Convective Characteristics and Formation Conditions in an Extreme Rainstorm on the Eastern Edge of the Tibetan Plateau

From 7 July to 11 July 2013, an extreme rainstorm occurred in the Sichuan Basin (SCB) of China, which is located at the eastern edge of the Tibetan Plateau, causing severe floods and huge economic losses. The rainstorm event was associated with mesoscale convection systems (MCSs). In this paper, we analyze the evolution characteristics and formation conditions of the MCSs, and the results show that: (1) the continuous activity of MCSs was a direct cause of the formation of extreme rainstorms. Under an “east high and west low” circulation mode, the MCSs formed a “cloud cluster wave train” phenomenon from the plateau to the basin; that is, the MCSs over the basin developed strongly in the process of the MCSs over the plateau area weakening. (2) The activities of MCSs over the rainstorm area was related to ascending branches of the two vertical circulations and topographic gravity wave. Under the influence of meridional vertical circulation, MCSs could move in the south–north direction in the western SCB, while under the influence of zonal circulation, it was difficult for MCSs to develop in the descending airflow east of 106°E. (3) In the mountainous area of the western part of the SCB, the gravity wave stress was obvious and its direction was opposite to the direction of the lower southeast warm–moist airflow. This configuration was able to form a drag effect in the low-level airflow, which was conducive to the convergence of the wind field and strengthening of the vertical ascending movement. These findings help in further understanding the effects of vertical circulation and terrain on MCSs and extreme rainstorms.

Black sea marine litter pollution related to naval operations

The Black Sea, due to its weak exchange of waters and poor vertical circulation, has an increased sensibility to pollution. Even though this maritime basin is subject to numerous regulations at the national, regional, and international levels, the pollution issue is still actual and stringent. The present paper analyses the findings of three studies focused on marine litter issues and provide, in the concluding part, few directions which can improve the pollution prevention and containment effort. As the studies related to Black Sea litter pollution are scarce and fragmented, the authors took the opportunity and analyzed three different studies conducted in different periods and concluded that a significant part of marine debris is related to naval operations.

1. Watching the tide

The tide is the ocean’s response to the variation in gravitational pull of the Moon and the Sun over the surface of the Earth. ‘Watching the tide’ considers the importance of tides, from tide knowledge for safe navigation of ships in coastal waters to tides as a source of mechanical energy in the form of potential and kinetic energy. Tides also mix the sea, maintaining vertical circulation of the ocean and pumping heat from the tropics to the poles. Tidal rhythms (or harmonics), including diurnal and semi-diurnal tides, are discussed along with tidal range, neap tides, spring tides, and meteorological effects called surges, which can cause serious flooding.

Enhanced Radiation of Near-Inertial Energy by Frontal Vertical Circulations

Near-inertial waves (NIWs) radiate energy out of the mixed layer when they develop small lateral scales. Refraction of these waves by gradients in planetary and vertical vorticity has traditionally been invoked to explain this phenomenon. Here, a new mechanism for the enhancement of NIW radiation is described involving the interaction of NIWs with vertical circulations at fronts undergoing frontogenesis. Frontal vertical circulations drive a Doppler shift that is proportional to the wave’s vertical wavenumber m and that changes sign across a front, inducing large lateral differences in wave phase within a few inertial periods. Theory predicts that the process should generate a vertical energy flux that varies inversely with m in contrast to the m−3 dependence expected from refraction. As a consequence, high-mode NIWs are much more effective at radiating energy when fronts and their vertical circulation are present. Numerical simulations initialized with fronts, an array of eddies that drive frontogenesis, and NIWs of various modes are used to test the theory. In the simulations, the interaction of the NIWs with the frontal vertical circulations generates wave beams that radiate down from the fronts. The resultant downward energy flux varies with m following the theoretical scaling laws. In the beams, the Eulerian frequency is inertial within a few percent, yet the waves’ potential and kinetic energies are comparable, thus indicating a superinertial intrinsic frequency. The downshift in Eulerian frequency from the intrinsic frequency is due to horizontal advection of the waves by the eddies.