Feeding Ecology of the Red‐Backed Sandpiper (Calidris Alpina) in Arctic Alaska

The meridional displacement of the western North Pacific subtropical high (WNPSH) on an intraseasonal time scale is investigated, with emphasis on differences between early (May–June) and late (July–August) summer. The intraseasonal variation (ISV) of the meridional displacement of the WNPSH is dominated by the 10–30-day period, and the variation amplitude is larger in late summer. The ISV of the WNPSH is attributed mainly to the evolution of an anomalous cyclone/anticyclone north of the WNPSH in early summer, whereas it is due to a south-to-north dipole of an anomalous anticyclone and cyclone over East Asia in late summer. Moreover, the WNPSH tends to shift westward when it moves northward, and vice versa, especially in early summer. Both tropical convection and mid- to high-latitude teleconnection across Eurasia are responsible for the ISV of the meridional displacement of the WNPSH in early and late summer. The role of mid- to high-latitude teleconnection is more important in early summer, whereas tropical convection over the South China Sea is more crucial in late summer, through triggering a Pacific–Japan (PJ) pattern. In early summer, as the WNPSH shifts northward, rainfall increases over the Yangtze River valley and decreases over Southeast China, and vice versa. In late summer, deficient rainfall over North China persists when the WNPSH is at its southernmost location and during its northward shift, and vice versa. The characteristics, underlying processes, and impacts of the 10–30-day meridional displacement of the WNPSH are significantly different in early and late summer.

The Silk Road Pattern (SRP) is an upper-tropospheric teleconnection pattern along the Asian westerly jet in summer on the interannual time scale, and it exerts great influences on the climate of the Eurasian continent. Results in the present study indicate that the SRP exhibits considerable distinctions between early and late summers (i.e., 1 June–9 July and 10 July–31 August, respectively). The SRP is stronger and more geographically fixed in late summer in comparison with its counterpart in early summer. Furthermore, the SRP is closely connected with the summer North Atlantic Oscillation (SNAO) in late summer, but not in early summer. This closer connection in late summer is manifested clearly in the leading mode of upper-tropospheric meridional wind anomalies over the North Atlantic–Eurasian continent domain. The intensified SNAO–SRP relationship in late summer can be explained by the subseasonal change of the SNAO: albeit being a seesaw pattern common in both early and late summers, there is a shift of this pattern toward the northwest–southeast one in late summer from a north–south one in early summer. The southeastern pole of SNAO in late summer extends into the Eurasian continent, and efficiently triggers the SRP to propagate along the Asian jet. By contrast, the south pole of SNAO in early summer is confined over the North Atlantic and is thus less effective to trigger the SRP propagation.

Recent change in summer chlorophyll a dynamics of southeastern Lake Michigan

Understanding the relationship between alfalfa (Medicago sativa L.) yield and nutritive value throughout the growing season will permit optimum timing of harvest. Our objective was to determine the rate at which alfalfa yield and fiber components change during each of four harvest periods. In spring, early summer, late summer, and fall of 2004 and 2005 at Pennsylvania, Wisconsin, and Idaho, primary growth of three alfalfa cultivars was initially harvested at late vegetative stage and every 5 d thereafter for 20 d. Forage dry matter (DM) yield, neutral detergent fiber (NDF), and in vitro neutral detergent fiber digestibility (NDFD) were measured at each harvest. Rate of DM production of all cultivars was greatest both years during the spring at Pennsylvania (222.5 and 702.2 kg ha−1 d−1, respectively) and early summer at Wisconsin (83.4 and 278.8 kg ha−1 d−1, respectively), and in early and late summer at Idaho (198.4 and 194.4 kg DM ha−1 d−1, respectively, in 2005 only). The rate of increase in NDF was generally greatest during spring at Pennsylvania and Wisconsin, and during early summer at Idaho, while the rate of decrease in NDFD was generally greatest during early summer at all locations. The results suggest that the negative association between yield and nutritive value has greatest impact on timing of harvests made in spring and early summer in humid environments, and in early and late summer in more arid regions.

Summer weather extremes (e.g., heavy rainfall, heat waves) in China have been linked to anomalies of summer monsoon circulations. The East Asian subtropical westerly jet (EASWJ), an important component of the summer monsoon circulations, was investigated to elucidate the dynamical linkages between its intraseasonal variations and local weather extremes. Based on EOF analysis, the dominant mode of the EASWJ in early summer is characterized by anomalous westerlies centered over North China and anomalous easterlies centered over the south of Japan. This mode is conducive to the occurrence of precipitation extremes over Central and North China and humid heat extremes over most areas of China except Northwest and Northeast China. The centers of the dominant mode of the EASWJ in late summer extend more to the west and north than in early summer, and induce anomalous weather extremes in the corresponding areas. The dominant mode of the EASWJ in late summer is characterized by anomalous westerlies centered over the south of Lake Baikal and anomalous easterlies centered over Central China, which is favorable for the occurrence of precipitation extremes over northern and southern China and humid heat extremes over most areas of China except parts of southern China and northern Xinjiang Province. The variability of the EASWJ can influence precipitation and humid heat extremes by driving anomalous vertical motion and water vapor transport over the corresponding areas in early and late summer.摘要东亚副热带西风急流是影响中国极端天气的重要原因之一, 然而之前的研究主要关注整个夏季急流的变率, 对其早夏和晚夏变率的区别及其对极端天气的影响关注较少. 本文研究了早夏和晚夏东亚副热带西风急流季节内变化特征的区别, 以及这种区别带来的极端天气的差异及其可能的动力学机制. 研究结果表明, 相比于早夏, 晚夏急流季节内变化中心位置偏西偏北, 通过改变垂直运动和水汽输送可以影响极端降水和湿热浪在相应区域的发生概率.

The Indochina Peninsula (ICP) has a critical effect in shaping the Asian summer monsoon (ASM). However, the seasonal responses of the ASM to the ICP are not fully understood. This study employs a 1° atmospheric general circulation model to examine the different contributions of the ICP’s orography and land–sea contrast to the ASM during the early and late summer. Results indicate that the orographic effect increases South Asian rainfall and reduces the rainfall over the South China Sea (SCS) and North China in early summer, but its influence on monsoonal circulation and rainfall is limited to East Asia in late summer. The impact of the ICP’s land–sea contrast is basically opposite in the two summer stages. With the presence of the ICP, SCS rainfall is enhanced but South Asian rainfall is weakened in early summer. In late summer, however, rainfall from the ICP to the northwestern Pacific is strikingly reduced, accompanied by intensified rainfall over South Asia. Relatively, the orographic effect seems to be more important in modulating the South Asian monsoon in early summer, while the land–sea contrast is dominant in strengthening the SCS monsoon and suppressing the northwest Pacific monsoon via the interaction between the induced local circulation and multilevel ASM subsystems. In late summer, the orographic effect on the ASM is much weaker compared to the land–sea contrast, which plays a critical role by shifting the subtropical high southwestward and through the “thermal adaption” feedback mechanism. Therefore, the orographic impact of the ICP on the ASM differs from that of the land–sea contrast in the two summer stages.

Several climate factors were identified that affect the surface air temperature (SAT) variations in Korea during summer (June‐July‐August). Korean summer SAT variation exhibits remarkable differences between early summer (June) and late summer (July and August). On one hand, the significant warming trend during early summer is primarily influenced by the global‐scale trend that is manifested in East Asia. The residual variability, obtained by removing warming trend from total SAT, represents Korean SAT variability independent of the global‐scale trend. This residual variability is closely related to the meridional dipole‐like air temperature structure between Korea and northeastern China, which is largely controlled by the atmospheric circulations over East Asia. However, this atmospheric structure does not originate from the remote oceanic forcing such as sea surface temperature (SST) variability over Pacific. During late summer, on the other hand, the Korean SAT is dominantly regulated by the atmospheric variability, which is closely related to the Pacific SST variability, while the contribution of global warming signal is insignificant. The SST anomalies in the central to eastern tropical Pacific lead to a dipole‐like atmospheric circulation from the tropics to East Asia, which modulates SAT in Korea. These results imply that the Korean SAT variability during early and late summer has different sources. That is, both the global‐scale trend and atmospheric variability over the East Asia should be considered in monitoring Korean SAT during early summer, whereas the SST variability in the central to eastern tropical Pacific needs more attention during late summer.

Accurate representation of mesoscale scale convective systems (MCSs) in climate models is of vital importance to understanding global energy, water cycles, and extreme weather. In this study, we evaluate the simulated MCS features over the United States from the newly developed GFDL global high-resolution (∼50 km) AM4 model by comparing them with the observations during spring to early summer (April–June) and late summer (July–August). The results show that the spatial distribution and seasonality of occurrence and genesis frequency of MCSs are reasonably simulated over the central United States in both seasons. The model reliably reproduces the observed features of MCS duration, translation speed, and size over the central United States, as well as the favorable large-scale circulation pattern associated with MCS development over the central United States during spring and early summer. However, the model misrepresents the amplitude and the phase of the diurnal cycle of MCSs during both seasons. In addition, the spatial distribution of occurrence and genesis frequency of MCSs over the eastern United States is substantially overestimated, with larger biases in early spring and summer. Furthermore, while large-scale circulation patterns are reasonably simulated in spring and early summer, they are misrepresented in the model during summer. Finally, we examine MCS-related precipitation, finding that the model overestimates MCS-related precipitation during spring and early summer, but this bias is insufficient to explain the significant dry bias observed in total precipitation over the central United States. Nonetheless, the dry biases in MCS-associated precipitation during late summer likely contribute to the overall precipitation deficit in the model.

Using Global Precipitation Climatology Project daily rainfall and ERA interim reanalysis data, we investigate the distinct characteristic of quasi-biweekly variation (QBV: 12–20 days) over East Asia (EA) during early (June 10–July 20) and late (July 21–August 31) summer. The QBV maximum variance is found over the core region of EA (30°–40°N, 110°–130°E), which includes eastern China (lower reaches of the Yellow, Huaihe, and Yangtze rivers) and the Korean Peninsula. At both its peak wet and dry phases, QBV over the core region has a baroclinic structure, but with different spatial distributions, different lower-level prevalent wind anomalies, and different upper-level major circulation anomalies in the two subseasons. Meanwhile, the two subseasons have different propagating tracks prior to reaching the peak phase, and different precursors associated with the local genesis of QBV. Furthermore, during the transition from the peak dry to peak wet phase of QBV, the major monsoon circulations have different behaviors that tropical monsoon trough extends eastward in early summer but retreats westward in late summer and the South Asia high (SAH) and western North Pacific (WNP) subtropical high move toward (away from) each other in early (late) summer. The abrupt change of mean state in mid to late July, which includes the northward migration of westerly jet, SAH and WNP, and the weakening and broken of westerly jet, is considered the root cause of the change in behavior of QBV. Finally, we indicate that the tropical monsoon trough and midlatitude westerly jet are possible sources of QBV over subtropical EA in both subseasons and provide useful guidance for 2–3 week predictions over EA.

Objective:The effect of seasonality needs to be considered in designing future studies because global warming has caused a rise in ambient temperatures. The objective of the present study is to investigate the effect of high ambient temperatures on fecal score and fecal microflora in dairy cows during summer.Materials and Methods:During the 7 days before the sampling of feces, the daily mean temperatures were 19.9°C in early summer and more than 27.5°C in late summer. Fecal samples were collected from the rectum of cows and the fecal score was evaluated on a 4-point scale. The equalized samples were used to extract the genomic deoxyribonucleic acid (DNA) of the bacteria (Escherichia coli, Salmonella, Lactobacillus, and Bifidobacterium). Results:There was no significant difference in fecal scores between the sampling times in early and late summer. In the populations of the bacteria, there was no significant difference between sampling days in the DNA level of Salmonella, and E. coli in late summer increased to more than three times the level in early summer. However, both levels of Lactobacillus and Bifidobacterium in early summer significantly decreased after 2 months.Conclusion:These data suggest that the increase in temperature in late summer may adversely affect the populations of bacteria in the intestinal environment of dairy cows. In addition, the method used in the present study was sufficient to evaluate the changes in internal and external environmental conditions of dairy cattle.

This study investigates dynamic and thermodynamic components of moisture flux convergence in Southwest China (SW-MFC) and their underlying physical mechanisms during early and late summer. Using precipitation observation and CRA-40 reanalysis datasets from 1979 to 2023, the results show that both dynamic and thermodynamic processes modulate the SW-MFC in early summer (May-June), with dynamics playing a pivotal role. In contrast, the precipitation anomaly in late summer (July-August) is predominantly driven by the dynamic factors. Meanwhile, the large-scale circulation over the northern Indian Peninsula significantly modulates the SW-MFC. In early summer, anomalous convection around the Maritime Continent with the tripole sea surface temperature (SST) mode in the tropical Indo-Pacific can trigger the formation of “double ring” vertical zonal circulation cells. A large-scale westerly anomaly at the lower troposphere over the northern Arabian Sea foster cyclone strengthening over the northern Indian Peninsula, enhancing southerly moisture transport and increasing precipitation over Southwest China. During the late summer, large-scale dipole SST pattern between the subtropical central-eastern Pacific and the Indo-Pacific warm pool generates significant easterly anomalies towards the Maritime Continent. The SST gradient stimulates an extensive anticyclonic shear zone over the western equatorial Pacific, with an intensified low-pressure zone to its north. This atmospheric pattern over Southwest China and Indian Peninsula can form a vertical circulation circle that largely intensifies widespread precipitation. Numerical model experiments can reproduce the mechanisms of tropical Indo-Pacific joint effects on the Southwest precipitation in both early and late summer, providing a theoretical basis for understanding and forecasting summer precipitation over Southwest China.

Field-grown poplar trees (Populus nigra L. x P. maximowiczii Henry, clone Kamabuchi) were exposed to severe drought twice during the growing season to evaluate the impact on wood cell development. The drought treatment caused a reduction in leaf water potential, leaf wilting and a decreased concentration of osmotically active solutes in the cambial zone. Drought-induced changes in the anatomy of developing xylem cells were examined in stem sections and macerated wood samples. In early summer, drought significantly reduced the length and cross-sectional area of newly formed fibers, whereas no such effects were observed in late summer. In well-watered trees, fiber cross-sectional area declined between early and late summer. Similarly, drought reduced the cross-sectional area of vessel elements in early summer but not in late summer, whereas in both control and drought-treated trees, the cross-sectional area of vessel elements decreased between early and late summer. The vessel area to xylem area ratio was unaffected by drought because the drought-induced decrease in vessel size was matched by an increase in the number of newly formed vessel cells. In contrast to its effect in early summer, late-summer drought had no significant effect on fiber and vessel cell development, indicating that sensitivity of wood cell development to drought varies seasonally.

The Silk Road pattern (SRP) is an important summer teleconnection pattern across the midlatitude Eurasia and is featured by alternate southerly and northerly wind anomalies along the upper-tropospheric westerly jet. It affects significantly the boreal summer climate, including those around the Tibetan Plateau (TP), which has been investigated much based on the summer mean results. However, the SRP shows substantial differences between early and late summer, which are separated at early July. This study identifies that the SRP’s impacts on precipitation surrounding the TP differ much between the two periods: The SRP-related precipitation anomalies are significant over the northeastern TP (NETP) in early summer, but shift northwestwards to domains around the northwestern TP (NWTP) in late summer. These differences can be attributed to the subseasonal change of the SRP and its configurations with the thermal condition surrounding the TP. The SRP is located more westward in late summer than in early summer. Correspondingly, the SRP-related southerly anomalies around the TP prevail over the NETP in early summer but over the NWTP in late summer. Superimposed onto the climatological thermal contrast between the humid southern TP and the dry north, these southerly anomalies favor the northward moisture transport and local precipitation genesis. NETP and NWTP are two domains with greater precipitation amount surrounding the northern TP and are crucial for the Asian ecological and environmental balance. Therefore, the present study holds practical implications for enhancing the accuracy of summer precipitation forecasts surrounding the TP on a subseasonal time scale and further improves regional climate adaptation and water resource management.

Sexual segregation is a common phenomenon in temperate bats, but little is known about driving forces or spatiotemporal patterns. Sexual segregation of the tree-dwelling Daubenton’s bat (Myotis daubentonii) was analyzed. Day roosts and foraging areas of radio-tracked animals were recorded during late spring, early summer, and late summer. Home ranges were calculated for each sex based on identified locations. Distance analysis between sex-specific roosts and foraging areas was conducted for each period. Mixed colonies were confirmed by trapping at roosts. Home range of males was larger (47.3 km2) than of females (9.7 km2). During late spring, distances between male and female roosts were larger (median = 715 m) than during early (median = 474 m) and late summer (median = 489 m). Distances between sex-specific foraging areas were larger during early summer (median = 2,134 m) than during both late spring (median = 1,116 m) and late summer (median = 628 m). The proportion of males in mixed groups increased from late spring (0.2 ± 0.1) to late summer (0.5 ± 0.2). These results show that sexual segregation is not static, but depends on energetic demand of individuals and mating willingness. A high energetic demand in females and low mating willingness in both sexes leads to distinct sexual segregation during late spring. When mating willingness increases, despite an increasing energy demand in males, sexes aggregate to mate.

Climatic effect on alfalfa dry matter production Part II. Summer harvests