Supplemental Material: Profiling interactions between the Westerlies and Asian summer monsoons since 45 ka: Insights from biomarker, isotope, and numerical modeling studies in the Qaidam Basin
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Figures S1–S2 and Tables S1–S3.Keywords:
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Profiling (computer programming)
We offer a new perspective on a relationship between sea surface temperature (SST) over the windward region of the Philippines and rainfall in the western Philippines during the Asian summer monsoon season, which has been known as the negative correlation, using observational daily SST, rainfall, and atmospheric circulation datasets. This study focuses on the local SST effect rather than the remote effect. A warmer local SST results in greater rainfall over the western Philippines under similar monsoon westerlies conditions, particularly during moderate and relatively stronger monsoon regimes. This result is obtained after selecting only the moderate or relatively stronger monsoon days, because the positive effect of SST on rainfall is masked by the apparent negative correlation between SST and rainfall. The warmer SSTs being associated with less rainfall correspond to weaker cooling by weaker monsoon westerlies and the cooler SSTs being associated with more rainfall correspond to stronger cooling by stronger monsoon westerlies. The cooler SSTs are the result of stronger monsoon cooling and are not the cause of the greater rainfall, which is the apparent statistical relationship. This also implies that the monsoon westerly is the primary driver of the variation in rainfall in this region. We conclude that the local SST makes a positive contribution toward rainfall, although it does not primarily control rainfall. This conclusion can be applicable to coastal regions where, climatologically, rainfall is controlled by winds from the ocean.
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The paper presents the results of a study of the daily precipitation, temperature at 6 km and winds between 6 and 9 km a.s.l. Over the Everest area during the months of May and June for the period 1952 to 1962. The indications are that there is no well marked 'monsoon lull' or a 'monsoon onset' over the Everest. The transition from the strong and steady westerlies between 6 and 9 km a.s.1. of ,the pre-monsoon season to the steady easterlies of the monsoon season occurs over a period highly variable in duration and can occasionally extend over the whole of May and June. Winds over Everest during this period can be moderate or weak westerlies or weak easterlies. With weak westerlies precipitation can occur practically every day and in most of the years it is not possible to distinguish the onset of the monsoon rains as distinct from the’pre-monsoon thundershower activity'. The temperature of the strong and steady westerlies at 6 km a.s.l. over Everest increases gradually from -10oC in early May to about 0°C by the time the variable winds set in. From a consideration of the weather features that were obtained by the successful and uJ18uccessful expeditions to the Mount Everest since 1952 it is considered more profitable for future expeditions to get to the high reaches of the Everest by early May instead of late May.
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Westerlies
Atmospheric Circulation
East Asian Monsoon
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Westerlies
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Westerlies
Paleoclimatology
East Asian Monsoon
Atmospheric Circulation
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In this study, the European Centre for Medium-Range Weather Forecasts reanalysis v5 (ERA5) wave height reanalysis data and sea-level pressure data from two seasonal prediction systems were used to study the wave characteristics of the Southern Ocean and the seasonal prediction of difficulty for the vessels crossing the westerlies. The results show that significant wave height, extreme wave height, and extreme wave processes were all much stronger in austral winter than in austral summer, making it more difficult for vessels to cross the westerlies in winter. Furthermore, the difficulty of crossing the westerlies has increased over the last 40 years, except in areas east of South America. We found that the monthly frequency of crossing the westerlies between 100° E and 75° W could be accurately estimated point by point using the monthly mean sea-level pressure difference between 30° S and 65° S. With a 1-month lead, the multi-model forecasts gave a fairly accurate forecast of such sea-level pressure difference signal between 150° E to 60° W for target months from May to December. Based on these assessments, we could estimate the difficulty of crossing the westerlies in some specific months in advance using a seasonal prediction system. We also found that the seasonal prediction system produced inaccurate predictions of sea-level pressure at high latitudes, which is the main barrier to further accurately estimating the difficulty of crossing the westerlies. These findings may provide support for predicting difficulty for the vessels crossing the westerlies with a 1-month lead and can provide planning for the route and the allocation of material reserves.
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Abstract The variation and interplay of westerlies and the Asian summer monsoon (ASM) are important for understanding climate change in the Northern Hemisphere. Yet their spatial and temporal evolution is still debatable. Here, we present a stable isotopic record from the center of the Badain Jaran Desert, in Northwestern China, which records the variations and interplay of the two climate systems during the past 1200 ka. The results indicate that the westerlies dominated the Badain Jaran area at least from 1200 to 600 ka, and possibly earlier. Associated with ASM enhancement since 600 ka, the westerlies and ASM alternatively dominated the regional warm season precipitation during glacial‐interglacial cycles, respectively. Meanwhile, the δ 18 O carb of the Badain Jaran area showed high‐frequency fluctuations which may reveal the joint impact of ASM and westerlies on regional hydrology after 450 ka. Affected by the westerlies and ASM changes, the C4 plants stepwise expanded at 600, 450, and 300 ka. These stepwise variations of westerlies and ASM are response to the global climate change which significantly influenced the ASM at 600 and 450 ka, and westerlies at 300 ka, respectively. In addition, the uplift of the Pamir‐Tibetan Plateau during the middle Pleistocene also exerts a profound effect on westerlies and ASM pattern across the East Asia on a long‐term time scale.
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East Asian Monsoon
Marine isotope stage
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It is hypothesized that the South China Sea (SCS) monsoon and the Indian monsoon intensify each other in the boreal summer. The Indian monsoon westerlies strengthen the SCS monsoon through the WE (Wind- Evaporation feedback) mechanism, but weaken it through the reduction in SCS SST. The SCS monsoon may have a positive feedback to enhance the Indian monsoon westerlies through the Walker circulation. Further question is how the convective activity over the Western North Pacific (WNP) interacts the Indian monsoon westerlies. The WNP SST may affect the Indian monsoon through the WNP precipitation. In this study, we investigate the relationships among the Indian monsoon, SCS monsoon and WNP activities from various observational data. The regression coefficient analyses are made. The data are NCEP reanalysis data, the CMAP precipitation data and ICOADS SST data averaging over June-July-August (JJA) for 21 years (1982-2002). First, the precipitation anomalies are regressed to the Indian monsoon westerly anomaly. The result shows that the Indian monsoon westerlies are positively correlated with the SCS precipitation. It indicates that the surface heating exchange over the SCS region is largely induced by the Indian monsoon westerlies and/or the SCS monsoon enhances the Indian monsoon westerlies. Another map of the regression of the 850hPa wind field anomalies to the WNP precipitation anomaly also shows that the Indian monsoon westerlies are positively correlated with the WNP precipitation. Completing this result, we confirm that the WNP precipitation and WNP SST have a positive correlation. Thus, the strengthening of the Indian monsoon westerlies and SCS westerlies may be also induced by the precipitation increase on the WNP region through the stronger east-west circulation associated with the warmer WNP SST. From the above results, it is found that the Indian monsoon westerlies are strongly correlated with the SCS monsoon activity and the WNP precipitation. Probably, the SCS monsoon is affected by the Indian monsoon through the WE, and affects the Indian monsoon through the diabatic heating. Further link is found to the precipitation over the WNP. To confirm the mechanism of correlation, the model study is underway.
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East Asian Monsoon
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