Climatic and volcanic forcing of tropical belt northern boundary over the past 800 years

Alfaro‐Sánchez, Raquel; Nguyen, Hanh; Klesse, Stefan; Hudson, A.; Belmecheri, Soumaya; Köse, Nesibe; Díaz, Henry F.; Monson, Russell K.; Villalba, Ricardo

doi:10.1038/s41561-018-0242-1

Cited by 25 publications

(19 citation statements)

References 67 publications

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“…Recently, increasing evidence has pointed to a substantial role played by natural variability in the widening the tropics (Alfaro‐Sánchez et al, ; D'Agostino & Lionello, ), particularly over recent decades (see the review by Staten et al, ; also, Allen & Kovilakam, ; Amaya et al, ; Grise et al, ; Simpson, ). This examination of the patterns of RC intensification, weakening, and widening leaves us to conclude that natural variability has also played a decisive role in regional meridional overturning trends as well, but the forced responses to individual forcings, including greenhouse gas increases, stratospheric ozone depletion, and anthropogenic aerosols on Ψ ϕ ,500 , and the RC should also be examined and compared to the reanalysis trend, particularly during NH SON, when neither the forced response to CO 2 nor interannual variability associated with HC variations from year to year in CESM can explain the pattern of the observed trend (see also Grise et al, ).…”

Section: Resultsmentioning

confidence: 99%

Regional Widening of Tropical Overturning: Forced Change, Natural Variability, and Recent Trends

et al. 2019

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The width of the tropical Hadley circulation (HC) has garnered intense interest in recent decades, owing to the emerging evidence for its expansion in observations and models and to the anticipated impacts on surface climate in its descending branches. To better clarify the causes and impacts of tropical widening, this work generalizes the zonal mean HC to the regional level by defining meridional overturning cells (RC) using the horizontally divergent wind. The edges of the RC are more closely connected to surface hydroclimate than more traditional metrics of regional tropical width (such as the sea level pressure ridge) or even than the zonal mean HC. Simulations reveal a robust weakening of the RC in response to greenhouse gas increases, along with a widening of the RC in some regions. For example, simulated widening of the zonal mean HC in the Southern Hemisphere appears to arise in large part from regional overturning anomalies over the Eastern Pacific, where there is no clear RC. Unforced interannual variability in the position of the zonal mean HC edge is associated with a more general regional widening. These distinct regional signatures suggest that the RCs may be well suited for the attribution of observed circulation trends. The spatial pattern of regional meridional overturning trends in reanalyses corresponds more closely to the pattern associated with unforced interannual variability than to the pattern associated with CO2 forcing, suggesting a large contribution of natural variability to the recent observed tropical widening trends.

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Section: Resultsmentioning

confidence: 99%

Regional Widening of Tropical Overturning: Forced Change, Natural Variability, and Recent Trends

et al. 2019

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“…170,171 Although changes in hemispheric energy imbalance drive relatively small (<1 o latitude, multidecadal) shifts in the zonally averaged ITCZ position based on observationally constrained simulations, 172,173 short-term (1-2 years) responses to volcanic eruptions and internal variability can produce more rapid changes. 174 Large shifts in the ITCZ (>1 o latitude, decades timescale) and regional monsoons are possible following a potential substantial slowdown or collapse of the Atlantic meridional overturning ocean circulation. 175,176 Although a dynamical understanding of changes in ITCZ width and strength currently lags understanding of the controls on ITCZ position, energetic and dynamic theories have been developed.…”

Section: Large-scale Responses In Atmospheric Circulation Patternsmentioning

confidence: 99%

Advances in understanding large‐scale responses of the water cycle to climate change

Allan

Barlow

Byrne

et al. 2020

Annals of the New York Academy of Sciences

366

153

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Globally, thermodynamics explains an increase in atmospheric water vapor with warming of around 7%/°C near to the surface. In contrast, global precipitation and evaporation are constrained by the Earth's energy balance to increase at ∼2-3%/°C. However, this rate of increase is suppressed by rapid atmospheric adjustments in response to greenhouse gases and absorbing aerosols that directly alter the atmospheric energy budget. Rapid adjustments to forcings, cooling effects from scattering aerosol, and observational uncertainty can explain why observed global precipitation responses are currently difficult to detect but are expected to emerge and accelerate as warming increases and aerosol forcing diminishes. Precipitation increases with warming are expected to be smaller over land than ocean due to limitations on moisture convergence, exacerbated by feedbacks and affected by rapid adjustments. Thermodynamic increases in atmospheric moisture fluxes amplify wet and dry events, driving an intensification of precipitation extremes. The rate of intensification can deviate from a simple thermodynamic response due to in-storm and larger-scale feedback processes, while changes in large-scale dynamics and catchment characteristics further modulate the frequency of flooding in response to precipitation increases. Changes in atmospheric circulation in response to radiative forcing and evolving surface temperature patterns are capable of dominating water cycle changes in some regions. Moreover, the direct impact of human activities on the water cycle through water abstraction, irrigation, and land use change is already a significant component of regional water cycle change and is expected to further increase in importance as water demand grows with global population.

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“…Based on their locations and degree of coherence ( Figure S10), we combined the 23 tree-ring records in three regional composite chronologies (Figure 3a and Text S4) representing Pakistan and India (WESTERN), Nepal (CENTRAL), and Bhutan (EASTERN). Each composite chronology was developed by combining all 10.1029/2020GL089631 individual ring width series from each contributing site chronology within that region ( Figure S11; Alfaro-Sánchez et al, 2018;Trouet, 2014).…”

Section: Tree-ring Reconstruction Of the Hjlmentioning

confidence: 99%

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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Climatic and volcanic forcing of tropical belt northern boundary over the past 800 years

Abstract: Valerie. (2018). Climatic and volcanic forcing of tropical belt northern boundary over the past 800 years. Nature Geoscience.

Cited by 25 publications

References 67 publications

Regional Widening of Tropical Overturning: Forced Change, Natural Variability, and Recent Trends

Regional Widening of Tropical Overturning: Forced Change, Natural Variability, and Recent Trends

Advances in understanding large‐scale responses of the water cycle to climate change

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

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