Quantifying the link between heavy precipitation and Northern Hemisphere blocking—A Lagrangian analysis

Lenggenhager, Sina; Martius, Olivia

doi:10.1002/asl.999

Cited by 11 publications

(5 citation statements)

References 54 publications

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“…The mechanisms involved in a blocking system can relate in some cases directly to its impacts. For example, storm activity upstream of the blocking system can lead to high wind and precipitation impacts there (e.g., Lenggenhager and Martius, 2020), while in other cases amplified planetary waves can be associated with simultaneous impacts in remote regions (e.g., Kornhuber et al, 2020).…”

Section: Relevant Mechanisms For Blocking Formation Maintenance and D...mentioning

confidence: 99%

Atmospheric blocking and weather extremes over the Euro-Atlantic sector – a review

Kautz

Martius

Pfahl³

et al. 2022

Weather Clim. Dynam.

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155

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Abstract. The physical understanding and timely prediction of extreme weather events are of enormous importance to society due to their associated impacts. In this article, we highlight several types of weather extremes occurring in Europe in connection with a particular atmospheric flow pattern, known as atmospheric blocking. This flow pattern effectively blocks the prevailing westerly large-scale atmospheric flow, resulting in changing flow anomalies in the vicinity of the blocking system and persistent conditions in the immediate region of its occurrence. Blocking systems are long-lasting, quasi-stationary and self-sustaining systems that occur frequently over certain regions. Their presence and characteristics have an impact on the predictability of weather extremes and can thus be used as potential indicators. The phasing between the surface and the upper-level blocking anomalies is of major importance for the development of the extreme event. In summer, heat waves and droughts form below the blocking anticyclone primarily via large-scale subsidence that leads to cloud-free skies and, thus, persistent shortwave radiative warming of the ground. In winter, cold waves that occur during atmospheric blocking are normally observed downstream or south of these systems. Here, meridional advection of cold air masses from higher latitudes plays a decisive role. Depending on their location, blocking systems also may lead to a shift in the storm track, which influences the occurrence of wind and precipitation anomalies. Due to these multifaceted linkages, compound events are often observed in conjunction with blocking conditions. In addition to the aforementioned relations, the predictability of extreme events associated with blocking and links to climate change are assessed. Finally, current knowledge gaps and pertinent research perspectives for the future are discussed.

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Section: Relevant Mechanisms For Blocking Formation Maintenance and D...mentioning

confidence: 99%

Atmospheric blocking and weather extremes over the Euro-Atlantic sector – a review

Kautz

Martius

Pfahl³

et al. 2022

Weather Clim. Dynam.

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155

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“…A temporal and spatial overlapping criterion is used to find each blocking life cycle. Here, at each time step, blocking masks are determined from the VAPV field where it falls below a threshold value of −1.3 pvu (1 pvu (potential vorticity unit) = 10 −6 m 2 s −1 K kg −1 ), which is based on previous studies (e.g., Croci-Maspoli et al, 2007;Pfahl et al, 2015;Steinfeld and Pfahl, 2019;Lenggenhager and Martius, 2020). Then, these masks are connected in time if at two consecutive time steps they overlap by at least 70 %.…”

Section: Blocking Identificationmentioning

confidence: 99%

Interaction between Atlantic cyclones and Eurasian atmospheric blocking drives wintertime warm extremes in the high Arctic

Murto

Caballero

Svensson

et al. 2022

Weather Clim. Dynam.

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Abstract. Atmospheric blocking can influence Arctic weather by diverting the mean westerly flow and steering cyclones polewards, bringing warm, moist air to high latitudes. Recent studies have shown that diabatic heating processes in the ascending warm conveyor belt branch of extratropical cyclones are relevant to blocking dynamics. This leads to the question of the extent to which diabatic heating associated with mid-latitude cyclones may influence high-latitude blocking and drive Arctic warm events. In this study we investigate the dynamics behind 50 extreme warm events of wintertime high-Arctic temperature anomalies during 1979–2016. Classifying the warm events based on blocking occurrence within three selected sectors, we find that 30 of these events are associated with a block over the Urals, featuring negative upper-level potential vorticity (PV) anomalies over central Siberia north of the Ural Mountains. Lagrangian back-trajectory calculations show that almost 60 % of the air parcels making up these negative PV anomalies experience lifting and diabatic heating (median 11 K) in the 6 d prior to the block. Further, almost 70 % of the heated trajectories undergo maximum heating in a compact region of the mid-latitude North Atlantic, temporally taking place between 6 and 1 d before arriving in the blocking region. We also find anomalously high cyclone activity (on average five cyclones within this 5 d heating window) within a sector northwest of the main heating domain. In addition, 10 of the 50 warm events are associated with blocking over Scandinavia. Around 60 % of the 6 d back trajectories started from these blocks experience diabatic heating, of which 60 % undergo maximum heating over the North Atlantic but generally closer to the time of arrival in the block and further upstream relative to heated trajectories associated with Ural blocking. This study suggests that, in addition to the ability of blocks to guide cyclones northwards, Atlantic cyclones play a significant role in the dynamics of high-latitude blocking by providing low-PV air via moist-diabatic processes. This emphasizes the importance of the mutual interactions between mid-latitude cyclones and Eurasian blocking for wintertime Arctic warm extremes.

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“…Atmospheric blocking describes the formation of persistent and quasi-stationary anticyclonic circulation anomalies that disrupt the large-scale westerly flow and eastward progression of synoptic weather systems (Berggren et al 1949, Rex 1950. Blocks are often associated with and contribute to extreme weather such as heatwaves Wernli 2012, Wehrli et al 2019), cold spells (Buehler et al 2011, Sillmann et al 2011, Brunner et al 2017, heavy precipitation (Lenggenhager and Martius 2020) and compound events (Kautz et al 2022). As a result, there is considerable interest in understanding how the occurrence of blocks and their contribution to extreme surface weather might change as the climate warms (Sillmann and Croci-Maspoli 2009, Brunner et al 2018, Woollings et al 2018, Nabizadeh et al 2021.…”

Section: Introductionmentioning

confidence: 99%

Response of moist and dry processes in atmospheric blocking to climate change

Steinfeld

Sprenger

Beyerle

2022

Environ. Res. Lett.

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Weather extremes are often associated with atmospheric blocking, but how the underlying physical processes leading to blocking respond to climate change is not yet fully understood. Here we track blocks as upper-level negative potential vorticity (PV) anomalies and apply a Lagrangian analysis to 100 years of present-day (∼2000) and future (∼2100, under the RCP8.5 scenario) climate simulations restarted from the CESM Large Ensemble Project runs (CESM-LENS) to identify different physical processes and quantify how their relative importance changes in a warmer and more humid climate. The trajectories reveal two contrasting airstreams that both contribute to the formation and maintenance of blocking: latent heating in strongly ascending airstreams (moist processes) and quasi-adiabatic flow near the tropopause with weak radiative cooling (dry processes). Both are reproduced remarkably well when compared against ERA-Interim reanalysis, and their relative importance varies regionally and seasonally. The response of blocks to climate change is complex and differs regionally, with a general increase in the importance of moist processes due to stronger latent heating (+1K in the median over the Northern Hemisphere) and a larger fraction (+15%) of strongly heated warm conveyor belt airmasses, most pronounced over the storm tracks. Future blocks become larger (+7%) and their negative PV anomaly slightly intensifies (+0.8%). Using a Theil-Sen regression model, we propose that the increase in size and intensity is related to the increase in latent heating, resulting in stronger cross-isentropic transport of air with low PV into the blocking anticyclones. Our findings provide evidence that moist processes become more important for the large-scale atmospheric circulation in the midlatitudes, with the potential for larger and more intense blocks.

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Quantifying the link between heavy precipitation and Northern Hemisphere blocking—A Lagrangian analysis

Cited by 11 publications

References 54 publications

Atmospheric blocking and weather extremes over the Euro-Atlantic sector – a review

Atmospheric blocking and weather extremes over the Euro-Atlantic sector – a review

Interaction between Atlantic cyclones and Eurasian atmospheric blocking drives wintertime warm extremes in the high Arctic

Response of moist and dry processes in atmospheric blocking to climate change

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