Spatio-temporal distribution of atmospheric blocking events in the Northern and Southern Hemispheres

Nejad, Meysam Toulabi; Hejazizadeh, Zahra; Lupo, Anthony R.; Saligheh, Mohammad

doi:10.1007/s00704-022-04175-5

Cited by 3 publications

(2 citation statements)

References 49 publications

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“…Nonetheless, the most commonly employed methodology is the TM90 one. In particular, in the southern hemisphere, where much fewer blocking studies exist compared to the northern hemisphere, this has been by far the prevailing approach (Damiâo and Machado, 2008; Damião et al., 2012; Mendes et al., 2011; Toulabi Nejad et al., 2022). The choice of TM90 in our work, therefore allows us to verify the correctness of the algorithm outputs by comparison with previous studies.…”

Section: Methodsmentioning

confidence: 99%

Wave Breaking Events and Their Link to Rossby Wave Packets and Atmospheric Blockings During Southern Hemisphere Summer

Pérez‐Fernández,

Barreiro,

Ehstand

et al. 2024

JGR Atmospheres

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Rossby Wave Packets (RWPs) are atmospheric perturbations located at upper levels in mid‐latitudes which, in certain cases, terminate in Rossby Wave Breaking (RWB) events. When sufficiently persistent and spatially extended, these RWB events are synoptically identical to atmospheric blockings, which are linked to heatwaves and droughts. Thus, studying RWB events after RWPs propagation and their link with blocking is key to enhance extreme weather events detection 10–30 days in advance. Hence, here we assess (a) the occurrence of RWB events after the propagation of transient RWPs, (b) whether long‐lived RWPs (RWPs with a lifespan above 8 days, or LLRWPs) are linked to large‐scale RWB events that could form a blocking event, and (c) the proportion of blocking situations that occur near RWB events. To do so, we applied a tracking algorithm to detect transient RWPs in the southern hemisphere during summertime between 1979 and 2021, developed a wave breaking algorithm to identify RWB events, and searched for blocking events with different intensities. Results show that LLRWPs and the other RWPs displayed large‐scale RWB events around 40% of the time, and most RWB events in both distributions last around 1–2 days, which is not long enough to identify them as blocking situations. Nearly 17% of blockings have a RWB event nearby, but barely 5% of blockings are linked to RWPs, suggesting that transient RWPs are not strongly linked to blocking development. Lastly, large‐scale RWB events associated with RWPs that lasted less than 8 days are influenced by El Niño‐Southern Oscillation.

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Section: Methodsmentioning

confidence: 99%

Wave Breaking Events and Their Link to Rossby Wave Packets and Atmospheric Blockings During Southern Hemisphere Summer

Pérez‐Fernández,

Barreiro,

Ehstand

et al. 2024

JGR Atmospheres

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“…A8). The higher persistence of extremes in the NH compared to the SH is related to the different characteristics of synoptic scale circulation, such as higher blocking frequency and lower RWP phase speed in the NH (Toulabi Nejad et al, 2022;Fragkoulidis and Wirth, 2020). Moreover, the role of topography in NH is important, as topography located along the mid-latitude jet increases heatwave frequency upstream of the topographic forcing (Jiménez-Esteve and Domeisen, 2022).…”

Section: Southern Hemispherementioning

confidence: 99%

Rossby wave packets driving concurrent and non-concurrent heatwaves in the Northern and Southern Hemisphere mid-latitudes

Pyrina,

Wicker,

de Vries

et al. 2024

Preprint

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Abstract. Heatwaves that occur simultaneously over several regions, termed concurrent heatwaves, pose compounding threats to society and the environment. Amplified quasi-stationary circumglobal Rossby wave patterns (CGWPs) and high-amplitude transient non-circumglobal Rossby Wave Packets (RWPs) have been proposed as two possible explanations for the occurrence of heatwaves. The relation of these mechanisms for heatwaves has been investigated over different timescales, but their relevance for concurrent and non-concurrent heatwaves remains unexplored. In the present study we focus on daily time scales and investigate the relevance of the global CGWP amplitude and of the local RWP amplitude for the occurrence of concurrent and non-concurrent heatwaves over the Northern Hemisphere (NH) and Southern Hemisphere (SH) mid-latitudes. To distinguish between concurrent and non-concurrent heatwaves we apply a k-means clustering algorithm on all heatwaves detected in ERA5 reanalysis data within the 1959–2021 period. We identify 42 spatial clusters of heatwaves in the NH and 53 in the SH. In all identified clusters, mid-latitude heatwaves typically occur at the leading edge of RWPs where Rossby wave breaking takes place in the form of ridge building or block formation. No specific zonal wavenumber is more frequently related to the concurrent or to the non-concurrent heatwave category. However, for high global CGWP amplitudes concurrent heatwaves occur more often in the NH when the dominant zonal wavenumber is k = 7, and non-concurrent heatwaves occur more often in the SH for k = 5. The mid-latitude regions exhibiting increased heatwave probabilities under the influence of either global or local high wave amplitude, include western North America, central Europe, Black Sea, Tibet, the southwest coast of Australia, as well as the southern Indian and Atlantic Oceans. Over those regions, the local high amplitude RWPs increase heatwave probabilities by a factor ranging from 4 to 7, whereas the maximum factor for high global CGWP amplitude is 2. These results emphasize the importance of the daily RWP amplitude and the weak association of the global CGWP amplitude to heatwave occurrence over the NH and SH mid-latitudes. This research for the first time investigates the underlying atmospheric dynamical processes that contribute to the development of concurrent and non-concurrent heat extremes, a crucial step towards improving our understanding and ability to predict heatwave variability at weather and longer time scales.

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The effect of northern hemisphere blocking systems on wet and dry periods in Iran under climate change conditions

Nejad

sharifi

Lupo

2022

Preprint

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The present research was carried with the aim of investigating the relationship between blockings in the northern hemisphere and widespread wet periods and droughts in Iran. The data of the research include: precipitation of 43 synoptic stations of Iran, data of 500 hPa height geopotential and blocking factors from 1973 up to 2018. Blocking indicator (BI) was used for studying blockings and ZSI indicator was used to extract wet periods and droughts. Pearson's correlation was also used to investigate the relationship between blocking components and droughts and wet periods. Results from investigating widespread wet periods and droughts showed that before global warming, 7 wet periods occurred broadly while during the global warming, this number decreased to 5 years. Nevertheless, widespread droughts increased from 16 years to 18 years. Results from data analysis reveals that during a 46-year period of time, 977 blocking's cores have been shaped in the whole region 41 percent of which have been formed in pre-climate change period and the rest 59 percent in the second period. Regarding the intensity of blocking'sformation, it can be said that more than 77% of blockings have been medium, 10.5 % strong and 12% have been weak and with the occurrence of global warming got even weaker and inclined more to dryness and latitudes above 55 55º N. As a result, their power has decreased and they reached Iran less effectively. Blockings migration to upper latitudes can be attributed to the Increase in the subtropical high-pressure force and reduction of polar vortex penetration (polar low pressure) toward middle latitudes due to climate change. Thus, with the transference of blocking cores to upper latitudes the landing position of the troughs resulted from the blocking systems, has lesser reached to Iran and as a result, drought in Iran has increased. The results from correlation of factors of blocking and wet periods and droughts showed that in the situation of climate change, the intensity of blocking systems affecting Iran has decreased and led to decrease of wet periods and increase of droughts.

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Spatio-temporal distribution of atmospheric blocking events in the Northern and Southern Hemispheres

Cited by 3 publications

References 49 publications

Wave Breaking Events and Their Link to Rossby Wave Packets and Atmospheric Blockings During Southern Hemisphere Summer

Wave Breaking Events and Their Link to Rossby Wave Packets and Atmospheric Blockings During Southern Hemisphere Summer

Rossby wave packets driving concurrent and non-concurrent heatwaves in the Northern and Southern Hemisphere mid-latitudes

The effect of northern hemisphere blocking systems on wet and dry periods in Iran under climate change conditions

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