Search

Data on internal gravity and infrasound waves recorded during the passage of both warm and cold fronts throughout Moscow, which are associated with the atmospheric storm of May 29, 2017, are given. These waves were recorded by four microbarographs located in the city of Moscow and Moscow region (and marked IFA, MGU, MSR, and ZNS in Fig. 1) and the data obtained were compared with data on infrasound waves recorded at the IS43 station in the town of Dubna. Time variations in the characteristics of internal gravity and infrasound waves (coherence, propagation azimuths, phase velocities, characteristic periods, and frequency spectra) during the passage of both warm and cold fronts are studied. The transition from the gravity to acoustic dispersive branch of acoustic-gravity waves due to increasing frequency and the temporal modulation of the phase velocity of infrasound waves due to internal gravity waves (IGWs) are also studied. Data on both aerosol (PM10) and gas (NO2) concentrations measured at different Moscow stations during the approaching atmospheric storm are given. The possibility of detecting wave precursors of atmospheric storms in simultaneous variations in atmospheric pressure, wind velocity, and pollutant concentrations is studied. [ABSTRACT FROM AUTHOR]

ABSTRACT This study shows a synoptic climatology of warm fronts in Southeastern South America ( SESA). Data from Climate Forecast System Reanalysis ( CFSR) was used to identify warm fronts from 1979 to 2010. The identification method was based on the magnitude of meridional gradient of 850- hPa equivalent potential temperature ( θe) and 850- hPa wind fields. Composites of the most important atmospheric variables were constructed from 1 day before until 1 day after the formation of the warm front. An average frequency of two warm fronts per month is observed, with higher frequencies in austral winter. Most warm fronts precede the formation of extratropical cyclones over Uruguay and form because of the southward movement of previous cold/stationary fronts. Warm fronts form on average around southern Paraguay, northeastern Argentina and western part of southern Brazil and Uruguay, coupled to the eastern edge of the Chaco Low ( CL) and the Northwestern Argentinean Low ( NAL) where north/northwesterly flow predominates. An upper-level wave of wavenumber eight supports warm frontogenesis. Location and intensity of synoptic systems associated with a warm front event differ from winter to summer. Elevated instability is commonly present near warm fronts, and the average warm-front slope is 1 : 110, agreeing with other studies. Instability indices increase after the warm-front passage, leading to greater rainfall 1 day after the warm front forms. [ABSTRACT FROM AUTHOR]

ABSTRACT This study investigates the structure and evolution of line-shaped convective systems ( LCSs) associated with the Changma front observed over Chujado in the southwestern Korean Peninsula by using intensive observational data from upper-air sounding and Doppler radars. LCSs embedded as a multicellular precipitation system developed north of the warm front and persisted for 4 h. With continuous new cells development, the convective cells gradually strengthened and merged into the LCSs and exhibited a high low-level mixing ratio, weak vertical wind shear, and negligible instability. A rear-to-front jet corresponding to a low-level jet ( LLJ) was concurrent with a high equivalent potential temperature ( θ e) environmental inflow over the warm front, which suggests that the rear-to-front jet with moist air induced destabilization. Three-dimensional kinematic and reflectivity structures of the LCSs exhibited homogeneous southerly and southwesterly winds with height, small horizontal wind shear, and convergence. Transfer of positive u and v momentum upward by convective eddies into the LCSs and of horizontal momentum occurred through organized convection; both these transfers acted to intensify the LLJ. [ABSTRACT FROM AUTHOR]

Abstract: In the afternoon of 28 July 2005, a damaging F2 tornado in Birmingham, United Kingdom, was one of three tornadoes developing on the immediate cool side of a surface warm front. An analysis is performed to find out why the narrow zone on this side of the front was apparently so favourable for tornadoes in spite of lower surface temperatures. It is investigated how three ingredients for tornadogenesis are distributed and how these distributions evolve. These ingredients — the presence of a convective storm, low-level wind shear, and a low LCL height — and the presence of SBCAPE, which is a prerequisite for surface-based convective storms, are studied using surface, upper-air and satellite data, as well as a convection-permitting model. At some distance on the cool side of the front, strong wind shear existed across the lowest 1km (around 15m s−1 bulk shear), but no surface-based instability to support surface-based convection. In contrast, the air mass on the front''s warm side exhibited weak SBCAPE (50–200J kg−1) but only fairly weak low-level shear (0–1km bulk shear ~6m s−1). The analysis suggests that between these regions, within a narrow zone on the cold side of the front, surface-based instability was considerably higher (~450J kg−1 of SBCAPE) and the 0- to 1-km bulk wind shear was estimated to be 10.5m s−1. Moreover, the higher relative humidity in this zone resulted in a lower lifted condensation level (~200m in this zone, compared to ~700m on the warm side of the front). It is concluded that an overlap of all these four ingredients only existed within this zone that was only about 30km wide. [Copyright &y& Elsevier]

Flash flooding is an important issue as it has a devastating impact over a short time and in a limited area. However, predicting flash floods is challenging because they are connected to convection systems that rapidly evolve and require a high-resolution forecasting system. In addition, modeling a case study of a mesoscale convective complex (MCC) is the key to improving our understanding of the heavy rainfall systems that trigger flash floods. In this study, we aim at improving modeling skills to simulate a heavy rainfall system related to flash-flood-producing MCCs. We simulated a heavy rainfall event related to a severe flash flood in Luwu, Sulawesi, Indonesia, on 13 July 2020. This flood was preceded by persistent heavy rainfall from 11 to 13 July 2020. In this case, we investigated the role of sea surface temperature (SST) in producing the persistent heavy rainfall over the region. Therefore, we explore the physical and dynamic processes that caused the heavy rainfall using a convection-permitting model with 1 km resolution and an experiment comparing the situation with and without updated SST. The results show that the heavy rainfall was modulated by the development of a pair of MCCs during the night. The pair of MCCs was triggered by a meso-low-pressure system with an anti-cyclonic circulation anomaly over the Makassar Strait and was maintained by the warm front passing between the sea and land over central Sulawesi. This front was characterized by moist–warm and cold–dry low-level air, which may have helped extend the lifetime of the MCCs. The north-westward propagation of the MCCs was due to the interaction between predominantly a south-easterly monsoon and SST anomalies. This study suggested that the long-lived (>10 h) MCCs (>80,000 km2 cloud shield) and persistent precipitation are reproduced well in the updated SST scenario in the WRF model. This relatively simple technique in the running model provides a new strategy for improving flash flood forecasting by better predicting rainfall as an input in the hydrological model. Our findings also indicated a long-lived MCC maintained by back-building mechanisms from night to morning inland as an exceptional MCC, which does not correspond to a previous study. [ABSTRACT FROM AUTHOR]