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The interdecadal variability of tropical cyclone precipitation (TCP) over the western North Pacific (WNP) has not been thoroughly explored in previous studies. Here, we show that the TCP variations are modulated by both the Atlantic Multidecadal Oscillation (AMO) and Interdecadal Pacific Oscillation (IPO) as evidenced by reanalysis data and model experiments. A clustering analysis of tropical cyclone tracks shows that the AMO dominates a dipole pattern of TCP anomalies in the South China Sea and along the coastal eastern China. Meanwhile, the IPO dominates TCP over the southeastern WNP. Further analyses show that the AMO, particularly its extratropical component, affects TCP over the WNP by triggering an eastward‐propagating Rossby‐wave train, resulting in a pair of anomalous gyres over the WNP. Contrastly, the IPO modulates TCP by stimulating tropical circulation anomalies via the tropical pathway. These findings shed light on improving near‐term TCP forecast and its regional influence on East Asia. Plain Language Summary: Tropical cyclone precipitation (TCP) is a topic of great concern owing to its destructive nature. Here, we find that TCP over the western North Pacific (WNP) exhibits significantly interdecadal variability and regional characteristics, a departure from the previous studies focusing on the entire WNP. The Atlantic Multidecadal Oscillation (AMO) mainly causes a dipole response of decadal changes in TCP over the South China Sea and coastal eastern China. Moreover, the AMO primarily affects TCP over the sub‐regional WNP through the extra‐tropical pathway by exciting a Rossby wave train. On the other hand, the Interdecadal Pacific Oscillation (IPO) predominantly affects TCP over the southeastern part of the WNP through the tropical pathway, inducing significant circulation anomalies over the tropical WNP. These findings offer valuable insights for future research and forecasting of TCP. Key Points: The Atlantic Multidecadal Oscillation (AMO) contributes to the dipole pattern of interdecadal tropical cyclone precipitation (TCP) anomalies over the South China Sea and coastal eastern ChinaThe AMO affects TCP by triggering a westerly jet‐guided Rossby‐wave train via the extra‐tropical pathwayThe Interdecadal Pacific Oscillation dominates the TCP anomalies over the southeastern part of western North Pacific by modulating tropical circulation anomalies [ABSTRACT FROM AUTHOR]

The multi‐model ensemble mean sea surface temperature (SST) of CMIP5 models shows an El Niño‐like Pacific warming (PW) trend, contradictory with the observational result which manifests a La Niña‐like PW pattern. Here, we demonstrate that these two SST PWs coexist in the CMIP5 models and they are largely determined by the model's tropical Indo‐Pacific SST gradient. When the Pacific warms faster than the Indian Ocean (IO), the model tends to project an El Niño‐like PW pattern. In contrast, a La Niña‐like warming trend prevails if a more rapid IO warming is simulated. We suggest that the PW pattern in an individual model is nonstationary and may transform from a La Niña‐like to an El Niño‐like when its interbasin SST gradient changes with more robust warming in the Pacific, and vice versa. Our conclusions shed great light on the future SST PW pattern change projected by the coupled models. Plain Language Summary: Previous studies demonstrate that an El Niño‐like SST warming pattern prevails in a majority of CMIP5 models. But a La Niña‐like warming pattern is detected based on historical SST records. This inconsistency between the observations and model simulation triggers an intense debate in the climate community. In this study, we find that both El Niño‐like and La Niña‐like SST warming patterns can be identified in the CMIP5 model simulations. The warming pattern is largely determined by the SST gradient between the Indian and Pacific oceans. Distinct from previous studies, an El Niño‐like pattern in an individual model can shift to a La Niña‐like pattern when the Indian warming is stronger than the Pacific warming trend, and vice versa. Key Points: El Niño‐like and La Niña‐like Pacific sea surface temperature warming patterns coexist and are interchangeable in climate model projectionsThe tropical Pacific warming pattern is primarily determined by a zonal gradient in the Indo‐Pacific sea surface warmingThis Pacific warming pattern diversity sheds light on future sea surface temperature change under greenhouse gases concentrations [ABSTRACT FROM AUTHOR]

Complement pathways participate in the regulation of innate immune system, and complement activation is inhibited in normal pregnancy. The liver plays key roles in the modulation of immunity and tolerance, but it is unclear that early pregnancy induces the changes in expression of complement components in the ovine maternal liver. The aim of the present study was to explore the expression of complement components in the liver using quantitative real‐time polymerase chain reaction (PCR), Western blot, and immunohistochemistry. Maternal livers were collected on Day 16 of the estrous cycle and Days 13, 16, and 25 of gestation. The results indicated that early pregnancy suppressed the expression of C1q, C1r, C1s, C2, C4a, C5b, and C9 in the maternal liver, but C3 expression was increased. In addition, C3 protein was located in the endothelial cells of the proper hepatic arteries and portal veins and hepatocytes. In summary, the downregulaltion of C1q, C1r, C1s, C2, C4a, C5b, and C9 may be involved in the suppression of complement activation, and upregulation of C3 is related to the modulation of maternal immune tolerance in ovine liver. [ABSTRACT FROM AUTHOR]

Summary: As a pineal gland hormone, melatonin acts through its receptors to modulate the immune system. The immune system is composed of primary and secondary organs, and immune organs are adapted to the presence of the fetal alloantigen during pregnancy. However, it is unclear whether melatonin affects maternal immune organs during early pregnancy in sheep. In this study, the ovine thymus, lymph node, spleen and liver were sampled at day 16 of the oestrous cycle, and at days 13, 16 and 25 of pregnancy. The expression of melatonin receptor 1A (MT1), melatonin receptor 1B (MT2) and cluster of differentiation 4 (CD4) was detected by quantitative real‐time polymerase chain reaction, Western blot and immunohistochemistry experiments. Our results showed that during early pregnancy there was an upregulation of MT1 mRNA and protein in the thymus, lymph node and liver, and there was a downregulation in the spleen. The expression of MT2 mRNA and protein was increased in the thymus but decreased in the spleen and liver, and there was no significant change in the lymph node during early pregnancy. CD4 protein was upregulated in the thymus, lymph node and liver, but there were no significant changes in the spleen during early pregnancy. In conclusion, early pregnancy induces tissue‐specific expression of MT1, MT2 and CD4, which may be due to the different functions of the thymus, lymph node, spleen and liver. Further, melatonin is involved in immune regulation of the maternal thymus, lymph node, spleen and liver during early pregnancy in sheep. [ABSTRACT FROM AUTHOR]

This study has discovered a significant linear relationship between the Southern Hemisphere (SH) annular mode (SAM) and the mid‐latitude Northern Hemisphere (NH) circulation in February using two reanalysis data sets. Significant positive height anomalies corresponding to the positive SAM appear over the mid‐latitude region of the NH, and significant positive surface air temperature anomalies prevail over Western Europe and Northeast Asia. The realistic vorticity forcing associated with the SAM is applied in a dry linear baroclinic model, and the results demonstrate that the SAM in February can induce height anomalies with the same sign at 300 hPa over the mid‐latitudes of the NH and that these anomalies have amplitudes as large as 22% of their counterparts in the SH. Further numerical experiments show that the positive height response over the mid‐latitudes of the NH mainly comes from the influence of the realistic positive vorticity over the mid‐latitudes of the SH and that the vorticity forcing over the southern Indian Ocean seems to be the most effective at exciting the NH circulation anomalies. The numerical experiments also demonstrate that the transient eddy feedback forcing contributes to the formation of mid‐latitude NH circulation anomalies, especially over Northeast Asia. The maintenance of the negative vorticity anomalies over Europe is further diagnosed through vorticity budget analysis. In December, however, the significant vorticity anomalies associated with the SAM are not limited to the middle and high latitudes of the SH but also appear over the subtropics of the SH (approximately 30°S). The numerical experiments show that cancellation occurs between the responses to the subtropical vorticity forcing and the mid‐latitude vorticity forcing, thereby accounting for the independence of the NH circulation from the December SAM variability. Simultaneous regression coefficients of the geopotential height at 300 hPa (a) and the surface air temperature (b) at 2 m on the Southern Hemisphere annular mode index in February. The contour intervals are 15 gpm for h300. For T2m, contours are drawn at every −2.5, −1.5, −0.5, 0.5, 1.5 and 2.5°C. In all of the panels, the red solid contours and the blue dashed contours denote positive and negative values, respectively. The zero lines are omitted. Shading denotes the statistically significant region at the 0.05 significance level. [ABSTRACT FROM AUTHOR]

The spleen is a unique lymphoid organ that plays a key role in immune regulation. Interferon‐tau induces upregulation of interferon‐stimulated gene 15‐kDa protein (ISG15) in the uterus during early pregnancy in sheep. Prostaglandins (PGs) have important effects in both the activation and the inhibition of immune response through an autocrine and paracrine manner. In this study, splenic samples were obtained at Day 16 of the estrous cycle, and Days 13, 16, and 25 of pregnancy from ewes, and the expression of ISG15 and PG synthases, including cyclooxygenase 1 (COX‐1), COX‐2, PGE synthase (PTGES), and PGF synthase (aldo‐keto reductase family 1, member B1, AKR1B1), was detected through quantitative real‐time PCR, western blot, and immunohistochemistry analysis. Our results showed that there was upregulation of COX‐2 mRNA and protein at Day 25 of pregnancy, and ISG15 mRNA and conjugated proteins, and AKR1B1 mRNA and dimer at Days 16 and 25 of pregnancy. COX‐2 and AKR1B1 proteins were limited to the capsule, trabeculae, and splenic cords. However, the expression of COX‐1 and PTGES was not affected by early pregnancy. In conclusion, ISG15‐conjugated proteins, COX‐2 and AKR1B1 upregulated in maternal spleen during early pregnancy, which may be beneficial for the placentation in sheep. [ABSTRACT FROM AUTHOR]

ABSTRACT: The North Pacific subtropical front (NPSTF) of sea surface temperature (SST) is an important subtropical feature in the North Pacific. In this study, we reveal that the inter‐annual variability of the spring NPSTF has a robust correlation with the El Niño‐Southern Oscillation (ENSO) in the following winter over the period of 1961–2016. When there is a strong spring NPSTF, anomalous cyclonic and anticyclonic circulations in the low troposphere occur to its north and south, respectively. The northeasterly wind anomaly associated with the anticyclonic circulation increases the climatological northeasterly wind over the subtropical Northeast Pacific, resulting in SST decrease via the wind–evaporation–SST feedback. The SST and wind perturbations propagate southwards from the subtropical to the eastern central equatorial Pacific in summer and grow via the Bjerknes feedback from summer to winter, eventually leading to a La Niña event in winter. A strong spring NPSTF induces an anomalous anticyclonic circulation to its south through both transient eddy activity and atmospheric heat source anomaly. The enhanced air temperature gradient due to a strong NPSTF increases the atmospheric baroclinicity, favouring an enhanced transient eddy activity over the NPSTF and to the north. The enhanced transient eddy activity triggers a significant negative height anomaly to the north via high‐frequency transient eddy feedback forcing, which is conductive to an anticyclonic circulation over the subtropical North Pacific through the downstream effect of Rossby waves. On the other hand, the convergence and increased atmospheric baroclinicity related to the strong NPSTF act to enhance precipitation over the NPSTF and to the north, corresponding to the increased atmospheric heat source, which can also excite an anomalous anticyclonic circulation over the subtropical North Pacific. [ABSTRACT FROM AUTHOR]

Roles of the Tibetan Plateau (TP) in forming and changing the seasonal Asian climate system have been widely explored. However, little is known about modulation effects of the TP on extratropical transient eddies (TEs) and subsequent synoptic responses of the East Asian rainfall. In this study, the Community Atmosphere Model version 5.1 coupled with a slab ocean model is employed to highlight the important role of the TP in regulating the upper-tropospheric transient wave train. Comparison between sensitivity experiments with and without the TP shows that the northern TP excites a strong anomalous anticyclone, which shifts the upper-level East Asian westerly jet northward and helps transfer barotropic and baroclinic energy from the mean flow to the synoptic TE flow. The transient wave train is primarily shifted northward by northern TP and is forced to propagate southeastward along the eastern flank of the TP until reaching eastern China. Before the strengthening of monsoonal southerlies, the TP-modulated transient wave train cools the troposphere, which decreases the static stability over northern China. Meanwhile, the associated anomalous warm advection induces ascending motion, leading to excessive rainfall by releasing unstable energy as the southerly strengthens. Due to the southeastward propagation of the wave train, anomalous heavy rainfall subsequently appears over eastern China from north to south, which increases day-to-day rainfall variation in this region. Additionally, occurrence of this upper-tropospheric transient wave train associated with low-level southerly peak is substantially increased by northern TP. [ABSTRACT FROM AUTHOR]