Subtropical High Research Articles

Toxicity and Field Efficiency of Certain Insecticides Against the Subterranean Termite, Psammotermes hypostoma Desneux (Isoptera: Rhinotermitidae)

The subterranean termite, Psammotermes hypostoma Desneux (Isoptera: Rhinotermitidae)is considered one of the most dangerous termites in urban, rural and agricultural areas in the desert belt of Assiut governorate, Egypt. Organophosphate insecticides such as chlorpyrifos have been recommended to control subterranean termites in Egypt. The present research was conducted to evaluate the toxicity, persistency and effectiveness of chlorpyrifos (chlorzan 48% EC), imidacloprid (imidammex 70% WG), chlorantraniliprole (coragen 20% SC), indoxacarb (avaunt 15% EC) and spinosad (tracer 24% SC) against subterranean termites. The toxicity of these insecticides was tested against field strain of the subterranean termites using the cardboard dip-bioassay technique under laboratory conditions. The toxicity index after 12 and 24 hr exposure showed that chlorpyrifos has the highest termiticidal activity, with LC50s 1.19 and 0.13 ppm, followed by imidacloprid with LC50s 3.24 and 0.61 ppm, while spinosad was the least toxic one with LC50s.9.96 and 4.95 ppm. Furthermore, chlorpyrifos, imidacloprid and chlorantraniliprole registered significantly high percent reduction of the infested rural homes by subterranean termite, P. hypostoma, while indoxacarb and spinosad recorded the lowest reduction percentage after 30, 60, 90 and 120 days of treatment. In addition, the efficiency and residual effects of chlorpyrifos persisted up to 120 days followed by imidacloprid and chlorantraniliprole after treatment. Results of this study indicated that, chlorpyrifos exhibited the most powerful pesticide among all the insecticides tested, and imidacloprid and chlorantraniliprole were highly effective and it is given as unique and hopeful trends against subterranean termites under field conditions.

Comparison on Relationship between Western Pacific Subtropical High and Summer Precipitation over Dongting Lake Basin Based on Different Datasets

The Western Pacific Subtropical High (WPSH) is a principal component of the East Asian summer monsoon system. This study was to compare the relationship between the WPSH and summer precipitation in Dongting Lake basin (24°35′-30°27′N, 107°13′-114°18′E) based on different datasets by employing the multivariate regression analysis. The observed precipitation data was from China Meteorological Data (CMD) sharing service system and the six gridded precipitation datasets were CFSR, ERA–Interim, CMAP, GPCP, CRU, and PREC/L, respectively. The WPSH exerted different influences on the precipitation of summer months. The indexes including westward extension ridge point index and northern boundary index in June, ridge line index and northern boundary index in July and August had important effect on the precipitation over Dongting Lake Basin. The gridded data could generally reproduce the relationship between the ridge line index and precipitation in July. The relationship between the northern boundary and the precipitation from gridded data was similar to that from observed data in June and July, while the relationship between the western extension ridge index and the precipitation in June could be reproduced by the gridded data except CFSR and ERA-Interim. Only in part area, the relationship between the intensity index and the CMD precipitation could be reproduced by gridded precipitation. The fitness of correlation in some area from the CMD could be reproduced by the gridded data. General speaking, GPCP precipitation data was more applicable to the Dongting Lake Basin in studying on the relationship between the precipitation and a single index of WPSH.

Potential Vorticity Diagnostic Analysis on the Impact of the Easterlies Vortex on the Short-term Movement of the Subtropical Anticyclone over the Western Pacific in the Mei-yu Period

By employing NCEP-NCAR 1°×1° reanalysis datasets, the mechanism of the easterlies vortex (EV) affecting the short-term movement of the subtropical anticyclone over the western Pacific (WPSA) in the mei-yu period is examined using potential vorticity(PV) theory. The results show that when the EV and the westerlies vortex (WV) travel west/east to the same longitude of 120°E, the WPSA suddenly retreats. The EV and WV manifest as the downward transport of PV in the upper troposphere, and the variation of the corresponding high-value regions of PV significantly reflects the intensity changes of the EV and WV. The meridional propagation of PV causes the intensity change of the EV. The vertical movement on both sides of the EV is related to the position of the EV relative to the WPSA and the South Asian high (SAH). When the high PV in the easterlies and westerlies arrive at the same longitude in the meridional direction, the special circulation pattern will lower the position of PV isolines at the ridge line of the WPSA. Thus, the cyclonic circulation at the lower level will be strengthened, causing the abnormally eastward retreat of the WPSA. Analysis of the PV equation at the isentropic surface indicates that when the positive PV variation west of the EV intensifies, it connects with the positive PV variation east of the WV, forming a positive PV band and making the WPSA retreat abnormally. The horizontal advection of the PV has the greatest effect. The contribution of the vertical advection of PV and the vertical differential of heating is also positive, but the values are relatively small. The contribution of the residual was negative and it becomes smaller before and after the WPSA retreats.

Statistical Relationship between Atmospheric Rivers and Extratropical Cyclones and Anticyclones

AbstractStatistical relationships between atmospheric rivers (ARs) and extratropical cyclones and anticyclones are investigated on a global scale using objectively identified ARs, cyclones, and anticyclones during 1979–2014. Composites of circulation and moisture fields around the ARs show that a strong cyclone is located poleward and westward of the AR centroid, which confirms the close link between the AR and extratropical cyclone. In addition, a pronounced anticyclone is found to be located equatorward and eastward of the AR, whose presence together with the cyclone leads to strong horizontal pressure gradient that forces moisture to be transported along a narrow corridor within the warm sector of the cyclone. This anticyclone located toward the downstream equatorward side of the cyclone is found to be missing for cyclones not associated with ARs. These key features are robust in composites performed in different hemispheres, over different ocean basins, and with respect to different AR intensities. Furthermore, correlation analysis shows that the AR intensity is much better correlated with the pressure gradient between the cyclone and anticyclone than with the cyclone/anticyclone intensity alone, although stronger cyclones favor the occurrence of AR. The importance of the horizontal pressure gradient in the formation of the AR is also consistent with the fact that climatologically ARs are frequently found over the region between the polar lows and subtropical highs in all seasons.

Changing Trends in Rainfall Extremes in the Metropolitan Area of São Paulo: Causes and Impacts

This study analyses observed trends in extreme rainfall events in the Metropolitan Area of São Paulo (MASP). Rainfall data sets with more than 60 years of record in MASP are used. In MASP, extreme rainfall events represent hydro meteorological hazards that trigger flash floods and landslides. Changes in rainfall extremes can be partly due to natural climate variability. In addition, it can also be related to global warming and/or urbanization. Total annual precipitation and the number of days with precipitation of 20 mm exhibit the largest significant increase during 1930-2019. This is better noticed during summer. This tendency is also noticed in the number of days with precipitation of 100 mm or more. Therefore, the positive trend in annual precipitation is mainly due to an increase in the frequency of extreme precipitation events. On the other hand, our analysis shows that the number of consecutive dry days increased. Though these results appear to be contradictory, they indicate an important climate change in recent times. Intense precipitation is concentrated in few days, separated by longer dry spells. The focus is on how atmospheric circulation variations are contributing to these changes. During 1960-2019 the South Atlantic Subtropical Anticyclone has intensified and slightly moved southwestward of its normal position. This change influences the transport of humidity and therefore impact precipitation. This can explain the increase in the precipitation extremes in the MASP. However, other atmospheric systems may also be important.

Impacts of Shifting Subtropical Highs on the California Current and Canary Current Systems

AbstractUpwelling in eastern boundary current regions is crucial to bringing nutrient‐rich water to the photic zone and supporting the associated ecosystems. This upwelling is a result of the wind‐driven ocean circulation and is therefore susceptible to changes in the atmospheric circulation. We use the Community Earth System Model and observational data to explore the response of upwelling in the California Current and Canary Current systems to shifts in the Northern Hemisphere subtropical high‐pressure systems. We find that shifts in the North Pacific subtropical high explain a substantial fraction of both the short‐term variability and projected trend in upwelling in the California Current system during boreal summer. By contrast, the Canary Current system is less affected by shifts of the North Atlantic subtropical high, mostly because the strongest wind anomalies associated with shifts of this high‐pressure system occur too far north. We also find little impact from the Northern Hemisphere Hadley cell.

Synoptic condition-driven summertime ozone formation regime in Shanghai and the implication for dynamic ozone control strategies

Regarding the continuous worsening of tropospheric ozone pollution, the scenario in Shanghai is a microcosm of the entire China. Understanding the ozone formation regimes (OFRs), their variations, and driving factors is a prerequisite for formulating effective ozone control strategies. Traditional OFR estimation by numerical model, which often involves sensitivity analysis on at least tens of scenarios, is labor-intensive and time-consuming; therefore, it is not appropriate to make OFR forecasts to guide ozone contingency control. In this study, by using a localized modeling system consisting of the Weather Research and Forecasting, Sparse Matrix Operator Kernel Emissions, and Community Multiscale Air Quality models and considering the latest emission inventory over the Yangtze River Delta of China, we discovered a strong connection between the variations of large-scale circulation (LSC) and OFRs over Shanghai in July 2017, thereby providing an alternative way to infer OFR. During the northward movement of Western Pacific Subtropical High from South China Sea, the wind field over Shanghai changed from weak westerly to moderate southwesterly and to one without a distinct direction. The local OFR shifted from anthropogenic volatile organic compounds (AVOCs)-limited to NOx-limited and ultimately to the transitional regime. Such a variation in OFR is essentially driven by the spatial heterogeneity of NOx and AVOC emissions in different directions of Shanghai, brought on by the wind under different LSC patterns. With the existing weather forecasting technology, the LSC patterns can be well-predicted 48–72 h in advance. Hence, we propose the adoption of a dynamic ozone control strategy for Shanghai with the priority control target on AVOC or NOx emission sources adjusted according to the LSC pattern and OFR forecasts in a forthcoming O3 pollution episode. This would serve to maximize the peak ozone reduction under varying pollution conditions.

Predictability of the mid‐summer surface air temperature over the Yangtze River valley in the National Centers for Environmental Prediction Climate Forecast System

AbstractBy using the hindcast and forecast data from the National Centers for Environmental Prediction Climate Forecast System version 2 (NCEP CFSv2) for the 1982–2018 period, we investigate the forecasting skills of the mid‐summer (July and August) surface air temperature (SAT) at interannual timescales in this study. Although CFSv2 predictions show a warm bias for the climatological mean SAT over the Yangtze River valley (25°–32°N, 105°–122°E), they show a consistent and great performance in predicting the interannual variability of the mid‐summer SAT over this region until 4 months in advance, where the linear correlation coefficient between the predicted and observed time series reaches +0.65, +0.51 and + 0.68 for 4, 2 and 0 months in advance, respectively. The CFSv2 predictions well simulate the linkage between the SAT anomalies over the Yangtze River valley and the anomalous atmospheric circulation aloft, including the circumglobal teleconnection and zonal extension of the Western Pacific Subtropical High. However, CFSv2 has trouble in simulating the associated vertical velocity, cloud cover and solar radiation anomalies, except for 0 months in advance. The persistent forecasting skills result from the accurate response of the circumglobal teleconnection and Western Pacific Subtropical High to the El Niño/Southern Oscillation and sea surface temperature (SST) anomalies over the mid‐latitude North Atlantic. Correspondingly, the forecasting skill, signal and signal‐to‐noise ratio are effectively improved in the years with strong mid‐summer SST anomalies over the tropical central‐eastern Pacific or mid‐latitude North Atlantic. These results are useful for understanding the predictability of the mid‐summer SAT over the Yangtze River valley.

Climatological Large-Scale Circulation Patterns over The Middle Americas Region

In this study, twenty large-scale circulation patterns are identified to generate a synoptic classification of Weather Types (WT) over a region that comprises Mexico, the Intra-Americas Seas, Central America, and northern South America. This classification is performed using Self-Organizing Maps (SOMs) with mean sea-level pressure standardized anomalies from reanalysis. The influence of quasi-permanent pressure centers over the region, such as North Atlantic Subtropical High (NASH) and North Pacific High (NPH) are well captured. Seasonal variability of high-pressure centers for dry (November–April) and wet (May–October) periods over the entire region are also well represented in amplitude and pattern among the WTs. The NASH influence and intensification of the Caribbean low-level jet and the North American monsoon system is well captured. During the dry period, a strong trough wind advects cold air masses from mid-latitudes to the subtropics over the western Atlantic Ocean. High-frequency transitions among WTs tend to cluster around the nearest neighbors in SOM space, while low-frequency transitions occur along columns instead of rows in the SOM matrix. Low-frequency transitions are related to intraseasonal and seasonal scales. The constructed catalog can identify near-surface atmospheric circulation patterns from a unified perspective of synoptic climate variability, and it is in high agreement with previous studies for the region.

Variations in the Sensible Heating of Tibetan Plateau and Related Effects on Atmospheric Circulation Over South Asia

Thermal effects of the Tibetan Plateau (TP) play an important role in the atmospheric circulation over south Asia, which may have complex implications on the development of regional climate. In the study, we utilized 86 station-based observations (1980–2018) to investigate the variations in sensible heating on the plateau surface and their possible impacts on south Asian atmospheric circulation in terms of the Indian Subtropical High. With 10-year records expansion relative to prior studies, our results suggested the significant increasing trend in regional sensible heat (SH) flux from 2001 to 2018 (0.259 W m− 2 a− 1, p < 0.05) contrary to the earlier pronounced decrease (-0.172 W m− 2 a− 1, p < 0.05; 1980–2000) especially in cold season. Most (33) of the 35 stations that decreased in cold-season SH flux before the shift year 2000, did not remain such temporal trend after 2000. Totally, there were respectively 44 and 5 stations showing increasing and decreasing trends in cold-season SH flux from 2001 to 2018, in contrast to the corresponding 6 and 35 stations during the period of 1980–2000. Our results also indicated that the later stronger sensible heating from the TP exhibited statistically close correlation (-0.574~-0.445 o/(W m− 2), p < 0.05) with the Indian Subtropical High, which tended to move southerly and shrink. Our study highlighted the possible weakening effect of the TP’s intensifying sensible heating on the atmospheric circulation over south Asia due to climate warming.

Climatology of the Mascarene High and Its Influence on Weather and Climate over Southern Africa

Globally, subtropical circulation in the lower troposphere is characterized by anticyclones over the oceans. Subtropical anticyclones locate over subtropical belts, modulating weather and climate patterns in those regions. The Mascarene High is an anticyclone located over the Southern Indian Ocean and has a vital role in weather and climate variability over Southern Africa. The warm Western Indian Ocean is a major source of moisture for the subcontinent also permitting tropical cyclone genesis. In this study, we review the dynamics of the Mascarene High, its interactions with the ocean, and its impact on weather and climate over Southern Africa. We also review studies on the evolution of subtropical anticyclones in a future warmer climate. The links between SST modes over the Indian Ocean and the strengthening and weakening of the Mascarene High have been demonstrated. One important aspect is atmospheric blocking due to the Mascarene High, which leads to anomalous rainfall and temperature events over the subcontinent. Blocking leads to landfall of tropical cyclones and slow propagation of cut-off lows resulting in severe weather and flooding over the subcontinent. Understanding how expansion of the Mascarene High due to warming will alter trade winds and storm tracks and change the mean climate of Southern Africa is crucial.

Impact of Dust-Cloud-Radiation-Precipitation Dynamical Feedback on Subseasonal-to-Seasonal Variability of the Asian Summer Monsoon in Global Variable-Resolution Simulations With MPAS-CAM5

In this study, we investigate the effects of increased dust emission from the Middle East deserts on subseasonal-to-seasonal (S2S) variability of the Asian summer monsoon (ASM). Numerical experiments are performed using the Model for Prediction Across Scales (MPAS) coupled with the Community Atmosphere Model (CAM5) physics, with regional refinement at 30 km grid resolution over South Asia and the surrounding regions. Result shows that increased dust emission and transport from the Middle East/West Asia region induces a strong dust-cloud-radiation-precipitation-circulation feedback, resulting in a colder surface over the desert regions and the western Tibetan Plateau, but warmer and moister troposphere with enhanced cloudiness and precipitation over the Pakistan/Northwest India (PNWI) region. The latter changes are amplified by the dust aerosol induced Elevated Heat Pump (EHP) mechanism along the West Himalayas/Iranian Plateau foothill regions, most pronounced during May-June. During July-August, cloud radiation feedback further enhances the warming of the upper troposphere, and cooling of the land surface over the PNWI and adjacent regions over West Asia. The upper tropospheric heating and increased precipitation over PNWI spur a large-scale anomalous Rossby wavetrain and a northward displacement of the subtropical jetstream, manifesting in a contraction of the South Asian High and westward shift of the Western Pacific Subtropical High. As a result, the entire ASM precipitation-cloud system is displaced westward. Precipitation and cloudiness are intensified over northwest and western India and west Asia, but suppressed over southern and central East Asia. Analyses of the S2S variability of the upper level vorticity balance suggests that heating by Middle East dust plays an important role in exciting, and anchoring a teleconnection pattern through interactions among dust-cloud radiation, precipitation heating over the PNWI, the development of an upper level Rossby wavetrain and the northward shift of the boreal summer jetstream over Eurasia.

N-Alkanes and compound carbon isotope records from Lake Yiheshariwusu in the Hulun Buir sandy land, northeastern China

The Hulun Buir sandy land in northern China is located at the northern limit region of the East Asian summer monsoon (EASM) and is therefore sensitive to the extension of the front of the rainfall belt. Here we report an n-alkane and compound-specific carbon isotope record from the Holocene sediments of Lake Yiheshariwusu in the middle of the Hulun Buir sandy land. The sediments contain a suite of n-alkanes with a strong odd over even carbon number predominance, with the maximum contribution from nC31, which is a typical distribution in grassland regions. The low temperatures in this cold region greatly limit the growth of C4 plants and thus the long-chain n-alkanes in lake sediments are mainly derived from leaf wax lipids of C3 plants growing within the sandy land. In this C3-vegetation-dominated region, the δ13C27–33 value (weighted carbon isotope values of nC27– nC33) are regulated mainly by the physiological and biochemical responses of plants to water stress and are therefore interpreted as a proxy of effective precipitation or humidity. The δ13C27–33 time series shows a trend of gradually decreasing values that suggests an increase in effective precipitation since 8.5 ka (1 ka = 1000 cal yr BP). Relative droughts occurred during the intervals of 6.3–5.5, 4.1–3.6 ka, and during the last 200 years. In addition, the δ13C27–33 time series and comparable paleoenvironmental records from neighboring sites suggest opposite trends of summer monsoon rainfall between northeastern and southeastern China. We suggest that a coupled process between low and high latitudes (the western Pacific Subtropical High and the Okhotsk High) may have played a fundamental role in regulating the shift of the frontal rainfall belt and monsoon rainfall distribution in eastern China during the Holocene.

Correction to: How will southern hemisphere subtropical anticyclones respond to global warming? Mechanisms and seasonality in CMIP5 and CMIP6 model projections

The original article can be found online.

Magnetostratigraphy and Paleoenvironments of the Kuntila Lake Sediments, Southern Israel: Implications for Late Cenozoic Climate Variability at the Northern Fringe of the Saharo-Arabian Desert Belt

The Negev Desert in southern Israel hosts a number of late Cenozoic lacustrine and palustrine sedimentary sequences that attest for past wetter conditions in what today constitutes one of the driest deserts on Earth. These sequences are of special importance because the Negev Desert forms part of the Levantine Corridor, which was probably the only continental bridge that enabled initial out-of-Africa expansion of our genus Homo.Yet, the paleoclimatic significance of these sequences still remains unknown, mainly due to their uncertain (late Pliocene to early Pleistocene) age. Here we present a combined sedimentologic, paleontologic and magnetostratigraphic study of one of these sedimentary sequences, the so-called Kuntila Lake sediments, which was carried out at the 30 m-thick Kuntila Gate section in the Nahal Paran basin, southern Israel.Sedimentological evidence and ostracod faunas indicate that these sediments accumulated in a long-lasting lacustrine basin that underwent periodic lake-level variations. Magnetostratigraphic measurements enable the recognition of a normal (N1) and a reverse (R1) polarity zones in the lower and upper halves, respectively, of the Kuntila Gate section. Correlation of N1 to the Olduvai Subchron (1.778 and 1.945 Ma) appears as the most likely option in view of previously published 10 Be ages derived for the uppermost part of the Kuntila Member in nearby sections. The large errors associated with these ages, however, suggest that correlation of N1 to Subchron C2An.1n (2.582-3.032 Ma) is also possible. Although our results do not resolve the age of the Arava Formation, they unequivocally relate the Kuntila Lake sediments with a long period of enhanced climatic variability because the tops of both subchrons are associated with 400 kyr eccentricity maxima. The inferred wetter conditions in the Negev Desert concurred, regardless of the age correlation, with periods of lake expansion in East Africa and clusters of short-lived expansions of the savannah throughout much of the Sahara. This would have led to the biogeographic connection between Africa and Eurasia, greening the path for the initial out-of-Africa dispersal of Homo. Further research on the Kuntila Lake sediments will be necessary to better determine the timing, extent and significance of such biogeographic connection.

The Impact of SST on the Zonal Variability of the Western Pacific Subtropical High in Boreal Summer

AbstractSummertime western Pacific subtropical high (WPSH) is closely related to remote sea surface temperature anomalies (SSTA) in the tropical oceans (TO) and local SSTA in the western North Pacific (WNP). Based on atmospheric reanalysis and multimodel ensemble products, the warming (cooling) of the tropical Indian, tropical central‐eastern Pacific, and tropical Atlantic (tropical western Pacific and WNP) can lead to westward extension of the WPSH, and vice versa. A series of numerical experiments are conducted to quantify the relative importance of remote and local SSTA, including the separate impact of different TO basins. In response to warming (cooling) of the tropical Indian, tropical central‐eastern (western) Pacific, and tropical Atlantic, ascending (descending) motions develop locally and subsequently excite remote baroclinic and barotropic responses. The baroclinic anticyclone west of 140°E contributes to the westward extension of the WPSH. The barotropic anticyclone and descending motion over the WNP can further increase the sea level pressure and strengthen the WPSH. Based on the quasi‐geostrophic omega equation, we find that the anomalous vorticity advection (thermal advection) primarily accounts for the anomalous descending motion in response to remote (local) SSTA. Compared to local SSTA, the remote SSTA can induce larger perturbations, subsequently making the zonal variability of the WPSH more significant. Furthermore, it is found that the westward extension of the WPSH is primarily induced by atmospheric baroclinic (barotropic) response to the SSTA in tropical Indian and tropical Atlantic (tropical Pacific). Overall, the tropical Indian plays the most important role on the zonal movement of the WPSH.

Direct impacts of different types of El Niño in developing summer on East Asian precipitation

This study revisits the impacts of different types of El Niño on East Asian summer precipitation (EASP) with observed and re-analyzed data from 1958 to 2015. It focuses on the boreal summer preceding peaks of El Niño when prominent SST anomalies are mainly situated in the tropical Pacific. Distinct responses of EASP are obtained for the three identified types of SST anomalies noted as summer EP (Eastern Pacific) El Niño, summer MP (Mixed-type Pacific) El Niño, and summer CP (Central Pacific) El Niño. In the case of summer EP El Niño, there is a robust south-north rainfall dipole with anomalous dry conditions in North China and wet conditions in Southeast China. Such a rainfall pattern is mainly attributed to a low-pressure anomaly over Northeast Asia. For summer MP El Niño, it presents a tripolar pattern of precipitation anomalies with wetness along the Yangtze-Huaihe River valley and dryness in both South and North China. This is due to the presence of low-pressure anomalies over Northeast China and a westward shift of the Western Pacific Subtropical High. Summer CP El Niño shows a triangle-pattern of precipitation anomalies with wet conditions in both southern and northern China, but dry conditions in the Jianghuai region (north of the Yangtze River in East China), caused by low-pressure anomalies over central-north China. Further study investigates how different types of summer El Niño induce different changes of the Walker circulation and associated large-scale convergence/divergence outside the tropics, and ultimately provoke different responses of atmospheric circulation. For summer EP El Niño, tropical perturbations over the east-central tropical Pacific and over North India can enter into the subtropical jet and make a mid-latitude low pressure belt response at upper levels of the atmosphere. For summer MP El Niño, the perturbation over the east-central tropical Pacific seems ineffective in transmitting atmospheric anomalies to mid-latitudes. As a result, they are mainly confined to the tropics and lead to a general rise of the upper-level geopotential height over the entire tropics. However, the perturbation over Northwest Africa can excite northeastward propagating Rossby waves in mid-high latitudes. For summer CP El Niño, the induced fluctuant wave train within the subtropical jet is likely the competing effect of perturbations over the east-central tropical Pacific, North India and North Africa. Furthermore, for all the three types of summer El Niño, perturbations can trigger a similar low-level meridional wave train along the East Asian coast through the monsoon trough. However, a slight westward shift of the wave train makes a sensitive impact on EASP.

Emergent constraints on future projections of the western North Pacific Subtropical High

The western North Pacific Subtropical High (WNPSH) is a key circulation system controlling the summer monsoon and typhoon activities over the western Pacific, but future projections of its changes remain hugely uncertain. Here we find two leading modes that account for nearly 80% intermodel spread in its future projection under a high emission scenario. They are linked to a cold-tongue-like bias in the central-eastern tropical Pacific and a warm bias beneath the marine stratocumulus, respectively. Observational constraints using sea surface temperature patterns reduce the uncertainties by 45% and indicate a robust intensification of the WNPSH due to suppressed warming in the western Pacific and enhanced land-sea thermal contrast, leading to 28% more rainfall projected in East China and 36% less rainfall in Southeast Asia than suggested by the multi-model mean. The intensification of the WNPSH implies more future monsoon rainfall and heatwaves but less typhoon landfalls over East Asia.

How will southern hemisphere subtropical anticyclones respond to global warming? Mechanisms and seasonality in CMIP5 and CMIP6 model projections

The anticyclonic high-pressure systems over the southern-hemisphere, subtropical oceans have a significant influence on regional climate. Previous studies of how these subtropical anticyclones will change under global warming have focused on austral summer while the winter season has remained largely uninvestigated, together with the extent to which the dominant mechanisms proposed to explain the multi-model-mean changes similarly explain the inter-model spread in projections. This study addresses these gaps by focusing on the mechanisms that drive the spread in projected future changes across the Coupled Model Intercomparison Project Phase 5 and 6 archives during both the summer and winter seasons. The southern hemisphere anticyclones intensify in strength at their center and poleward flank during both seasons in the future projections analyzed. The inter-model spread in projected local diabatic heating changes accounts for a considerable amount of the inter-model spread in the response of the South Pacific anticyclone during both seasons. However, model differences in projected zonal-mean tropospheric static stability changes, which in turn influence baroclinic eddy growth, are most influential in determining the often-strong increases in sea level pressure seen along the poleward flank of all the anticyclones during both seasons. Increased zonal-mean tropospheric static stability over the subtropics is consistent with the poleward shift in Hadley cell edge and zonal-mean sea level pressure increases. The results suggest that differences in the extent of tropical-upper-tropospheric and subtropical-lower-tropospheric warming in the southern hemisphere, via their influence on tropospheric static stability, will largely determine the fate of the anticyclones over the coming century.

Annual Cycle of Tropical and Subtropical Precipitation Estimated from TMPA 3B42 Dataset

The annual cycles of tropical and subtropical precipitation were estimated by parameterizing them using the inferential circular statistics approach. The Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis (TMPA) version 7 dataset which has spatial coverage from 50°S to 50°N and temporal coverage from 1998 to 2018 (21 years) was used to compute the monthly precipitation climatology data. Their annual cycles can be estimated using the bimodal von Mises distribution. The estimated parameters were found to sufficiently capture some interesting characteristics such as the non-uniformity and bimodality of precipitation rate associated with regions of convergence zones and subtropical highs. The difference in timings of maximum and minimum precipitation suggest that precipitation maxima over the continent were found to follow the position of the Sun at an average time lag of 1.2 months. Three examples of applying these parameters are given including the regional classification of precipitation which emphasizes on the bimodality the non-uniformity and the bimodality of their annual cycles, the evolution of the southern Intertropical Convergence Zone (ITCZ) in the Pacific Ocean which was found to propagate westward from 90°W in mid-March to 150°W in early-April at an estimated speed of 21.6 km/h, and the precipitation variability in the case of Paris in France in which the precipitation anomaly tend to decrease at a highly significant rate of −9.716 mm/month per decade (p value ≤0.01).