Abstract
In coastal regions, the complex interaction of synoptic-scale dynamics and breeze regimes influence the local atmospheric circulation, permitting to distinguish typical yet alternative patterns. In this paper, the k-means clustering algorithm is applied to the hourly time series of wind intensity and direction collected by in-situ weather stations at seven locations within 30 km from the western coastline of central Italy, in the proximity of Rome, over the period 2014–2020. The selection of both wind-integral quantities and ad hoc objective parameters allows for the identification of three characteristic clusters, two of which are closely related to the synoptic circulation and governed by persistent winds, blowing from either the northeast or the southeast direction throughout the day. In the latter case, synoptic and mesoscale contributions add up, giving rise to a complex circulation at the ground level. On the contrary, the third cluster is closely related to the sea breeze regime. The results allow the identification of some general information about the low-level circulation, showing that the synoptic circulation dominates in winter and, partly, in spring and autumn, when high ventilation and low recirculation conditions occur. Conversely, during summer the sea breeze regime is more frequent and stronger, generating intense air recirculation. Our analysis permits to discern rigorously and objectively the typical coastal meteorological patterns, only requiring anemological in-situ data.
Highlights
Coastal meteorology focuses on the meteorological phenomena that are directly caused—or significantly influenced—by the rapid changes in atmospheric conditions that occur at the land-sea transition zone (National Research Council 1994)
The separation of the breeze regime from the synoptic conditions is one of the major problems encountered in sea breeze regime (SBR) studies (Zhong and Takle 1993), whose investigation is made even harder in the urban environment of coastal cities, where the SBR interacts with the urban heat island (UHI) effect (Bauer 2020)
The observations of wind intensity and direction provided by seven ground-based meteorological stations, located in a coastal area of central Italy, are used to describe the anemological peculiarities of the region
Summary
Coastal meteorology focuses on the meteorological phenomena that are directly caused—or significantly influenced—by the rapid changes in atmospheric conditions that occur at the land-sea transition zone (National Research Council 1994). The sea breeze regime (SBR) is a relevant topic in the context of coastal meteorology, as it characterizes the mesoscale circulation, accounting for many spatially and temporally nested phenomena (Miller et al 2003), and with cascading impacts on the local environment (Masselink 1998). In addition to the thermal forcing, the SBR is affected by other factors, such as the coastline curvature (Steele et al 2013), the proximity of reliefs and orography (He et al 2020), and, above all, the synopticscale weather conditions (Di Bernardino et al 2021a). The separation of the breeze regime from the synoptic conditions is one of the major problems encountered in SBR studies (Zhong and Takle 1993), whose investigation is made even harder in the urban environment of coastal cities, where the SBR interacts with the urban heat island (UHI) effect (Bauer 2020). The UHI main characteristic are: (1) the local increase in temperature, especially at night
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