An intimate coupling of ocean–atmospheric interaction over the extratropical North Atlantic and Pacific

The inter-basin teleconnection between the North Atlantic and the North Pacific ocean–atmosphere interaction is studied using a coupled ocean–atmosphere general circulation model. In the model, an idealized oceanic temperature anomaly is initiated over the Kuroshio and the Gulf Stream extension region to track the coupled evolution of ocean and atmosphere interaction, respectively. The experiments explicitly demonstrate that both the North Pacific and the North Atlantic ocean–atmosphere interactions are intimately coupled through an inter-basin atmospheric teleconnection. This fast inter-basin communication can transmit oceanic variability between the North Atlantic and the North Pacific through local ocean-to-atmosphere feedbacks. The leading mode of the extratropical atmospheric internal variability plays a dominant role in shaping the hemispheric-scale response forced by oceanic variability over the North Atlantic and Pacific. Modeling results also suggest that a century (two centuries) long observations are necessary for the detection of Pacific response to Atlantic forcings (Atlantic response to Pacific forcing).     

Statistical distributions of daily rainfall regime in Europe for the period 1951–2000

Amount and time distributions, X and Y, of daily rain amounts in Europe along the second half of 20th century have been studied from 267 rain gauge records. Different geographical features, such as latitude, vicinity to Mediterranean Sea or the Atlantic Ocean or altitude above sea level, cause the averages of daily rain and annual number of rainy days to vary within a wide range. The largest daily percentiles of amount and time distributions are reached at latitudes south of 50°N and in southwestern Norway. The amount of distribution, X, is well-modelled by the exponential function, with parameters derived from probability graphs. Time distributions, Y, are well-fitted by Pearson type III (Gamma) and Weibull models, their parameters being estimated by L-moments. Normalised rainfall curves (NRC) have been modelled by the analytical function $ X = Y \cdot \exp \left\{ { - b{{\left( {1 - Y} \right)}^c}} \right\} $ , with b and c parameters depicting spatial variability. Alternatively, the beta distribution also describes quite well the empirical NRCs, with parameters estimated by statistical moments. The coordinates of the average daily amount (X _r , Y _r ) and the values of X ^* and Y ^* , which are defined as the fraction of rain amount for a half of rainy days and the fraction of number of rainy days accounting for a half of total rain amount, respectively, depict very similar spatial distribution throughout Europe. In fact, X _r and X ^* keep a linear relationship, as well as Y _r and Y ^* , the four coordinates depending on the coefficient of variation of daily rain amounts. A similar linear relationship is found for the pair (X ^* , Y ^* ). Finally, the Average Linkage algorithm applied to the coordinates X _r , Y _r , X ^* and Y ^* characterising every one of the 267 NRCs permits to group the rain gauges into several spatial clusters, each of them related to a different normalised daily pluviometric regime.     

Circulation anomalies in the atmospheric centers of action during the Eastern Pacific and Central Pacific El Niño

Based on the statistical analysis the teleconnections between circulation anomalies in the atmospheric centers of action and sea surface temperature anomalies are revealed for two types of El Niño. It is demonstrated that for the Eastern Pacific El Niño stronger teleconnections are registered in the Northern Hemisphere whereas the response to the Central Pacific El Niño is much stronger in the Southern Hemisphere. The Central Pacific El Niño is characterized by the more rapid signal propagation from the tropical zone to distant regions. In some cases the pattern of interaction with the atmospheric circulation considerably differs for two types of El Niño that defines differences in the fields of weather anomalies.     

Analysis of tropical cyclone intensification trends and variability in the North Atlantic Basin over the period 1970–2003

Summary Over the past three decades, the sea-surface temperatures of the lower latitudes of the North Atlantic basin have increased while the lower-tropospheric temperatures show no upward trend. This differential warming of the atmosphere may have a destabilizing effect that could influence the development and intensification of tropical cyclones (TCs). In this investigation, we find that in general, TC intensification (a) is higher during the daytime period and during the later months of the storm season, (b) tends to be higher in the western portion of the North Atlantic basin, and (c) is not explained by current month or antecedent SSTs. Any changes associated with warming of the surface compared to a smaller temperature rise in the lower-troposphere (and resultant changes in atmospheric stability) have not produced detectable impacts on intensification rates of tropical cyclones in the North Atlantic basin.     

Spatial and temporal variability of precipitation in Serbia for the period 1961–2010

Monthly, seasonal and annual sums of precipitation in Serbia were analysed in this paper for the period 1961–2010. Latitude, longitude and altitude of 421 precipitation stations and terrain features in their close environment (slope and aspect of terrain within a radius of 10 km around the station) were used to develop a regression model on which spatial distribution of precipitation was calculated. The spatial distribution of annual, June (maximum values for almost all of the stations) and February (minimum values for almost all of the stations) precipitation is presented. Annual precipitation amounts ranged from 500 to 600 mm to over 1100 mm. June precipitation ranged from 60 to 140 mm and February precipitation from 30 to 100 mm. The validation results expressed as root mean square error (RMSE) for monthly sums ranged from 3.9 mm in October (7.5% of the average precipitation for this month) to 6.2 mm in April (10.4%). For seasonal sums, RMSE ranged from 10.4 mm during autumn (6.1% of the average precipitation for this season) to 20.5 mm during winter (13.4%). On the annual scale, RMSE was 68 mm (9.5% of the average amount of precipitation). We further analysed precipitation trends using Sen’s estimation, while the Mann-Kendall test was used for testing the statistical significance of the trends. For most parts of Serbia, the mean annual precipitation trends fell between −5 and +5 and +5 and +15 mm/decade. June precipitation trends were mainly between −8 and +8 mm/decade. February precipitation trends generally ranged from −3 to +3 mm/decade.

     

Spatiotemporal variations in rainfall erosivity during the period of 1960–2011 in Guangdong Province,southern China

Rainfall erosivity, which shows a potential risk of soil loss caused by water erosion, is an important factor in soil erosion process. In consideration of the critical condition of soil erosion induced by rainfall in Guangdong Province of southern China, this study analyzed the spatial and temporal variations in rainfall erosivity based on daily rainfall data observed at 25 meteorological stations during the period of 1960–2011. The methods of global spatial autocorrelation, kriging interpolation, Mann–Kendall test, and continuous wavelet transform were used. Results revealed that the annual rainfall erosivity in Guangdong Province, which spatially varied with the maximum level observed in June, was classified as high erosivity with two peaks that occur in spring and summer. In the direction of south–north, mean annual rainfall erosivity, which showed significant relationships with mean annual rainfall and latitude, gradually decreased with the high values mainly distributed in the coastal area and the low values mainly occurring in the lowlands of northwestern Guangdong. Meanwhile, a significant positive spatial autocorrelation which implied a clustered pattern was observed for annual rainfall erosivity. The spatial distribution of seasonal rainfall erosivity exhibited clustering tendencies, except spring erosivity with Moran’s I and Z values of 0.1 and 1.04, respectively. The spatial distribution of monthly rainfall erosivity presented clustered patterns in January–March and July–October as well as random patterns in the remaining months. The temporal trend of mean rainfall erosivity in Guangdong Province showed no statistically significant trend at the annual, seasonal, and monthly scales. However, at each station, 1 out of 25 stations exhibited a statistically significant trend at the annual scale; 4 stations located around the Pearl River Delta presented significant trends in summer at the seasonal scale; significant trends were observed in March (increasing trends at 3 stations), June (increasing trends at 4 stations located in the Beijiang River Basin), and October (decreasing trends at 4 stations) at the monthly scale. In accordance with the mean annual rainfall over Guangdong Province, the mean annual rainfall erosivity showed two significant periodicities of 3–6 and 10–12 years at a confidence level of 95 %. In conclusion, the results of this study provide insights into the spatiotemporal variation in rainfall erosivity in Guangdong Province and support for agrolandscape planning and water and soil conservation efforts in this region.     

Trends in the frequency of synoptic types in central-southern Chile in the period 1961–2012 using the Jenkinson and Collison synoptic classification

Atmospheric circulation patterns in southern Chile (42° 30′ S) were studied in order to determine and analyse the most characteristic synoptic types and their recent trends, as well as to gain an understanding of how they are associated with low-frequency variability patterns. According to the Jenkinson and Collison (J&C) classification method, a 16-point grid of sea-level pressure data was employed. The findings reveal that some synoptic types show statistically significant trends with a 95% confidence level, positively for anticyclonic westerly hybrids (AW) and advective types for third and fourth quadrant wind flows (W, NW, and N) and negatively for SW and cyclonic hybrids (CS and CSW). A model has been constructed of the linear regression of some weather types with teleconnections that most affect Chile: the undetermined types (U), AW were associated with El Niño or the warm phase of the Pacific Decadal Oscillation (PDO), whereas the cyclonic northerly and cyclonic northeasterly types (CN and CNE) were associated with La Niña or cool phase of the PDO. The weather types associated with Antarctic Oscillation (AAO) in its positive phase are anticyclonic northerly and northeasterly and northerly advection types, while in its negative phase are cyclonic southwesterly and advection types.     

The heterogeneity of Meiyu rainfall over Yangtze–Huaihe River valley and its relationship with oceanic surface heating and intraseasonal variability

Increasing heavy concentrated Meiyu precipitation over the Yangtze–Huaihe river valley (YHRV) during recent years has been previously reported. In fact, the concentrated Meiyu rainfall occurring in a small region or a certain period easily results in floods, thus it is worthy to analyze the heterogeneity of Meiyu rainfall over YHRV. In this study, we use both of precipitation concentration period (PCP) and precipitation concentration degree (PCD) based on vector analysis to identify the heterogeneity of Meiyu rainfall over YHRV. On the climatological mean, the concentrated heavy precipitation occurs in late summer over the Yangtze River Delta, where is usually suffered by floods. The dominant two patterns of PCP and PCD variations are northeast–southwest dipole pattern, homogeneous anomalies and homogeneous variation, north–south dipole pattern, respectively. In addition, the relationship on heterogeneity of Meiyu rainfall with sea surface temperature (SST) and the low level summer intraseasonal oscillation (ISO) are investigated. Two key regions of SST activities are found: Bay of Bengal (BOB) and Equatorial eastern Pacific. From BOB, more abundant water vapor has been brought. On the El Niño-Southern Oscillation variation, it is closely relative with PCD–PC1 during the decaying phase of El Niño, while PCP–PC2 is accompanied with developing phase of La Nina events, suggesting a negative feedback of PCP–PC2 on the Niño3.4 SST, and changes to positive during the later winter. On the ISO activities, the robust regions are located over the high-latitude areas, which are closely related with northeastern cold vortex. The north “cold and dry” air southwardly invaded with the lower-level strong warm air in the rainy area, and easily formed an “upper-wet and lower-dry” unstable layer. Under the trigger of the upward motion, the concentrated heavy rainfall easily occurred over YHRV. In all, the homogeneity variation of the concentrated heavy precipitation over YHRV is closely associated with both of the heating forcing (SST) and dynamical atmospheric forcing (low-level ISO).     

Trends of seasonal maximum and minimum temperatures and precipitation in Southern Brazil for the 1913–2006 period

Long-term variations of monthly average maximum and minimum temperature (TMAX and TMIN) and precipitation records in southern Brazil are investigated for the 1913–2006 period. These variations are carefully analyzed for seasonal and annual indices, taken as regional averages. For this purpose, the serial correlation and trend of the indices are investigated using the run and Mann–Kendall tests. The significant trends are obtained from linear least-square fits. The annual and seasonal TMIN indices show significant warming trends with magnitudes (1.7°C per 100 years for annual index) comparable to those reported by the Intergovernmental Panel on Climate Change, but lower than those found for the southern Brazil in another previous work. Regarding the two other variables, the indices show significant trends only for summer, being a cooling trend of 0.6°C per 100 years for the TMAX and an increasing trend of 93 mm per 100 years over an average summer precipitation of 367 mm. Concerning the decadal analysis, the 1920s present the lowest annual, autumn, and spring TMIN and the 1990s, the highest ones. The 1970s is the decade with the lowest summer TMAX, and the 1940s the decade with the highest one. The driest decade is the 1940s and the wettest, the 1980s.     

Statistical characteristics,trends, and variability of rainfall in Shanxi province,China, during the period 1957–2019

Theoretical and Applied Climatology - Under the background of global warming, an analysis of the trend and variability of rainfall time series on various timescales is very important for...     

Variation in the number of days with heavy precipitation on the territory of Russia for the period of 1936–2000

Time variations in the number of days with heavy precipitation based on data of 93 stations on the territory of Russia are analyzed. Time series of precipitation, corrected by the elimination of main systematic errors of their measurement at the level of their diurnal sums, are used, when computing. The diurnal precipitation sum, exceeding the average long-term diurnal precipitation maximum by three times, was taken as the threshold quantitative criterion, defining “the day with heavy precipitation” concept. This value varies within 10–15 mm/day on the territory of Russia. Extremums fluctuate from 5 to 40 mm/day. Absolute values of linear trends of the annual number of days with heavy precipitation are comparatively small, they fluctuate within ±4 days on the whole territory of Russia. In relative terms, these variations are rather significant, reaching ±40% and more of the corresponding average value for 65 years. The comparison of the spatial distribution of characteristics of linear trends of the annual number of days with heavy precipitation and annual precipitation sum indicates their close conformity.     

Sea-ice anomalies observed in the Greenland and Labrador seas during 1901–1984 and their relation to an interdecadal Arctic climate cycle

Two independent ice data sets from the Greenland and Labrador Seas have been analyzed for the purpose of characterizing interannual and decadal time scale sea-ice extent anomalies during this century. Sea-ice concentration data for the 1953–1984 period revealed the presence of a large positive anomaly in the Greenland Sea during the 1960s which coincided with the great salinity anomaly, an upper-ocean low-salinity water mass that was observed to travel cyclonically around the northern North Atlantic during 1968–1982. This ice anomaly as well as several smaller ones propagated into the Labrador Sea and then across to the Labrador and east Newfoundland coast, over a period of 3 to 5 years. A complex empirical orthogonal function analysis of the same data also confirmed this propagation phenomenon. An inverse relation between sea-ice and salinity anomalies in the Greenland-Labrador Sea region was also generally found. An analysis of spring and summer ice-limit data obtained from Danish Meteorological Institute charts for the period 1901–1956 indicated the presence of heavy ice conditions (i.e., positive ice anomalies) in the Greenland Sea during 1902–1920 and in the late 1940s, and generally negative ice anomalies during the 1920s and 1930s. Only limited evidence of the propagation of Greenland Sea ice anomalies into the Labrador Sea was observed, however, probably because the data were from the ice-melt seasons. On the other hand, several large ice anomalies in the Greenland Sea occurred 2–3 years after large runoffs (in the early 1930s and the late 1940s) from northern Canada into the western Arctic Ocean. Similarly, a large runoff into the Arctic during 1964–1966 preceded the large Greenland Sea ice anomaly of the 1960s. These facts, together with recent evidence of climatic jumps in the Northern Hemisphere tropospheric circulation, suggest the existence of an interdecadal self-sustained climate cycle in the Arctic. In the Greenland Sea, this cycle is characterized by a state of large sea-ice extent overlying an upper layer of cool, relatively fresh water that does not convectively overturn, which alternates every 10–15 years with a state of small sea-ice extent and relatively warm saline surface water that frequently overturns.Dedicated to Robert W. Stewart on the occasion of his retirement     

Low-frequency oscillations of the East Asia–Pacific teleconnection pattern and their impacts on persistent heavy precipitation in the Yangtze–Huai River valley

Based on the daily reanalysis data from NCEP NCAR and daily precipitation data from the China National Meteorological Information Center,an ensemble empirical mode decomposition method is employed to extract the predominant oscillation modes of the East Asia Pacific(EAP) teleconnection pattern.The influences of these low-frequency modes on persistent heavy precipitation in the Yangtze Huai River(YHR)valley are investigated.The results indicate that the EAP pattern and rainfall in YHR valley both exhibit remarkable 10 30- and 30 60-day oscillations.The impacts of the EAP pattern on the YHR persistent heavy precipitation can be found on both the 10 30- and 30 60-day timescales the 10 30-day scale for most cases.Composite analysis indicates that,on the 10 30-day timescale,formation of the EAP pattern in the lower and middle troposphere is determined by convective systems near the tropical western Pacific;whereas in the middle troposphere,the phase transition is jointly contributed by both the dispersion of zonal wave energies at higher latitudes and convective systems over the South China Sea.In the context of the10 30-day EAP pattern,the anomalously abundant moisture is transported by an anomalous subtropical anticyclone system,and strong moisture convergence results from that anomalous anticyclone system and a cyclonic system in the midlatitude East Asia.Such a combination of systems persists for at least three days,contributing to the formation of persistent heavy precipitation in the YHR valley.     

On the relationship between cloud–radiation interaction, atmospheric stability and Atlantic tropical cyclones in a variable-resolution climate model

We compare two 28-year simulations performed with two versions of the Global Environmental Multiscale model run in variable-resolution mode. The two versions differ only by small differences in their radiation scheme. The most significant modification introduced is a reduction in the ice effective radius, which is observed to increase absorption of upwelling infrared radiation and increase temperature in the upper troposphere. The resulting change in vertical lapse rate is then observed to drive a resolution-dependent response of convection, which in turn modifies the zonal circulation and induces significant changes in simulated Atlantic tropical cyclone activity. The resulting change in vertical lapse rate and its implication in the context of anthropogenic climate change are discussed.     

Verification of Toronto temperature and precipitation forecasts for the period 1960–1979

Abstract

The accuracy of temperature and precipitation forecasts for Toronto was studied for the 20‐year period 1960–1979. Since any archive of official forecasts extends for only a small part of this period, it was necessary to retrieve the forecasts from newspaper records. The possible errors involved in such a data source were examined through a comparison of newspaper reported observations and the official record. On only a few occasions were significant differences observed.

For temperature forecasts, the record indicates a significant loss of skill over the 20‐year periodin the prediction of maximum temperature for the first day. This was observed not only for the Bloor Street observing station for which the entire 20‐year record was analysed, but also for observing stations at Toronto Island, Downsview and Malton. The loss of skill over the years is greatest in winter when temperature is consistently predicted too low at all stations.

For the entire period under study, precipitation forecasts consisted only of words and no quantitative information (such as probability of precipitation forecasts) was issued. Word choice is intended to carry information on the duration and expected spatial coverage of precipitation, but substantial inconsistencies between word choice and subsequent precipitation occurrence were found. Consequently, the verification procedure for these forecasts was very simple and ignored any differences implied in word choice. With this technique precipitation forecasts were shown to have improved over the 20‐year period.