Extreme Anomalies Research Articles

Circulation anomalies associated with winter temperature extremes in Athens during the period 19002004

We use the long series of temperature observed at the National Observatory of Athens, Greece, to examine the extremes of this element together with associated anomalies in the general circulation of the atmosphere. The 13 extreme-cold and 20 extreme-warm winters during the period 1900-2004 (equal to or below minus one standard deviation, and equal to or above plus one standard deviation respectively) had opposite pressure anomalies, mainly over the North Atlantic and Eurasia. The temperature extremes at Athens were representative of most of the Mediterranean and the Balkans, and their associated pressure anomalies were robust. The extremes of the Index of the North Atlantic Oscillation (the pressure difference between Gibraltar and Iceland) were not a good indicator of the temperature extremes in the Mediterranean. Rather the extreme temperature anomalies over the Mediterranean region are to a large extent controlled by a bipolar pattern of SLP (see level pressure) anomalies with centers over the British Isles and the Arctic.

Placental Insufficiencies in Cloned Animals – A Workshop Report

This workshop focused on describing clinical problems identified in the placentae of cloned animals and some of the potential biological mechanisms by which these anomalies arise. It was shown that placental anomalies related to somatic cell nuclear transfer (SCNT) in cattle often can be detected by ultrasonography early in gestation, enabling preventive clinical intervention. On the mechanistic front, the vascular defects in the placenta appear to be associated with anomalies in the expression of VEGF system, which could lead to the aberrant placentomes and generalized oedema seen in some gestations. Moreover, an upstream transcription factor (Mash2) controlling the differentiation of trophoblast into binucleate cells may be involved in the poor implantation rates of SCNT embryos. Finally, epigenetic patterns in placenta can be disrupted by fairly simple in vitro manipulations, which could explain the extreme anomalies observed in the placenta of SCNT pregnancies.

Extreme intra-seasonal anomalies in the Amundsen and Bellingshausen sea-ice area, Antarctica, during the austral winter

AbstractWe examine the role of the propagation of atmospheric mid-latitudes wave trains in modulating the Amundsen and Bellingshausen sea-ice area (SIA), Antarctica, on intra-seasonal timescales (20–100 days). Spectral analysis of passive microwave estimates of SIA in the Amundsen and Bellingshausen Seas for 1979–2004 shows significant peaks on intra-seasonal timescales. Previous studies have suggested that variations in SIA are linked to disturbances in atmospheric circulation and sea surface temperature. We show that extreme SIA anomalies on intra-seasonal timescales lag the propagation of subtropical wave trains in the Southern Hemisphere by approximately 10–15 days. The sign of the SIA anomaly depends on the phase of the wave. We present evidence that the number of disturbances that cause extreme anomalies of SIA on intra-seasonal timescales has increased in the last 14 years.

Recent trends in the frequencies of extreme values of daily maximum atmospheric pressure at ground level in the central zone of the Iberian Peninsula

AbstractUsing data sets on the daily data of maximum atmospheric pressure at ground level collected at 14 weather stations located in the central zone of the Iberian Peninsula [Spanish central plateau (SCP)], the series of daily maximum pressure anomalies at each station, together with the difference between the daily value and mean daily value for each day of the year for the period between 1961 and 2003, have been established. The regional series of such anomalies were constructed for the whole study zone and for two differentiated parts of the same. As thresholds for the extreme values of the anomaly series, the values corresponding to the P05 and P95 percentiles were used. The series of annual frequencies of days with anomaly values below and above the threshold values were constructed for each of the weather stations, together with the average series for the whole study zone and each of its two parts. The corresponding regional average series of seasonal frequencies were also constructed.From an analysis of the trend of the series of the annual frequency of extreme anomaly values in daily maximum pressure it may be deduced that the lowest values show a decreasing annual trend, while the highest ones show an increasing frequency. This indicates that between 1961 and 2003 the number of days per year on the SCP with the highest extreme atmospheric pressure values at ground level increased along the study period. In contrast the number of days per year with lower extreme values decreased. Additionally, analysis of the seasonal frequency series indicated that it was the winter that dictated such behaviour. Copyright © 2007 Royal Meteorological Society

Statistical quality control for local‐scale extreme temperatures. Case study: Lisbon, Portugal

AbstractOne of the biggest constraints to the study of meteorological fields is the fact that ground‐based meteorological networks do not operate over a common period of adequate length. In general, the biggest drawback is that recorded data must be gap‐filled and quality controlled (coherent, consistent and homogeneous) to provide a reliable, continuous, reference daily/monthly/yearly series. This paper addresses procedures for statistical quality control of extremes of air temperature (daily maximum and minimum) time series. The diagnostic was accomplished based on the analysis of daily time series (1941–1996), monthly time series (1941–2001) and yearly time series (1941–2001) from 18 meteorological stations located in the Lisbon (Portugal) metropolitan region. To obtain insight into the quality of the series of the temperature data, objective statistical tests for departure from homogeneity were applied to the time series. To illustrate the procedures, one assesses the homogeneity of the reconstructed time series to check the quality of the ‘virtual’ observations and some tests were run over the annual, seasonal and monthly series of extreme temperatures. None of these assessments was able to detect a spatial non‐homogeneity in the temperature series around the tested years. As expected, the optimal interpolation approach for time series reconstruction, proposed by Lucio and Deus (2005), seems to be robust, considering a wide range of methods to test homogeneity of the reconstructed time series. Afterwards, one can apply the reconstituted monthly series of extreme air temperature anomalies, for each meteorological station, to analyse the respective trends, when they exist. Copyright © 2007 Royal Meteorological Society

Effects of El Niño–Southern Oscillation on sea level anomalies along the Gulf of Mexico coast

Analyses of daily sea level data show the impacts of El Niño–Southern Oscillation (ENSO) in the Gulf of Mexico (GOM). Data from three stations (St. Petersburg, Florida, Pensacola, Florida, and Galveston, Texas), all of which have at least 50 years of daily observations, are processed to identify the interannual signals. Although low frequency (interannual) signals in the sea level anomaly time series are not clearly evident, a low frequency modulation of the extreme anomaly events (upper 10% or lower 10% of the distributions) is identified. Results show that sea level variability is seasonally dependent at all stations, with maximum variability in the winter months. In the eastern GOM, low sea level events in the winter months are more frequent during El Niño (warm phase) conditions when compared to a neutral ENSO phase. This is consistent with ENSO‐related changes in the location where extratropical atmospheric low pressure systems form and in the tracks of these weather systems. The impacts of tropical systems in the summer through early fall months on coastal sea level in the GOM are shown by infrequent extreme high and low anomalies coinciding with individual storms. However, the number of storms affecting the data record from a particular sea level station is too small to confirm ENSO‐related variability. Statistical methods are employed to demonstrate a significant link between extreme sea level anomalies in the GOM and ENSO during the October to March period.

New aspects for fusion energy using inertial confinement

Magnetic confinement fusion (MCF) based on neutral particle beam irradiation reached the highest gains with JET and is discussed in relation to the ITER project for a possible re-orientation with respect to the ignition process. Ignition plays a similar role for inertial confinement fusion (ICF). After a short review about specific ICF developments, the fast igniter development offered a re-consideration of igniting DT fuel at modest or low compression. The observation of extreme anomalies (Sauerbrey 1996, Zhanget al., 1998 and Badziaket al., 1999) at interaction of picosecond (ps) laser pulses above TW power could be explained as a skin layer mechanism based on earlier computations (Horaet al., 2002) with nonlinear (ponderomotive) force acceleration. The resulting very high ion current density space charge neutral plasma blocks interacting as pistons to ignite DT may lead to a new scheme of laser fusion with low cost energy generation.

Dynamics of occurrence frequency of extreme anomalies of monthly mean air temperature in Georgia in the 20th century and its effect on precipitation and on the river water discharge

The dynamics of the occurrence frequency of extreme anomalies of monthly mean air temperature and its effect on precipitation and river water discharge in the 20th century are studied using weather observations at 40 stations and data on the hydrological regime of 34 rivers in Georgia.

Classification of synoptic patterns in the western Arctic associated with extreme events at Barrow, Alaska, USA

The coastal geography of Barrow, Alaska, makes the city vulnerable to weather events that cause flooding and erosion. This study uses the self-organizing map (SOM) algorithm, an unsu- pervised learning process that codifies large, multivariate datasets onto a 2-dimensional array, or map, to study large-scale circulation patterns associated with temperature and high wind extremes at Barrow. The analysis first uses the SOM algorithm to produce an automated 55 yr synoptic climatology of daily sea level pressure patterns for the western Arctic for August to November, when the area is potentially ice free. The results are in agreement with previous Arctic climatologies, showing the Aleutian Low to be dominant in southern Alaska, and high pressure prevalent over the Beaufort and Chukchi Seas. The SOM algorithm is then used to study circulation patterns associated with temperature and high wind extremes at Barrow. These results show that high winds are associ- ated with patterns containing a strong pressure gradient between the Aleutian Low and the Beaufort and Chukchi Seas and also with patterns that contain a low pressure system to the north of Barrow. High (low) air temperature extreme anomalies are associated with patterns that produce strong, southerly (northerly) air flow at Barrow. This study demonstrates the utility of using SOMs to investi- gate the relationship between local weather conditions and large-scale patterns. This approach can be applied to future global climate model (GCM) simulations to investigate the impact of changes in large-scale circulation patterns to local extreme events.

Detection of the recent 2000a climatic extreme anomalies based on a new kind of approach-the high-order moment method

Based on the normalized high-resolution climatic proxy data, high-order moment method is used to detect the climate extreme anomalies in recent 2000 years in this paper. Combining with filtering method to extract the dominant components at physical backgrounds from the normalized data, we analyzed the information and examined the contributions of each component of the climate extreme events. The results show that: 1) On the timescale of more than 100 years, climatic oscillation with the period of about 1000 years may exits; besides, the 20th century witnessed the most active climate extreme anomalous phenomenon in recent 2000 years, so it may correspond to an active period of climate extreme anomaly phenomenon. 2) On 20—60year timescale, climate extreme anomaly phenomenon in the period of A.D. 300—1100a is relatively distinct and that in time span of A.D.1100—1980a is comparatively mitigative. Possibly, this level makes no considerable contribution to the climatic anomaly of 20th century. This level and the century scale both reflect that for climatic change in recent 2000 years, the year around A.D. 1100a maybe the key period of climate transition. 3) On the interannual timescale (less than 20years), the years of occurrence of climatic extreme anomalies reflected in Beijing Shihua cave stalagmite proxy records has good correspondence with that of the E1 Ni?o or La Ni?a events (in this paper, only the period of 1960—1980a was considered). 4) high-order moment method has a good prospect in detecting the climatic extreme events.

On the variability and predictability of daily temperatures in the Arctic

Daily maximum and minimum temperature data from 54 stations in Alaska and northern Canada are used to evaluate temporal changes in the variance and autocorrelation of the daily anomalies from 1950–2000. To the extent that the variance and autocorrelation capture variability and anomaly persistence, the results provide a quantitative counterpart to reports from Arctic communities that weather is becoming increasingly variable and unpredictable. Although the results show indications of increased variance at some locations in some seasons, at least as many other stations show no such trends or show trends opposite to the hypothesized increase in variance and decrease in persistence of temperature anomalies. These findings apply to northern subsets as well as to the entire sample of stations. However, the frequency of extreme anomalies relative to single‐month means does show a modest but steady increase from the 1950s to the 1990s. The absence of a more generally apparent increase in variance and decrease in predictability is most likely attributable to either: (a) the choice of temperature as a measure of weather, (b) our use of simple statistical measures of variability and persistence, or (c) the role of technological and social changes in shaping perceptions of weather variability and predictability.

Effects of macro-circulation on local climatic conditions of plant development

Agricultural or ecological impact studies, related to future climate changes, require highly resolved meteorological input data both in space and time. Since present climate models can not fulfill this requirement, gaps between the necessary and available resolution, are filled by downscaling. A possible way to downscale GCM-output fields into regional climate scenarios can be to consider the changes in the frequency distribution of model-generated macro-circulation types and to combine them with conditional climatology of each macro-type. This approach can be successful, if a great part of local climate anomalies is connected to frequency anomalies of the macro-types. To test this assumption, a diagnostic method for separation of the local climate anomalies into circulation and non-circulation (physical) factors, allowing a mixed term, is developed, applying the subjective classification of pressure patterns by Péczely (1957). Results for monthly and seasonal anomalies of precipitation and temperature are presented for Debrecen, Hungary (47°N, 21°E). The investigated period is 30 years from 1966 to 1995. The main feature of the results is the secondary role of the macro-circulation factor. This conclusion is formulated from the comparison of contributions by these terms to moderate and extreme anomalies; to the standard deviation and to long-term variations; and also from the correlation between the three terms and their sum, i.e. the monthly anomaly. It is impossible, however, to consider this circulation term as the maximum information contained by a series of macro-types, because the succession of macro-types and conditional relation of the local weather on different days of a given type is not taken into account by the given separation. On the other hand, the circulation term exhibits fair statistical relation to the physical term and also to the whole anomaly in many cases, which is promising considering further improvement of this approach to downscaling based on frequency of macro-synoptic types.

The Sea Ice Extent Anomaly in the North Pacific and Its Impact on the East Asian Summer Monsoon Rainfall

Abstract The relationship between extreme anomalies of the spring sea ice extent over the Bering Sea and the Sea of Okhotsk and rainfall variability in the east Asian summer monsoon was examined through an analysis of observed data and modeling experiments. The results show that reduced sea ice extent leads to an enhanced summer monsoon rainfall in southeastern China. This relationship is well supported by the background atmospheric circulation changes and the stationary wave dynamics. A difference in the 500-hPa geopotential height composed from the NCEP–NCAR reanalysis data and model output between the light and heavy sea ice cases shows an anomalous high in the east Asian summer, which favors the invasion of a cold air mass into southern China and prevents the east Asian summer monsoon from advancing northward. Hence, the mei-yu front and its associated rainfall intensify and stay in southeastern China. The generation of the summer anomalous high and its interseasonal link to the spring sea ice extent ...

An extreme anomaly in stratospheric ozone over Europe in 1940–1942

Reevaluated historical total ozone data reveal extraordinarily high values over several European sites in 1940–1942, concurrent with extreme climatic anomalies at the Earth's surface. Using historical radiosonde data, reconstructed upper‐level fields, and total ozone data from Arosa (Switzerland), Dombås, and Tromsø (Norway), this unusual case of stratosphere‐troposphere coupling is analyzed. At Arosa, numerous strong total ozone peaks in all seasons were due to unusually frequent upper troughs over central Europe and related ozone redistribution in the lower stratosphere. At the Norwegian sites, high winter total ozone was most likely caused by major stratospheric warmings in Jan./Feb. 1940, Feb./Mar. 1941, and Feb. 1942. Results demonstrate that the dynamically driven interannual variability of total ozone can be much larger than that estimated based on the past 25–40 years.

Methyl bromide and methyl chloride in the Southern Ocean

Air and water concentrations of methyl bromide (CH3Br) and methyl chloride (CH3Cl) were measured in the Southern Ocean (latitudes 45°–67°S, longitudes 144°–139°E) from late October through mid‐December 2001. CH3Br and CH3Cl were undersaturated with mean saturation anomalies of −39 ± 11% and −37 ± 11% between 45° and 65°S. The minimum degradation rate constants needed to maintain these saturation anomalies are consistent with the observed total degradation rate constants, suggesting that there is no significant production of these gases in this region. Near the Antarctic coast (south of 65°S) the saturation anomalies for both gases decreased to approximately −80%, although CFC‐11 measurements suggest these extreme anomalies are associated with enhanced vertical mixing rather than with degradation in the surface waters.

Evapoclimatonomy modelling of four restoration stages following Krakatau’s 1883 destruction

Botanists have established that plant recolonization on Krakatau Island (6°S, 106°E) following the August 1883 eruption occurred in four distinct stages: (1) 1883–1886: bare rocks and sterile ash and pumice desert, (2) 1886–1919: grasses and ferns forming savanna, (3) 1919–1933: strand forest and young tree communities and (4) 1933–Present: tropical rainforest. Assuming no changes in macro climate conditions, meso–micro climates for each stage are assessed based on the analysis of soil water balance using climatonomic modelling techniques. Climate records at Jakarta (about 100 km to the east of Krakatau) were used to determine the climatonomic parameters for the rainforest climax; the parameter values for the transient stages were interpolated between values for climax and estimates for the volcanic ash desert. Large immediate runoff and small immediate evaporation are characteristics of the extreme anomaly of pumice and ash desert. The extremely low soil moisture of 21 mm in September (at the end of the dry season) is caused by high immediate runoff due to lack of vegetation cover. The average residence-time during this stage is, however, a little longer than 1 month. The abundant monsoon rains (2 m per year) collected in surface depressions in the lava rocks filled with ashes were most likely to offer relatively favourable conditions for the germination of living propagules, even during the first years after the eruption, due to significant evaporative cooling. In the savanna phase the evapotranspiration minimum was already twice as large in comparison with the desert extreme, and almost back to normal in the young forest phase.

Accounting Anomalies and Information Uncertainty

We examine whether rational investor responses to information uncertainty explain properties of and returns to accounting-based trading anomalies. We proxy for information uncertainty with two measures of earnings quality: the standard deviation of the residuals from a Dechow and Dichev [2002] model relating accruals to cash flows, and the absolute value of performanceadjusted abnormal accruals from a modified Jones [1991] model. Over 1982-2001, we find that accounting-based trading anomalies (post-earnings announcement drift, value-glamour, and accruals strategies) are correlated with earnings quality. Specifically, extreme anomaly portfolios have poorer earnings quality than non-extreme portfolios, and within the extreme anomaly portfolios, poor earnings quality securities are more prevalent and earn larger abnormal returns than good earnings quality securities. Consistent with greater resolution of uncertainty for poor earnings quality securities, the abnormal returns to poor quality securities converge to the abnormal returns to good quality securities as the post-portfolio formation period lengthens. Taken as a whole, these results indicate that information uncertainty plays an important role in explaining accounting anomalies.

Anomalies in the atmospheric circulation associated with the rainfall excess or deficit in the Pampa Region in Argentina

We have investigated the relationship between extreme anomalies in the monthly precipitation of the Pampa Region (PR), Argentina, and large‐scale circulation anomalies over the South American continent and the neighboring oceans. The composite maps of the extreme rainfall anomalies reveal that this atypical behavior extends beyond the PR and that comparable anomalies simultaneously take place in the center and south of Chile and in the western South Atlantic Ocean. We have analyzed the anomalies in the water vapor flux and in the circulation of the lower and upper levels of the troposphere that occurred in 85 months with extreme rainfall anomalies between 1955 and 1998. The study combines the use of a complete set of observed precipitation data and several atmospheric variables from the National Centers for Environmental Prediction Reanalysis. We have found well‐defined anomalous circulation patterns that embrace the south of the continent and the vicinity of the Pacific and Atlantic Oceans, which are very similar but of opposite signs for both rainfall extremes. The interaction between these anomalies in the high‐level flow and the subtropical jet stream generates the necessary conditions for vorticity advection and flow divergence, which is consistent with the expected vertical motions. The principal component analysis was applied to the pressure anomaly fields to distinguish those aspects of the large‐scale patterns that are more directly related with the rainfall extremes. The amplitudes of some of the dominant PC are significantly correlated with the precipitation anomalies, and they highlight the mechanisms leading to rainfall extremes during El Niño‐Southern Oscillation, and neutral periods.

El Niño–southern oscillation influences on rice production in Sri Lanka

AbstractDespite advances in the capacity to predict the evolution of the El Niño–southern oscillation (ENSO) phenomenon and advances in understanding the influence of ENSO on rainfall in tropical regions such as Sri Lanka, there has been limited use of climate predictions for agricultural decision‐making. Climatic fluctuations have a profound influence on the cultivation of crops such as rice, which is the staple food in Sri Lanka. Here, the relationship between the sea‐surface temperature‐based ENSO index of NINO3.4, rainfall and the departure of Sri Lankan rice production from long‐term trends, is analysed for the ‘Maha’ (October to March) and ‘Yala’ (April to September) cultivation seasons between 1952 and 1997.During the El Niño phase, the Maha rice production frequently increased (10 out of 15 seasons) and the Yala production frequently decreased (10 out of 14 seasons). Conversely, during the La Niña phase, the Maha production decreased (seven out of ten seasons) and Yala production increased (six out of eight seasons). Floods, state interventions, civil disturbances, fertilizer price hikes and extreme anomalies in the previous season were noted in the majority of seasons in which these ENSO–production linkages were violated.The correlation of the Maha rice production anomaly with the average NINO3.4 from October to December was significant at the 5% level and that with the aggregate October to December rainfall was significant at the 1% level. Yala rice production showed a significant relationship with concurrent NINO3.4 and a strong correlation (r = 0.60) with the previous season's rainfall. Yala cultivation is water constrained, and carryover storage from the previous season is often used to determine the extent of planting.The relationships between ENSO and seasonal rice production and the relationship between Yala rice production and previous Maha rainfall could be used for agricultural management and policy formulation. Copyright © 2002 Royal Meteorological Society.

Temporal accumulations of extreme daily meantemperature anomalies

Statistical characteristics of accumulated extreme low and high daily mean temperatures have been investigated for Hungary. Temperature extremes over periods of a few weeks were studied using 96-year temperature records. Temperature is defined as extreme in the lowest or highest five percent of the empirical distribution of anomalies. Recurrence frequencies of extreme anomalies were computed at 1, 2,…, 75 days after the initial anomalies, and compared with the respective characteristics of an appropriate 2nd order autoregressive model. In accordance with the high 1-day lagged autocorrelation in Hungarian temperature time series, model-frequencies are large for low lags, and approach the value for independence (0.05) for periods longer than 10–15 days. Considerable similarity of recurrence frequency between observed and simulated series is found but with some important exceptions. After only 1 extreme cold winter-day or an extreme warm summer-day, the probability of the next extreme occurring with the same sign remains significantly high for longer than 1 month. Empirical frequencies are very sensitive to the calendar date of the initial extreme value occurrence. Discrepancies between real and model characteristics were tested for statistical significance by Monte Carlo simulation technique. Recurrence frequencies for the last 30 years have also been computed, and intersting similarities and differences were found relative to the earlier part of the 20th century. To identify possible relationships between droughts and hot spells, extreme high daily temperatures and dry subperiods during summers were selected. Recurrence frequencies of extreme positive anomalies in dry periods, more than 15–20 days after an initial occurrence, are surprisingly high during the second half of the summer.