Is the subtropical jet shifting poleward?

Maher, Penelope; Kelleher, Michael E.; Sansom, Philip G.; Methven, John

doi:10.1007/s00382-019-05084-6

Cited by 30 publications

(39 citation statements)

References 55 publications

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“…10.1029/2020GL089631 Zhongda & Riyu, 2005). This lack of trend in STJ over Asia differs from the recent observed poleward displacements of other regional STJs, including those over the east Pacific and the Middle East (Fu & Lin, 2011;Maher et al, 2020;Strong & Davis, 2007) as well as the global mean STJs and Hadley Cell (Manney & Hegglin, 2018;Pena-Ortiz et al, 2013;Staten et al, 2018). However, these trends have been found to be season specific and their magnitude varies depending on the data and metrics used (Adam et al, 2014;D'Agostino & Lionello, 2017;Grise et al, 2018).…”

Section: 1029/2020gl089631mentioning

confidence: 78%

“…This result, which could reflect the influence of land‐ocean distribution (Hoskins & Valdes, 1990) and orographic effects (Held et al, 2002), confirms the unique character of the Himalayan jet in a global context. Because spring trends appear to be different for this region, it may be necessary to conduct season‐ and region‐specific analyses of jet stream behavior, as recommended by prior studies (Belmecheri et al, 2017; Grise et al, 2018; Maher et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

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Poleward Excursions by the Himalayan Subtropical Jet Over the Past Four Centuries

Thapa

George

2020

Geophysical Research Letters

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Since the 1980s, the subtropical jet stream has generally moved poleward, but its behavior varies by region and season. Here we examine the interannual variability and trends in the latitudinal position of the spring subtropical jet over the Himalayas. During the modern period (1948 to 2018), the spring (March-April-May) jet is typically anchored immediately south of the Himalayas but has rarely (in 1956, 1971, 1984, and 1999) moved poleward to pass over Kyrgyzstan and northwest China. A tree-ring reconstruction of the jet's latitude indicates that such poleward excursions may have become more frequent after 1950, but it is not clear whether that behavior is unprecedented within the past four centuries. These insights into the behavior of the Himalayan subtropical jet may improve seasonal weather forecasts for the region and provide a target for climate simulations to test whether the recent spate of excursions is unusual and due to anthropogenic warming. Plain Language Summary The subtropical jet stream (STJ) is a band of high-speed westerly winds in the upper atmosphere located near the subtropics. Since the 1980s, the STJ has generally moved poleward, but its behavior varies strongly by region and season. We studied the STJ over the Himalayas and found, during 1948-2018, that the spring STJ is typically anchored near the Himalayan foothills. In a few years (1956, 1971, 1984, and 1999); however, it has moved far north to pass over Kyrgyzstan and northwest China. A tree-ring reconstruction of the jet's north-south position suggests that this type of poleward tracks has happened before, but the past few decades may be unusual due to the number of such events. Including the potential north-south range of the Himalayan subtropical jet into forecasting models might help improve the accuracy of spring weather predictions in this region. Our multicentury record can be used to test how well models simulate the Himalayan jet and investigate whether anthropogenic warming is the cause of the recent poleward extremes.

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Section: 1029/2020gl089631mentioning

confidence: 78%

Section: Discussionmentioning

confidence: 99%

Poleward Excursions by the Himalayan Subtropical Jet Over the Past Four Centuries

Thapa

George

2020

Geophysical Research Letters

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“…Last, we find the STJ as in Davis and Birner (2016), who define it as the most equatorward zonal mean zonal wind maximum below 50 hPa after subtracting the surface zonal wind component to distinguish it from the EDJ. We remove the 850 hPa wind from the column instead as in Maher et al (2020) and similarly find a distinct STJ core ( Figure S4). Figure 3b shows KDEs of daily STJ position for each SST run.…”

Section: Circulation Responsementioning

confidence: 90%

Sensitivity of Atmospheric River Vapor Transport and Precipitation to Uniform Sea Surface Temperature Increases

2020

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Filaments of intense vapor transport called atmospheric rivers (ARs) are responsible for the majority of poleward vapor transport in the midlatitudes. Despite their importance to the hydrologic cycle, there remain many unanswered questions about changes to ARs in a warming climate. In this study we perform a series of escalating uniform SST increases (+2, +4, and +6K, respectively) in the Community Atmosphere Model version 5 in an aquaplanet configuration to evaluate the thermodynamic and dynamical response of AR vapor content, transport, and precipitation to warming SSTs. We find that AR column integrated water vapor (IWV) is especially sensitive to SST and increases by 6.3-9.7% per degree warming despite decreasing relative humidity through much of the column. Further analysis provides a more nuanced view of AR IWV changes: Since SST warming is modest compared to that in the midtroposphere, computing fractional changes in IWV with respect to SST results in finding spuriously large increases. Meanwhile, results here show that AR IWV transport increases relatively uniformly with temperature and at consistently lower rates than IWV, as modulated by systematically decreasing low-level wind speeds. Similarly, changes in AR precipitation are related to a compensatory relationship between enhanced near-surface moisture and damped vertical motions.

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“…Nguyen et al, 2015;Tao et al, 2016), stratospheric ozone depletion (Kang et al, 2011;McLandress et al, 2011;Min and Son, 2013;Polvani et al, 2011;Son et al, 2010), and changes in anthropogenic aerosols (Allen et al, 2012;Allen and Ajoku, 2016;Kovilakam and Mahajan, 2015). However, other studies concluded that the observed trends strongly reflected natural climate variability (Allen and Kovilakam, 2017;Amaya et al, 2018;Mantsis et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…Traditionally, the edge of the Hadley circulation has been defined using the poleward boundary of the zonal-mean meridional mass streamfunction in the mid-troposphere, but departures from mass conservation in reanalyses (particularly in older-generation reanalyses) can lead to large spurious trends in the location of the Hadley cell edge defined using the mass streamfunction . Consequently, many studies have sought to estimate trends in the location of the Hadley cell edge using other metrics, including the transition from zonal-mean surface easterlies to zonal-mean surface westerlies (Grise et al, 2018, hereafter G18;Grise et al, 2019, hereafter G19), the subtropical sea level pressure maximum (Choi et al, 2014), the latitude of the subtropical jet (Maher et al, 2020), the altitude break in tropopause height in the subtropics (Seidel and Randel, 2007;Lucas et al, 2012), thresholds in outgoing longwave radiation (Hu and Fu, 2007;Mantsis et al, 2017), and total column ozone (Hudson et al, 2006). Some of the largest trends in recent decades arise from the metrics derived from tropopause height and outgoing longwave radiation, but it appears that these metrics are measuring changes unrelated to the poleward expansion of the Hadley circulation.…”

Section: Introductionmentioning

confidence: 99%

Hadley cell expansion in CMIP6 models

Grise

Davis

2020

Atmos. Chem. Phys.

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Abstract. In response to increasing greenhouse gases, the subtropical edges of Earth's Hadley circulation shift poleward in global climate models. Recent studies have found that reanalysis trends in the Hadley cell edge over the past 30–40 years are within the range of trends simulated by Coupled Model Intercomparison Project Phase 5 (CMIP5) models and have documented seasonal and hemispheric asymmetries in these trends. In this study, we evaluate whether these conclusions hold for the newest generation of models (CMIP6). Overall, we find similar characteristics of Hadley cell expansion in CMIP5 and CMIP6 models. In both CMIP5 and CMIP6 models, the poleward shift of the Hadley cell edge in response to increasing greenhouse gases is 2–3 times larger in the Southern Hemisphere (SH), except during September–November. The trends from CMIP5 and CMIP6 models agree well with reanalyses, although prescribing observed coupled atmosphere–ocean variability allows the models to better capture reanalysis trends in the Northern Hemisphere (NH). We find two notable differences between CMIP5 and CMIP6 models. First, while both CMIP5 and CMIP6 models contract the NH summertime Hadley circulation equatorward (particularly over the Pacific sector), this contraction is larger in CMIP6 models due to their higher average climate sensitivity. Second, in recent decades, the poleward shift of the NH annual-mean Hadley cell edge is slightly larger in CMIP6 models. Increasing greenhouse gases drive similar trends in CMIP5 and CMIP6 models, so the larger recent NH trends in CMIP6 models point to the role of other forcings, such as aerosols.

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Is the subtropical jet shifting poleward?

Cited by 30 publications

References 55 publications

Poleward Excursions by the Himalayan Subtropical Jet Over the Past Four Centuries

Poleward Excursions by the Himalayan Subtropical Jet Over the Past Four Centuries

Sensitivity of Atmospheric River Vapor Transport and Precipitation to Uniform Sea Surface Temperature Increases

Hadley cell expansion in CMIP6 models

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