related to the shallow convection. Both the upward transport of vorticity related to the deep convection and the horizontal convergence associated with the stratiform precipitation contributed to the formation and intensification of the MV. Even though the latter was dominant, the former could not be ignored, especially in the early stage of the MV. The MV played dual roles in the formation of Megi. On the one hand, the formation and intensification of MV were primarily associated with the stratiform precipitation, which induced the low-level divergence inhibiting the spin-up of the near-surface cyclonic circulation. On the other hand, the coupled low-level cold core under the MV benefited the accumulation of the convective available potential energy (CAPE), which was favorable for the convective activity. A sensitivity experiment with the evaporative cooling turned off indicated that the development of the MV retarded the genesis process of Megi.

Reexamination of the Climatology and Variability of the Northwest Pacific Monsoon Trough Using a Daily Index

AbstractThis study developed a daily index to represent the northwest Pacific monsoon trough using westerly related cyclonic vorticity after removing tropical cyclones (TCs) from the reanalysis dataset. This index sufficiently captures the spatial and temporal variations in the monsoon trough. The use of this daily index revealed new features in the monsoon trough, including daily statistical characteristics, the active period over a year, and the main periodicity. A monsoon trough can be identified as active when the daily index is greater than 2.0 × 10−4 s−1. Active monsoon troughs occur during half of the summertime, and these is no monsoon trough on one-third of days, with the remaining days categorized as inactive. The most active month is August, in which approximately 20 days exhibit an active monsoon trough. Using this index, an active monsoon trough period, which is related to vigorous TC activity, was determined by identifying the establishment and decay dates for each year from 1979 to 2016. During most years, the active monsoon trough is established in mid-July and decays in late October, persisting for 3–5 months during the boreal summer. Moreover, spectral and wavelet analyses demonstrated the presence of intraseasonal, interannual, and interdecadal variabilities in the monsoon trough. The dominant periodicity for the interannual variability varied from 1.5 to 4 years in different decades. The relationship between the monsoon trough and TCs is also revealed using this index, showing that approximately 60% of TC formations were related to an active monsoon trough.

Balanced ellipsoidal vortex at finite Rossby number

ABSTRACT Here we examine the motion of an isolated ellipsoidal vortex in a rotating stratified fluid. We derive an analytical solution to a set of balanced equations at the next order to quasi-geostrophic theory, providing insights into geophysical vortices at finite Rossby number ε. This is achieved through the solution of a set of complicated Poisson equations. Though complicated, the analytical solution give rise to a velocity field that depends linearly on the spatial coordinates inside the vortex, and, thus preserves the ellipsoidal form. From this general solution, we determine a number of equilibria where the vortex rotates steadily about the vertical axis and examine their stability. At the next order to QG, one finds asymmetry in the behaviour of cyclonic and anti-cyclonic vortices, with anti-cyclonic vortices rotating faster and generally more unstable than cyclonic vortices.

Lagrangian Analysis of Tropical Cyclone Genesis Simulated by General Circulation Models Compared with Observations

AbstractAs a contribution to understanding the genesis of tropical cyclones (TCs), we compared TC genesis processes simulated by the Seoul National University Atmosphere Model version 0 with a Unified Convection Scheme (SAM0) and the Community Atmosphere Model version 5 (CAM5) with those from the ERA-Interim reanalysis (ERA-Interim, hereafter ERAI) and best track observations. In contrast to previous studies that estimated the TC genesis potential using the Eulerian mean environmental conditions, we calculated the probability of a pre-existing weak cyclonic embryo vortex (EV) developing into a TC by analyzing changes in the environmental conditions along the EV trajectories. Our analysis indicates that the spatial distribution and annual cycles of TCs obtained from the SAM0 and ERAI are similar to those obtained from the best track observation data. With the exception of the mesoscale convective organization and associated variables, most environmental variables along the trajectories of DEVs (EVs developing into TCs) showed monotonic variations. When EVs were born, environmental conditions of DEVs were significantly different from those of nondeveloping EVs, allowing for the prediction of TC genesis. In general, TC genesis probability increased as the environment became more cyclonic, moist, unstable, and with a weaker wind shear. Rapidly strengthening EVs were more likely to develop into TCs. SAM0 and ERAI have the same combination of environmental variables with the best prediction skill for TC genesis—absolute vorticity at 850 hPa, column saturation deficit, sea surface temperature, vertical shear of horizontal winds between 200 and 850 hPa, and latitude—with similar sensitivities to individual environmental variables, indicating that SAM0 well simulates the observed TC genesis processes.

Barotropic vorticity balance of the North Atlantic subpolar gyre in an eddy-resolving model

Abstract. The circulation in the North Atlantic subpolar gyre is complex and strongly influenced by the topography. The gyre dynamics are traditionally understood as the result of a topographic Sverdrup balance, which corresponds to a first-order balance between the planetary vorticity advection, the bottom pressure torque, and the wind stress curl. However, these dynamics have been studied mostly with non-eddy-resolving models and a crude representation of the bottom topography. Here we revisit the barotropic vorticity balance of the North Atlantic subpolar gyre using a new eddy-resolving simulation (with a grid space of ≈2 km) with topography-following vertical coordinates to better represent the mesoscale turbulence and flow–topography interactions. Our findings highlight that, locally, there is a first-order balance between the bottom pressure torque and the nonlinear terms, albeit with a high degree of cancellation between them. However, balances integrated over different regions of the gyre – shelf, slope, and interior – still highlight the important role played by nonlinearities and bottom drag curls. In particular, the Sverdrup balance cannot describe the dynamics in the interior of the gyre. The main sources of cyclonic vorticity are nonlinear terms due to eddies generated along eastern boundary currents and time-mean nonlinear terms in the northwest corner. Our results suggest that a good representation of the mesoscale activity and a good positioning of mean currents are two important conditions for a better representation of the circulation in the North Atlantic subpolar gyre.

Southern hemisphere circulation anomalies and impacts over subtropical South America due to different El Niño flavours

AbstractEl Niño–Southern Oscillation (ENSO) exhibits different flavours with worldwide impacts. However, the associated teleconnections with subtropical South America (SSA) are still controversial and modelling studies are needed. Here, we analyse the Southern Hemisphere (SH) circulation anomalies and the impacts over SSA during the austral summer due to different El Niño patterns (Canonical and El Niño Modoki). The analysis is performed considering reanalysis data and two different Atmospheric General Circulation Models (SPEEDY and UCLA–AGCM). Results from reanalysis show that positive precipitation anomalies develop over SSA during Canonical El Niño events. These anomalies are induced through an increase of upper‐level cyclonic vorticity advection and a stronger low‐level southward moisture transport. However, in El Niño Modoki events, rainfall anomalies are observed over SSA only for the strongest events. Both models are able to reproduce the precipitation signal over SSA in the Canonical El Niño case, although the underlying physical mechanism depends on the model. In SPEEDY, the increased rainfall is due to an increase of the moisture transport toward SSA, while in UCLA–AGCM it is related to both, an increase of the low‐level moisture transport toward SSA and the increase of upper‐level cyclonic vorticity advection. The precipitation signal associated with El Niño Modoki is more controversial. While UCLA–AGCM suggests a rainfall increase over SSA, SPEEDY, in agreement with observations, does not show any statistically significant signal. However, the upper‐level circulation anomalies reproduced by UCLA–AGCM are more consistent with reanalysis than those from SPEEDY, which makes UCLA–AGCM to be more reliable. This result suggests increased rainfall over SSA during El Niño Modoki.

The influence of nonlinearities and different SST spatial patterns on the summertime anomalies in subtropical South America during strong ENSO events

In this study we analyze the impacts of the strongest ENSO events on subtropical South America (SSA) rainfall during the austral summer in the period (1979–2014). We consider reanalysis data and model experiments. For the strongest El Nino events, the precipitation pattern over SSA presents a monopole structure. The reanalysis shows a short Rossby wave train that causes an increase of the baroclinicity and advection of cyclonic vorticity toward SSA. Together with an increase in the moisture transport by the South American Low Level jet (SALLJ), they induce strong positive precipitation anomalies over SSA. The model reproduces this rainfall anomaly as consequence of a strengthening of the upper level jet and of the SALLJ, although it does not simulate the short wave train from the Pacific. For the strongest La Nina events, the precipitation pattern presents a tripole like-structure with centers located over: (1) Uruguay, (2) the continental part of the South Atlantic Convergence Zone (C-SACZ) and (3) the northwestern Argentina (NW-Arg). In both cases, reanalysis and model experiments, the tripole is associated with a weakening of the SALLJ that increases (reduces) rainfall anomalies over C-SACZ (Uruguay), and with an anomalous increase of the lower level moisture convergence over NW-Arg that increases precipitation over there. Differences in precipitation responses to the strongest ENSO events are mainly associated to changes in the spatial pattern of the sea surface temperature anomalies, however, there is also a contribution of nonlinearities.

STUDY ON SENSITIVITY OF WIND FIELD VARIATION TO STRUCTURE AND DEVELOPMENT OF CONVECTIVE STORMS

In order to study the impacts of wind field variations in the middle and lower troposphere on the development and structure of storms, we carried out numerical experiments on cases of severe convection in the Jianghuai area under the background of cold vortex on April 28, 2015. The results show that the structure and development of convective storms are highly sensitive to the changes of wind fields, and the adjustment of wind fields in the middle or lower troposphere will lead to significant changes in the development and structure of storms. When the wind field in the middle or lower troposphere is weakened, the development of convective storms attenuates to some extent compared with that in the control experiment, and the ways of attenuation in the two experiments are different. In the attenuation test of wind field at the middle level, convective storms obviously weaken at all stages in its development, while for the wind field at the low level, the convective storms weaken only in the initial stage of storm. On the contrary, the enhancement of the wind field in the middle or lower troposphere is conducive to the development of convection, especially the enhancement in the middle troposphere. In contrast, the convective storms develop rapidly in this test, as the most intensive one. The wind field variations have significant impacts on the structure and organization of the storm. The enhancement of wind field in the middle troposphere facilitates the intension of the middle-level rotation in convective storm, the reduction of the storm scale, and the organized evolution of convective storms. The strengthening of the wind field in the lower troposphere is conducive to the development of the low-level secondary circulation of the storm and the cyclonic vorticity at the middle and low levels on the inflowing side of the storms.

Automated Detection Algorithm for SACZ, Oceanic SACZ, and Their Climatological Features

The South Atlantic Convergence Zone (SACZ) is responsible for a large amount of the total summer precipitation over Brazil and is related with severe droughts and extreme floods over the southeast of Brazil. This paper aims to demonstrate the feasibility of an objective, simplified and automated method based on satellite outgoing longwave radiation (OLR) for SACZ and oceanic SACZ (SACZOCN) detection to characterize their climatological features. SACZ dates and characteristics (intensity and size) detected by an automated algorithm have been made available for the first time in the literature. The method accurately detected 77% of SACZ occurrences compared with 21 years of SACZ observations. The temporal criterion of permanency of the SACZ convective activity for at least four days was essential to differentiate the SACZ from the transient frontal systems over the Brazilian Southeast. About 30% of the SACZ days occurred in November and March, therefore the December to February period is not sufficient to represent its activity. A barotropic through near the Uruguay coast determines the intensity and position of the coastal and oceanic SACZ portions. When this trough closes into a cyclonic vortex Southwest of the SACZ cloud band it characterizes an oceanic SACZ episode. SACZOCN episodes were objectively identified for the first time in the literature, being characterized by a more intense and northward displaced convective activity. We show that some oceanic SACZ episodes are associated with extreme floods and severe droughts over Brazil, therefore its identification is extremely important to the Brazilian society. In addition, oceanic surface currents and temperature over the Southwestern Atlantic Ocean are modified during the SACZOCN active phase. The method presented here is a viable alternative to objectively classify SACZ and SACZOCN episodes, it can be implemented operationally and used to SACZ studies in the context of climate change.

The Importance of Horizontal Rolls in the Rapid Intensification of Tropical Cyclones

The present laboratory study is focused on the role of convective rolls in the enhancement of the heat flux from the sea and triggering of the process of rapid intensification of tropical cyclones. The appearance of coherent convective structures such as thermals and rolls is registered by different optical techniques and temperature measurements. Two-dimensional velocity fields are used for the investigation of the structure and characteristics of the flow. The heat flux from the heating plate to the fluid is measured directly. Obtained results clearly show that rapid intensification of a laboratory analog of a tropical cyclone is tightly linked with the heat transfer process in the boundary layer. Formation of secondary convective structures strongly increases the heat transfer and intensity of convective circulations. The intensity of radial inflow is a crucial aspect for the intensification of cyclonic vortex, hence rapid variation of the heat transfer is a factor that has a substantial influence on the dynamics of a laboratory vortex. Time series of maximal radial and azimuthal velocities are in a good qualitative agreement with those from a theoretical model. It is shown that the mean square of the velocity depends linearly on the temperature difference between the inflow and the heating surface.

Classification of Intense Rainfall Days in Southern West Africa and Associated Atmospheric Circulation

Daily rainfall in southern West Africa (4–8° N, 7° W–3° E) is analyzed with the aim of documenting the intense rainfall events which occur in coastal Ivory Coast, Ghana, Togo, and Benin. The daily 99th percentile (P99) shows that the coastline experiences higher intensity rainfall than inland areas. Using Tropical Rainfall Measuring Mission (TRMM) rainfall data for 1998–2014, a novel way of classifying the intense events is proposed. We consider their space-time structure over a window of 8° latitude-longitude and five days centered on the event. A total 39,680 events (62 at each location) are classified into three major types, mainly found over the oceanic regions south of 5° N, the Bight of Benin, and the inland regions respectively. These types display quite distinct rainfall patterns, propagation features, and seasonal occurrence. Three inland subtypes are also defined. The atmospheric circulation anomalies associated with each type are examined from ERA-interim reanalysis data. Intense rainfall events over the continent are mainly a result of westward propagating disturbances. Over the Gulf of Guinea, many intense events occur as a combination of atmospheric disturbances propagating westward (mid-tropospheric easterly waves or cyclonic vortices) and eastward (lower tropospheric zonal wind and moisture anomalies hypothesized to reflect Kelvin waves). Along the coast, there is a mixture of different types of rainfall events, often associated with interacting eastward- and westward-moving disturbances, which complicates the monitoring of heavy precipitation.

Strengthened Connection between Springtime North Atlantic Oscillation and North Atlantic Tripole SST Pattern since the Late 1980s

AbstractThis study reveals a marked enhancement in the relationship between the North Atlantic Oscillation (NAO) and North Atlantic tripole (NAT) sea surface temperature (SST) anomaly pattern during boreal spring since the late 1980s. A comparative analysis is conducted for two periods before and after the late 1980s to understand the reasons for the above interdecadal change. During both periods, SST cooling in the northern tropical Atlantic during the positive phase of the NAT SST pattern results in an anomalous anticyclone over the subtropical western North Atlantic via a Rossby wave–type atmospheric response. The westerly wind anomalies along the north flank of the anomalous anticyclone are accompanied by a marked decrease in synoptic-scale eddies over the midlatitudes as well as cyclonic (anticyclonic) vorticity forcings at the north (south) side. As such, an NAO-like dipole atmospheric anomaly is induced over the North Atlantic, which in turn helps to maintain the NAT SST anomaly via modulating surface heat fluxes. The intensity of the synoptic-scale eddy feedback to mean flow is stronger after than before the late 1980s, which is related to interdecadal increase in the intensity of North Atlantic synoptic-scale eddies. This is followed by a stronger NAO-like atmospheric response to the NAT SST anomaly since the late 1980s. Further analysis shows that changes in the spatial structure of the spring NAO may also partly contribute to changes in the spring NAO–NAT SST connection around the late 1980s. In particular, spring NAO-related atmospheric anomalies are weaker and shift northward before the late 1980s, which reduces the contribution of the NAO to a tripole SST anomaly pattern in the North Atlantic.

Collective effects in a dusty plasma with a magnetic field irradiated by hard radiation

The transfer coefficients of a rarefied low-temperature plasma (hereinafter referred to as LTP) with a condensed dispersed phase (hereinafter referred to as CDF) were calculated for characteristic temperatures T = 50 – 100 K in weak external magnetic fields (B = 10–6 – 1 Gauss). These effects of irradiation of LTP CDF plasma with X-ray and γ-ray fluxes, highenergy charged particles (electrons, positrons, protons and α-particles) are shown. For systems of positively charged monodisperse nanoparticles, new frequencies of collective MHD oscillations are determined. Significant physical differences between such interacting systems and their influence on the redistribution between the kinetic energy of particle flows and (also the energy of incident quanta of hard radiation) to magnetic and vice versa are shown. In this regard, the degree of dissipative scattering of energy entering the system is relevant for the interpretation of experimental spectroscopic data on scattering. The effects of such scattering are considered on specific examples. By its nature, the first type of scattering of the energy entering the physical systems under consideration consists in local energy losses due to pair interactions with atoms, molecules, and CDF of the medium. The second type of interactions considered is the scattering of charged particle flows and turbulent (like cyclonic vortices) LTP structures with CDF located in an external magnetic field. Comparison of these two mechanisms of dissipative losses shows their comparability.For the physical systems considered above, the transfer coefficients we are received. The relaxation times–τand gyrofrequencies– ω for a two-component electron gas during its interaction with CDF and ions of atoms and molecules in an external magnetic field are shown.For this multicomponent plasma, based on the Braginsky criteria (ωτ≫1, or ωτ≪1), for applying the previously obtained relations for the transfer coefficients between various plasma components are shown. It was found that the thermal, low-energy electronic component of the LTP is responsible for the recombination of atomic ions and the discharge of CDFs. The high-energy electrons Auger component leads to large temperature gradients and, as a consequence, significant heat fluxes. In turn, it has been shown that large temperature gradients cause significant currents of the charged component of NTP (electrons, atomic and molecular ions, CDF). It is shown that, in turn, the plasma generates local magnetic fields. The magnetic Reynolds number ea ≫ 1who was calculated in this work are shown that the plasma becomes turbulent. The main conclusion of the work is the proof that a charged monodisperse ultra-low density CDF in the field of hard radiation and an external magnetic field is almost always turbulent.

Flow structures and kinetic-potential exchange in forced rotating stratified turbulence

Flow structures and the kinetic-potential energy exchange in rotating stratified turbulence are studied by simulations. Differences of cyclonic and anticyclonic vortices are shown. The intense kinetic-potential energy exchange is found to be associated with the cyclonic structures.

Formation of a kind of heavy‐precipitation‐producing mesoscale vortex around the Sichuan Basin: An along‐track vorticity budget analysis

AbstractThis study investigates the formation of a type of mesoscale vortex around the Sichuan Basin (i.e., the southwest vortex [SWV]) that usually induces heavy precipitation, based on a semi‐idealized simulation of eight similar SWV‐formation events. After producing a reasonable SWV that shares salient features with the events used in composite, a trajectory analysis is conducted and an along‐track vorticity budget is constructed. The results show that approximately 64.7% of the air particles related to SWV formation originate from four source regions outside the vortex. The largest contribution of cyclonic vorticity associated with the SWV formation (approximately 67.7%) comes from the lower levels southwest of the vortex and is due mainly to tilting. The second‐largest contribution (approximately 19.4%) is made by air particles that originate from the upper levels south of the SWV and is also due mainly to tilting. By contrast, for the other two sources (the upper levels west and southwest of the vortex), the convergence‐related horizontal shrinking generally dominates their cyclonic‐vorticity production. Overall, along the tracks of the air particles, vertical motions and water‐vapor phase transitions affect the vorticity variation significantly via modulating divergence‐related vorticity production/dissipation (i.e., the stretching effect), and this is vital for the SWV formation.

An idealized numerical study of tropical cyclogenesis and evolution at the Equator

AbstractTropical cyclone formation and evolution at, or near, the Equator is explored using idealized three‐dimensional model simulations, starting from a prescribed, initial, weak counterclockwise rotating vortex in an otherwise quiescent, nonrotating environment. Three simulations are carried out in which the maximum tangential wind speed (5 m s) is specified at an initial radius of 50, 100, or 150 km. After a period of gestation lasting between 30 and 60 hr, the vortices intensify rapidly, the evolution being similar to that for vortices away from the Equator. In particular, the larger the initial vortex size, the longer the gestation period, the larger the maximum intensity attained, and the longer the vortex lifetime. Beyond a few days, the vortices decay as the cyclonic vorticity source provided by the initial vortex is depleted and negative vorticity surrounding the vortex core is drawn inwards by the convectively driven overturning circulation. In these negative vorticity regions, the flow is inertially/centrifugally unstable. The vortex evolution during the mature and decay phases differs from that in simulations away from the Equator, where inertially unstable regions are much more limited in area. Vortex decay in the simulations appears to be related intimately to the development of inertial instability, which is accompanied by an outward‐propagating band of deep convection. The degree to which this band of deep convection is realistic is unknown.

Deep Learning Algorithm for Satellite Imaging Based Cyclone Detection

Satellite images are primary data in weather prediction modeling. Deep learning-based approach, a viable candidate for automatic image processing, requires large sets of annotated data with diverse characteristics for training purposes. Accuracy of weather prediction improves with data having a relatively dense temporal resolution. We have employed interpolation and data augmentation techniques for enhancement of the temporal resolution and diversifications of characters in a given dataset. Algorithm requires classical approaches during preprocessing steps. Three optical flow methods using 14 different constraint optimization techniques and five error estimates are tested here. The artificially enriched data (optimal combination from the previous exercise) are used as a training set for a convolutional neural network to classify images in terms of storm or nonstorm. Several cyclone data (eight cyclone datasets of a different class) were used for training. A deep learning model is trained and tested with artificially densified and classified storm data for cyclone classification and locating the cyclone vortex giving minimum 90% and 84% accuracy, respectively. In the final step, we show that the linear regression method can be used for predicting the path.

Predicting the submesoscale circulation inshore of the East Australian Current

Abstract Submesoscale flows dominate the vertical transport in the upper ocean and play an important role in air-sea fluxes, the distribution of nutrients and biota, the connectivity of populations. Yet submesoscale predictability is a new frontier and presents additional challenges to that of mesoscale flows. This study assesses the capacity of an operational system to predict the circulation along the landward edge of the East Australian Current where the cyclonic band of vorticity allows small scale instabilities to grow. We use a downscaling approach in which a fine-scale resolution (750–1000 m) coastal model is one-way nested within a coarser resolution (2.5–6 km) mesoscale eddy-resolving regional model that assimilates all available data, including coastal high-frequency radar radial velocities. Assimilation of the surface radial velocities into the regional model provides improved representation of the cyclonic band inshore of the current, however forecasts at this resolution perform poorly in representing this cyclonic vorticity. Downscaling to the higher resolution coastal model produces a sharper across-current vorticity gradient within the EAC and leads in turn to more intense submesoscale features growing on its inshore side. Boundary forcing error from the regional model propagates into the nested coastal model. The results motivate improved representation of fine-scale flows in regional forecasts for downscaling purposes.

Upwellings and water circulation of the north-western shelf of the Black Sea in the summer of 2017

On the basis of satellite and field atmospheric and marine observations, the water circulation processes of the north-western shelf (the NWS) of the Black Sea in the summer of 2017 were studied. The study indicated high stability of summer offshore winds of northern and north-northwest directions and 12 cases of coastal upwelling. Three cases of upwelling were instrumentally detected on the across-the-shore oceanographic sections during seasonal field works performed by the oceanographic unit of the branch “Odesa Area of State Hydrographic Service” of the state institution "State Hydrographic Service of Ukraine (SHSU)". The increase of coastal water density led to an abnormally active transfer along the coast of the Danube-Dniester interfluve area to the northernmost parts of the NWS. In 2017 a visual manifestation of anticyclonic character of summer circulation of the NWS's water could be observed. The obtained data confirm the previous conclusions on frequent cases of change in summer periods of traditional cyclonic water circulation to the anticyclonic one.
 The abnormal development of the summer circulation regime allowed us to record for the first time the transfer of coccolithophores phytoplankton from the open sea to the northern regions of the NWS and to reveal its intraseasonal spatial transformation and development process duration.
 In the seaward part of the Gulf of Odessa a frequently repeated vortex formation of cyclonic vorticity with spatial dimensions of up to 7-8 miles and orbital velocities, according to the presented data, of 0.12–0.18 m.c-1, and according to the latest field work, of over 0.30 m.c-1, was found.
 When analyzing the considered situations associated with transfer and vorticity of sea water a significant role was played by high-resolution visual images obtained from Sentinel-2 and Landsat-8 satellites having a spatial resolution of 10 and 30 meters respectively, as well as by similar satellites of earlier modifications.

Generation of a large-scale vorticity in a fast-rotating density-stratified turbulence or turbulent convection.

We find an instability resulting in generation of large-scale vorticity in a fast-rotating small-scale turbulence or turbulent convection with inhomogeneous fluid density along the rotational axis in anelastic approximation. The large-scale instability causes excitation of two modes: (i) the mode with dominant vertical vorticity and with the mean velocity being independent of the vertical coordinate; (ii) the mode with dominant horizontal vorticity and with the mean momentum being independent of the vertical coordinate. The mode with the dominant vertical vorticity can be excited in a fast-rotating density-stratified hydrodynamic turbulence or turbulent convection. For this mode, the mean entropy is depleted inside the cyclonic vortices, while it is enhanced inside the anticyclonic vortices. The mode with the dominant horizontal vorticity can be excited only in a fast-rotating density-stratified turbulent convection. The developed theory may be relevant for explanation of an origin of large spots observed as immense storms in great planets, e.g., the Great Red Spot in Jupiter and large spots in Saturn. It may be also useful for explanation of an origin of high-latitude spots in rapidly rotating late-type stars.