Dynamics of tilted atmospheric vortices under asymmetric diabatic heating

Päschke et al. (J Fluid Mech, 2012) studied the nonlinear dynamics of strongly tilted vortices subject to asymmetric diabatic heating by asymptotic methods. They found, inter alia, that an azimuthal Fourier mode 1 heating pattern can intensify or attenuate such a vortex depending on the relative orientation of the tilt and the heating asymmetries. The theory originally addressed the gradient wind regime which, asymptotically speaking, corresponds to vortex Rossby numbers of order unity in the limit. Formally, this restricts the applicability of the theory to rather weak vortices. It is shown below that said theory is, in contrast, uniformly valid for vanishing Coriolis parameter and thus applicable to vortices up to low hurricane strengths. An extended discussion of the asymptotics as regards their physical interpretation and their implications for the overall vortex dynamics is also provided in this context. The paper’s second contribution is a series of three-dimensional numerical simulations examining the effect of different orientations of dipolar diabatic heating on idealized tropical cyclones. Comparisons with numerical solutions of the asymptotic equations yield evidence that supports the original theoretical predictions of Päschke et al. In addition, the influence of asymmetric diabatic heating on the time evolution of the vortex centerline is further analyzed, and a steering mechanism that depends on the orientation of the heating dipole is revealed. Finally, the steering mechanism is traced back to the correlation of dipolar perturbations of potential temperature, induced by the vortex tilt, and vertical velocity, for which diabatic heating not necessarily needs to be responsible, but which may have other origins.

Surface and deep ocean connectivity inferred from robust extraction of coherent sets in ocean flow using models and sparse, scattered, and incomplete float data with transfer operator and dynamic Laplacian methods.

<p>Transport and mixing properties of the ocean's circulation is crucial to dynamical analyses, and often have to be carried out with limited observed information. Finite-time coherent sets are regions of the ocean that minimally mix (in the presence of small diffusion) with the rest of the ocean domain over the finite period of time considered. In the purely advective setting (in the zero diffusion limit) this is equivalent to identifying regions whose boundary interfaces remain small throughout their finite-time evolution. Finite-time coherent sets thus provide a skeleton of distinct regions around which more turbulent flow occurs. Well known manifestations of finite-time coherent sets in geophysical systems include rotational objects like ocean eddies, ocean gyres, and atmospheric vortices. In real-world settings, often observational data is scattered and sparse, which makes the difficult problem of coherent set identification and tracking challenging. I will describe mesh-based numerical methods [3] to efficiently approximate the recently defined dynamic Laplace operator [1,2], and rapidly and reliably extract finite-time coherent sets from models or scattered, possibly sparse, and possibly incomplete observed data. From these results we can infer new chemical and physical ocean connectivities at global and intra-basin scales (at the surface and at depth), track series of eddies, and determine new oceanic barriers.</p><p>[1] G. Froyland. Dynamic isoperimetry and the geometry of Lagrangian coherent structures. <em>Nonlinearity</em>, 28:3587-3622, 2015</p><p>[2] G. Froyland and E. Kwok. A dynamic Laplacian for identifying Lagrangian coherent structures on weighted Riemannian manifolds. <em>Journal of Nonlinear Science</em>, 30:1889–1971, 2020.</p><p>[3] Gary Froyland and Oliver Junge. Robust FEM-based extraction of finite-time coherent sets using scattered, sparse, and incomplete trajectories. <em>SIAM J. Applied Dynamical Systems</em>, 17:1891–1924, 2018.</p>

Tracking of mesoscale atmospheric phenomena in satellite mosaics using deep neural networks

<p>Polar Lows (PLs) are intense atmospheric vortices that form mostly over the ocean. Due to their strong impact on the deep ocean convection and also on engineering infrastructure, their accurate detection and tracking is a very important task that is demanded by industrial end-users as well as academic researchers of various fields. While there are a few PL detection algorithms, there are no examples of successful automatic PL tracking methods that would be applicable to satellite mosaics or other data, which would as reliably represent PLs as remote sensing products. The only reliable way for the tracking of PLs at the moment is the manual tracking which is highly time-consuming and requires exhaustive examination of source data by an expert.</p><p>At the same time, visual object tracking (VOT) is a well-known problem in computer vision. In our study, we present the novel method for the tracking of PLs in satellite mosaics based upon Deep Convolutional Neural Networks (DCNNs) of a specific architecture. Using the Southern Ocean Mesocyclones database gathered in the Shirshov Institute of Oceanology, we trained our model to perform the assignment task, which is an essential part of our tracking algorithm. As a proof of concept, we will present preliminary results of our approach for PL tracking for the summer period of 2004 in the Southern Ocean.</p>

Influence of Cosmic Ray Invasions and Aerosol Plasma on Powerful Atmospheric Vortices

The Earth’s atmosphere is affected by various ionizing sources. The maximum ionization of atmospheric particles by cosmic rays corresponds to the altitude of formation of tropospheric clouds. In the high-latitude troposphere for the region of the geomagnetic polar cap, in the winter period, the excitation of local cyclonic structures are observed which are accompanied with ice storms, with invasions into middle and subtropical latitudes. The time of excitation of such cyclones is about a day that is comparable with the time of excitation of tornadoes, which are generated at low latitudes. Localization of polar cyclones is not accidental. The region of the polar cap is connected with geomagnetic field lines extended into the tail of the Earth’s magnetosphere. This area is open for the penetration of cosmic rays. The ionization of aerosols in the stratosphere and the upper troposphere by precipitating particles of cosmic rays enhances the vortex activity of the atmosphere. The important role of the aerosol impurity is manifested in the generation of plasma vortices and in the accumulation of energy and mass in the atmosphere by vortices during condensation of moisture. Due to the cascade character of the ionization process, the influence of cosmic radiation turns out to be non-linear and increases with increasing pollution of the atmosphere. Aperiodic electrostatic perturbations, which play a remarkable role in the genesis of vortices, are stochastically excited in plasma inhomogeneities. During the interaction of plasma vortices and Rossby vortices, a large-scale vortex structure is formed and grows.

Analysis of the conditions for the occurrence of "the voice of the sea" using infrasound observations in marine waters

We study the conditions for the occurrence of "the voice of the sea" in the infrasound range can occur and determine its parameters from infrasound measurements in the Black Sea water area conducted in 2011 and 2016 and in the water area of the Sea of Okhotsk in 2017. To this end, we compared the observations of different parameters (mean correlation, spectra of acoustic arrivals, direction and phase velocity) of the high-frequency infrasound (1–10 Hz), recorded in Katsiveli (Crimea) in 2011 and 2016. We performed a detailed study of the wind conditions in the Black Sea water area during the measurement period, as well as the conditions for the propagation of acoustic waves along the direction of their arrivals. In both cases the atmospheric vortices in the direction of the arrival of infrasound were detected, which caused changes in wind velocity vector above the sea surface. The infrasound recorded in 2011 was caused by the interaction of two differently rotating atmospheric vortices over the sea. In 2016, a vortex was observed to the West from the registration point. The possibility of generating "the voice of the sea" due to the rotation of the wind velocity, which causes a nonlinear interaction of surface waves propagating in opposite directions to each other, and the formation of their 2nd harmonic in the form of a standing surface wave is discussed. From the analysis of the wind speed and wind direction profiles along the infrasound arrival path, as well as the acoustic pressure fields calculated by the parabolic equation method for the effective sound speed profiles in the direction of infrasound propagation, the most probable areas of infrasound generation were determined. In both cases these areas coincided with the zones in which the wind speed drops to zero, and the direction of the wind changes to the opposite. An example of simultaneous detection from one direction of the microbaroms with frequencies 0.2–0.3 Hz and "the voice of the sea" with a higher frequency of 5.5 Hz is given.

Decline and poleward shift in Indian summer monsoon synoptic activity in a warming climate

Cyclonic atmospheric vortices of varying intensity, collectively known as low-pressure systems (LPS), travel northwest across central India and produce more than half of the precipitation received by that fertile region and its ∼600 million inhabitants. Yet, future changes in LPS activity are poorly understood, due in part to inadequate representation of these storms in current climate models. Using a high-resolution atmospheric general circulation model that realistically simulates the genesis distribution of LPS, here we show that Indian monsoon LPS activity declines about 45% by the late 21st century in simulations of a business-as-usual emission scenario. The distribution of LPS genesis shifts poleward as it weakens, with oceanic genesis decreasing by ∼60% and continental genesis increasing by ∼10%; over land the increase in storm counts is accompanied by a shift toward lower storm wind speeds. The weakening and poleward shift of the genesis distribution in a warmer climate are confirmed and attributed, via a statistical model, to the reduction and poleward shift of low-level absolute vorticity over the monsoon region, which in turn are robust features of most coupled model projections. The poleward shift in LPS activity results in an increased frequency of extreme precipitation events over northern India.