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1.
The winters of 1997/1998 and 1998/1999,corresponding to El Ni(?)o and La Ni(?)a episodes,respectively, were two typical rain-abundant and-scarce seasons for the southern China.In order to understand the cause of the anomalous precipitation during the two winters,a comparative analysis technique has been employed to investigate the differences in general circulation and moisture transportation between the two seasons. The results show that the abundant rainfall during the winter of 1997/1998 was associated with the ENSO warm episode event,eastward shifted weak westerly trough/ridge,weakened East Asian winter monsoon (EAWM),strengthened subtropical high,and presented two anti-cyclonic circulations over Hokkaido and the Philippine Sea,respectively,as well as one cyclonic circulation over the Yangtze River Basin in the anomalous wind fields of the lower troposphere.During the rain-scarce winter,however,the patterns of equatorial sea surface temperature anomalies and the circulation systems both in upper and lower levels were nearly the opposite of those during the rain-abundant winter.It has also been discovered that the water vapor over southern China during the winters came mainly from the southwesterly flow ahead of troughs in the southern branch of westerlies and the turning flow over the South China Sea-Indo-China Peninsula area;and the moisture transportation channels varied significantly with regard to height.The intensified flow in the southern branch of westerlies and the anti-cyclonic circulation anomaly over the Philippine Sea during the winter of 1997/1998 were favorable for moisture transportation to mainland China,however the two moisture transportation streams were dramatically weakened during the winter of 1998/1999 due to weak westerly flow and the dominance of a cold high system in the lower level over the southeast coast of China.Such a significant inter-annual change of moisture transportation is a key factor resulting in the obvious difference in precipitation between the two winters. 相似文献
2.
This study examines the diversity of low-level jet(LLJ) formation and related physical processes over southern China.A total of 171 LLJ formation events with enhanced daily southwesterlies and early-morning maximum wind speeds were observed during the mei-yu seasons of 1989–2018. The LLJs can be further categorized into four types based on the increases in the daily mean and diurnal amplitude of the low-level winds. Analysis of the synoptic-scale disturbances shows that the two types of LLJ form... 相似文献
3.
Nazzareno Diodato Gianni Bellocchi Chiara Bertolin Dario Camuffo 《Theoretical and Applied Climatology》2013,113(1-2):187-196
This paper has exploited, for Central and Southern Italy (Mediterranean Sub-regional Area), an unprecedented historical dataset as an attempt to model seasonal (winter and summer) air temperatures in pre-instrumental time (back to 1500). Combining information derived from proxy–documentary data and large-scale simulation, a statistical downscaling approach in the form of mixed regression model was developed to adapt larger-scale estimations (regional component) to the sub-regional temperature pattern (local component). It interprets local temperature anomalies by means of monthly based Temperature Anomaly Scaled Index in the range ?5 (very cold conditions in June) to 2 (very warm conditions). The modelled response agrees well with the independent data from the validation sample (Nash–Sutcliffe efficiency coefficient, >0.60). The advantage of the approach is not merely increased accuracy in estimation. Rather, it relies on the ability to extract (and exploit) the right information to replicate coherent temperature series in historical times. 相似文献
4.
Amita Prabhu Ramesh Kripalani Jaiho Oh Bhaskar Preethi 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(2):217-228
We demonstrate that a large-scale longitudinally symmetric global phenomenon in the Southern Hemisphere sub-polar region can transmit its influence over a remote local region of the Northern Hemisphere traveling more than 100° of latitudes (from ~70°S to ~40°N). This is illustrated by examining the relationship between the Southern Annular Mode (SAM) and the Korean Monsoon Rainfall (KMR) based on the data period 1983-2013. Results reveal that the May-June SAM (MJSAM) has a significant in-phase relationship with the subsequent KMR. A positive MJSAM is favorable for the summer monsoon rainfall over the Korean peninsula. The impact is relayed through the central Pacific Ocean. When a negative phase of MJSAM occurs, it gives rise to an anomalous meridional circulation in a longitudinally locked air-sea coupled system over the central Pacific that propagates from sub-polar to equatorial latitudes and is associated with the central Pacific warming. The ascending motion over the central Pacific descends over the Korean peninsula during peak-boreal summer resulting in weakening of monsoon rainfall. The opposite features prevail during a positive phase of SAM. Thus, the extreme modes of MJSAM could possibly serve as a predictor for ensuing Korean summer monsoon rainfall. 相似文献
5.
The atmospheric conditions that lead to strong offshore surface winds in Southern California, commonly referred to as Santa
Ana winds, are investigated using the North American Regional Reanalysis and a 12-year, 6-km resolution regional climate simulation
of Southern California. We first construct an index to characterize Santa Ana events based on offshore wind strength. This
index is then used to identify the average synoptic conditions associated with Santa Ana events—a high pressure anomaly over
the Great Basin. This pressure anomaly causes offshore geostrophic winds roughly perpendicular to the region’s mountain ranges,
which in turn cause surface flow as the offshore momentum is transferred to the surface. We find, however, that there are
large variations in the synoptic conditions during Santa Ana conditions, and that there are many days with strong offshore
flow and weak synoptic forcing. This is due to local thermodynamic forcing that also causes strong offshore surface flow:
a large temperature gradient between the cold desert surface and the warm ocean air at the same altitude creates an offshore
pressure gradient at that altitude, in turn causing katabatic-like offshore flow in a thin layer near the surface. We quantify
the contribution of “synoptic” and “local thermodynamic” mechanisms using a bivariate linear regression model, and find that,
unless synoptic conditions force strongly onshore winds, the local thermodynamic forcing is the primary control on Santa Ana
variability. 相似文献
6.
The October rains (at the onset of the rainy season that extends to April) in southern Israel have steeply increased in the last quarter century relative to the prior two decades. A less pronounced, but appreciable, increase is noted for the rest of the rainy season. This apparent reversal of desertification is attributed here to land use changes. Afforestation, increased cultivation and limitations on grazing after the establishment of the State of Israel resulted in an increased vegetation cover over the inherently high-albedo soils in this region (an area of 104 km2). The changes are shown in a July 1985 Landsat image of the area.The increase in precipitation is specifically attributed to intensification of the dynamical processes of convection and advection resulting from plant-induced enhancement of thedaytime sensible heat flux from the generally dry surface. This enhancement results both from the reduced surface albedo and the reduced soil heat flux (reduced day-to-night heat storage in the soil) in October when insolation is strong. Stronger daytime convection can lead to penetration of the inversions capping the planetary boundary layer (which are weaker in October than in summer) while strengthened advection (sea breeze) can provide moist air from the warm Mediterranean Sea. This suggested mechanism is consistent with previous studies showing that the autumn rains in southern Israel exhibit convective mesoscale characteristics and occur predominantly in the daytime. However, other causes, such as a shift in the synoptic-scale circulation, cannot be ruled out at this stage. 相似文献
7.
Changes in wintertime 10 m winds due to the El Niño-Southern Oscillation are examined using a 6 km resolution climate simulation of Southern California covering the period from 1959 through 2001. Wind speed statistics based on regional averages reveal a general signal of increased mean wind speeds and wind speed variability during El Niño across the region. An opposite and nearly as strong signal of decreased wind speed variability during La Niña is also found. These signals are generally more significant than the better-known signals in precipitation. In spite of these regional-scale generalizations, there are significant sub-regional mesoscale structures in the wind speed impacts. In some cases, impacts on mean winds and wind variability at the sub-regional scale are opposite to those of the region as a whole. All of these signals can be interpreted in terms of shifts in occurrences of the region’s main wind regimes due to the El Niño phenomenon. The results of this study can be used to understand how interannual wind speed variations in regions of Southern California are influenced by the El Niño phenomenon. 相似文献
8.
Little is known about the influence of hurricanes on precipitation extremes (PEs) in Southern Ontario, Canada. We examine PEs and their spatial–temporal link with hurricanes events in Southern Ontario during the period of 1950–2000. On average, 5.4 PEs or 11 % of the 50 wettest days in the selected five locations occurred under the influence of hurricanes within this 51-year period. Our results indicate hurricane-influenced PEs are most frequent in September and derive from storms that had reached major hurricane status (>50 m/s) at some point during their lifetime. An absence of landfalling hurricanes in Southern Ontario during the 1960s to 1980s suggests either that the direct impact of hurricanes occurs on a multidecadal time scale or that recent years are experiencing unprecedented change. 相似文献
9.
Observations indicate that the Atlantic zonal mode influences El Ni?o Southern Oscillation (ENSO) in the Pacific, as already suggested in previous studies. Here we demonstrate for the first time using partial coupled experiments that the Atlantic zonal mode indeed influences ENSO. The partial coupling experiments are performed by forcing the coupled general circulation model (ECHAM5/MPI-OM) with observed sea surface temperature (SST) in the Tropical Atlantic, but with full air-sea coupling allowed in the Pacific and Indian Ocean. The ensemble mean of a five member simulation reproduces the observational results well. Analysis of observations, reanalysis, and coupled model simulations all indicate the following mechanism: SST anomalies associated with the Atlantic zonal mode affect the Walker Circulation, driving westward wind anomalies over the equatorial Pacific during boreal summer. The wind stress anomalies increase the east-west thermocline slope and enhance the SST gradient across the Pacific; the Bjerknes positive feedback acts to amplify these anomalies favouring the development of a La Ni?a-like anomalies. The same mechanisms act for the cold phase of Atlantic zonal mode, but with opposite sign. In contrast to previous studies, the model shows that the influence on ENSO exists before 1970. Furthermore, no significant influence of the Tropical Atlantic on the Indian Monsoon precipitation is found in observation or model. 相似文献
10.
《Journal of Meteorological Research》2021,(2):271-281
Winter rainfall over southern China is usually enhanced when Madden–Julian oscillation(MJO) is active over the Indian Ocean, but it can be weakened under certain conditions. Here, the diversity of MJO impacts on winter rainfall and its mechanisms are explored by using scenarios of enhanced and suppressed rainfall anomalies over southern China when MJO is active over the Indian Ocean. The combined effects of low-frequency background moisture and intraseasonal winds are the major contributors to the different rainfall anomalies. Anomalous circulation in mid–high latitudes, especially on intraseasonal timescales, is almost opposite in the two scenarios, which can modulate the response of extratropical atmosphere to MJO heating and then induces the different circulations over southern China. In the enhanced scenario, mid–high latitudes of Eurasia and southern China are dominated by positive and negative sea level pressure anomalies, respectively. The southerly over southern China and the South China Sea induced by MJO heating promotes the anomalous moisture convergence and ascending motion over southern China, resulting in the enhanced rainfall. In the suppressed scenario, however, the circulation in mid–high latitudes does not favor rainfall over southern China and leads to the northerly response to MJO heating over southern China, which enhances moisture divergence and weakens rainfall over southern China. 相似文献
11.
Ｍｏｄｅｌ ｆｏｒ Ｍｅｔｈａｎｅ Ｅｍｉｓｓｉｏｎ ｆｒｏｍ Ｒｉｃｅ Ｆｉｅｌｄｓ ａｎｄ Ｉｔｓ Ａｐｐｌｉｃａｔｉｏｎ ｉｎ Ｓｏｕｔｈｅｒｎ ＣｈｉｎａＤｉｎｇＡｉｊｕａｎｄＷａｎｇＭｉｎｇｘｉｎｇ（ＩｎｓｔｉｔｕｔｅｏｆＡｔｍｏｓｐｈｅｒ... 相似文献
12.
To explain the recent three-year La Ni?a event from 2020 to 2022, which has caused catastrophic weather events worldwide, Fasullo et al.(2023) demonstrated that the increase in biomass aerosol resulting from the 2019-20 Australian wildfire season could have triggered this multi-year La Ni?a. Here, we present compelling evidence from paleo-proxies,utilizing a substantial sample size of 26 volcanic eruptions in the Southern Hemisphere(SH), to support the hypothesis that ocean cooling in the SH can... 相似文献
13.
Impact of Ocean-Continent Distribution over Southern Asia on the Formation of Summer Monsoon 总被引：2，自引：0，他引：2 
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下载免费PDF全文 Using the CCM3/NCAR, a series of numerical experiments are designed to explore the effect of ocean-land interlaced distributions of Africa-Arabian Sea-India Peninsula-Bay of Bengal (BOB)-Indo-China Peninsula-South China Sea on the formation of the Asian summer monsoon circulation (ASMC). The results show that the thermal difference between African or Indian Subcontinent and nearby areas including the Indian Ocean, Arabian Sea, and part of BOB is the primary mechanism that maintains the Indian monsoon circulation. In the experiment getting rid of these two continents, the Indian monsoon system (IMS) members, i.e., the Somali cross-equatorial jet (40°E) and the southwesterly monsoon over the Arabian Sea and BOB, almost disappear. Moreover, the Hadley circulation weakens dominantly. It also proves that Africa has greater effect than Indian Subcontinent on the IMS. However, the existence of Indo-China Peninsula and Australia strengthens the East Asian monsoon system (EAMS). The thermal contrast between Indo-China Peninsula and SCS, Australia and western Pacific Ocean plays an important role in the formation of the tropical monsoon to the south of the EAMS. When the Indo-China Peninsula is masked in the experiment, the cross-equatorial flow (105°E and 125°E) vanishes, so does the southwesterly monsoon usually found over East Asia, and EAMS is enfeebled significantly. In addition, the impacts of these thermal contrasts on the distribution of the summer precipitation and surface temperature are investigated. 相似文献
14.
It has long been acknowledged that there are two types of El Nio events, i.e., the eastern Pacific El Nio (EE) and the central Pacific El Nio (CE), according to the initial position of the anomalous warm water and its propagation direction. In this paper, the oceanic and atmospheric evolutions and the possible mechanisms of the two types of El Nio events were examined. It is found that all the El Nio events, CE or EE, could be attributed to the joint impacts of the eastward advection of warm water from the western Pacific warm pool (WPWP) and the local warming in the equatorial eastern Pacific. Before the occurrence of CE events, WPWP had long been in a state of being anomalous warm, so the strength of eastward advection of warm water was much stronger than that of EE, which played a major role in the formation of CE. While for the EE events, most contribution came from the local warming of the equatorial eastern Pacific. It is further identified that the immediate cause leading to the difference of the two types of El Nio events was the asynchronous variations of the Southern Oscillation (SO) and the Northern Oscillation (NO) as defined by Chen in 1984. When the transition from the positive phase of the NO (NO+) to NO- was prior to that from SO+ to SO-, there would be eastward propagation of westerly anomalies from the tropical western Pacific induced by NO and hence the growth of warm sea surface temperature anomalies in WPWP and its eastward propagation. This was followed by lagged SO-induced weakening of southeast trade winds and local warming in the equatorial eastern Pacific. These were conducive to the occurrence of the CE. On the contrary, the transition from SO+ to SO- leading the transition of NO would favor the occurrence of EE type events. 相似文献
15.
It has long been acknowledged that there are two types of El Nio events, i.e., the eastern Pacific El Nio (EE) and the central Pacific El Nio (CE), according to the initial position of the anomalous warm water and its propagation direction. In this paper, the oceanic and atmospheric evolutions and the possible mechanisms of the two types of El Nio events were examined. It is found that all the El Nio events, CE or EE, could be attributed to the joint impacts of the eastward advection of warm water from... 相似文献
16.
17.
Pascal Terray 《Climate Dynamics》2011,36(11-12):2171-2199
The main goal of this paper is to shed additional light on the reciprocal dynamical linkages between mid-latitude Southern Hemisphere climate and the El Ni?o-Southern Oscillation (ENSO) signal. While our analysis confirms that ENSO is a dominant source of interannual variability in the Southern Hemisphere, it is also suggested here that subtropical dipole variability in both the Southern Indian and Atlantic Oceans triggered by Southern Hemisphere mid-latitude variability may also provide a controlling influence on ENSO in the equatorial Pacific. This subtropical forcing operates through various coupled air?Csea feedbacks involving the propagation of subtropical sea surface temperature (SST) anomalies into the deep tropics of the Atlantic and Indian Oceans from boreal winter to boreal spring and a subsequent dynamical atmospheric response to these SST anomalies linking the three tropical basins at the beginning of the boreal spring. This atmospheric response is characterized by a significant weakening of the equatorial Atlantic and Indian Inter-Tropical Convergence Zone (ITCZ). This weakened ITCZ forces an equatorial ??cold Kelvin wave?? response in the middle to upper troposphere that extends eastward from the heat sink regions into the western Pacific. By modulating the vertical temperature gradient and the stability of the atmosphere over the equatorial western Pacific Ocean, this Kelvin wave response promotes persistent zonal wind and convective anomalies over the western equatorial Pacific, which may trigger El Ni?o onset at the end of the boreal winter. These different processes explain why South Atlantic and Indian subtropical dipole time series indices are highly significant precursors of the Ni?o34 SST index several months in advance before the El Ni?o onset in the equatorial Pacific. This study illustrates that the atmospheric internal variability in the mid-latitudes of the Southern Hemisphere may significantly influence ENSO variability. However, this surprising relationship is observed only during recent decades, after the so-called 1976/1977 climate regime shift, suggesting a possible linkage with global warming or decadal fluctuations of the climate system. 相似文献
18.
The El Niño Southern Oscillation (ENSO) affects weather around the globe, particularly in regions where developing countries typically lie. These countries are known to be most vulnerable to weather anomalies, and ENSO thereby has the potential to influence their economic growth. In this study, we investigate the effect of ENSO on economic growth in 69 developing countries, using annual data from 1961 to 2015. We find regime-dependent nonlinearity in the growth response to ENSO shocks. An El Niño event, equivalent to a 1 °C deviation in sea surface temperatures in the Niño3.4 region of the equatorial Pacific, results in one-to-two percent annual growth reduction during the El Niño regime, but the effect is absent during the La Niña regime. In addition, we find that the effect of El Niño is twice-as-large in the tropics relative to temperate areas, and particularly pronounced in Africa and Asia-Pacific. The findings of this study have two important implications. From the modeling standpoint, we find that the growth impacts of ENSO shocks are nonlinear, and vary across regions and climatic zones. From the policy-making standpoint, our findings suggest opportunities for short-term adjustments to climate shock management and international aid programs, depending on the existing state and the intermediate-term patterns of the ENSO cycle. 相似文献
19.