Winter Precipitation Variations Research Articles

Asymmetry of winter precipitation event predictions in South China

Winter precipitation anomalies in South China (SC) frequently result in severe disasters. However, the evaluation of prediction performance and distinctions between positive precipitation anomaly events (PPA, wet condition) and negative precipitation anomaly events (NPA, dry condition) in current operational models remains incomplete. This study employed the Climate Forecast System version 2 (CFSv2) to assess winter precipitation prediction accuracy in SC from 1983 to 2021. Differences in predicting PPA and NPA events and the underlying physical mechanisms were explored. The results indicate that CFSv2 can effectively predict interannual variations in winter precipitation in SC, as there is a significant time correlation coefficient of 0.68 (0.62) between observations and predictions, with a lead time of 0 (3) months. The model revealed an intriguing asymmetry in prediction skills: PPA outperformed NPA in both deterministic and probabilistic prediction. The higher predictability of PPA, as indicated by the perfect model correlation and signal-to-noise ratio, contributed to its superior prediction performance when compared to NPA. Physically, tropical signals from the ENSO and extratropical signals from the Arctic sea ice anomaly, were found to play pivotal roles in this asymmetric feature. ENSO significantly impacts PPA events, whereas NPA events are influenced by a complex interplay of factors involving ENSO and Arctic sea ice, leading to low NPA predictability. The capability of the model to replicate Arctic sea ice signals is limited, but it successfully predicts ENSO signals and reproduces their related circulation responses. This study highlights the asymmetrical features of precipitation prediction, aiding in prediction models improvement.

Interactions between thresholds and spatial discretizations of snow: insights from estimates of wolverine denning habitat in the Colorado Rocky Mountains

Abstract. Thresholds can be used to interpret environmental data in a way that is easily communicated and useful for decision-making purposes. However, thresholds are often developed for specific data products and time periods, changing findings when the same threshold is applied to datasets or periods with different characteristics. Here, we test the impact of different spatial discretizations of snow on annual estimates of wolverine denning opportunities in the Colorado Rocky Mountains, defined using a snow water equivalent (SWE) threshold (0.20 m) and threshold date (15 May) from previous habitat assessments. Annual potential wolverine denning area (PWDA) was thresholded from a 36-year (1985–2020) snow reanalysis model with three different spatial discretizations: (1) 480 m grid cells (D480), (2) 90 m grid cells (D90), and (3) 480 m grid cells with implicit representations of subgrid snow spatial heterogeneity (S480). Relative to the D480 and S480 discretizations, D90 resolved shallower snow deposits on slopes between 3050 and 3350 m elevation, decreasing PWDA by 10 %, on average. In years with warmer and/or drier winters, S480 discretizations with subgrid representations of snow heterogeneity increased PWDA, even within grid cells where mean 15 May SWE was less than the SWE threshold. These simulations increased PWDA by upwards of 30 % in low-snow years, as compared to the D480 and D90 simulations without subgrid snow heterogeneity. Despite PWDA sensitivity to different snow spatial discretizations, PWDA was controlled more by annual variations in winter precipitation and temperature. However, small changes to the SWE threshold (±0.07 m) and threshold date (±2 weeks) also affected PWDA by as much as 82 %. Across these threshold ranges, PWDA was approximately 18 % more sensitive to the SWE threshold than the threshold date. However, the sensitivity to the threshold date was larger in years with late spring snowfall, when PWDA depended on whether modeled SWE was thresholded before, during, or after spring snow accumulation. Our results demonstrate that snow thresholds are useful but may not always provide a complete picture of the annual variability in snow-adapted wildlife denning opportunities. Studies thresholding spatiotemporal datasets could be improved by including (1) information about the fidelity of thresholds across multiple spatial discretizations and (2) uncertainties related to ranges of realistic thresholds.

Hysteretic Behavior of Global to Regional Monsoon Area Under CO2 Ramp‐Up and Ramp‐Down

AbstractWhen projecting future monsoon changes by carbon dioxide (CO2) pathway, most studies have analyzed precipitation responses without considering monsoon area (total area of monsoon domain, MA) variations. However, how MA responds to CO2 removal remains uncertain. This study evaluates MA variations and impacts in idealized CO2 ramp‐up (toward CO2 quadrupling), ramp‐down, and stabilized simulations using the Community Earth System Model version 1. Global MA negatively overshoots (i.e., recovery with decreasing tendency beyond the original MA) during the ramp‐down period due to reduced or rapidly recovered MA in several regional monsoons, including Northern and Southern Africa, South and East Asia, and South America, showing hysteresis when comparing CO2 ramp‐up and ramp‐down periods despite similar global warming levels. These non‐linear regional MA variations come from distinct regional summer and winter precipitation variations, which are found to be mostly associated with Intertropical Convergence Zone movements and El Niño‐like response. Further, regional monsoon precipitation characteristics also vary through CO2 ramp‐up and ramp‐down periods consistently with overall hysteresis. Changes in total monsoon precipitation resemble the distinct responses of MA. Our results suggest that regions characterized by a monsoonal climate may experience reduced seasonal rainfall variations under net‐negative CO2 emissions.

Interdecadal variation in winter precipitation over non-monsoonal Eurasian regions

This study investigated the interdecadal variations in winter precipitation over the nonmonsoonal Eurasian regions (30°-70°N, 0°-80°E) (NER) and possible contributions of the Arctic sea ice for the period 1948‐2019. The dominant mode of the interdecadal variations in winter precipitation over NER (DM_NWPE) features opposite loading over the Mediterranean region and over the northern NER and Central Asia. The positive phase of DM_NWPE with enhanced precipitation over the Mediterranean region and suppressed precipitation over the northern NER and central Asia is associated with positive height anomalies over the high-latitude North Atlantic and Eurasia and negative height anomalies extending from the subtropical North Atlantic Ocean to western Eurasia. Increased sea ice in the Barents Sea may promote an atmospheric wave pattern extending to the downstream Eurasian regions, contributing to decreased precipitation over northern NER and Central Asia. Reduced sea ice in the Baffin Bay-Davis Strait-Labrador Sea (BDL) can promote a southeastward atmospheric wave pattern, contributing to enhanced precipitation over the Mediterranean region. The atmospheric response to the Arctic sea ice forcing is confirmed by experiments with a linear baroclinic model. A dipole pattern of sea surface temperature (SST) anomalies in the North Atlantic Ocean may contribute to the interdecadal variation in DM_NWPE. Further analysis showed that the Arctic sea ice-DM_NWPE relationship is primarily SST independent and the Arctic sea ice plays a more critical role in DM_NWPE variations than the North Atlantic SST anomalies.

Interdecadal Variation in Winter Precipitation Over Non-Monsoonal Eurasian Regions

Interdecadal Variation in Winter Precipitation Over Non-Monsoonal Eurasian Regions

Mechanism of winter precipitation variations in the southern arid Central Asia

AbstractThe southern arid central Asia (SACA, 35.25°–45°N, 46.25°–80°E) is influenced by Mediterranean type of climate with wet cool season. This study analysed the variations of winter precipitation and their mechanisms during 1979–2017. The results suggest the variations of winter precipitation in SACA are influenced by two water vapour pathways, which are closely linked to a low‐latitude high‐pressure anomaly near Indian subcontinent and the mid‐high latitude North Atlantic Oscillation (NAO), respectively. Specifically, at low latitudes, the northern Indian Ocean heated by El Niño causes the anomalous intensification of the subtropical high throughout the low latitude region, especially over the Indian subcontinent, resulting in increased water vapour transport from the northern Indian Ocean to SACA. This result of low latitude is also supported by model simulations. At middle and high latitudes, the negative NAO phase leads to a southward displacement of the water vapour pathway and carries water vapour to pass over number of upwind water bodies, resulting in the transport of more westerly‐associated water vapour to SACA. Further analysis showed that there is a northwest‐southeast teleconnection wave train, from the North Atlantic to Central Asia and to the Indian subcontinent, which allows wave fluxes originating in the North Atlantic and the northern Indian Ocean to propagate from high and low latitudes, respectively, to the study area. At the same time, high‐latitude cold air advection, brought by the low‐pressure system in Central Asia, converges with the flow of warm water vapour from the low‐latitude northern Indian Ocean, generating an ascending motion and reducing atmospheric static stability, and thereby lead to increasing precipitation in SACA. Therefore, the key to determining the origin of precipitation variations in SACA is understanding the interaction of large‐scale circulation systems at low and mid‐high latitudes.Key wordsarid Central Asia, precipitation, dynamic mechanism

Effect of Siberian high and remote forcings on winter precipitation in the Kingdom of Saudi Arabia

AbstractIn the current literature, little is known about the role of Siberian High (SbH) on precipitation variability over the Kingdom of Saudi Arabia. The technique of centers of action (COA) has been employed here to study the possible impact of SbH on interannual variations in winter precipitation over the kingdom because the COA methodology helps us to find changes in interannual variations of pressure intensity, latitudinal and longitudinal positions of the pressure system using sea-level pressure data. The results show that there are two regions of the kingdom whose precipitation is significantly affected by SbH, the southeast region and the region from northeast to central Saudi Arabia. The precipitation over the southeastern region is significantly influenced by the intensity of SbH as well as its meridional displacement whereas the precipitation variability from northeast to the central kingdom is significantly influenced by the meridional displacement of SbH. The effect of remote forcings of North Atlantic Oscillation and El Niño–Southern Oscillation on precipitation of the kingdom has also been discussed in the paper. The empirical results can be understood by the mechanism of changes and circulations in the atmosphere.

Potential predictability of boreal winter precipitation over central-southwest Asia in the North American multi-model ensemble

The potential predictability and skill of boreal winter (December to February: DJF) precipitation over central-southwest Asia (CSWA) is explored in six models of the North American Multimodel Ensemble project for the period 1983–2018. The seasonal prediction data for DJF precipitation initialized at Nov. (Lead-1) observed initial condition is utilized. The potential skill is estimated by perfect model correlation (PMC) method, while observed real skill is calculated by the temporal anomaly correlation coefficient (TCC). The main focus is over the Northern Pakistan (NP: 68°–78°E, 31°–37°N), which is a dominant winter precipitation sub-region in CSWA. All participating models generally capture the observed climatological pattern and variation in winter precipitation over the region. However, there are some systematic biases in the prediction of the climatological mean DJF precipitation, specifically an overestimation of precipitation over the foothills of the Himalayas in all models. The substantial internal atmospheric variability (noise) in the seasonal mean (signal) means that the regional winter precipitation is poorly predictable. The NCEP climate forecast system (CFSv2) and two Geophysical Fluid Dynamics Laboratory models (FLOR-A and FLOR-B) show the lowest potential and real skill. The COLA and NASA models show moderate but statistically significant PMC and TCC values. Each model captures the observed relationship between spatially averaged DJF precipitation over NP, with sea surface temperature (SST) and 200 hPa geopotential height (Z200), in varying details. The COLA and NASA models skillfully matched the observed teleconnection patterns, which could be a reason for their good performance as compared to other models. It also found that SSTs in the tropical oceans are relatively well predicted by NASA model when compared with other models. A critical outcome of the predictive analysis is that the multimodel ensemble (MME: A combination of six models and 79 members) does not show many advantages over the individual models in predicting boreal winter precipitation over the region of interest. Together, these results indicate that reliable prediction of the boreal winter precipitation over CSWA remains a big challenge in initialized models.

Characteristics and mechanisms of the diurnal variation of winter precipitation in Taiwan

Using gridded precipitation data remapping from rain‐gauge observations of the time period of 2001–2015 winter months (December, January and February), this study examines the spatio‐temporal characteristics of the climatological diurnal winter precipitation in Taiwan. Our results show that the timings of the maximum values of the diurnal precipitation in Taiwan exhibit clear east–west regional differences, with night‐time maxima over eastern Taiwan but early morning maxima over western Taiwan. Analyses also show that the climatological characteristics of diurnal winter precipitation documented in this study are not controlled by some unusual, heavy precipitation events and can be seen as the common features. By examining the changes in meteorological variables (including winds, relative humidity and temperature) extracted from the in situ observations and the MERRA (Modern‐Era Retrospective Analysis for Research and Applications) reanalysis, this study further suggests that (a) the radiative cooling effect and (b) the surface wind convergence induced by the interaction between the local orography, the local land–sea breeze and the large‐scale diurnal circulation changes over the East Asian–western North Pacific (EAWNP) region are two of the possible formation mechanisms responsible for the spatio‐temporal differences of the climatological diurnal winter precipitation in Taiwan. This finding sheds light on the importance of understanding the role of the large‐scale diurnal circulation changes over the EAWNP region in modulating local diurnal precipitation properties during the winter months.

Mid- to late Holocene climate-driven regime shifts inferred from diatom, ostracod and stable isotope records from Lake Son Kol (Central Tian Shan, Kyrgyzstan)

Arid Central Asia represents a key region for understanding climate variability and interactions in the Northern Hemisphere. Patterns and mechanisms of Holocene climate change in arid Central Asia are, however, only partially understood. Multi-proxy data combining diatom, ostracod, sedimentological, geochemical and stable isotope analyses from a ca. 6000-year-old lake sediment core from Son Kol (Central Kyrgyzstan) show distinct and repeated changes in species assemblages. Diatom- and ostracod-inferred conductivity shifts between meso-euhaline and freshwater conditions suggest water balance and regime shifts. Organism-derived data are corroborated by stable isotope, mineralogical and geochemical records, underlining that Son Kol was affected by strong lake level fluctuations of several meters. The δ13Ccarb/δ18Ocarb correlation shows repeated switchovers from a closed to an open lake system. From 6000 to 3800 and 3250 to 1950 cal. yr BP, Son Kol was a closed basin lake with higher conductivities, increased nutrient availability and a water level located below the modern outflow. Son Kol became again a hydrologically open lake at 3800 and 1950 cal. yr BP. Comparisons to other local and regional paleoclimate records indicate that these regime shifts were largely controlled by changing intensity and position of the Westerlies and the Siberian Anticyclone that triggered changes in the amount of winter precipitation. A strong influence of the Westerlies ca. 5000–4400, 3800–3250 and since 1950 cal. yr BP enhanced the amount of precipitation during spring, autumn and winter, whereas cold and dry winters prevailed during phases with a strong Siberian Anticyclone and southward shifted Westerlies at ca. 6000–5000, 4400–3800 and 3250–1950 cal. yr BP. Similarities between variations in winter precipitation at Son Kol and records of the predominant NAO-mode further suggest a teleconnection between wet (dry) winter climate in Central Asia and a positive (negative) NAO-mode. Thus, this study identifies climate fluctuations as the main driver for hydrological regime shifts in Son Kol controlling physicochemical conditions and consequently causing abrupt species assemblage changes. This emphasizes the importance of multi-proxy approaches to identify triggers, thresholds and cascades of aquatic ecosystem transformations.

Variations of winter precipitation over southeastern China in association with the North Atlantic Oscillation

The synoptic-scale winter precipitation variations over southeastern China (22°–32°N, 105°–125°E) and their association with the North Atlantic Oscillation (NAO) during 1951–2007 are investigated in this paper. The variability of wintertime precipitation is characterized by meridional displacement of its maximum center. Two precipitation regimes, with maximum centers located over the Yangtze and Pearl River basins, are identified via cluster analysis. Time-lagged analyses suggest that the two precipitation regimes are connected with the decaying phases of positive NAO (NAO+) events of different amplitudes. A strong (medium) NAO+ event is defined as one when the maximum amplitude of the NAO index exceeds 1.0 (in the range of 0.7–1.0) for at least 4 consecutive days and drops to less than 0.3 within 7 days following the peak index. After the peak of a strong NAO+, southerly winds expand northward to the Yangtze River (about 30°N), a northeast–southwest-tilted trough migrates to east of Lake Baikal, and cold air intrudes into central eastern China; thus, precipitation is strengthened over the Yangtze River basin where warm and cold air masses converge. In comparison, during the decaying phase of medium NAO+ events, the southerly winds are relatively weak, and precipitation tends to be enhanced at lower latitudes (around 25°N). Further analysis indicates that downstream Rossby-wave propagation may account for the latitudinal expansion of the southerly wind anomalies over the eastern coastal area of China during the decaying phase of NAO+ events of different strengths.

Recent changes in area and thickness of Torngat Mountain glaciers (northern Labrador, Canada)

Abstract. The Torngat Mountains National Park, northern Labrador, Canada, contains more than 120 small glaciers: the only remaining glaciers in continental northeast North America. These small cirque glaciers exist in a unique topo-climatic setting, experiencing temperate maritime summer conditions yet very cold and dry winters, and may provide insights into the deglaciation dynamics of similar small glaciers in temperate mountain settings. Due to their size and remote location, very little information exists regarding the health of these glaciers. Just a single study has been published on the contemporary glaciology of the Torngat Mountains, focusing on net mass balances from 1981 to 1984. This paper addresses the extent to which glaciologically relevant climate variables have changed in northern Labrador in concert with 20th-century Arctic warming, and how these changes have affected Torngat Mountain glaciers. Field surveys and remote-sensing analyses were used to measure regional glacier area loss of 27 % from 1950 to 2005, substantial rates of ice surface thinning (up to 6 m yr−1) and volume losses at Abraham, Hidden, and Minaret glaciers, between 2005 and 2011. Glacier mass balances appear to be controlled by variations in winter precipitation and, increasingly, by strong summer and autumn atmospheric warming since the early 1990s, though further observations are required to fully understand mass balance sensitivities. This study provides the first comprehensive contemporary assessment of Labrador glaciers and will inform both regional impact assessments and syntheses of global glacier mass balance.

Connection between November snow cover over Eastern Europe and winter precipitation over East Asia

ABSTRACTIn this study, the connected spatial and temporal features of winter precipitation over East Asia and November snow cover over Eurasia are analysed using the singular value decomposition (SVD) method. The results show that a strong consistent variation of winter precipitation occurs over East Asia, especially north of 35°N, closely related to the snow cover change over Eastern Europe. Mechanism analysis indicates that the processes behind the physical link between the November snow cover over Eastern Europe and East Asian winter precipitation are different in December compared to January and February. In December, the persistence of the snow cover anomaly can ‘memorize’ the signal of the November snow cover and impact December circulation and precipitation over East Asia. During January–February, the snow cover anomaly disappears, while the variability of the polar vortex resulting from the interaction of the troposphere and stratosphere serves as a bridge connecting the November snow cover over Eastern Europe and the January–February precipitation over East Asia. Revealing the role of the November snow cover is significant not only for understanding East Asian winter precipitation variability but also for its prediction.

Long‐term variation of winter precipitation linked to sea‐surface heat fluxes around the Japan/East Sea

AbstractWe revealed long‐term variation of winter precipitation at the northwest coast of Japan and its link to decadal variation of autumn‐to‐winter sea‐surface fluxes from the Japan/East Sea with observational data of sea‐surface fluxes, sea‐surface temperature (SST), and ocean heat content (OHC) data. Much precipitation was observed after 1995 because both SST and OHC were significantly higher in the Japan/East Sea. In a numerical experiment forced by the climatological SST that excluded the decadal change, the decadal variation of the land precipitation did not appear, suggesting that the decadal variation of the coastal precipitation is sensitive to SST.

Stream water carbon controls in seasonally snow-covered mountain catchments: impact of inter-annual variability of water fluxes, catchment aspect and seasonal processes

Stream water carbon (C) export is one important pathway for C loss from seasonally snow-covered mountain ecosystems and an assessment of overarching controls is necessary. However, such assessment is challenging because changes in water fluxes or flow paths, seasonal processes, as well as catchment specific characteristics play a role. For this study we elucidate the impact of: (i) changes in water flux (by comparing years of variable wetness), (ii) catchment aspect [north-facing (NF) vs. south-facing (SF)] and (iii) season (snowmelt vs. summer) on all forms of dissolved stream water C [dissolved organic C (DOC), chromophoric dissolved organic matter (CDOM) and dissolved inorganic C (DIC)] in forested catchments within the Valles Caldera National Preserve, New Mexico. The significant correlation between annual water and C fluxes (e.g. DOC r2 = 0.83, p < 0.02) confirms annual stream water discharge as the overarching control on C efflux, likely from a well-mixed ground water reservoir as indicated by previous research. However, CDOM exhibited a dominantly terrestrial fluorescence signature (59–71 %) year round, signaling a strong riparian and near stream soil control on CDOM composition. During snowmelt, the role of water as C transporter was superimposed on its control as C reservoir, when the NF stream transported significantly more soil C (40 % DOC, 56 % DIC) than the SF stream as a result of hillslope flushing. Inter-annual variations in winter precipitation were paramount in regulating annual stream C effluxes, e.g., reducing C effluxes three-fold after a dry (relative to wet) winter season. During the warmer summer months % dissolved oxygen saturation decreased, δ13CDIC increased and CDOM assumed a more microbial signature, consistent with heterotrophic respiration in the stream and riparian soils. As a result of stream C incubation and soil respiration, \( P_{{{\text{CO}}_{2} }} \) increased up to 12 times atmospheric values leading to substantial degassing.

SWAT-Based Streamflow Estimation and Its Responses to Climate Change in the Kadongjia River Watershed, Southern Tibet

AbstractRunoff estimation and its response to climate change in ungauged or poorly gauged basins based on hydrological models are frontier research issues of the hydrological cycle. For the Kadongjia River watershed (KRW), a poorly gauged watershed located in southern Tibet, China, the Soil and Water Assessment Tool (SWAT) was adapted to model streamflow and its responses to climate change. The average annual streamflow was simulated to be roughly 124.6 mm with relatively small interannual variation during 1974–2010. The seasonal distribution of streamflow was uneven with a maximum in summer and a minimum in winter. Snowmelt, which was mainly produced in April–May, accounted for 4.0% of annual streamflow. Correlations and regression analysis between the interannual variations of major climatic and hydrological variables indicated that precipitation (temperature) had positive (negative) influence on the annual streamflow variation. For the interannual streamflow variations, warmer temperature was slightly more important than the variation of winter precipitation. Comparing streamflow changes in the current years (1980–99) with the future (2030–49), streamflow variations were more sensitive to changing climate in winter and spring than in the other two seasons. Model improvement is expected to enhance the simulation efficiency of SWAT and the analyses of hydrological responses to climatic change in KRW, thus supporting the model's credibility for hydrological cycle research in alpine regions.

Glacier response to current climate change and future scenarios in the northwestern Italian Alps

We analyze longtime series of annual snout positions of several valley glaciers in the northwestern Italian Alps, together with a high-resolution gridded dataset of temperature and precipitation available for the last 50 years. Glacier snout fluctuations are on average negative during this time span, albeit with a period of glacier advance between about 1970 and 1990. To determine which climatic variables best correlate with glacier snout fluctuations, we consider a large set of seasonal predictors, based on our climatic dataset, and determine the most significant drivers by a stepwise regression technique. This in-depth screening indicates that the average glacier snout fluctuations strongly respond to summer temperature and winter precipitation variations, with a delay of 5 and 10 year, respectively. Snout fluctuations display also a significant (albeit weak) response to concurrent (same year) spring temperature and precipitation conditions. A linear regressive model based on these four climatic variables explains up to 93 % of the variance, which becomes 89 % when only the two delayed variables are taken into account. When employed for out-of-sample projections, the empirical model displays high prediction skill, and it is thus used to estimate the average glacier response to different climate change scenarios (RCP4.5, RCP8.5, A1B), using both global and regional climate models. In all cases, glacier snout fluctuations display a negative trend, and the glaciers of this region display an accelerated retreat, leading to a further regression of the snout position. By 2050, the retreat is estimated to be between about 300 and 400 m with respect to the current position. Glacier regression is more intense for the RCP8.5 and A1B scenarios, as it could be expected from the higher severity of these emission pathways.

Characteristics of Central Southwest Asian Water Budgets and Their Impacts on Regional Climate

Water budgets terms, evapotranspiration (E), precipitation (P), runoff (N), moisture convergence (MC) and both surface as well as atmospheric residual terms have been computed with National Centers for Environmental Prediction (NCEP) (1948-2007) and European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 (1958-2001) reanalysis data sets for Central Southwest Asia (CSWA).The domain of the study is 45° - 75°E & 25° - 40°N. Only the land area has been used in these calculations. It is noted in the comparison of both reanalysis data sets with Global Precipitation Climatology Centre (GPCC) that all three data sets record different precipitation before 1970. The maximum is from NCEP and the minimum with ERA-40. However, after 1970 all the data sets record almost the same precipitation. ERA-40 computes two phases of MC. Before 1975, the domain acts as a moisture source, whereas after 1975 it behaves as a moisture sink. The region CSWA is divided into six sub areas with rotational principle factor analysis and we distinguish them by different approached weather systems acting on each area. Finally, NCEP yearly precipitation is further divided into seasons; winter (November to April) and summer (May to October) and two phases have been noted. The variation in winter precipitation is more than summer during last 60-year analysis.

An east‐west SST anomaly pattern in the midlatitude North Atlantic Ocean associated with winter precipitation variability over eastern China

Winter precipitation tends to vary consistently over most regions of eastern China. The present study reveals that the variation in winter precipitation over eastern China is positively correlated to an east‐west sea surface temperature (SST) anomaly pattern in the midlatitudes and high latitudes of the North Atlantic Ocean. When the SST is higher (lower) in the eastern North Atlantic Ocean and lower (higher) in the western North Atlantic Ocean, winter precipitation over eastern China tends to be above (below) normal. The east‐west SST anomaly pattern in the North Atlantic modifies the atmospheric circulation over the Atlantic Ocean and Europe, and the anomalous circulation extends to downstream East Asia through the propagation of Rossby waves and exerts influence on winter precipitation over eastern China. The formation of the east‐west SST anomaly pattern in the North Atlantic may be associated with anomalies in the North Atlantic thermohaline circulation and in surface winds over the North Atlantic Ocean.

Longitudinal trends in climate drive flowering time clines in North American Arabidopsis thaliana

Introduced species frequently show geographic differentiation, and when differentiation mirrors the ancestral range, it is often taken as evidence of adaptive evolution. The mouse-ear cress (Arabidopsis thaliana) was introduced to North America from Eurasia 150–200 years ago, providing an opportunity to study parallel adaptation in a genetic model organism. Here, we test for clinal variation in flowering time using 199 North American (NA) accessions of A. thaliana, and evaluate the contributions of major flowering time genes FRI, FLC, and PHYC as well as potential ecological mechanisms underlying differentiation. We find evidence for substantial within population genetic variation in quantitative traits and flowering time, and putatively adaptive longitudinal differentiation, despite low levels of variation at FRI, FLC, and PHYC and genome-wide reductions in population structure relative to Eurasian (EA) samples. The observed longitudinal cline in flowering time in North America is parallel to an EA cline, robust to the effects of population structure, and associated with geographic variation in winter precipitation and temperature. We detected major effects of FRI on quantitative traits associated with reproductive fitness, although the haplotype associated with higher fitness remains rare in North America. Collectively, our results suggest the evolution of parallel flowering time clines through novel genetic mechanisms.