Eddy transport, wave–mean flow interaction, and Eddy forcing during the 2013 Uttarakhand extreme event in the reanalysis and <scp>S2S</scp> retrospective forecast data

Kalshetti, Mahesh; Chattopadhyay, Rajib; Hunt, Kieran M. R.; Phani, M. K.; Joseph, Susmitha; Pattanaik, D. R.; Sahai, A. K.

doi:10.1002/joc.7706

Cited by 5 publications

(5 citation statements)

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“…3a) indicate a much bigger relative increase in WD frequency. This is potentially important for two reasons: firstly, as we have seen, these months are not typically well studied in the context of WD meteorology, and so trends here have thus far remained undiscovered, and secondly, this increases the chance of WDs coming into contact with the summer monsoon, which can lead to catastrophic flooding (Ranalkar et al, 2016;Kalshetti et al, 2022).…”

Section: Resultsmentioning

confidence: 99%

Increasing frequency and lengthening season of western disturbances are linked to increasing strength and delayed northward migration of the subtropical jet

Hunt

2024

Weather Clim. Dynam.

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Abstract. Western disturbances (WDs) are cyclonic storms that travel along the subtropical jet, bringing the majority of seasonal and extreme precipitation to the Hindu Kush, Karakoram, and western Himalaya in the winter months. They are a vital component of the region's water security. Although typically most common in the winter, WDs can also interact with the summer monsoon, leading to catastrophic consequences. These seem to be happening more frequently, and along with increasingly harsh winter seasons, questions are now being asked about how climate change is affecting WD frequency and intensity in both summer and winter seasons. An analysis of 17 previous studies assessing trends in WD frequency revealed no consensus, at least in part because they quantified trends in different regions, seasons, and time periods. In this study, a more robust approach is used, quantifying trends in WD frequency and intensity by region and month using a track catalogue derived from 70 years of European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) data. Winter WDs have increased significantly over the western and central Himalaya and the Hindu Kush in the last 70 years. This trend is attributed to a strengthening of the subtropical jet. The WD season has also significantly lengthened with WDs becoming far more common in May, June, and July, months where they were previously rare. For example, WDs have been twice as common in June in the last 20 years than during the previous 50. This is attributed to a delayed northward retreat of the subtropical jet, which historically has occurred before the onset of the summer monsoon. The most important implication is that the frequency of “monsoonal” WDs is increasing significantly, and therefore, due to climate change, catastrophic events like the 2013 Uttarakhand floods and the 2023 north India floods are becoming much more frequent.

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Section: Resultsmentioning

confidence: 99%

Increasing frequency and lengthening season of western disturbances are linked to increasing strength and delayed northward migration of the subtropical jet

Hunt

2024

Weather Clim. Dynam.

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“…This difference demonstrates that not all WDs arise as instabilities on the subtropical jet -but also as extratropical cutoff lows that migrate equatorward (Wernli and Sprenger, 2007;Portmann et al, 2021). Cutoff lows arise when tongues of high PV upper-tropospheric air detach from the extratropical westerlies and they tend to move more slowly than WDs embedded in the subtropical jet, sometimes leading to severe weather (Kalshetti et al, 2022). They comprise about 10% of all WDs (Thomas et al, 2023), but this number is uncertain given difference in tracking methodologies.…”

Section: Track Densitymentioning

confidence: 99%

“…WDs are most commonly associated with the winter months, when the subtropical westerly jet is furthest south (Schiemann et al, 2009). However, they can occasionally occur during the ISM (June-September), either due to southward excursions of the jet, or as elongated, 'digging' troughs or cutoff lows (Kalshetti et al, 2022). Perhaps the most notorious example occurred in June 2013, when a WD interacted with a monsoon low-pressure system, resulting in devastating floods over Uttarakhand (Kotal et al, 2014).…”

Section: Landslides and Avalanchesmentioning

confidence: 99%

Western disturbances and climate variability: a review of recent developments

Hunt,

Baudouin,

Turner

et al. 2024

Preprint

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Abstract. Western disturbances (WDs) are synoptic-scale weather systems embedded within the subtropical westerly jet. Manifesting as upper-level troughs often associated with a lower-tropospheric low over Western India, they share some dynamical features with extratropical cyclones. WDs are most common during the boreal winter (December to March), during which they bring the majority of precipitation – both rain and snow – to the Western Himalaya, as well as to surrounding areas of north India, Pakistan and the Tibetan Plateau. WDs are also associated with weather hazards such as heavy snowfall, hailstorms, fog, cloudbursts, avalanches, frost, and coldwaves. In this paper, we review the recent understanding and development on WDs. Recent studies have collectively made use of novel data, novel analysis techniques, and the increasing availability of high-resolution weather and climate models. This review is separated into six main sections – structure and thermodynamics, precipitation and impacts, teleconnections, modelling experiments, forecasting at a range of scales, and paleoclimate and climate change – each motivated with a brief discussion of the accomplishments and limitations of previous research. A number of step changes in understanding are synthesised. Use of new modelling frameworks and tracking algorithms has significantly improved knowledge of WD structure and variability, and a more frequentist approach can now be taken. Improved observation systems have helped quantification of water security over the Western Himalaya. Convection-permitting models have improved our understanding of how WDs interact with the Himalayas to trigger natural hazards. Improvements in paleoclimate and future climate modelling experiments have helped to explain how WDs and their impacts over the Himalaya respond to large-scale natural and anthropogenic forcings. We end by summarising unresolved questions and outlining key future WD research topics.

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Section: Track Densitymentioning

confidence: 99%

“…There is an important implication to this arrangement: intensifying the jet downstream means that WDs can trigger jet streaks, whose associated ageostrophic circulation can result in regions of strong ascent. As they often behave like Rossby waves, WDs can also impart this ascent through eddy momentum flux from the extratropics (Kalshetti et al, 2022). We will discuss the impacts of such dynamics later.…”

Eddy transport, wave–mean flow interaction, and Eddy forcing during the 2013 Uttarakhand extreme event in the reanalysis and S2S retrospective forecast data

Cited by 5 publications

References 64 publications

Increasing frequency and lengthening season of western disturbances are linked to increasing strength and delayed northward migration of the subtropical jet

Increasing frequency and lengthening season of western disturbances are linked to increasing strength and delayed northward migration of the subtropical jet

Western disturbances and climate variability: a review of recent developments

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