A recent weakening of winter temperature association between Arctic and Asia

Arctic warming and its association with the mid-latitudes have been hot topic over the past two decades. Although many studies have explored these issues it is not clear that how their linkage has changed over time. The results show that winter low tropospheric temperatures in Asia experienced two phases over the past two decades. Phase I (2007/2008 to 2012/2013) was characterized by a warm Arctic and cold Eurasia, and phase II by a warm Arctic and warm Eurasia (2013/2014 to 2018/2019). A strengthened association in winter temperature between the Arctic and Asia occurred during phase I, followed by a weakened linkage during phase II. Simulation experiments forced by observed Arctic sea ice variability largely reproduce observed patterns, suggesting that Arctic sea ice loss contributes to phasic (or low-frequency) variations in winter atmosphere and make the Arctic-Asia temperature association fluctuate over time. The weakening of the Arctic-Asia linkage post-2012/2013 was associated with amplified and expanded Arctic warming. The corresponding anomalies in SLP resembled a positive phase North Atlantic Oscillation (NAO) during phase II. This study implies that the phasic warm Arctic-cold Eurasia and warm Arctic-warm Eurasia patterns would alternately happen in the context of Arctic sea ice loss, which increase the difficulty to correctly predict Asian winter temperature.

Sclerochronological evidence of pronounced seasonality from the late Pliocene of the southern North Sea Basin, and its implications

Oxygen isotope (δ18O) sclerochronology of benthic marine molluscs provides a means of reconstructing the seasonal range in seafloor temperature, subject to use of an appropriate equation relating shell δ18O to temperature and water δ18O, reasonably accurate estimation of water δ18O, and due consideration of growth-rate effects. Taking these factors into account, δ18O data from late Pliocene bivalves of the southern North Sea Basin (Belgium and the Netherlands) indicate a seasonal seafloor range at times larger than now in the area. Microgrowth-increment data from Aequipecten opercularis, together with the species-composition of the bivalve assemblage and aspects of preservation, suggest a setting below the summer thermocline for all but the latest material investigated. This implies a higher summer temperature at the surface than on the seafloor and consequently a greater seasonal range. A conservative (3 °C) estimate of the difference between maximum seafloor and surface temperature under circumstances of summer stratification points to seasonal surface ranges in excess of the present value (12.4 °C nearby). Using model-constrained estimates of water δ18O, summer surface temperature was initially in the cool temperate range (< 20 °C) and then (during the Mid-Piacenzian Warm Period; MPWP) increased into the warm temperate range (> 20 °C) before reverting to cool temperate values (in conjunction with shallowing and a loss of summer stratification). This pattern is in agreement with biotic-assemblage evidence. Winter temperature was firmly in the cool temperate range (< 10 °C) throughout, contrary to previous interpretations. Averaging of summer and winter surface temperatures for the MPWP provides a figure for mean annual sea-surface temperature that is 2–3 °C higher than the present value (10.9 °C nearby) and in close agreement with a figure obtained by averaging alkenone- and TEX86-temperatures for the MPWP from the Netherlands. These proxies, however, respectively underestimate summer temperature and overestimate winter temperature, giving an incomplete picture of seasonality. A higher mean annual temperature than now is consistent with the notion of global warmth in the MPWP, but a low winter temperature in the southern North Sea Basin suggests regional reduction in oceanic heat supply, contrasting with other interpretations of North Atlantic oceanography during the interval. Carbonate clumped isotope (Δ47) and biomineral unit thermometry offer means of checking the δ18O-based temperatures.

Changing Lake Ice Intermittency in the Northern Hemisphere

As the global climate warms, lakes are expected and have been observed to experience changes in seasonal ice cover. Previous research has observed decreasing freeze durations, but relatively few studies have investigated the impact of climate change on lake ice intermittency - the tendency of lakes to freeze over in some years but not others. Here we conduct an analysis of a lake dataset that includes nineteen intermittent ice-covered lakes in the northern hemisphere. We use logistic and binomial regression to model the relationship between historical climate changes and freeze events, with log CO2 concentration and mean winter temperature as covariates. Across the lakes, we observe a decrease in freeze probability and years with freeze events, with nine out of nineteen lakes showing a significant relationship between freeze years and log CO2 concentration. Additionally, we find that mean winter temperature can be a simple, readily accessible predictor for intermittent lake freeze. We also examine Lake Carnegie in Princeton, NJ as a case study, taking into account both quantitative data and anecdotal evidence, and find that the probability of ice skating has decreased from nearly 1 to 0.2 over the past century. Accordingly, local newspaper archives semantically suggest that local expectations for lake freezing have reversed over the last century as a societal response to climate change.

El Niño Southern Oscillation (1896 to 2016): Quantifying Effects on Winter Precipitation and Temperature in Southwest Ohio, USA

Continental-scale studies of North America suggest that the El Niño Southern Oscillation (ENSO) can cause winters to be warmer, with less precipitation, during El Niño conditions and colder, with more precipitation, during La Niña conditions in the Midwest United States. Two sources of historical records of precipitation and temperature in southwest Ohio from 1896 to 2016 were analyzed. Three statistical methodologies were used to test the hypothesis that anomalies in winter temperature and precipitation occurred in relation to ENSO phases. Eighty percent of El Niño winters had below-average winter precipitation; the average anomaly was −5 cm. Precipitation decreased with increase in El Niño strength as measured by the Multivariate ENSO Index (MEI). These results were statistically significant beyond the 95% level. However, variation in MEI only accounted for 3% of the overall variability in winter precipitation. Many of the drier winters on record, including the extrema, occurred during neutral winters. During La Niña winters precipitation was not statistically significantly different from that in neutral winters. Winter temperature was not statistically significantly different during El Niño and La Niña winters within the century of record. The results were consistent between separate analyses of data from the 2 different sources.

Abrupt Temperature Change In Winter Over The Mongolian Plateau For The Past 60 Years

Studying the abrupt temperature change in winter over the Mongolian Plateau (MP) is of great significance for understanding the spatiotemporal distribution of temperature and the mechanism of global climate change. Monthly temperature data of MP were collected during 1961–2017, the abrupt-change point was determined by the Mann–Kendall test and sliding t-test to analyze the characteristics and causes of abrupt temperature change in winter. The results showed that (a) The increase rate of winter temperature was 0.41 ℃/10a, with a contribution rate of 30.7 % to annual temperature change, which was significantly higher than that of mainland China, indicating that climate change in the MP was more sensitive to global warming. (b) The abrupt-change point occurred in 1988, with temperatures of -15.5 ℃ and − 14.1°C before and after 1988, respectively, the increasing range was 9%. The abrupt temperature change in high latitudes was 1–3 years later than that in low latitudes. (c) The isotherms of different temperatures in winter moved northward by 10–200 km, especially − 16°C isotherm moved approximately 200 km northward after 1988, thereby the MP warmed significantly. (d) there was a good coupling relationship between the Arctic Oscillation (AO) and winter temperature. AO affects temperature change by influencing the Mongolia–Siberian High, therefore, it may be an important factor to drive the abrupt temperature change in winter.

Seesawing of Winter Temperature Extremes between East Asia and North America

In recent winters, there have been repeated observations of extreme warm and cold spells in the midlatitude countries. This has evoked questions regarding how winter temperature extremes are induced. In this study, we demonstrate that abnormally warm winter weather in East Asia can drive the onset of extremely cold weather in North America approximately one week forward. These seesawing extremes across the basin are mediated by the North Pacific Oscillation (NPO), one of the recurrent atmospheric patterns over the North Pacific. Budget analysis of the quasigeostrophic geopotential tendency equation shows that intense thermal advection over East Asia is able to trigger the growth of the NPO. Vorticity fluxes associated with the upper-level stationary trough then strengthen and maintain the NPO against thermal damping following the onset of the NPO. Differential diabatic heating accompanied by changes in circulation also positively contribute to the growth and maintenance of the NPO. These results imply that recurrent cold extremes, seemingly contrary to global warming, may be an inherent feature resulting from strengthening warm extremes.

Overwintering mortality of the oak lace bug (Corythucha arcuata) in Hungary – a field survey

The North American oak lace bug (Corythucha arcuata) was first discovered in Europe (Norhern Italy) in 2000. It started a rapid area expansion in the last decade and has been reported in 20 countries so far. Almost all European oaks are suitable hosts. On top of the host availability, abiotic factors like weather/climate may also have a decisive impact on its further spread and future outbreaks. We conducted a simple field survey within three years, at five locations to estimate the overwintering mortality of the species. Our results suggest that not even a relatively harsh winter (as 2016/2017) caused severe mortality in the overwintering populations. The average mortality of the nine year/location combinations was 30.6% (range 9.1–58.5%). Based on this, the low winter temperature is unlikely to restrict its further spread, therefore continuing area expansion can be predicted.