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1.
Tibet’s ancient topography and its role in climatic and biotic evolution remain speculative due to a paucity of quantitative surface-height measurements through time and space, and sparse fossil records. However, newly discovered fossils from a present elevation of ∼4,850 m in central Tibet improve substantially our knowledge of the ancient Tibetan environment. The 70 plant fossil taxa so far recovered include the first occurrences of several modern Asian lineages and represent a Middle Eocene (∼47 Mya) humid subtropical ecosystem. The fossils not only record the diverse composition of the ancient Tibetan biota, but also allow us to constrain the Middle Eocene land surface height in central Tibet to ∼1,500 ± 900 m, and quantify the prevailing thermal and hydrological regime. This “Shangri-La”–like ecosystem experienced monsoon seasonality with a mean annual temperature of ∼19 °C, and frosts were rare. It contained few Gondwanan taxa, yet was compositionally similar to contemporaneous floras in both North America and Europe. Our discovery quantifies a key part of Tibetan Paleogene topography and climate, and highlights the importance of Tibet in regard to the origin of modern Asian plant species and the evolution of global biodiversity.

The Tibetan Plateau, once thought of as entirely the product of the India–Eurasia collision, is known to have had significant complex relief before the arrival of India early in the Paleogene (13). This large region, spanning ∼2.5 million km2, is an amalgam of tectonic terranes that impacted Asia long before India’s arrival (4, 5), with each accretion contributing orographic heterogeneity that likely impacted climate in complex ways. During the Paleogene, the Tibetan landscape comprised a high (>4 km) Gangdese mountain range along the southern margin of the Lhasa terrane (2), against which the Himalaya would later rise (6), and a Tanghula upland on the more northerly Qiangtang terrane (7). Separating the Lhasa and Qiangtang blocks is the east–west trending Banggong-Nujiang Suture (BNS), which today hosts several sedimentary basins (e.g., Bangor, Nyima, and Lunpola) where >4 km of Cenozoic sediments have accumulated (8). Although these sediments record the climatic and biotic evolution of central Tibet, their remoteness means fossil collections have been hitherto limited. Recently, we discovered a highly diverse fossil assemblage in the Bangor Basin. These fossils characterize a luxuriant seasonally wet and warm Shangri-La forest that once occupied a deep central Tibetan valley along the BNS, and provide a unique opportunity for understanding the evolutionary history of Asian biodiversity, as well as for quantifying the paleoenvironment of central Tibet.*Details of the topographic evolution of Tibet are still unclear despite decades of investigation (4, 5). Isotopic compositions of carbonates recovered from sediments in some parts of central Tibet have been interpreted in terms of high (>4 km) Paleogene elevations and aridity (9, 10), but those same successions have yielded isolated mammal (11), fish (12), plant (1318), and biomarker remains (19) more indicative of a low (≤3-km) humid environment, but how low is poorly quantified. Given the complex assembly of Tibet, it is difficult to explain how a plateau might have formed so early and then remained as a surface of low relief during subsequent compression from India (20). Recent evidence from a climate model-mediated interpretation of palm fossils constrains the BNS elevation to below 2.3 km in the Late Paleogene (16), but more precise paleoelevation estimates are required. Further fossil discoveries, especially from earlier in the BNS sedimentary records, would document better the evolution of the Tibetan biota, as well as informing our understanding of the elevation and climate in an area that now occupies the center of the Tibetan Plateau.Our work shows that the BNS hosted a diverse subtropical ecosystem at ∼47 Ma, and this means the area must have been both low and humid. The diversity of the fossil flora allows us to 1) document floristic links to other parts of the Northern Hemisphere, 2) characterize the prevailing paleoclimate, and 3) quantify the elevation at which the vegetation grew. We propose that the “high and dry” central Tibet inferred from some isotope paleoaltimetry (9, 10) reflects a “phantom” elevated paleosurface (20) because fractionation over the bounding mountains allowed only isotopically light moist air to enter the valley, giving a false indication of a high elevation (21).  相似文献   
2.
A high-resolution multiproxy record, including pollen, foraminifera, and alkenone paleothermometry, obtained from a single core (DG9603) from the Okinawa Trough, East China Sea (ECS), provided unambiguous evidence for asynchronous climate change between the land and ocean over the past 40 ka. On land, the deglacial stage was characterized by rapid warming, as reflected by paleovegetation, and it began ca. 15 kaBP, consistent with the timing of the last deglacial warming in Greenland. However, sea surface temperature estimates from foraminifera and alkenone paleothermometry increased around 20–19 kaBP, as in the Western Pacific Warm Pool (WPWP). Sea surface temperatures in the Okinawa Trough were influenced mainly by heat transport from the tropical western Pacific Ocean by the Kuroshio Current, but the epicontinental vegetation of the ECS was influenced by atmospheric circulation linked to the northern high-latitude climate. Asynchronous terrestrial and marine signals of the last deglacial warming in East Asia were thus clearly related to ocean currents and atmospheric circulation. We argue that (i) early warming seawater of the WPWP, driven by low-latitude insolation and trade winds, moved northward via the Kuroshio Current and triggered marine warming along the ECS around 20–19 kaBP similar to that in the WPWP, and (ii) an almost complete shutdown of the Atlantic Meridional Overturning Circulation ca. 18–15 kaBP was associated with cold Heinrich stadial-1 and delayed terrestrial warming during the last deglacial warming until ca. 15 kaBP at northern high latitudes, and hence in East Asia. Terrestrial deglacial warming therefore lagged behind marine changes by ca. 3–4 ka.  相似文献   
3.
From the deglacial period to the mid-Holocene, North Africa was characterized by much wetter conditions than today. The broad timing of this period, termed the African Humid Period, is well known. However, the rapidity of the onset and termination of the African Humid Period are contested, with strong evidence for both abrupt and gradual change. We use optically stimulated luminescence dating of dunes, shorelines, and fluviolacustrine deposits to reconstruct the fluctuations of Lake Mega-Chad, which was the largest pluvial lake in Africa. Humid conditions first occur at ∼15 ka, and by 11.5 ka, Lake Mega-Chad had reached a highstand, which persisted until 5.0 ka. Lake levels fell rapidly at ∼5 ka, indicating abrupt aridification across the entire Lake Mega-Chad Basin. This record provides strong terrestrial evidence that the African Humid Period ended abruptly, supporting the hypothesis that the African monsoon responds to insolation forcing in a markedly nonlinear manner. In addition, Lake Mega-Chad exerts strong control on global biogeochemical cycles because the northern (Bodélé) basin is currently the world’s greatest single dust source and possibly an important source of limiting nutrients for both the Amazon Basin and equatorial Atlantic. However, we demonstrate that the final desiccation of the Bodélé Basin occurred around 1 ka. Consequently, the present-day mode and scale of dust production from the Bodélé Basin cannot have occurred before 1 ka, suggesting that its role in fertilizing marine and terrestrial ecosystems is either overstated or geologically recent.The West African monsoon (WAM) is key to our understanding of the African climate system and the impacts of future climate change upon its population. Climatically, the WAM is a major component of the global monsoon belt, which regulates moisture availability in the low latitudes and is sensitive to climate dynamics in both the high latitudes and the tropics. From a human perspective, the WAM represents the dominant control upon agricultural productivity in a densely populated region that is heavily reliant on subsistence agriculture (1). The broad pattern of WAM dynamics since the Last Glacial Maximum (LGM) is well known, with initially arid conditions being replaced by a more humid phase, sometimes termed the African Humid Period (AHP), which lasted from the deglacial period to the mid-Holocene. However, paleoclimate proxy data from North Africa and adjacent areas of the Atlantic provide contrasting evidence for the rate and timing of these changes, leading to uncertainty over the controls upon WAM dynamics.  相似文献   
4.

Background:

To utilise an autopsy-based approach to study the febrile deaths and deaths due to malaria during monsoon period of three years at a tertiary care teaching hospital in Mumbai, India.

Materials and Methods:

All autopsies done at the hospital during monsoon period from 2005 to 2007 when fever was the main presenting symptom were included in the study. Monsoon period was defined from June to September. A study on the duration of hospital stay of malaria deaths was also attempted.

Results:

There were 202 autopsies of febrile illness during the study period. Malaria resulted in 20.8% of the deaths besides other causes. A majority of deaths had intrapulmonary haemorrhages as the only pathological finding. Incidence of malaria deaths was more during monsoon period than the non-monsoon period. Plasmodium falciparum was the most common species responsible for malaria deaths while cerebral malaria was the most common mode of death. In 27% of the cases, post-mortem examination helped to arrive at the correct final diagnosis. In 88.1% of the cases, malaria deaths occurred within the first 24 hours of admission to the hospital.

Conclusion:

The study reiterates the fact that malaria remains a preventable but major cause of death in India, predominantly during the monsoon period. The study also emphasises the importance of developing treatment protocols for malaria during such crucial times besides reinforcing the existing preventive measures.  相似文献   
5.
Purpose: To explore the impact of subtropical maritime monsoon climate on the frequency of ambulance use for trauma patients in a coastal region in China. Method: Statistical analysis of data on ambulance use from the 120 Emergency Command Center in Shantou City, Guangdong Province, from January to December 2012 as well as daily meteorological data from a Shantou observatory was performed to determine how climatic factors (seasons, time, and weather) affect the frequency of ambulance use for trauma patients. Results: The daily ambulance use for trauma patients differed between spring and summer or autumn (p < 0.05), between sunny and rainy days (p < 0.05), and between cloudy and lightly or moderately rainy days (p < 0.05). We found a linear correlation between daily maximum temperature and daily ambulance use for trauma patients (R2 ¼ 0.103, p < 0.05). In addition, there was significant difference in ambulance use between good and bad weather (p < 0.05). Conclusion: Frequency of ambulance use for trauma patients is affected by the subtropical maritime monsoon climate in the coastal region. Better weather contributes to increased daily frequency of ambulance use, which is the highest in autumn and lowest in spring.  相似文献   
6.
Preindustrial changes in the Asian summer monsoon climate from the 1700s to the 1850s were estimated with an atmospheric general circulation model (AGCM) using historical global land cover/use change data reconstructed for the last 300 years. Extended cultivation resulted in a decrease in monsoon rainfall over the Indian subcontinent and southeastern China and an associated weakening of the Asian summer monsoon circulation. The precipitation decrease in India was marked and was consistent with the observational changes derived from examining the Himalayan ice cores for the concurrent period. Between the 1700s and the 1850s, the anthropogenic increases in greenhouse gases and aerosols were still minor; also, no long-term trends in natural climate variations, such as those caused by the ocean, solar activity, or volcanoes, were reported. Thus, we propose that the land cover/use change was the major source of disturbances to the climate during that period. This report will set forward quantitative examination of the actual impacts of land cover/use changes on Asian monsoons, relative to the impact of greenhouse gases and aerosols, viewed in the context of global warming on the interannual, decadal, and centennial time scales.  相似文献   
7.
A speleothem δ18O record from Xiaobailong cave in southwest China characterizes changes in summer monsoon precipitation in Northeastern India, the Himalayan foothills, Bangladesh, and northern Indochina over the last 252 kyr. This record is dominated by 23-kyr precessional cycles punctuated by prominent millennial-scale oscillations that are synchronous with Heinrich events in the North Atlantic. It also shows clear glacial–interglacial variations that are consistent with marine and other terrestrial proxies but are different from the cave records in East China. Corroborated by isotope-enabled global circulation modeling, we hypothesize that this disparity reflects differing changes in atmospheric circulation and moisture trajectories associated with climate forcing as well as with associated topographic changes during glacial periods, in particular redistribution of air mass above the growing ice sheets and the exposure of the “land bridge” in the Maritime continents in the western equatorial Pacific.The Indian summer monsoon (ISM), a key component of tropical climate, provides vital precipitation to southern Asia. The ISM is characterized by two regions of precipitation maxima: a narrow coastal region along the Western Ghats, denoted by ISMA, with moisture from the Arabian Sea, and a broad “Monsoon Zone” around 20°N in northeastern India, denoted by ISMB, where storms emanate from the Bay of Bengal and whose rainfall variability is well correlated with that of “All India” rainfall (1). Multiple proxies obtained from Arabian Sea sediments have revealed the variability of summer monsoon winds on timescales of 101 to 105 y (e.g., refs. 26). Our understanding of the paleo-precipitation variability of ISMB remains incomplete, owing to the scarcity of long and high-resolution records. Here we present a 252,000-y-long speleothem δ18O record from Xiaobailong cave, southwest China and characterize variability in the ISMB precipitation on multiple timescales.Xiaobailong (XBL, “Little White Dragon”) cave is located in Yunnan Province, southwestern China, near the southeastern edge of the Tibetan Plateau (103°21′E, 24°12′N, ∼1,500 m above sea level; SI Appendix, Fig. S1). Local climate is characterized by warm/wet summers and cool/dry winters. The mean annual precipitation of ∼960 mm (1960–2000) falls mostly from June through September (∼80%) (SI Appendix, Fig. S2), indicating the summer monsoon rainfall dominates the annual precipitation at the cave site. The temperature in the cave is 17.2 °C, close to local mean annual air temperature (17.3 °C).Eight stalagmites were collected from the inner chamber (∼350 m from the entrance) of the cave, where humidity is ∼100% and ventilation is confined to a small crawl-in channel to the outer chamber. One hundred four 230Th dates were determined on inductively coupled plasma mass spectrometers with typical relative error in age (2σ) of less than 1% (Methods and SI Appendix, Table S1 and Figs. S3 and S4). The ages vary monotonically with depth in the stalagmites (SI Appendix, Fig. S4) and the 230Th dates were linearly interpolated to establish chronologies. Measurements of calcite δ18O (δ18Oc) were made by isotope ratio mass spectrometer on a total of 1,896 samples from the eight stalagmites (Methods and SI Appendix, Table S2). By matching the chronology established by the absolute 230Th dates the δ18Oc time series of the different stalagmites were combined to form a single time series. The resulting XBL record (Fig. 1) covers the past 252,000 y, with an average resolution of 70 y between 5.0 and 80.0 thousand years before the present (ka BP, before 1950 AD) and 260 y between 80.0 and 252.0 ka BP, excluding several interruptions of calcite deposition (e.g., during the periods of 52.4–59.8, 164.0–167.2, 204.5–214.1, and 216.8–222.2 ka BP).Open in a separate windowFig. 1.(A) The δ18Oc record of the stalagmites from Xiaobailong cave: XBL-3 (yellow), XBL-4 (green), XBL-7 (blue), XBL-26 (orange), XBL-27 (violet), XBL-29 (red), XBL-48 (pink), XBL-65 (dark blue), and XBL-1 (brown) (12). The gray curve shows a previously established δ18Oc record from the Tibetan Plateau (Tianmen Cave), indicating ISM variations during Marine Isotope Stage 5 (21). The 230Th dates and errors (2σ error bars) are color-coded by stalagmites. (B) The δ18Oc records of Hulu cave (dark green) (18), Dongge cave (blue) (19), Sanbao cave (sky blue) (20), and Linzhu cave (light green) (20). The δ18O scales for all records shown are reversed (increasing downward). Summer insolation at 30°N (gray dashed line) is integrated over June, July, and August (44).In principle, variations in calcite δ18Oc of stalagmites could capture variations of δ18O in precipitation (δ18Op), cave temperature, which is close to the surface annual mean temperature, and kinetic loss of CO2 and evaporation of water during the calcite deposition. We rule out the kinetic fractionation processes, because δ18Oc records from different stalagmites in the XBL cave agree with one another within quoted dating errors over contemporaneous growth periods (Fig. 1), and δ13C records also replicate across speleothems within the cave, suggesting dominant climate control (SI Appendix, Fig. S5). Furthermore, the XBL δ18Oc records broadly resemble, on precessional and millennial timescales for overlapping periods (Fig. 1), speleothem records from Hulu, Dongge, Sanbao, and Linzhu caves (HL-DG-SB-LZ) in East China (7), providing another robust replication test and indicating that the δ18Oc signal in these stalagmites is primarily of climatic origin. The range of calcite δ18Oc change at XBL is ∼8.0‰ over 252 kyr. Because temperature-dependent fractionation between calcite and water is likely to be below 2‰ [estimated using ∼−0.23‰/°C (8), and assuming a maximum 8 °C difference between glacial and interglacial periods (9)], the shifts in stalagmite δ18Oc are primarily due to changes in meteoric precipitation δ18Op at the cave site.We interpret XBL δ18Oc as an index of ISMB rainfall at a region denoted the Monsoon Zone-B, which encompasses the Monsoon Zone of northeastern India (1), the Himalayan foothills, Bangladesh, and northern Indochina. First, the Bay of Bengal supplies the bulk of moisture to both the Monsoon Zone-B and to XBL across the Indochinese Peninsula, and present-day summer precipitation in the two regions is positively correlated (SI Appendix, Fig. S6). Second, multiple climate model simulations show similar 850-hPa wind trajectories for these two regions for both present day and Last Glacial Maximum (LGM), suggesting moisture paths from the Bay of Bengal to XBL were relatively stable in the past (SI Appendix, Fig. S7). Third, the XBL δ18Oc record shows good agreement (r = 0.56), over the past 100 ka, with the salinity proxy, and by inference fluvial runoff proxy, reconstructed from ODP core 126 KL in the Bay of Bengal (10), with decreased δ18Oc values at XBL corresponding with lower salinity and hence increased precipitation, and vice versa (SI Appendix, Fig. S8). We hereafter define a “strong” ISMB as an increase of precipitation over the Monsoon Zone-B, and a corresponding decrease of δ18Oc value at XBL (SI Appendix, SI Materials and Methods).  相似文献   
8.
In this paper, using idealized climate model simulations, we investigate the biogeophysical effects of large-scale deforestation on monsoon regions. We find that the remote forcing from large-scale deforestation in the northern middle and high latitudes shifts the Intertropical Convergence Zone southward. This results in a significant decrease in precipitation in the Northern Hemisphere monsoon regions (East Asia, North America, North Africa, and South Asia) and moderate precipitation increases in the Southern Hemisphere monsoon regions (South Africa, South America, and Australia). The magnitude of the monsoonal precipitation changes depends on the location of deforestation, with remote effects showing a larger influence than local effects. The South Asian Monsoon region is affected the most, with 18% decline in precipitation over India. Our results indicate that any comprehensive assessment of afforestation/reforestation as climate change mitigation strategies should carefully evaluate the remote effects on monsoonal precipitation alongside the large local impacts on temperatures.Historical land cover change has been one of the major drivers of climate change. By the 1750s, ∼6–7% of the global land surface area had been deforested for agriculture. Today, croplands and pasture lands make up approximately one third of the global land surface (14). In terms of area, croplands and pasture lands increased globally from 620 million ha in 1700 to 4,960 million ha by 2000 (1). This large-scale conversion of forests to croplands or grasslands can impact climate through biogeochemical (changes in atmospheric composition) and biogeophysical (changes in physical land surface characteristics such as albedo, evapotranspiration, and roughness length) processes.The impacts of past, present, and future biogeochemical and biogeophysical effects from land use change have been investigated by numerous studies (510). These studies find that the biogeochemical process primarily causes global effects while biogeophysical processes cause strong local effects. The combined biogeochemical and biogeophysical effects from land cover change in the Holocene before 1850 were modeled as a global mean warming of 0.73 K (9).During the historical period (1750 to present day), deforestation-associated CO2 emissions have contributed ∼180 ± 80 PgC to the cumulative anthropogenic CO2 emissions (11) and a warming of ∼0.16–0.30 K (biogeochemical effect) to anthropogenic climate change (5, 6). This warming is probably partly offset by the biogeophysical effect of albedo increase, which may have caused a global mean cooling by ∼0.03–0.27 K (5, 7, 8). However, other major biogeophysical processes, such as reduction in evapotranspiration and roughness length due to deforestation, could result in warming (12).Several studies have investigated the link between land cover change and local climate change (1316). For example, deforestation (16) in the tropics (18.75°S−15°N) reduces precipitation over Amazon by 138 mm/y (9.2%) and increases the temperature by 1.6 K. Another study (17) simulates a 266 mm/y reduction in precipitation over tropics due to tropical deforestation. The biogeophysical effects can also have remote effects via changes in atmospheric circulation (13, 1820). For instance, recent studies (13, 21) find a shift in Intertropical Convergence Zone (ITCZ) due to afforestation in entire midlatitudes or over Eurasia. These studies suggest that the ITCZ shifts can have consequences for precipitation in the monsoon regions of northeast Asia and South Asia.Most of the monsoon regions are located within the vicinity of ITCZ. Thus, the ITCZ shift due to land cover change via remote effects can affect the monsoon regions. To our knowledge, no study has quantified the ITCZ shift and its effect, due to large-scale deforestation, on all of the monsoon regions. In this paper, we show that the remote effect of large-scale deforestation has a larger influence on precipitation in monsoon regions than the local effect, although the local effect has a larger impact on surface temperature changes as shown in several previous studies (1315, 21). The remote effect can be quantified through a relationship between the ITCZ location and the atmospheric heat transport at the equator. Our investigation has direct relevance to changes in precipitation in monsoon regions in the past [for instance, during the Last Glacial Maximum (LGM) and at the Cretaceous–Tertiary boundary when large areas of forests were completely removed], to make improved assessment of risks to agriculture from changes to rainfall in the tropics (22) and to integrated assessments of afforestation/reforestation as climate change mitigation strategies.  相似文献   
9.
The El Niño−Southern Oscillation (ENSO) phenomenon, the most pronounced feature of internally generated climate variability, occurs on interannual timescales and impacts the global climate system through an interaction with the annual cycle. The tight coupling between ENSO and the annual cycle is particularly pronounced over the tropical Western Pacific. Here we show that this nonlinear interaction results in a frequency cascade in the atmospheric circulation, which is characterized by deterministic high-frequency variability on near-annual and subannual timescales. Through climate model experiments and observational analysis, it is documented that a substantial fraction of the anomalous Northwest Pacific anticyclone variability, which is the main atmospheric link between ENSO and the East Asian Monsoon system, can be explained by these interactions and is thus deterministic and potentially predictable.The El Niño−Southern Oscillation (ENSO) phenomenon is a coupled air−sea mode, and its irregular occurring extreme phases El Niño and La Niña alternate on timescales of several years (18). The global atmospheric response to the corresponding eastern tropical Pacific sea surface temperature (SST) anomalies (SSTA) causes large disruptions in weather, ecosystems, and human society (3, 5, 9).One of the main properties of ENSO is its synchronization with the annual cycle: El Niño events tend to grow during boreal summer and fall and terminate quite rapidly in late boreal winter (918). The underlying dynamics of this seasonal pacemaking can be understood in terms of the El Niño/annual cycle combination mode (C-mode) concept (19), which interprets the Western Pacific wind response during the growth and termination phase of El Niño events as a seasonally modulated interannual phenomenon. This response includes a weakening of the equatorial wind anomalies, which causes the rapid termination of El Niño events after boreal winter and thus contributes to the seasonal synchronization of ENSO (17). Mathematically, the modulation corresponds to a product between the interannual ENSO phenomenon (ENSO frequency: fE) and the annual cycle (annual frequency: 1 y-1), which generates near-annual frequencies at periods of  ~  10 mo (1 + fE) and  ~  15 mo (1 − fE) (19).In nature, a wide variety of nonlinear processes exist in the climate system. Atmospheric examples include convection and low-level moisture advection (19). An example for a quadratic nonlinearity is the dissipation of momentum in the planetary boundary layer, which includes a product between ENSO (E) and the annual cycle (A) due to the windspeed nonlinearity: vE⋅ vA (17, 19). In the frequency domain, this product results in the near-annual sum (1 + fE) and difference (1 − fE) tones (19). The commonly used Niño 3.4 (N3.4) SSTA index (details in SI Appendix, SI Materials and Methods) exhibits most power at interannual frequencies (Fig. 1A). In contrast, the near-annual combination tones (1 ± fE) are the defining characteristic of the C-mode (Fig. 1B).Open in a separate windowFig. 1.Schematic for the ENSO (E) and combination mode (ExA) anomalous surface circulation pattern and corresponding spectral characteristics. (A) Power spectral density for the normalized N3.4 index of the Hadley Centre Sea Ice and Sea Surface Temperature data set version 1 (HadISST1) 1958–2013 SSTA using the Welch method. (B) As in A but for the theoretical quadratic combination mode (ExA). (C) Regression coefficient of the normalized N3.4 index and the anomalous JRA-55 surface stream function for the same period (ENSO response pattern). (D) Regression coefficient of the normalized combination mode (ExA) index and the anomalous JRA-55 surface stream function (combination mode response pattern). Areas where the anomalous circulation regression coefficient is significant above the 95% confidence level are nonstippled.Physically, the dominant near-annual combination mode comprises a meridionally antisymmetric circulation pattern (Fig. 1D). It features a strong cyclonic circulation in the South Pacific Convergence Zone, with a much weaker counterpart cyclone in the Northern Hemisphere Central Pacific. The most pronounced feature of the C-mode circulation pattern is the anomalous low-level Northwest Pacific anticyclone (NWP-AC). This important large-scale atmospheric feature links ENSO impacts to the Asian Monsoon systems (2025) by shifting rainfall patterns (SI Appendix, Fig. S1B), and it drives sea level changes in the tropical Western Pacific that impact coastal systems (26). It has been demonstrated using spectral analysis methods and numerical model experiments that the C-mode is predominantly caused by nonlinear atmospheric interactions between ENSO and the warm pool annual cycle (19, 20). Local and remote thermodynamic air−sea coupling amplify the signal but are not the main drivers for the phase transition of the C-mode and its associated local phenomena (e.g., the NWP-AC) (20).Even though ENSO and the C-mode are not independent, their patterns and spectral characteristics are fundamentally different, which has important implications when assessing the amplitude and timing of their regional climate impacts (Fig. 1). Here we set out to study the role of nonlinear interactions between ENSO and the annual cycle (10) in the context of C-mode dynamics. Such nonlinearities can, in principle, generate a suite of higher-order combination modes, which would contribute to the high-frequency variability of the atmosphere—in a deterministic and predictable way.  相似文献   
10.
Microsporidia are emerging ocular pathogens. In this study, we describe the seasonal trends of microsporidial keratitis. The incidence of microsporidial keratitis is increasing in India, with a seasonal trend towards disease onset during the monsoon.  相似文献   
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