Large-scale drivers of the mistral wind: link to Rossby wave life cycles and seasonal variability

Givon, Yonatan; Keller, D. V.; Silverman, Vered; Pennel, Romain; Drobinski, Philippe; Raveh‐Rubin, Shira

doi:10.5194/wcd-2-609-2021

Cited by 16 publications

(29 citation statements)

References 62 publications

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“…In contrast to Case I, here the temperature anomalies arise over North Africa and the Mediterranean ascent region, without notable anomalies near the Atlantic block (Figure 14b). Interestingly, the surface pressure and precipitation in this event (Figure 13b) highly resembles a blocked mistral winter regime (Givon et al ., 2021), suggesting a non‐local dynamical link between the mistral and heavy precipitation on both sides of the cyclone (Figure 13b) and with the downstream warm anomaly over the EM.…”

Section: Resultsmentioning

confidence: 99%

Persistent warm and dry extremes over the eastern Mediterranean during winter: The role of North Atlantic blocking and central Mediterranean cyclones

Berkovic

Raveh‐Rubin

2022

Quart J Royal Meteoro Soc

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Persistent dry winter events over the eastern Mediterranean (EM) disrupt the rainy (winter) season precipitation patterns and dramatically reduce water availability in the region. Here we objectively identify persistent dry, warm winter events over Israel, and apply a Lagrangian approach to three case-studies, aiming to understand the relation between the synoptic setting, precursor Rossby waves, and how the dry, warm conditions emerge. Self-organizing map classification of atmospheric profile data over Israel shows that the most persistent (at least 5 days) dry and warm winter events are induced by a stagnant upper tropospheric ridge over the EM, a pronounced trough or cut-off low over the western/central Mediterranean and blocking over the North Atlantic. The leading mechanisms of the warm and dry conditions are: adiabatic heating during slantwise subsidence, heating by sensible heat fluxes from the surface, and advection of warm and dry continental air. The relative contributions of the mechanisms and geographical locations of the back trajectories vary greatly both within and among the events. In addition, the Atlantic blocking and EM ridge are supported by upstream diabatic heating in warm conveyor belts of North Atlantic cyclones and Mediterranean cyclones, respectively. A quantitative classification of the back trajectories above the Atlantic and the Mediterranean has shown transitions from adiabatic to diabatic contributions and vice versa along these paths. The sequential relation between Atlantic ridge (or block), trough over Europe and ridge over EM and/or west Russia places local persistent warm and dry extremes into a large-scale context and thus provides new opportunities for understanding their predictability at weather and climate scales.

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Section: Resultsmentioning

confidence: 99%

Persistent warm and dry extremes over the eastern Mediterranean during winter: The role of North Atlantic blocking and central Mediterranean cyclones

Berkovic

Raveh‐Rubin

2022

Quart J Royal Meteoro Soc

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“…However, it also features signal strength in the lower frequencies on the seasonal scale. This is due to the fact that the mistral becomes stronger, longer, and more frequent during the preconditioning phase than during the rest of the annual cycle (Givon et al, 2021). The moving window averaging we have applied to filter the mistral out of the atmospheric forcing primarily removes the higher-frequency portion of the mistral's presence.…”

Section: Atmospheric Forcingmentioning

confidence: 99%

“…1. northerly flow with a streamwise flow direction ±45 2. the presence of a Genoa Low, defined as a closed sea level pressure contour around a minimum in the field, using 0.5 hPa intervals, anywhere in the box defined by the latitudes 38 and 44 • N and longitudes 4 and 14 • E (a slightly different domain than that of Givon et al, 2021).…”

Section: Mistral Eventsmentioning

confidence: 99%

“…The events during the preconditioning period, 30 August 2012 to 21 February 2013, were then manually checked and edited to remove single-day gaps to better represent the data according to a visual inspection of the atmosphericforcing data. For k mistral events, each event's duration, t k , and period from the beginning of the event to the next event, τ k , was determined and is provided in Table 1 for the entire ocean simulation period (for further analysis regarding the selection of these criteria; see Givon et al, 2021).…”

Section: Mistral Eventsmentioning

confidence: 99%

“…There are three distinct sections of the deep-convection cycle: the preconditioning phase in the fall, the main large overturning phase in the winter and early spring (when deep convection occurs), and the restratification and spreading phase during the summer (MEDOC, 1970;The Lab Sea Group, 1998). The focus of study is on the preconditioning and overturning phase where the mistral is stronger and more frequent (Givon et al, 2021) and therefore plays a larger role in the deep-convection cycle.…”

Section: Introductionmentioning

confidence: 99%

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Untangling the mistral and seasonal atmospheric forcing driving deep convection in the Gulf of Lion: 2012–2013

et al. 2022

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Abstract. Deep convection in the Gulf of Lion is believed to be primarily driven by the mistral winds. However, our findings show that the seasonal atmospheric change provides roughly two-thirds of the buoyancy loss required for deep convection to occur for the year 2012 to 2013, with the mistral supplying the final third. Two NEMOMED12 ocean simulations of the Mediterranean Sea were run from 1 August 2012 to 31 July 2013, forced with two sets of atmospheric-forcing data from a RegIPSL coupled run within the Med-CORDEX framework. One set of atmospheric-forcing data was left unmodified, while the other was filtered to remove the signal of the mistral. The control simulation featured deep convection, while the seasonal simulation did not. A simple model was derived by relating the anomaly scale forcing (the difference between the control and seasonal runs) and the seasonal scale forcing to the ocean response through the stratification index. This simple model revealed that the mistral's effect on buoyancy loss depends more on its strength rather than its frequency or duration. The simple model also revealed that the seasonal cycle of the stratification index is equal to the net surface heat flux over the course of the year, with the stratification maximum and minimum occurring roughly at the fall and spring equinoxes.

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Decomposing the role of dry intrusions for ocean evaporation during mistral

Givon,

Keller,

Pennel

et al. 2024

Quart J Royal Meteoro Soc

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The mistral is a northerly gap‐wind regime blowing through the Rhone Valley in Southern France. It is held responsible for the sea‐surface cooling necessary to produce deep convection in the Gulf of Lion through turbulent ocean heat loss. The mistral is tightly connected to lee‐cyclogenesis in the Gulf of Genoa, where topography forces substantial downward motion. Dry intrusions (DIs) are airstreams forming the descending branch of extratropical cyclones. Known to induce cold and dry surface anomalies, DIs are potential contributors to enhanced surface evaporation during mistral. In this study, a climatological database (ERA‐INTERIM, 1981–2016) of mistral–DI co‐occurrence is constructed, allowing quantification of the impact of DIs on the mistral evaporative hot spot for the first time. We find that, on average, mistral–DI evaporation rates are doubled, compared to mistral without DIs. Moreover, cluster‐composite analysis reveals amplifications exceeding 300% between dynamically similar mistral events, with response to DIs. Daily latent heat‐flux anomalies in the Gulf of Lion are decomposed into contributions from the various parameters to analyse the mistral evaporation response to DIs. Mistral–DI events are shown to produce extreme evaporation rates through increased mistral wind speeds. The results highlight the downward momentum flux delivered by DIs to the mistral at the Gulf of Lion as the primary driver of the evaporation amplification mechanism. We further explore the variability between different mistral–DI events and conclude that extreme mistral–DI evaporation events are linked to descending air trajectories entering the Gulf of Lion at an early stage of their lifetimes. These DIs charge the mistral with maximum vertical momentum fluxes, which act to intensify surface winds and hence evaporation rates.

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Large-scale drivers of the mistral wind: link to Rossby wave life cycles and seasonal variability

Cited by 16 publications

References 62 publications

Persistent warm and dry extremes over the eastern Mediterranean during winter: The role of North Atlantic blocking and central Mediterranean cyclones

Persistent warm and dry extremes over the eastern Mediterranean during winter: The role of North Atlantic blocking and central Mediterranean cyclones

Untangling the mistral and seasonal atmospheric forcing driving deep convection in the Gulf of Lion: 2012–2013

Decomposing the role of dry intrusions for ocean evaporation during mistral

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