Influence of Summer Monsoon on Asymmetric Bimodal Pattern of Tropical Cyclogenesis Frequency over the Bay of Bengal

The influence of summer monsoon on tropical cyclone (TC) genesis over the Bay of Bengal (BoB) is explored using an empirical genesis potential (GP) index. The annual cycle of cyclogenesis frequency over the BoB shows an asymmetric bimodal pattern with the maximum genesis number appearing in late October and the second largest in early May. The two peaks correspond to the withdrawal and onset of the BoB summer monsoon, respectively. The semimonthly GP index calculated without TC days over the BoB is consistent with TC genesis frequency, indicating that the index captures the monsoon-induced changes in the environment that are responsible for the seasonal variation of TC genesis frequency. Of the four environmental variables (i.e., low-level vorticity, mid-level relative humidity, potential intensity, and vertical wind shear) that enter into the GP index, the potential intensity makes the largest contribution to the bimodal distribution, followed by vertical wind shear due to small wind speed during the summer monsoon onset and withdrawal. The difference in TC genesis frequency between autumn and late spring is mainly owing to the relative humid-ity difference because a divergence (convergence) of horizontal moisture flux associated with cold dry northerlies (warm wet wester-lies) dominates the BoB in late spring (autumn).

Control of Asymmetric Flow Fields of Slender Bodies at High Angle of Attack

The wind tunnel experiments is conducted to get inspiration for understanding the mechanism of the asymmetric flow pattern and developing an innovative flow control technique for a slender body at high angle of attack. The bi-stable situation of the side forces is observed, which could be easily switched by a tiny disturbances either from coming flow or from artificial disturbances at nose tip （including manufacturing defect）. In turbulent flows the side forces switched randomly between positive and negative. There exists a hysteresis loop of side force with the rolling angle. A rod in front of the slender body is used to change the vortex pattern, which could be kept even the rod is moved out from the stream. A miniature strake attached to the nose tip of the model can be moved to different circumferential position. When the strake is stationary, the hysteresis loop disappears and the side force does not change with the turbulent fluctuation of coming flow. The results from dynamic measurements of section side force indicates that when the strake swung at lower frequency the side force can follow the cadence of the swinging strake. With increasing frequency, the magnitude of the side force decreases. At still high frequency, the side force diminishes to zero. If the strake is swinging, while the middle position can be changed to different circumferential angle Фs on either left or right side, the side forces can be changed proportionally with the angle Фs. On the basis of the experimental results, the mechanism of the asymmetry is discussed.

Zonally Asymmetric Temperature Trends near the Northern Middle and High Latitude Stratopause during Winter

The temperature trend near the stratopause is rarely evaluated owing to the limited long-term observations of global temperature. In this study, the spatial patterns of the temperature trends near the northern stratopause are investigated by using satellite and reanalysis datasets. Our analysis reveals a zonally asymmetric temperature trend pattern near the northern mid-to-high latitude stratopause during January, and this pattern underwent an evident transition around the 2000s. From 1980 to 2003, there was a cooling trend in the Western Hemisphere and a warming trend in the Eastern Hemisphere. In contrast, a reversed zonally asymmetric temperature trend pattern existed in the east–west direction from 2003 to 2020. Although the warming trends are statistically insignificant, they contrasted with the overall cooling trend in the upper stratosphere due to ozone depletion and an increase in well-mixed greenhouse gases in recent decades. The zonally asymmetric temperature trends were induced by the transition in the intensity of quasi-stationary planetary wavenumber 1(wave 1) near the stratopause. The increasing(decreasing) trend of the intensity of wave 1 enhanced(weakened) its meridional temperature advection near the stratopause before(after) the 2000s;consequently, a zonally asymmetric temperature trend pattern exists in the east–west direction near the stratopause. The transition in the intensity of the stratospheric wave 1 around the 2000s is most likely caused by the transition in the intensity of wave 1 activity in the troposphere.

Synchronization and bursting transition of the coupled Hindmarsh-Rose systems with asymmetrical time-delays

The study of synchronization and bursting transition is very important and valuable in cognitive activities and action control of brain as well as enhancement for the reliability of the cortex synapses. However, we wonder how the synaptic strength and synaptic delay, especially the asymmetrical time-delays between different neurons can collectively influence their synchronous firing behaviors. In this paper, based on the Hindmarsh-Rose neuronal systems with asymmetrical time-delays, we investigate the collective effects of various delays and coupling strengths on the synchronization and bursting transition. It is shown that the interplay between delay and coupling strength can not only enhance or destroy the synchronizations but also can induce the regular transitions of bursting firing patterns. Specifically, as the coupling strength or time-delay increasing, the firing patterns of the time-delayed coupling neuronal systems consistently present a regular transition, that is, the periods of spikes during the bursting firings increase firstly and then decrease slowly. In particular, in contrast to the case of symmetrical time-delays,asymmetrical time-delays can lead to the paroxysmal synchronizations of coupling neuronal systems, as well as the concentration level of synchronization for the non-identically coupled system is superior to the one of identical coupling. These results more comprehensively reveal the rich nonlinear dynamical behaviors of neuronal systems and may be helpful for us to have a better understanding of the neural coding.