Search Results (6)

Here, we examine extreme ocean winds associated with intense wintertime extratropical windstorms over the North Pacific. The study was mainly based on NASA Soil Moisture Active Passive (SMAP) L-band radiometer observations allowing the retrieval of ocean wind speeds up to 70 m/s regardless of precipitation intensity. Additionally, we assessed the ability of atmospheric reanalysis ERA5 and the Climate Forecast System Version 2 (CFSv2) to reproduce high-wind features within severe windstorms, particularly those associated with “explosive” cyclogenesis. The analysis identified 145 windstorm events with hurricane-force (HF) wind zones within the SMAP L-band radiometer swath from 2015 to 2023. These windstorms develop most frequently over two areas: southeast of Kamchatka and south of Alaska, spanning 40–47°N latitudes. Both reanalysis datasets significantly underestimated HF wind speeds compared to SMAP measurements, but CFSv2 tends to reproduce more-intense windstorms than ERA5. Among the notable new findings is that the SMAP data revealed two distinct groups in maximum wind speed distribution, indicating the existence of a separate class of severe windstorm events with a distinct mechanism for extreme wind formation related probably to a Shapiro–Keyser cyclogenesis and the presence of sting jet (SJ) feature. The study highlights the potential of SMAP measurements to study wind extremes and underscores the need for improvements in operational predictive models to better reproduce the formation of SJ windstorms. Full article

The objective of this study is the evaluation of the physical processes responsible for the genesis and evolution of an explosive cyclone in the central Mediterranean with the aid of the surface pressure tendency equation. For this reason, the equation is solved numerically, providing the opportunity to quantitatively specify the relative significance of the diabatic processes in Mediterranean explosive cyclogenesis, contrary to the qualitative approach of previous studies. Our approach allows for the first time a direct comparison of the physical mechanisms between the cyclogenesis over the northern and the southern part of the central Mediterranean. The results demonstrate that the interaction between the upper level baroclinic and low-level diabatic processes triggered the development of the explosive cyclone, but low-level baroclinicity and diabatic processes prevailed during the cyclone evolution. Full article

At the end of June 2020, an explosive extratropical cyclone was responsible for an environment in which a squall line developed and caused life and economic losses in Santa Catarina state, southern Brazil. The aims of this case study are the following: (a) to describe the drivers of the cyclogenesis; (b) to investigate through numerical simulations the contribution of sea–air interaction to the development of the cyclone as an explosive system; and (c) to present the physical properties of the clouds associated with the squall line. The cyclogenesis started at 1200 UTC on 30 June 2020 on the border of southern Brazil and Uruguay, having a trough at middle-upper levels as a forcing, which is a common driver of cyclogenesis in the studied region. In addition, the cyclone’s lifecycle followed Bjerknes and Solberg’s conceptual model of cyclone development. A special feature of this cyclone was its fast deepening, reaching the explosive status 12 h after its genesis. A comparison between numerical experiments with sensible and latent turbulent heat fluxes switched on and off showed that the sea–air interaction (turbulent heat fluxes) contributed to the cyclone’s deepening leading it to the explosive status. The cold front, which is a component of the cyclone, favored the development of a pre-frontal squall line, responsible for the rough weather conditions in Santa Catarina state. While satellite images do not clearly show the squall line located ahead of the cold front in the cyclone wave due to their coarse resolution, radar reflectivity data represent the propagation of the squall line over southern Brazil. On 30 June 2020, the clouds in the squall line had more than 10 km of vertical extension and a reflectivity higher than 40 dBZ in some parts of the storm; this is an indicator of hail and, consequently, is a required condition for storm electrification. In fact, electrical activity was registered on this day. Full article

Local air-sea interaction over the Mediterranean may amplify the effects of climate change. This study investigates the sensitivity of simulations of two different high impact weather events to changes in the specification of sea surface temperature (SST) using a regional atmospheric model. First we assess the impact of specifying SST from two reanalysis data sets with differing spatial resolution. The simulated tropical-like cyclone (TLC) is slightly stronger in the case of the lower resolution SST which is warmer over the formation region, most notably in the maximum rainfall which is ~7% higher. The differences in the two explosive cyclone simulations are negligible, most likely due to intensification occurring mainly over land. We then test the sensitivity of the storms to a range of SST anomalies. The TLC showed a clear trend of increasing storm intensity as SST rises. These results suggest that SST plays a direct role in determining the intensity of the storm. For the explosive cyclone there is no clear trend in dynamical intensity except for the highest warming anomalies. However, the rainfall increases with the magnitude of the SST anomaly. Our results suggest that extreme weather events over the Mediterranean will become more extreme if SST increases as the climate warms, assuming that upper air conditions do not change. Full article

In this study, the moisture sources for the explosive cyclogenesis Miguel that occurred during 4–9 June 2019 in the North Atlantic were investigated. To determine the moisture sources, the Lagrangian FLEXPART particle dispersion model was used. The moisture uptake pattern revealed the western North Atlantic Ocean extending to north-western North America, the south-eastern coast of Greenland, and the central North Atlantic Ocean around 45° N and 50°–20° W as the main moisture sources for Miguel explosive cyclogenesis. Furthermore, the moisture uptake from these regions was higher than the climatology. During the intensification of Miguel, the moisture contribution from oceanic sources was higher than terrestrial sources. Although the total amount of atmospheric moisture achieved during the explosive intensification was similar to that absorbed the 24 h prior, they changed in intensity geographically, being more intense the local support over central and northern North Atlantic basin. Full article

An explosive cyclone event that occurred near the Korean Peninsula in early May 2016 is simulated using the Weather Research and Forecasting (WRF) model to examine the developmental mechanisms of the explosive cyclone. After confirming that the WRF model reproduces the synoptic environments and main features of the event well, the favorable environmental conditions for the rapid development of the cyclone are analyzed, and the explosive development mechanisms of the cyclone are investigated with perturbation potential vorticity (PV) fields. The piecewise PV inversion method is used to identify the dynamically relevant meteorological fields associated with each perturbation PV anomaly. The rapid deepening of the surface cyclone was influenced by both adiabatic (an upper tropospheric PV anomaly) and diabatic (a low-level PV anomaly associated with condensational heating) processes, while the baroclinic processes in the lower troposphere had the smallest contribution. In the explosive phase of the cyclone life cycle, the diabatically generated PV anomalies associated with condensational heating induced by the ascending air in the warm conveyor belt are the most important factors for the initial intensity of the cyclone. The upper-level forcing is the most important factor in the evolution of the cyclone’s track, but it is of secondary importance for the initial strong deepening. Full article