Wind patterns associated with the development of daytime thunderstorms over Istria

Abstract

Abstract. The northeastern (NE) Adriatic in the northernMediterranean is the area with (i) the highest frequency of thunderstorms in Croatia, and (ii) frequent appearances of sea breeze (SB) along the coast. This study investigates the impact of the combined large-scale wind (associated with particular synoptic conditions) and the SB on the moist convection development over the NE Adriatic. The four selected cases were (i) chosen on the basis of a daytime moist convection; (ii) supplemented by one of the dominant large-scale winds with seaward (NE, NW) and landward (SW, SE) directions and (iii) simulated by WRF numerical model.The near-surface wind patterns consisted of SBs along the coastline, generated a narrow eastward-moving convergence zone (CZ) along the area if the large-scale wind was less than 9 m s −1 (below 500 hPa). Apart from the low-level CZ, the advection of large-scale wind influenced the lifetime and movement of the initial Cb cells. While the local front collision with the NE wind advection caused the thunderstorm to propagate southward, the CZ and fronts interaction determined the afternoon northwestward storm movement against the NW large-scale wind. Due to particular synoptic background, the thunderstorm event in SE case was the shortest with only a minor impact on the SB. While the origins and locations of storm cells were completely controlled by the low-level CZ and the upward advection of low-level moisture at the SB front, the most typical convective case with SW warm-wet wind only partially supported the SB-Cb interaction.

Hail Climatology Along the Northeastern Adriatic

“…The convex shape of the peninsula contributes to the development of local winds (particularly in summer) that often form a centrally placed convergence zone in the wind field (Kehler‐Poljak et al, 2017; Telišman Prtenjak & Grisogono, 2007; Telišman Prtenjak et al, 2006). Interactions between gust front(s) and local convergence zone(s) are neither unusual nor rare (Poljak et al, 2014). Since convection development is supported by mountains to the north and east and by near‐surface wind convergence (i.e., which reflects constant forcing), under favorable midtropospheric conditions (e.g., Sow et al, 2011), convective cells tend to circle over the peninsula and reach coastal areas later in the day.…”

Evolution of convective systems across Hangzhou Bay during a sea-breeze-effect thunderstorm event

“…Besides sea-land temperature contrast, boundary layer convergence on coastal areas can also be impacted by onshore friction and atmospheric circulation conditions (Wexler 1946;Azorin-Molina et al 2009;Poljak et al 2014). The results of Fric indicated that BL convergence zone would move inland after the friction along the coastline was intensified (Fig.…”

Statistical characterization of the sea‐breeze physical mechanisms through in‐situ and satellite observations

“…Convection is also present over the land under SB conditions that might be enhanced by the topography (Melas et al, 1998), specially in the central part of islands with spatial scales of tens to a few hundred kilometres (Ramis and Alonso, 1998;Melas et al, 2000). Storms can be reported if there are unstable conditions at higher levels and enough moisture between 850 and 700 hPa to sustain the vertical development (as it is reported in south-eastern Italy in Nelci et al (2015) or in Istria, Croatia, in Poljak et al (2014)).…”