Abstract:The seasonal variation of Indo-Pacific warm pool (IPWP) plays an important role in the oceanographic and climatological processes. While the IPWP expansion under greenhouse warming has been widely discussed, the response of the IPWP seasonality to climate change has received limited attention. In this study, we found an obvious seasonal diversity in the IPWP expansion from 1950–2020, with a maximal (minimal) expansion trend of 0.28×107 km2/decade in winter (0.17×107 km2/decade in spring), which consequently re… Show more
“…In the following, we try to dig into the problem by conducting a set of sensitivity experiments which assume different ideal conditions of topical Indo-Paci c Oceanic warming. Previous researches have de ned the capacity for warm pool expansion 22,54 and revealed its signi cant in uence on the seasonal difference in surface IPWP expansion 24 . In this section, we nd that the seasonal diversity in the capacity for IPWP volume expansion, which is determined by the spatial characteristics of climatological subsurface ocean temperature, is the primary driver of the seasonally different IPWP expansion trends.…”
Section: Cause Of the Seasonal Diversity In Ipwp Expansionmentioning
confidence: 99%
“…This observation unveils a crucial information: the cooler subsurface temperature background in autumn and winter during P1 allows for a larger spatial extent for IPWP expansion in these two seasons during P2. In line with the de nition from previous researches on such spatial extent for warm pool expansion, we adopt the concept of the capacity for warm pool volume expansion 22,24,54 (see Methods). That is to say that the capacity for IPWP volume expansion may be greater in autumn and winter compared to spring and summer, as these seasons have more grids with temperatures around 28°C (Fig.…”
Section: Cause Of the Seasonal Diversity In Ipwp Expansionmentioning
confidence: 99%
“…The capacity for volume change is regarded as the potential for the 3D warm pool body expansion 22,24,54 and is determined by the climatological ocean temperature pattern over tropical Indo-Paci c Ocean. Here, by assuming that the warming of tropical Indo-Paci c is spatially and seasonally uniform (the assumptions of the SSUE), we can quantitatively calculate the capacity for change of IPWP, IOWP and WPWP whose seasonality is merely determined by the climatological ocean temperature pattern over tropical Indo-Paci c, Indian, western Paci c Ocean.…”
Section: Capacity For Warm Pool Volume Changementioning
confidence: 99%
“…In particular, it was recently discovered that the surface IPWP size expansion exhibits signi cant seasonal diversity, which leads to a decrease in the seasonality of surface IPWP size and further impacts on the Walker circulation 24 . The changing seasonality of IPWP size is of particular importance due to its crucial role in modulating the seasonal cycle of atmospheric circulation 6, 24,28,42 .…”
The Indo-Pacific warm pool (IPWP) expansion under global warming has huge impacts on global climate. While recent studies have revealed the seasonal diversity of IPWP surface expansion and its climate impacts, understanding the changes in seasonality of the IPWP volume is of greater importance, especially given the crucial role of subsurface ocean in climate systems. Here, we find a significant difference in IPWP volume expansion rates across seasons from 1950–2020. The expansions of IPWP volume during boreal autumn and winter are faster compared to boreal spring and summer. This consequently weakens the seasonality of IPWP volume, particularly in the upper-layer, with a significant decreasing trend of -0.54×107 km3/decade. Further analyses suggest that this seasonal diversity in IPWP volume expansion is primarily caused by the seasonality of capacity for IPWP volume change, which is determined by the seasonal climatological Indo-Pacific subsurface temperature pattern. Furthermore, these variations may exert diverse impacts on atmospheric circulation and East Africa precipitation in rainy seasons. Specifically, the larger autumn IPWP expansion trend enhances ascending motion and precipitation over East Africa during short rains (October-November-December), while the relatively slower spring IPWP expansion leads to a decrease in rainfall during long rains (March-April-May). This study highlights the primary role of climatic subsurface Indo-Pacific Ocean temperature properties on the change of IPWP volume seasonality, which may have crucial effects on the precipitation in East Africa rainy seasons, and may hold important clues about how greenhouse warming affect oceanic seasonal cycle.
“…In the following, we try to dig into the problem by conducting a set of sensitivity experiments which assume different ideal conditions of topical Indo-Paci c Oceanic warming. Previous researches have de ned the capacity for warm pool expansion 22,54 and revealed its signi cant in uence on the seasonal difference in surface IPWP expansion 24 . In this section, we nd that the seasonal diversity in the capacity for IPWP volume expansion, which is determined by the spatial characteristics of climatological subsurface ocean temperature, is the primary driver of the seasonally different IPWP expansion trends.…”
Section: Cause Of the Seasonal Diversity In Ipwp Expansionmentioning
confidence: 99%
“…This observation unveils a crucial information: the cooler subsurface temperature background in autumn and winter during P1 allows for a larger spatial extent for IPWP expansion in these two seasons during P2. In line with the de nition from previous researches on such spatial extent for warm pool expansion, we adopt the concept of the capacity for warm pool volume expansion 22,24,54 (see Methods). That is to say that the capacity for IPWP volume expansion may be greater in autumn and winter compared to spring and summer, as these seasons have more grids with temperatures around 28°C (Fig.…”
Section: Cause Of the Seasonal Diversity In Ipwp Expansionmentioning
confidence: 99%
“…The capacity for volume change is regarded as the potential for the 3D warm pool body expansion 22,24,54 and is determined by the climatological ocean temperature pattern over tropical Indo-Paci c Ocean. Here, by assuming that the warming of tropical Indo-Paci c is spatially and seasonally uniform (the assumptions of the SSUE), we can quantitatively calculate the capacity for change of IPWP, IOWP and WPWP whose seasonality is merely determined by the climatological ocean temperature pattern over tropical Indo-Paci c, Indian, western Paci c Ocean.…”
Section: Capacity For Warm Pool Volume Changementioning
confidence: 99%
“…In particular, it was recently discovered that the surface IPWP size expansion exhibits signi cant seasonal diversity, which leads to a decrease in the seasonality of surface IPWP size and further impacts on the Walker circulation 24 . The changing seasonality of IPWP size is of particular importance due to its crucial role in modulating the seasonal cycle of atmospheric circulation 6, 24,28,42 .…”
The Indo-Pacific warm pool (IPWP) expansion under global warming has huge impacts on global climate. While recent studies have revealed the seasonal diversity of IPWP surface expansion and its climate impacts, understanding the changes in seasonality of the IPWP volume is of greater importance, especially given the crucial role of subsurface ocean in climate systems. Here, we find a significant difference in IPWP volume expansion rates across seasons from 1950–2020. The expansions of IPWP volume during boreal autumn and winter are faster compared to boreal spring and summer. This consequently weakens the seasonality of IPWP volume, particularly in the upper-layer, with a significant decreasing trend of -0.54×107 km3/decade. Further analyses suggest that this seasonal diversity in IPWP volume expansion is primarily caused by the seasonality of capacity for IPWP volume change, which is determined by the seasonal climatological Indo-Pacific subsurface temperature pattern. Furthermore, these variations may exert diverse impacts on atmospheric circulation and East Africa precipitation in rainy seasons. Specifically, the larger autumn IPWP expansion trend enhances ascending motion and precipitation over East Africa during short rains (October-November-December), while the relatively slower spring IPWP expansion leads to a decrease in rainfall during long rains (March-April-May). This study highlights the primary role of climatic subsurface Indo-Pacific Ocean temperature properties on the change of IPWP volume seasonality, which may have crucial effects on the precipitation in East Africa rainy seasons, and may hold important clues about how greenhouse warming affect oceanic seasonal cycle.
“…Given the nonzero trend in the hail event counts over the whole eastern US, the ordinary probability density function (PDF, or image histogram) and spatial PDF (SPDF) method [51][52][53] could visualize the changes in the spatial distribution of hail activity, neglecting the overall hail occurrence trend. In the calculation of the PDF of hail event latitude, the probability (𝑃𝐷𝐹 𝑦𝑒𝑎𝑟 ) that a hail event is observed at a certain latitude (𝑙𝑎𝑡 0 ) in a year is estimated by the number of hail event counts at…”
Section: Estimating the Changes In The Spatial Distribution Of Hail A...mentioning
Given its high population density and degree of urbanization, the eastern United States (US) is a region vulnerable to the impacts from hailstorms. Small changes in hail activity may indicate large impacts on the potential hail risks faced by the region. While contrasting hailstorm-favorable environmental changes between the northeastern and southeastern US have been documented, the meridional shift of hail activity in the eastern US has not been directly revealed based on observed hailstorm records. Here, using the official hailstorm database, we find a significant northward migration of hail activity (+0.33°N/decade) in the eastern US since 2000, which is mainly contributed by the increasing proportion of large hailstorm events (hail size 0.75–2.0 inch) hitting the northeastin July and August (+0.93°N/decade). The spatially inhomogeneous climatic mean state changes over the past two decades contribute a leading role: the intensified Bermuda High and the weakened upper-level jet stream over the central US tended to moisten (dry) the atmosphere over the northeastern (southeastern) US by enhancing the low-level poleward moisture transport. This not only provides more moisture for hailstorm formation in the northeast but also destabilizes (stabilizes) the atmosphere in the northeast (southeast) under an overall increase in dry instability over the eastern US. These factors together lead to a northward shift of large hailstorms toward the northeastern US, where hailstorms were relatively seldom reported. Incorporating this shift in knowledge may improve contingency and risk management strategies of both the public and private sectors in future climate change.
Given its high population density and degree of urbanization, the eastern United States (US) is a region vulnerable to the impacts from hailstorms. Small changes in hail activity may indicate large impacts on the potential hail risks faced by the region. While contrasting hailstorm-favorable environmental changes between the northeastern and southeastern US have been documented, the meridional shift of hail activity in the eastern US has not been directly revealed based on observed hailstorm records. In this letter, using the official hailstorm database, we find a significant northward migration of hail activity (+0.33°N/decade) in the eastern US since 2000, which is mainly contributed by the increasing proportion of large hailstorm events (hail size 0.75–2.0 inch) hitting the northeast in July and August (+0.93°N/decade). The spatially inhomogeneous climatic mean state changes over the past two decades contribute a leading role: the intensified Bermuda High and the eastward shift of upper-level jet stream over the central US tended to moisten (dry) the atmosphere over the northeastern (southeastern) US by enhancing the low-level poleward moisture transport. This not only provides more moisture for hailstorm formation in the northeast but also destabilizes (stabilizes) the atmosphere in the northeast (southeast) under an overall increase in dry instability over the eastern US. These factors together lead to a northward shift of large hailstorms toward the northeastern US, where hailstorms were relatively seldom reported. Incorporating this shift in knowledge may improve contingency and risk management strategies of both the public and private sectors in the future.
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