Abstract:Cold fronts are a primary feature of the day-to-day variability of weather in the midlatitudes, and feature in conceptual extratropical cyclone models alongside the dry intrusion airstream. Here the climatological frequency and spatial distribution of the co-occurrence of these two features are quantified, and the differences in cold front characteristics (intensity, size, and precipitation) when a dry intrusion is present or not are calculated. Fronts are objectively identified in the ECMWF ERA-Interim datase… Show more
“…2, 8 and the supplementary animation). The reader is encouraged to refer to Part I of this work (Catto and Raveh-Rubin 2019) for additional details on the identification and matching algorithm, its sensitivity to its controlling parameters and the resulting climatologies.Fig. 1Dry intrusion trajectories, coloured according to their pressure (hPa), and the cold trailing front it is associated with at 00 UTC 3 January 2005 (blue squares).…”
Section: Methodsmentioning
confidence: 99%
“…4, 10). Importantly, front intensity is significantly higher when it is accompanied by a DI (Catto and Raveh-Rubin 2019). Therefore, to study the specific aspects that relate to DIs, the front intensity is controlled by separating the composite analysis to three distinct front intensities (measured as the maximal 850-hPa gradient across the front), namely strong (2.5–3.0 K/100 km), medium (1.8–2.2 K/100 km) and weak (1.0–1.5 K/100 km).…”
Section: Methodsmentioning
confidence: 99%
“…The front is connected to a deep cyclone to its north east, between southern Greenland and Iceland. The cyclone hosts a bent-back warm front as well, and an additional front feature within the cyclone area, regarded as a ‘central front’ in Catto and Raveh-Rubin (2019). Being by construction outside the cyclone area, the trailing front stretches further between two anticyclones to its east and west, on both sides of the Atlantic basin (Fig.…”
Section: Dry Intrusions and Trailing Cold Frontsmentioning
confidence: 99%
“…The first climatological quantification of the co-occurrence of DIs and cold fronts is provided in Part I of this paper (Catto and Raveh-Rubin 2019). Statistically stronger front intensities in the presence of DIs, as well as longer fronts and enhanced precipitation are found both for fronts trailing from cyclones as well as for isolated fronts, that do not connect to any cyclone area of influence.…”
The conceptual picture of an extratropical cyclone typically includes a cold front and a dry intrusion (DI) behind it. By objectively identifying fronts and DIs in ECMWF ERA-Interim data for 1979–2014, Part I quantified the climatological relationship between cold fronts and DIs. Driven by the finding that front intensity and frontal precipitation are enhanced in the presence of DIs, here we employ a front-centred perspective to focus on the dynamical and thermodynamical environment of cold fronts with and without DIs in the Northern Hemisphere winter. Distinguishing between trailing fronts (that connect to a parent cyclone) and isolated fronts, examples of DIs behind each type illustrate the baroclinic environment of the trailing front, and the lack of strong temperature gradients across the isolated front. Composite analyses of North Atlantic and North Pacific fronts outline the major differences in the presence of DIs, compared to similar fronts but without DIs in their vicinity. The magnitude and spatial structure of the modification by DIs depends on the front intensity. Yet, generally with DIs, trailing fronts occur with stronger SLP dipole, deeper upper-tropospheric trough, stronger 10-m wind gusts, enhanced ocean sensible and latent heat fluxes in the cyclone cold sector and heavier precipitation. Isolated weak fronts exhibit similar behaviour, with different spatial structure. This study highlights the central role of DIs for shaping the variability of fronts and their associated environment and impact.
Electronic supplementary material
The online version of this article (10.1007/s00382-019-04793-2) contains supplementary material, which is available to authorized users.
“…2, 8 and the supplementary animation). The reader is encouraged to refer to Part I of this work (Catto and Raveh-Rubin 2019) for additional details on the identification and matching algorithm, its sensitivity to its controlling parameters and the resulting climatologies.Fig. 1Dry intrusion trajectories, coloured according to their pressure (hPa), and the cold trailing front it is associated with at 00 UTC 3 January 2005 (blue squares).…”
Section: Methodsmentioning
confidence: 99%
“…4, 10). Importantly, front intensity is significantly higher when it is accompanied by a DI (Catto and Raveh-Rubin 2019). Therefore, to study the specific aspects that relate to DIs, the front intensity is controlled by separating the composite analysis to three distinct front intensities (measured as the maximal 850-hPa gradient across the front), namely strong (2.5–3.0 K/100 km), medium (1.8–2.2 K/100 km) and weak (1.0–1.5 K/100 km).…”
Section: Methodsmentioning
confidence: 99%
“…The front is connected to a deep cyclone to its north east, between southern Greenland and Iceland. The cyclone hosts a bent-back warm front as well, and an additional front feature within the cyclone area, regarded as a ‘central front’ in Catto and Raveh-Rubin (2019). Being by construction outside the cyclone area, the trailing front stretches further between two anticyclones to its east and west, on both sides of the Atlantic basin (Fig.…”
Section: Dry Intrusions and Trailing Cold Frontsmentioning
confidence: 99%
“…The first climatological quantification of the co-occurrence of DIs and cold fronts is provided in Part I of this paper (Catto and Raveh-Rubin 2019). Statistically stronger front intensities in the presence of DIs, as well as longer fronts and enhanced precipitation are found both for fronts trailing from cyclones as well as for isolated fronts, that do not connect to any cyclone area of influence.…”
The conceptual picture of an extratropical cyclone typically includes a cold front and a dry intrusion (DI) behind it. By objectively identifying fronts and DIs in ECMWF ERA-Interim data for 1979–2014, Part I quantified the climatological relationship between cold fronts and DIs. Driven by the finding that front intensity and frontal precipitation are enhanced in the presence of DIs, here we employ a front-centred perspective to focus on the dynamical and thermodynamical environment of cold fronts with and without DIs in the Northern Hemisphere winter. Distinguishing between trailing fronts (that connect to a parent cyclone) and isolated fronts, examples of DIs behind each type illustrate the baroclinic environment of the trailing front, and the lack of strong temperature gradients across the isolated front. Composite analyses of North Atlantic and North Pacific fronts outline the major differences in the presence of DIs, compared to similar fronts but without DIs in their vicinity. The magnitude and spatial structure of the modification by DIs depends on the front intensity. Yet, generally with DIs, trailing fronts occur with stronger SLP dipole, deeper upper-tropospheric trough, stronger 10-m wind gusts, enhanced ocean sensible and latent heat fluxes in the cyclone cold sector and heavier precipitation. Isolated weak fronts exhibit similar behaviour, with different spatial structure. This study highlights the central role of DIs for shaping the variability of fronts and their associated environment and impact.
Electronic supplementary material
The online version of this article (10.1007/s00382-019-04793-2) contains supplementary material, which is available to authorized users.
“…The majority of such objective and automated front identification methods in the literature use thermal criteria [6,[9][10][11][12][13]. Most of these studies focus on large-scale fronts that develop and move across vast areas of oceans and continents.…”
The objective of this work is the development of an automated and objective identification scheme of cold fronts in order to produce a comprehensive climatology of Mediterranean cold fronts. The scheme is a modified version of The University of Melbourne Frontal Tracking Scheme (FTS), to take into account the particular characteristics of the Mediterranean fronts. We refer to this new scheme as MedFTS. Sensitivity tests were performed with a number of cold fronts in the Mediterranean using different threshold values of wind-related criteria in order to identify the optimum scheme configuration. This configuration was then applied to a 10-year period, and its skill was assessed against synoptic surface charts using statistic metrics. It was found that the scheme performs well with the dynamic criteria employed and can be successfully applied to cold front identification in the Mediterranean.
The goal of this study is to advance an automated and objective scheme for the identification of cold fronts over the Mediterranean based on wind-related criteria, MedFTS, by further incorporating thermal criteria, in order to improve the identification of cold fronts on a climatological basis. These thermal
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