Surface Air Temperature Extremes Research Articles

Modulated Trends in Arctic Surface Air Temperature Extremes as a Fingerprint of Climate Change

Abstract Strengthened by polar amplification, Arctic warming provides direct evidence for global climate change. This analysis shows how Arctic surface air temperature (SAT) extremes have changed throughout time. Using ERA5, we demonstrate a pan-Arctic (>60°N) significant upward SAT trend of +0.62°C decade−1 since 1979. Due to this warming, the warmest days of each month in the 1980s to 1990s would be considered average today, while the present coldest days would be regarded as normal in the 1980s to 1990s. Over 1979–2021, there was a 2°C (or 7%) reduction of pan-Arctic SAT seasonal cycle, which resulted in warming of the cold SAT extremes by a factor of 2 relative to the SAT trend and dampened trends of the warm SAT extremes by roughly 25%. Since 1979, autumn has seen the strongest increasing trends in daily maximum and minimum temperatures, as well as counts of days with SAT above the 90th percentile and decreasing trends in counts of days with SAT below the 10th percentile, consistent with rapid Arctic sea ice decline and enhanced air–ocean heat fluxes. The modulated SAT seasonal signal has a significant impact on the timing of extremely strong monthly cold and warm spells. The dampening of the SAT seasonal fluctuations is likely to continue to increase as more sea ice melts and upper-ocean warming persists. As a result, the Arctic winter cold SAT extremes may continue to exhibit a faster rate of change than that of the summer warm SAT extremes as the Arctic continues to warm. Significance Statement As a result of global warming, the Arctic Ocean’s sea ice is receding, exposing more and more areas to air–sea interactions. This reduces the range of seasonal changes in Arctic surface air temperatures (SAT). Since 1979, the reduced seasonal SAT signal has decreased the trend of warm SAT extremes by 25% over the background warming trend and doubled the trend of cold SAT extremes relative to SAT trends. A substantial number of warm and cold spells would not have been identified as exceptional if the reduction of the Arctic SAT seasonal amplitudes had not been taken into account. As the Arctic continues to warm and sea ice continues to diminish, seasonal SAT fluctuations will become more dampened, with the rate of decreasing winter SAT extremes exceeding the rate of increasing summer SAT extremes.

The increase in intensity and frequency of surface air temperature extremes throughout the western South Atlantic coast

The climate is changing. At this stage, it is important to specify an ‘extreme’ climate and identify patterns that indicate its potential harm worldwide, including the coastal zones. Herein, we considered extremes based on the “Peaks Over Threshold” method from the “Extreme Value Theory”. We looked after geographical patterns of surface air temperature (SAT) extremes (e.g., Tmax, Tmin, daily temperature range (DTR), and inter-daily temperature range) over the last 40 years throughout the Brazilian coast. Overall, we found a trend increase in intensity and frequency, but the duration was barely affected. The latitudinal pattern of extremes and the temperatures considered extremes followed the settled perception that areas in higher latitudes will be more affected by the extent of warming. Additionally, the seasonal pattern of DTR demonstrated to be a good approach to make inferences about air mass changes, but joint analyses on extremes with other atmospheric variables are desirable. Given the potential effects of extreme climates on society and natural systems over the world, our study highlights the urge for action to mitigate the effects of the increase in SAT in coastal zones.

The role of large-scale drivers in the Amundsen Sea Low variability and associated changes in water isotopes from the Roosevelt Island ice core, Antarctica

Here we examine the water stable-isotope data from the Roosevelt Island Climate Evolution (RICE) ice core. Roosevelt Island is an independent ice rise located at the northeastern margin of the Ross Ice Shelf. In this study, we use empirical orthogonal function (EOF) analysis to investigate the relationship between RICE ice-core oxygen-18 isotopes (δ18O) and Southern Hemisphere atmospheric circulation during the extended austral winter (April–November). The RICE δ18O record is correlated with Southern Annular Mode (SAM) and Pacific–South American pattern 1 (PSA1), which both project onto the Amundsen–Bellingshausen Sea (ABS) geopotential height field. Pacific sector Southern Ocean, eastern Ross Sea, and West Antarctic’s atmospheric circulation, sea ice, and surface air temperature (SAT) anomalies, as well as RICE δ18O, are strongest when El Niño–Southern Oscillation (ENSO) and SAM are “in-phase”. That is when the SAM − /PSA1 + (El Niño) and SAM + /PSA1 − (La Niña) phasing prevails. When in-phase, the δ18O correlation with the 500-hPa geopotential height (Z500) is strong in regions (e.g., the Amundsen Sea) where their anomalies associated with SAM and PSA1 show the same sign. SAM − /PSA1 + (El Niño) and SAM + /PSA1 − (La Niña) is associated with positive and negative δ18O anomalies, respectively. RICE δ18O can aid in establishing past natural variability of the strength of the SH high-latitude Pacific sector ENSO-SAM connection and associated atmospheric circulation, sea ice, and SAT extremes.

Evaluation of CMIP5 and CMIP6 simulations of historical surface air temperature extremes using proper evaluation methods

Reliable projections of extremes by climate models are becoming increasingly important in the context of climate change and associated societal impacts. Extremes are by definition rare events, characterized by a small sample associated with large uncertainties. The evaluation of extreme events in model simulations thus requires performance measures that compare full distributions rather than simple summaries. This paper proposes the use of the integrated quadratic distance (IQD) for this purpose. The IQD is applied to evaluate CMIP5 and CMIP6 simulations of monthly maximum and minimum near-surface air temperature over Europe and North America against both observation-based data and reanalyses. Several climate models perform well to the extent that these models’ performance is competitive with the performance of another data product in simulating the evaluation set. While the model rankings vary with region, season and index, the model evaluation is robust against changes in the grid resolution considered in the analysis. When the model simulations are ranked based on their similarity with the ERA5 reanalysis, more CMIP6 than CMIP5 models appear at the top of the ranking. When evaluated against the HadEX2 data product, the overall performance of the two model ensembles is similar.

The impact of soil moisture–atmosphere coupling on daily maximum surface temperatures in Southeastern South America

Based on a series of experiments conducted by two regional climate models (RCA4 and LMDZ) with and without soil moisture-atmosphere coupling, we investigate the role of soil moisture on the occurrence of surface air temperature extremes and its persistence in Southeastern South America. Our analysis reveals that both factors, soil moisture-atmosphere coupling and relatively drier soil conditions, enhance the temperature extremes. In addition, the existence of soil-atmosphere coupling and the associated soil moisture variability is crucial for the development of the extremes in SESA. The key role of soil-atmosphere coupling is also reflected in the intrinsic persistence of hot days, which is greater in simulations with interactive soil moisture than in those with prescribed soil conditions. In the absence of soil-atmosphere coupling, the imprint of the anomalous dry (and also wet) soil conditions on the intensity and persistence of hot days is weaker.

Impact of Atmospheric Blocking on South America in Austral Summer

Abstract This study investigates atmospheric blocking over eastern South America in austral summer for the period of 1979–2014. The results show that blocking over this area is a consequence of propagating Rossby waves that grow to large amplitudes and eventually break anticyclonically over subtropical South America (SSA). The SSA blocking can prevent the establishment of the South Atlantic convergence zone (SACZ). As such, years with more blocking days coincide with years with fewer SACZ days and reduced precipitation. Convection mainly over the Indian Ocean associated with Madden–Julian oscillation (MJO) phases 1 and 2 can trigger the wave train that leads to SSA blocking whereas convection over the western/central Pacific associated with phases 6 and 7 is more likely to lead to SACZ events. It is found that the MJO is a key source of long-term variability in SSA blocking frequency. The wave packets associated with SSA blocking and SACZ episodes differ not only in their origin but also in their phase and refraction pattern. The tropopause-based methodology used here is proven to reliably identify events that lead to extremes of surface temperature and precipitation over SSA. Up to 80% of warm surface air temperature extremes occur simultaneously with SSA blocking events. The frequency of SSA blocking days is highly anticorrelated with the rainfall over southeast Brazil. The worst droughts in this area, during the summers of 1984, 2001, and 2014, are linked to record high numbers of SSA blocking days. The persistence of these events is also important in generating the extreme impacts.

Asymmetry of Winter European Surface Air Temperature Extremes and the North Atlantic Oscillation

Abstract Interannual variations of winter warm and cold extremes in Europe are investigated. It is found that the variations are closely connected to the phase of the North Atlantic Oscillation (NAO). The leading EOF of the winter cold (warm) surface air temperature (SAT) extreme frequency shows an enhanced occurrence over western (eastern) Europe. The SAT probability distribution function of the cold extreme winter exhibits both a decrease of the mean SAT and a marked increase in SAT variance, whereas it shows only a shift of the mean SAT to the warmer side for extreme warm winters. This study reveals an asymmetry in location between the cold and warm extremes, caused by the NAO modulations of blocking events and other submonthly variations. Winters with frequent cold extremes are mainly accompanied by the eastern Atlantic blocking. The circulation causes not only marked local cooling but also increased SAT gradient, resulting in both enhanced SAT variance and increased occurrence of cold extremes. By contrast, winters with frequent warm extremes are associated with the northeast–southwest tilted positive NAO pattern. The warm advection by the submonthly perturbations is responsible for the development of warm extremes. The reduced SAT gradient due to enhanced warm advection weakens SAT variance over northern Europe. Thus, the cold extremes are larger in terms of deviations from the monthly mean than the warm extremes.

Trends and variability of daily temperature extremes during 1960–2012 in the Yangtze River Basin, China

The variability of surface air temperature extremes has been the focus of attention during the past several decades, and may exert a great influence on the global hydrologic cycle and energy balance through thermal forcing. Based on daily minimum (TN) and maximum temperature (TX) observed by the China Meteorological Administration at 143 meteorological stations in the Yangtze River Basin (YRB), a suite of temperature indices recommended by the Expert Team on Climate Change Detection and Indices, with a primary focus on extreme events, were computed and analyzed for the period of 1960–2012 for this area. The results show widespread significant changes in all temperature indices associated with warming in the YRB during 1960–2012. On the whole, cold-related indices, i.e., cold nights, cold days, frost days, icing days and cold spell duration index significantly decreased by −3.45, −1.03, −3.04, −0.42 and −1.6days/decade, respectively. In contrast, warm-related indices such as warm nights, warm days, summer days, tropical nights and warm spell duration index significantly increased by 2.95, 1.71, 2.16, 1.05 and 0.73days/decade. Minimum TN, maximum TN, minimum TX and maximum TX increased significantly by 0.42, 0.18, 0.19 and 0.14°C/decade. Because of a faster increase in minimum temperature than maximum temperature, the diurnal temperature range (DTR) exhibited a significant decreasing trend of −0.09°C/decade for the whole YRB during 1960–2012. However, the decreasing trends all occurred in 1960–1985, while increasing trends though insignificant were found in all sub-regions and the whole YRB during 1986–2012. Geographically, stations in the eastern Tibet Plateau and northeastern YRB showed stronger trends in almost all temperature indices. Time series analysis indicated that the YRB was dominated by a general cooling trend before the mid-1980s, but a warming trend afterwards. In general, the overall warming in the YRB was mainly due to the warming in 1986–2012. Strong relationships between temperature trends and elevation were detected in this study. The warming rates increased with elevation when elevation is above 350m, but decreased with elevation when elevation is below 350m.

Recent changes in daily precipitation and surface air temperature extremes in mainland Portugal, in the period 1941–2007

Changes in the climatology of precipitation and surface air temperature are being investigated worldwide, searching for changes in variability, the mean and extreme events (maximum and minimum). By exploring recent adjustments in the climate of mainland Portugal, particularly in the intensity, frequency and duration of extreme events, this study investigates trends in selected specific indices that are calculated from daily precipitation data from 57 and surface air temperature data from 23 measuring stations scattered across the territory. Special attention is paid to regional differences and variations in seasonality. The data cover the periods 1941–2007 for precipitation, and 1941–2006 for temperature. They are explored at the annual and seasonal scales and for different sub-periods.Results show that trends in annual precipitation indices are generally weak and, overall, not statistically significant at the 5% level. Nevertheless, a decreasing trend is revealed by regional indices of total wet-day precipitation and extreme precipitation (above the 99th percentile). Seasonal precipitation exhibits significant decreasing trends in spring precipitation, while extreme heavy precipitation events, in terms of both magnitude and frequency, have become more pronounced in autumn. Results for winter and summer suggest that the extremes have not suffered any significant aggravation.Trends for air temperature are statistically more significant and marked than for precipitation and indicate general warming across the territory. This warming trend is revealed very consistently by the time series of individual stations and regional mean temperature, and is also consistent with the findings reported in other studies for Portugal and at the European scale.

Evolution of extreme temperatures over Portugal: recent changes and future scenarios

Changes in surface air temperature extremes over mainland Portugal since the early 1940s were investigated on the basis of daily maximum and minimum temperatures available from time series from 23 weather stations. The maximum (minimum) temperature decreased by 0.17°C decade -1 (0.19°C decade -1 ) for 1941-1975 followed by an increase of 0.49°C decade -1 (0.54°C decade -1 ) for 1976-2006, significantly higher than similar trends computed at the global and Euro- pean scales. A large set of climatic indices was analysed to detect the presence of trends and quan- tify the variations of different indices for different periods. In the 1976-2006 period, many stations revealed statistically significant positive trends in the annual number of tropical nights, summer days, warm spells, warm nights and warm days. At the seasonal level, we detected statistically significant increments of extreme heat events for spring and summer, and a decrease of cold extremes in winter. We then used the HadRM3 output to study changes in the maximum and minimum temperature dis- tributions and associated changes in the likelihood of extreme events in the future (2071-2100) under 2 change scenarios. Changes obtained for the future are consistent with those found since the mid- 1970s in Portugal with an increase in maximum temperature of 3.2°C (4.7°C) for the B2 (A2) scenario in summer and ~3.4°C in both scenarios for spring. For minimum temperature, the results were simi- lar, with increases for summer (spring) ranging from 2.7°C (2.5°C) in the B2 scenario to 4.1°C (2.9°C) in the A2 scenario.

Relationships between Climate Variability and Winter Temperature Extremes in the United States

Time series representing two of the climate systems leading patterns of variability, namely El Niño–Southern Oscillation (ENSO) and the Arctic Oscillation (AO), are used together with 50 yr of daily mean surface air temperature data over the conterminous United States to diagnose relationships between winter temperature extremes and interannual climate variability. The aim is to focus attention on some of the physical phenomena that climate models must be able to simulate in order to be deemed credible for use in weather and climate forecasts and assessments. Since the 1950s there has been considerable decadal variability in winter surface air temperature extremes. At most locations in the United States the number of daily extremes is reduced during El Niño, and increased during La Niña and ENSO-neutral years. These changes are qualitatively consistent with a decrease in the daily mean surface air temperature variance during El Niño relative to La Niña and ENSO neutral. Changes in the number of warm extremes during a particular AO phase are largely compensated for by changes in the number of cold extremes, so that the net change in the numbers of surface air temperature extremes is close to zero. However, the AO is associated with larger changes in mean temperature than ENSO.