Invigoration of convection by an overrunning diabatically modified cloud‐top layer

Browning, K. A.; Smart, David

doi:10.1002/qj.3190

Cited by 3 publications

(2 citation statements)

References 33 publications

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“…(). It is also in good agreement with the role of evaporation in facilitating convection in the boundary layer, as described in Browning and Smart () in a different context. An analysis of the cloud‐base detrainment instability (CDI) has been also performed, showing that the CDI criterion is satisfied before the occurrence of the convective cells and largely disappears once the cells are well formed, suggesting that the instability is consumed after a while.…”

Section: Resultssupporting

confidence: 88%

The downward transport of momentum to the surface in idealized sting‐jet cyclones

Rivière

Ricard

Arbogast

2020

Quart J Royal Meteoro Soc

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Processes leading to the formation of strong surface wind gusts within an idealized sting‐jet extratropical cyclone are investigated using a high‐resolution mesoscale model. It is motivated by real case studies that have shown that damaging surface winds ahead of the bent‐back warm front of an extratropical cyclone are often due to the presence of a sting jet, which is a low‐level mesoscale jet, the air masses of which descend from the cloud head to the top of the boundary layer. Different numerical simulations show that surface winds below the leading edge of the sting jet increase with increased horizontal resolution and surface roughness. For typical land‐surface roughness, the intensity of near‐surface wind gusts increases rapidly with horizontal resolution, while the sting‐jet intensity above the boundary layer does not vary with resolution. A focus on the 1‐km grid‐spacing simulation with land‐surface roughness is then made. It shows stronger surface winds ahead of the bent‐back warm front than near the cold conveyor‐belt jet. It also exhibits multiple bands of strong surface wind speed, similar to real sting‐jet cyclones. These multiple bands are closely linked with multiple resolved convective rolls in the boundary layer, the descending branches of which are responsible for the downward transfer of momentum. Sensitivity experiments and a stability analysis show that cooling due to sublimation and melting of precipitating ice hydrometeors below the leading edge of the sting jet triggers and invigorates boundary‐layer convective rolls by reducing the buoyancy of air masses near the precipitation base and below. Closer to the surface, the transfer of momentum is predominantly taken over by subgrid‐scale turbulent fluxes.

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Section: Resultssupporting

confidence: 88%

The downward transport of momentum to the surface in idealized sting‐jet cyclones

Rivière

Ricard

Arbogast

2020

Quart J Royal Meteoro Soc

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“…This is coherent with the rapid decrease of temperature and relative humidity around this time, which may be associated with the dry cold air brought down by convective downdraughts. This mechanism, of transferring high momentum downwards, was previously documented [18,63].…”

Section: Sting Jetsupporting

confidence: 55%

Damaging Convective and Non-Convective Winds in Southwestern Iberia during Windstorm Xola

Pinto

Belo-Pereira

2020

Atmosphere

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On 23/12/2009, windstorm Xola struck mainland Portugal, causing serious damage in a small area north of Lisbon (Oeste region) and in the south region, inflicting economic losses of over EUR 100 million. In both areas, several power towers, designed to withstand up to 46 m s−1 winds, were destroyed. The causes of these two distinct damaging wind events were investigated. Xola was revealed to have a prominent cloud head and a split cold front structure. In the southern region, the damages were due to downburst winds, associated with a mesovortex, observed in a bow echo line triggered by an upper cold front. The cloud head presented several dry air intrusion signatures, co-located with tops progressively lowering towards the hooked tip. This tip revealed features consistent with the presence of slantwise convection, the descending branches of which may have been strengthened by evaporating cooling. At the reflectivity cloud head tip, a jet streak pattern was identified on weather radar, with Doppler velocities exceeding 55 m s−1, just 400 m above ground. This signature is coherent with the presence of a Sting jet, and this phenomenon was associated with the strongest wind gusts (over 40 m s−1) and the largest damages in the Oeste region.

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Origin of Strong Winds in an Explosive Mediterranean Extratropical Cyclone

Brancus

Schultz

Antonescu

et al. 2019

Monthly Weather Review

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During 2–3 December 2012, the Black Sea and east coast of Romania were affected by a rapidly deepening Mediterranean cyclone. The cyclone developed a bent-back front along which short-lived (2–4 h) strong winds up to 38 m s−1 were recorded equatorward of the cyclone center. A mesoscale model simulation was used to analyze the evolution of the wind field, to investigate the physical processes that were responsible for the strong winds and their acceleration, and to investigate the relative importance of the stability of the boundary layer to those strong winds. The origin of the air in the wind maximum equatorward of the cyclone center was twofold. The first was associated with a sting jet, a descending airstream from the midlevels of the cloud head and the lower part of the cyclonic branch of the warm conveyor belt. The sting jet started to descend west of the cyclone center, ending at the frontolytic tip of the bent-back front. The second was a low-level airstream associated with the cold conveyor belt that originated northeast of the cyclone center and traveled below 900 hPa along the cold side of the bent-back front, ending behind the cold front. Both airstreams were accelerated by the along-flow pressure gradient force, with the largest accelerations acting on the sting-jet air before entering into the near-surface strong-wind area. The sensible heat fluxes destabilized the boundary layer to near-neutral conditions south of the cyclone center, facilitating downward mixing and allowing the descending air to reach the surface. Mesoscale instabilities appeared to be unimportant in the sting-jet formation.

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Invigoration of convection by an overrunning diabatically modified cloud‐top layer

Cited by 3 publications

References 33 publications

The downward transport of momentum to the surface in idealized sting‐jet cyclones

The downward transport of momentum to the surface in idealized sting‐jet cyclones

Damaging Convective and Non-Convective Winds in Southwestern Iberia during Windstorm Xola

Origin of Strong Winds in an Explosive Mediterranean Extratropical Cyclone

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