Search

Mesoscale eddies are known to enhance diapycnal mixing in the ocean, yet direct observation of this effect remains a significant challenge, especially in the robust Antarctic Circumpolar Current (ACC). To quantify the diapycnal mixing induced by mesoscale eddies in the standing meander of the ACC, satellite altimeter and Argo profile data were combined to composite eddies, where the 1.6 m dynamic height contour was used for the first time instead of the climatological Northern Sub-Antarctic Front (SAFN) to define the northern boundary of the ACC to eliminate the influence of frontal shift. The 3D structures of the composite anticyclonic/cyclonic eddy (CAE/CCE) were obtained. Both the CAE and CCE were similar in shape to Taylor columns, from sea surface to the neutral surface of 28.085 kgm − 3 (1689 ± 66 dbar) for the CAE, and from sea surface to 28.01 kgm − 3 (1491 ± 202 dbar) for the CCE. On the same neutral surface, the diffusivity (κ) inside the CCE was one to two orders of magnitude higher than that inside the CAE. Vertically, the maximum influence depth of the CCE on κ reached 1200 dbar, while for the CAE, it reached 800 dbar, where κ exceeded O (10 − 4)   m 2 s − 1 , and κ gradually decreased from these depths downwards. [ABSTRACT FROM AUTHOR]

Characteristics of marine heatwaves (MHWs) in the East Asian Marginal Seas (EAMS) were investigated using the daily Optimum Interpolation Sea Surface Temperature for 37 years (1982–2018), focusing on seasonal changes and regional differences. The summer MHWs occur 54% more frequently (2.7 events/decade) in a relatively wide area than in other seasons. The strong (up to 3.7 °C) and long-lasting (up to 38 days/event) winter MHWs are concentrated along the subpolar front (SPF) in the East/Japan Sea (EJS) where the MHWs are 20% longer (2.2 days/event) than in the Yellow and East China Seas (YECS). The summer MHWs are primarily driven by increased shortwave radiation associated with reduced cloud cover and latent cooling from the weakened wind over the western flank of developing subtropical highs. Driving mechanisms of the winter MHWs differ by region. The YECS MHWs occur mainly due to the atmospheric processes associated with weakening continental highs, while the EJS MHWs are largely driven by the northward shift of the SPF. Although large-scale atmospheric processes primarily drive the summer MHWs occurring in a wide area in the EAMS, our findings suggest that ocean processes can be major contributors to intensified MHW generation in limited areas, especially in winter. [ABSTRACT FROM AUTHOR]

In this study, we investigate the characteristics of atmospheric parameters before, during, and after rain events in Bern, Switzerland. Ground-based microwave radiometer data of the TROpospheric WAter RAdiometer (TROWARA) with a time resolution of 7 s, observations of a weather station, and the composite analysis method are used to derive the temporal evolution of rain events and to identify possible rainfall precursors during a 10-year period (1199 available rain events). A rainfall climatology is developed using parameters integrated water vapor (IWV), integrated liquid water (ILW), rain rate, infrared brightness temperature (T IR ), temperature, pressure, relative humidity, wind speed, and air density. It was found that the IWV is reduced by about 2.2 mm at the end of rain compared to the beginning. IWV and T IR rapidly increase to a peak at the onset of the rainfall. Precursors of rainfall are that the temperature reaches its maximum around 30 to 60 min before rain, while the pressure and relative humidity are minimal. IWV fluctuates the most before rain (obtained with a 10 min bandpass). In 60% of rain events, the air density decreases 2 to 6 h before the onset of rain. The seasonality and the duration of rain events as well as the diurnal cycle of atmospheric parameters are also considered. Thus, a prediction of rainfall is possible with a true detection rate of 60% by using the air density as a precursor. Further improvements in the nowcasting of rainfall are possible by using a combination of various atmospheric parameters which are monitored by a weather station and a ground-based microwave radiometer. [ABSTRACT FROM AUTHOR]