bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal and regional 300 hpa heights, 300–1000 hpa thicknesses and associated 300 hPa zonal flow changes in the northern hemisphere between 1976 and 1990
Authors: Weber Gerd Rainer
Published: February 2007

Using monthly 300 hPa height and 300–1000 hPa thickness data published by the synoptic climatology group of the Free University of Berlin, height and associated zonal flow changes were analysed for the period 1976 through to 1990. The 300 hPa heights rose most notably in the tropics, somewhat less in the lower mid‐latitudes, and they were lower in high latitudes. Via the height gradient, an increase in the zonal flow at 300 hPa can be derived for the subtropics and in upper mid‐latitudes. Using correlation analysis, relationships between tropospheric thickness anomalies in the lower latitudes—where the bulk of the most recent tropospheric warming has occurred—and changes in the 300 hPa height field elsewhere are explored. It is found that warm (cold) anomalies in the tropical troposphere are related to 300 hPa gradient increases (decreases) in the subtropics, but to gradient decreases (increases) in mid‐latitudes. Gradient increases in the mid‐latitudes moreover are generally related more closely to high‐latitude cool anomalies than to lower mid‐latitude warm anomalies or low‐latitude cool anomalies.
Orthogonal rotation of complex principal components
Authors: Bloomfield Peter , Davis Jerry M.
Published: February 2007

Complex principal components analysis has been shown to be a useful tool for exhibiting propagating features in spatial‐temporal data sets. As in other applications of principal components analysis, rotation may lead to more interpretable components. Real orthogonal matrices have been used elsewhere, in combination with the varimax criterion, to find rotated solutions, but these fail to show invariance to complex scalings of the initial eigenvectors. It is shown that complex orthogonal, or unitary matrices have the desired invariance, and their use is illustrated on two examples, one synthetic and one involving sea‐level pressure data.
Climate anomalies north of 55 °N associated with tropical climate extremes
Authors: Klaßen Joachim , Hense Andreas , Römer Ulrich
Published: February 2007

The relationship between extremes in tropical climate phenomena, e.g. ENSO and Indian summer monsoon, and the lower tropospheric temperature north of 55 °N is examined. For this purpose we carry out a dynamic statistical analysis applied to the data set of monthly mean 500–1000 hPa thickness from January 1949 to December 1991 (German Weather Service (DWD) analyses). To test the null hypothesis of identical horizontal mean distributions of the polar temperature field in irrespective of the sign of extreme tropical episodes a multivariate significance test is performed and the level of recurrence is estimated. In order to improve the signal‐to‐noise ratio, the data are projected onto the eigenmodes of an advection‐diffusion model. Comparing composites of warm versus cold ENSO events, the model indicates a significant difference in the winter lower tropospheric temperature pattern in northern latitudes. This pattern contains a warmer lower troposphere over the northern North American continent in winter, corresponding to other studies. The multivariate analysis further shows that the Indian summer monsoons with deficient rainfall are preceded by a strong cold anomaly in the lower troposphere over the northern Asian continent early in the year, corresponding to the known hypothesis of Asian‐snow—monsoon coupling.
Variance contribution of luni‐solar and solar cycle signals in the St Lawrence and Nile river records
Authors: Curri Robert G.
Published: February 2007

Spectrum analysis of the St Lawrence River and three Nile River hydrological records yields evidence for two peaks with periods near 19 and 11 years. For each series the wavetrains of the peaks are obtained by bandpass filters, summed, superimposed on trend‐like components in the raw data, and plotted against the raw data. The contribution of the two waves to total variance in the St Lawrence data is 42 per cent, whereas the mean contribution in the Nile records varies from 20 to 28 per cent. The waves are identified as the 18–6‐year luni‐solar Mn 10–11‐year solar cycle Sc signals in climate, which have also recently been reported in other variables such as precipitation (USA, UK, South Africa, India), tree‐ring chronologies (world‐wide), air temperature and air pressure (world‐wide), height of sea‐level (world‐wide), and sea‐surface temperature, as well as in economic variables such as American crop yield, European fish catches, dates of wine harvest, and other macro‐economic data (Currie, 1988; Currie et al., 1993). The polarity of the 19‐year St Lawrence wave changed phase 180° between epochs 1936–1 and 1954–7 (epochs are dates of maximum in tidal forcing), and this phenomenon is commonly found in the much longer Nile records, as well as in virtually all of the above mentioned climate parameters.
Summer‐season mesoscale cyclones in the bellingshausen‐weddell region of the antarctic and links with the synoptic‐scale environment
Authors: Turner John , Thomas Jeremy P.
Published: February 2007

Results are presented from the first investigation into a summer‐season of mesoscale vortex activity in a large sector of the Antarctic coastal region. The study is based on an analysis of 3 months' meteorological satellite imagery collected at the British Research Station ‘Rothera’ on the Antarctic Peninsula. The study revealed the high frequency with which such systems occur, with 162 individual vortices being found during the period December 1983 to February 1984 inclusive. The preferred area for their development was in the latitude band 60–70°S over the marginal ice zone and ice‐free region of the eastern Bellingshausen Sea. A classification scheme for the vortices was developed based on the relationship with the broad‐scale synoptic flow, the sea ice, and the geographical location. The most common type of vortex found was the ‘classic’ polar low, which formed in the southerly flow to the west of synoptic‐scale disturbances. These vortices were very similar to the baroclinic type of polar lows observed south of Iceland during the Northern Hemisphere winter. A third of the vortices in total were found to be mesoscale features associated with synoptic‐scale troughs or the centres of major depressions. Vortices with comma‐shaped cloud signatures occurred about twice as frequently as those with spiraliform cloud. The vast majority of vortices had a diameter of less than 500 km, with very few systems being observed in the range 500–1000 km. Mean anomalies of 500 hPa geopotential height and surface pressure for the occasions when vortices were identified were —5.3 dm and — 0.5 hPa, respectively, indicating the association of these systems with upper air troughs and cold pools. Only 23 of the vortices found were correctly represented on the Meteorological Office analyses and of these 15 were small synoptic disturbances. The ‘polar low’ class of vortex was very poorly represented in the analyses, indicating that the available satellite sounder data could not resolve the systems and that the processes resulting in their formation were not handled well by forecast/data assimilation schemes. Comparison of the mean surface and 500 hPa height fields for this 3‐month period with the long‐term average data show that there were negative anomalies at both levels over the Bellingshausen Sea. The number of vortices over the Bellingshausen Sea in this summer period may have been greater than would be expected in an average year, but activity over the Weddell Sea was probably close to average.
Sunspot numbers as a possible indicator of annual rainfall at Addis Ababa, Ethiopia
Authors: Seleshi Yilma , Demarée G. R. , Delleur J. W.
Published: February 2007

The variability of the Sun's luminosity is thought to have effects on the world climate. This variability is partly measured by the sunspot numbers. In this paper the statistical link between sunspot numbers and Addis Ababa rainfall is established. For this purpose a transfer function plus noise model (TFN) is constructed, with Box‐Cox transformed annual sunspot numbers,Xvas input and annual Addis Ababa monsoon rainfall,Yvas output. This model explains 50·2 per cent of the annual rainfall variability in the period 1900–1990. The time series of the sunspot numbers is simulated by an autoregressive model and then used to provide the input forecasts to the TFN model; it explains 88·9 per cent of the annual sunspot numbers variability.

The TFN model is utilized for long‐range annual rainfall forecasts. A check of the forecasting skill of the TFN model is performed by fitting the TFN model to the 1900–1970 data and forecasts are made for 1971–1991. The results show that 14 out of 21 forecasts generally track the observed rainfall. The correlation coefficientCbetween the forecast and observed rainfall is 0·58, whereas for the sunspot numbersCyields 0·87. The pairedt‐test shows that the forecasts and the observed rainfall are statistically similar at the 95 per cent confidence level.

A general physical mechanism that may partly explain how the variability of the Sun's luminosity is related to the world climate is suggested. It is proposed that for those regions whose climatic variables exhibit the 11‐year periodicity, the TFN model approach can be used to find a statistical link between the sunspot numbers and the climatic variables. Furthermore if a global pattern in such a link is found, it may be used for exploring the physical mechanisms of Sun‐climate relationships.
Spatial variation of climatic aspects of temperature: Interdiurnal variability and lag
Authors: Driscol Dennis M. , Rice Peter B. , Fong Juan M. Yee
Published: February 2007

Two relatively neglected aspects of climatic temperature variability are mean interdiurnal temperature variability (MITV), and the lag of maximum and minimum temperature behind their respective solstices. After determining the length of record to attain stability for the former, and the dates (of the year) on which temperatures are a maximum and minimum, these parameters are mapped for North America. For MITV there is a general association with continentality and the location of the surface polar front zone; the lag patterns bear only a slight resemblance to continentality.
A Markov chain model for daily precipitation occurrence in South Korea
Authors: Moon Sung‐Euii , Ryoo Sang‐Boom , Kwon Jae‐Gi
Published: February 2007

The Markov chain properties of daily precipitation occurrence, namely, the dependency of the daily precipitation on that of the previous day, are studied based on the daily precipitation data for 30 years (1956–1985) at 14 stations in South Korea. The daily precipitation data at each station were classified into the wet and dry state, and transition probabilities between daily precipitation of two successive days were computed. Then the Markov chain properties and various aspects of daily precipitation occurrence from the Markov chain properties were investigated. The results are as follows: the transition probability of two successive wet days for 30 years at the 14 stations is 0.51, and the statistical tests show that the transitions of daily precipitation occurrence in South Korea can have the Markov chain property and be stationary in time, except at Ullung‐do, Seoul, Kangnung, and Mokpo, but heterogeneous in space. The n‐step Markov chain analysis shows that the ‘memory’ of the daily precipitation occurrences at 14 stations remains about 2–3 days. The weather cycle is 6.59 days.
Fluctuation of sunshine duration in central and South‐Eastern Europe
Authors: Brazdil R. , Flocas A. A. , Sahsamanoglou H. S.
Published: February 2007

Sunshine duration fluctuation in this century is studied from annual values for 26 stations in central and south‐eastern Europe. Possible sources of inhomogeneity are identified: ageing of the glass ball in the sunshine recorder, changes in instruments, the recording tape and its evaluation, and location of the station, and exposure to air pollution. Long‐term changes of annual sunshine duration are presented using a smoothed Gauss filter and principal component analysis. The main feature of sunshine duration fluctuation in this century is its sharp decrease after a maximum at the end of the 1940s. Principal component 1 shows, with small exceptions, positive loadings for the year and its seasons (for the period of 1931–1985). Principal component 2 divides the region studied into two parts, with positive loadings in the western and northern parts of central Europe and negative loadings over the rest of area analysed. A contradictory situation occurs only in autumn. Statistically significant cycles occur at intervals of about 2.3–2.4 years (western Germany), 3 years (Greece), 3.5–3.7 years (central Europe and Bucharest) and 3.7–4.0 years (Bulgaria). Some of the stations used indicate longer cycles (44–110 years). Comparison of coldest (1901–1920) and warmest (1934–1953) 20–year periods in the Northern Hemisphere shows for the warmest period an important increase in sunshine duration, with the exception of Athens and Bucharest and some other stations in winter. In the warmer period sunshine duration variability is generally higher in spring and winter and less in summer and autumn.
The air temperature in cracow from 1826 to 1990: Persistence, fluctuations and the urban effect
Authors: Kożuchowski Krzysztof , Trepińaska Janina , Wibig Joanna
Published: February 2007

Mean monthly air temperatures in Cracow for the period 1826–1990 were used. The temperatures of the coldest (Tlow) the warmest (Thigh) periods of the year, and mean annual temperatures (Ta), were calculated. The persistence of temperatures was examined using the correlation coefficients between monthly temperatures in succeeding months. A significant temperature persistence was found for a cold season (December‐March) and also for the summer (July‐August). Long‐term fluctuations were analysed by means of 20‐year and 30‐year running mean values and the positive and negative squared deviations of moving 20‐year subperiods. Two warm stages were found. One at the beginning of the present century, the second at the end of the period analysed. The first warm phase was connected with a decrease in the degree of continentality. Warm phases were also linked with a decrease in the temperature variability.

The spectrum and the moving spectrum in 40‐year subperiods of monthly and annual temperature records were calculated. An 8‐year period was found in Tlow, Ta, and in the monthly series of the cold season, and 4‐ and 5‐year periods were found in Thigh and in the monthly series of the warm season.

By comparing the temperature in Cracow with that at the neighbouring stations of Wieliczka, Bochnia, and Tarnów, it was found that the difference in annual means increased from −0.3°C at the end of the previous century to 1.0°C in the last two decades. About 0.5°C of this increase occurred in the last 40‐year period of abrupt expansion and industrialization of the city of Cracow.
Land‐surface characterization in greenhouse climate simulations
Authors: Henderson‐Sellers A. , McGuffie K.
Published: February 2007

A simplified Holdridge‐type vegetation prediction scheme has been coupled to a version of the NCAR community climate model (CCM1‐Oz) that includes the biosphere‐atmosphere transfer scheme (BATS) and a mixed‐layer ocean. This interactive vegetation climate model has been used to conduct two complementary CO2‐doubling experiments: an instantaneous 2 x CO2 simulation (15 years in total) and a fast, transiently increasing CO2 simulation (45 years in total). There are some differences in the predicted vegetation distributions and areas. However, there is agreement that in a warmed world the vegetation type termed ‘agriculture’ increases in area at the expense of deciduous needle‐leaf trees and short grass; and the tundra extent, already underestimated, decreases further whereas deserts and the deciduous broadleaf tree areas expand. The overall vegetation areas predicted are not particularly sensitive to initialization, although effects of different initialization can be monitored for 1–2 years. On the other hand, when the sensitivity of the modelled climate to the inclusion of some aspects of an interactive biosphere is examined, it is found that annually updated continental characteristics do not disrupt the climate simulation but do modify zonal temperatures and precipitation and increase continental evaporation. The latter intensifies the Hadley circulation, especially in July, and, thus, leads to increased evaporation globally. These results, if corroborated by other similar studies, indicate that simple, post facto application of vegetation diagnostic schemes once climatic equilibrium is achieved may be diagnosing vegetation from an incorrect climatic state.
Can interannual variations in stratospheric ozone be observed in the marine environment?
Authors: Topliss B. J.
Published: February 2007

The possibility of interannual variations in water colour measurements, taken in UK waters, being influenced directly by ultraviolet (UV) light was investigated. Total column ozone was used as the indicator for UV light. A data base of 30–40 years of UK atmospheric and marine monthly data was assembled in order to investigate where in the environment the total column ozone signals may be observed. Principal component analyses were used first to remove regional and then to remove seasonal variations. Statistically significant correlations were obtained between a component of total column ozone, 300 hPa geopotential height, and water colour data. The relations between ozone, stratospheric temperature and wind speed and the 300 hPa geopotential height data were interpreted in terms of atmospheric disturbances modifying the position of the tropopause. No other atmospheric or climatic variable in the data base exhibited these ‘ozone‐weather’ signals, lending support to the hypothesis that this particular ozone signal could have found its way into the marine environment via direct exposure of marine life to UV in the surface layers of the ocean. After examining the data base for all support for and against this hypothesis, however, it was determined that the overall evidence was still ‘circumstantial’. Interannual variations in stratospheric ozone could be linked to variations in water colour data but no exclusive mechanism could be identified from statistical analyses alone.
Trends in wind and sea‐level pressure in the tropical pacific ocean for the period 1950–1979
Authors: Inoue Masamichi , Bigg Grant R.
Published: February 2007

The COADS (Comprehensive Ocean‐Atmosphere Data Set) sea‐level pressure observations over the tropical Pacific Ocean during the period 1950–1979 are examined to check for dynamical consistency between the observed trends in wind‐speed components and the trends in sea‐level pressure pattern. There appears to be some evidence that the South east Pacific High and the equatorial trough in the central Pacific were gaining strength. As a result, trade winds appear to have been gaining strength along the northern flank of the South east Pacific High and in the eastern/central equatorial Pacific. However, there were considerable variations in those trends from decade to decade. The patterns of those decadal changes in sea‐level pressure appear to be dynamically consistent with those of wind tendency. An example of a quantitative consistency check for a region located at 160°W–150°W and 10°S–20°S demonstrates that the observed strengthening trend in zonal wind component in the region appears to be dynamically consistent with the observed air‐pressure field measured by both ships and the nearby island stations. It also demonstrates clearly that the overall magnitudes of change in the two independently measured fields (ship‐observed winds and sea‐level pressure) over the 30‐year period are quantitatively of the right order. These observations at least suggest that the qualitative nature of the observed trends in the trade winds in the Pacific since 1950 is real.
Temperature variations in a tropical‐subtropical environment: Queensland, Australia, 1910–1987
Authors: Lough J. M.
Published: February 2007

Minimum daily temperatures have increased significantly and the daily temperature range has decreased significantly in Queensland in both summer and winter over the period 1910–1987. Temperature variations in Queensland, particularly average and minimum temperatures, have largely paralleled those of the Australian region and Southern Hemisphere. Trends in minimum temperatures and the daily temperature range in Queensland cannot be attributed to urban warming. Effects of urban heat islands on temperature are, however, evident in some of the large coastal cities of the State. During the summer wet season, variations of the daily temperature range are controlled largely by variations of daily maximum temperatures. These are, in turn, linked to variations of rainfall, cloud amount and the Southern Oscillation. During the winter dry season, variations of the daily temperature range are controlled largely by variations of daily minimum temperatures. These are, in turn, associated closely with rainfall, cloud amount and sea‐surface temperatures (SSTs) in coastal waters. The recent rise in daily minimum temperatures and decrease in the daily temperature range in Queensland are not unprecedented in the 78‐year record. Variations of rainfall and SSTs in adjacent waters have generally acompanied the temperature changes.
Investigating impacts of anomalous land‐surface conditions on Australian climate with an advanced land‐surface model coupled with the BMRC GCM
Authors: Yang Z.‐L.
Published: February 2007

A new and complex land‐surface model, the bare essentials of surface transfer (BEST), has been incorporated into the Australian Bureau of Meteorology Research Centre (BMRC) atmospheric general circulation model (GCM). A series of experiments with anomalous land‐surface conditions using the BEST‐GCM were conducted.

Three sets of conditions were used for the winter, two of which were related to the soil moisture conditions. The soil over the entire Australian continent was saturated (hereafter WET) and dried (hereafter DRY) on the first time step of 4 July, and then allowed to evolve normally. In another experiment, values of all the 15 BEST parameters over the continent were set to those at a point in the Great Desert and kept unaltered throughout the integration period (hereafter DESERT). Two additional WET and DRY experiments were carried out for the summer, from 6 January for 60 days.

The results of these experiments differ significantly from those conducted with bucket‐type land‐surface parameterization schemes in that:

WET or DRY anomalies evolve differently in specific regions. The geographical distributions of responses are more disorganized, possibly because of the inclusion of vegetation, which may enhance the regional features and the non‐linear treatment of soil moisture content and surface wetness.

Magnitude of responses are larger because of the greater number of feedback mechanisms. For example, when the feedback of soil moisture and surface albedo is allowed, the increase of soil moisture leads to an increase of evaporation. The increase of soil moisture results in a decrease in albedo which in turn leads to an increase of absorbed solar radiation available for evaporation.

Time‐scales of adjustment are different for DRY and WET anomalies. WET anomalies persist much longer, have stronger responses and are more organized than DRY anomalies.

The summer WET or DRY anomalies have larger responses than the corresponding winter anomalies.

These results are physically interpreted and their implication in seasonal precipitation forecasting is discussed.
Spatio‐temporal patterns of drought in Morocco
Authors: Chbouki Nabil , Stockton Charles W. , Myers Donald E.
Published: February 2007

Past climatic moisture anomalies can be reconstructed from climatically sensitive tree‐ring chronologies of Cedrus atlantica in Morocco. A map‐pattern technique was utilized to derive 10 patterns of variability for the period 1845–1974. The individual patterns were examined, in space using geostatistical techniques, and in time using correlation coefficients. The results indicate a clear alternation of favourable‐unfavourable climatic regimes lasting 20–25 years. The spatial extent of the climatic moisture anomalies can be explained by a combination of three factors of the atmospheric circulation related to the Azores High, local cyclogenesis, and north‐eastern perturbations.
Climatologically aided interpolation (CAI) of terrestrial air temperature
Authors: Willmott Cort J. , Robeson Scott M.
Published: February 2007

A new and relatively straightforward approach to interpolating and spatially averaging air temperature from weather‐station observations is introduced and evaluated using yearly station averages taken from the Jones et al. archive. All available terrestrial station records over the period from 1881 through to 1988 are examined. Called climatologically aided interpolation, or CAI, our procedure makes combined use of (i) a spatially high‐resolution air‐temperature climatology recently compiled by Legates and Willmott, as well as (ii) spatially interpolated yearly temperature deviations (evaluated at the stations) from the climatology. Spherically based inverse‐distance‐weighting and triangular‐decomposition interpolation algorithms are used to interpolate yearly station temperatures and temperature deviations to the nodes of a regular, spherical lattice. Interpolation errors are estimated using a cross‐validation methodology.

Interpolation errors associated with CAI estimates of annual‐average air temperatures over the terrestrial surface are quite low. On average, CAI errors are of the order of 0.8°C, whereas interpolations made directly (and only) from the yearly station temperatures exhibit average errors between 1.3°C and 1.9°C. Although both the high‐resolution climatology and the interpolated temperature‐deviation fields explain non‐trivial portions of the space‐time variability in terrestrial air temperature, most of CAI's accuracy can be attributed to the spatial variability captured by the high‐resolution (Legates and Willmott's) climatology. Our results suggest that raw air‐temperature fields as well as temperature anomaly fields can be interpolated reliably.
Comment on D. E. Parker, ‘effects of changing exposure of thermometers at land stations’
Authors: Hughes Warwick S.
Published: February 2007

This short note reviews the Minutes of two Intercolonial Meteorological Conferences, held at Melbourne, Australia in 1881 and 1888, where the transcripts refer to the use of the Stevenson screen. Additional historical and modern material is reviewed demonstrating the use of the Stevenson screen in late nineteenth century Australia and Fiji. Some possible implications for the climate change debate in Australia are considered.
Climate trends in the South‐west Pacific
Authors: Salinger M. J. , Basher R. E. , Fitzharris B. B. , Hay J. E. , Jones P. D. , Macveigh J. P. , Schmidely‐Leleu I.
Published: February 2007

Temperature and precipitation trends are described for newly homogenized historical climate data sets for the South‐west Pacific. Regions that exhibit similar temperature and precipitation trends and variability are defined, and the temperature and precipitation time series aggregated according to these regions. Four temperature regions show distinctive trends: two regions south‐west of the South Pacific Convergence Zone (SPCZ), which display steady climate warming; two regions north‐east of the SPCZ, which cooled during the 1970s, and warmed in the 1980s. Annual anomalies differ in response to the El Niño‐Southern Oscillation (ENSO) phenomena, depending on the region's position with respect to a pivotal line along the SPCZ. The climate warming apparent throughout much of the south‐west Pacific comes from sites where there can be no question of any urban influence. Five main South‐west Pacific precipitation regions show distinctive trends that are connected to the main climatological features. Four New Zealand precipitation subregions relate to the interaction of the main climatological features with local orography. Annual precipitation anomalies show marked variability and are also affected by ENSO in most regions. The pivotal line for the response of precipitation regions lies just to the north‐east of the SPCZ. The ENSO relationships with precipitation appear consistent on both annual and interdecadal time‐scales. From these climatic trends four climatic response regions are recognized in the South‐west Pacific.
Seasonal variability of latent heat fluxes over the tropical Indian ocean using SSM/I and NOAA/AVHRR satellite data during 1988
Authors: Nair Nimmi , Pandey P. C. , Simon B. , Gautam N.
Published: February 2007

The monthly mean latent heat fluxes using Special Sensor Microwave Imager (SSM/I) and Advanced Very High Resolution Radiometer (AVHRR) data over the Indian Ocean have been estimated using a bulk parameterization technique for the year 1988. Liu's (1986) global relation between monthly mean precipitable water and surface‐level humidity has been applied to estimate surface‐level humidity from satellite‐derived precipitable water in this work. The month‐to‐month variation in latent heat fluxes have been studied along with oceanic and atmospheric parameters. The latent heat flux values were found to be higher over the Arabian Sea than those over the Bay of Bengal in the pre‐monsoon and monsoon months, and almost the same or less for the other months. The latent heat flux values over the Indian Ocean varies from 100 W m−2 in August near the Somali coast to 400 W m−2 in June. The latent heat flux associated with tropical systems are extremely high.
Missing data assessment in a solarimetric network
Authors: Ceballos Juan Carlos , Braga Célia Campos
Published: February 2007

Principal components analysis was applied to solar irradiation (energy per unit area integrated over a daily period) in Paraiba State, north‐east Brazil, in order to find homogeneous subregions. The network data set included measurements of 19 solarimetric stations, generated by bimetallic Robitzsch‐type actinographs with associated daily errors not greater than 5 per cent. Two months were considered (February and August 1976).

A simple procedure is developed for assessing missing data in time series of any station in the network, based on the remaining known data and on a small number of network eigenvectors. If applied over a homogeneous subregion, a specific new principal components analysis leads to a lower dimensioned system with even fewer eigenvectors used for proper assessment of missing data. Standard deviation of errors is lower than half the data standard deviation (the same order of expected instrumental errors). The method may be adapted easily in order to simulate (synthetize) time series of a site with no station, provided that time correlation fields vary smoothly within the region.
Daily precipitation maxima in Catalonia (north‐east Spain): Expected values and their spatial distribution
Authors: Lana X. , Mills G. Fernandez , Burgueño A.
Published: February 2007

The climatic diversity of Catalonia (north‐east Spain) is studied from the viewpoint of precipitation maxima. The spatial distribution of expected daily precipitation maxima is investigated for several return periods. The process is applied to the four traditional seasons and for the whole year by assuming the classical Gumbel theory of extremes (Gumbel I distribution), which is confirmed by the reasonable fit between predicted and empirical extremes. The analysis points towards a combination of several factors, such as the complex orography, the proximity of the Mediterranean Sea, the significant convective activity, and the dominant surface circulation, controlling the extreme daily amount distribution in Catalonia.
Luni‐solar 18.6‐ and solar cycle 10–11‐year signals in Chinese dryness‐wetness indices
Authors: Currie Robert G.
Published: February 2007

Power spectrum analysis of 81 long and 202 short Chinese dryness‐wetness indices yields evidence for two peaks with periods near 18.6 and 10.5 years, both of which are statistically significant at confidence levels of 99.9 per cent. They are identified as induced by the 18.6‐year luni‐solar, Mn, constituent tide and a 10–11‐year solar cycle, Sc, variation in the Sun's luminosity of the order of 0.1 per cent. Amplitude and phase of Mn wavetrains are highly non‐stationary with respect to both time and geography; in particular, abrupt 180° phase changes in wave polarity are often observed. Amplitude and phase of Sc waves are also highly non‐stationary, with those in northern China out of phase with waves in the south since 1895 (they were in phase from 1815 to 1845). For the 202 short records variance contribution of the two signals to total variance in raw data varied from 6 per cent to 53 per cent, with a mean of 22 per cent, again demonstrating their extreme non‐stationarity. Construction of a dry and very dry drought index (DVDI) shows that since 1470 by far the most prolonged, continuous, and serious drought (due to constructive interference and concomitant high amplitudes of the two waves) occurred from 1633 to 1643; the Ming Dynasty collapsed in 1644 and, in agreement with Hameed and Gong (1990), it is concluded that this climatic disaster was a causal factor in the fall of the Ming Empire.
Long‐term trends of precipitation and runoff in Louisiana, USA
Authors: Keim Barry D. , Faiers Gregory E. , Muller Robert A. , Grymes John M. , Rohli Robert V.
Published: February 2007

Changing precipitation patterns and their impact on surface water resources is an important climatic problem facing society today, especially as it relates to potential global change. Therefore, this paper analyses temporal variability and trends in the empirical precipitation record and modelled runoff in Louisiana, USA, during the past century. Long‐term trends in precipitation were identified and impacts on surface water resources were found. If general circulation model predictions for increasing precipitation in the south‐eastern US prove to be correct, surface water will likely increase at a disproportionately higher rate which should be of concern to water resource planners in the region.
Variations and trends in annual mean air temperatures in Turkey with respect to climatic variability
Authors: Türkeş Murat , Sümer Utku M. , Kiliç Gönül
Published: February 2007

The purpose of this study is to investigate the variations and trends in the long‐term annual mean air temperatures by using graphical and statistical time‐series methods. The study covers a 63‐year period starting from 1930 and uses temperature records from 85 climate stations. First, spatial distributions of the annual mean temperatures and coefficients of variation are studied in order to show normal conditions of the long‐term annual mean temperatures. Then variations and trends observed in the annual mean temperatures are investigated using temperature data from 71 climate stations and regional mean series. Various non‐parametric tests are used to detect abrupt changes and trends in the long‐term mean temperatures of both geographical regions within Turkey and individual stations. The analyses indicate some noticeable variations and significant trends in the long‐term annual mean temperatures. Among the geographical regions, only Eastern Anatolia appears to show similar behaviour to the global warming trends, except in the last 5 years. All the coastal regions, however, are characterized by cooling trends in the last two decades. Considering the results of the statistical tests applied to the 71 individual stations data, it could be concluded that annual mean temperatures are generally dominated by a cooling tendency in Turkey. The coldest years of the temperature records of the majority of the stations were 1933 and 1992, respectively.
Chaotic influences and the problem of deterministic seasonal predictions
Authors: Dix M. R. , Hunt B. G.
Published: February 2007

An analysis has been performed of three simulations made by forcing a global climatic model with observed sea‐surface temperature and sea‐ice distributions for the period 1979–1988. These simulations were started from different years of an extended control run, otherwise all conditions were identical. The analysis concentrates on the regional and local differences in the simulations caused by chaos attributable to the differing initial conditions interacting with the non‐linearities of the model climatic system. Of particular interest is whether the presence of sea‐surface temperature variations in individual years is able to overcome chaotic influences. This interest arises because of the increasing international appreciation that such temperature variations provide the basis for the development of multi‐seasonal prediction schemes.

The analysis shows that between about 20°N and 20°S a coherent climatic reponse is obtainable owing to the boundary value forcing associated with the sea‐surface temperature field. At high latitudes the signal‐to‐noise ratio rapidly deteriorates. Even at low latitudes, in a sensitive variable such as rainfall, chaos creates substantial differences between the three simulations, except over the Pacific Ocean where a very coherent response is found. In general, over land areas, even those within recognized regions of ENSO (El Niño‐Southern Oscillation) influence, the impact of chaos is much higher. Examination of Pacific North American teleconnection patterns for 1988 reveals substantial differences between the three simulations, and the associated impact on rainfall and surface temperatures over the North American continent. Agreement with observations ranges from rather good to poor, indicating the need for multiple runs for any given situation. Overall the results establish that sea‐surface temperature variations can overwhelm chaos in appropriate circumstances and specific regions. Importantly, this indicates that given accurate predictions of sea‐surface temperature anomalies a few seasons in advance, then model‐based predictions will be possible over many regions of the world despite the omnipresence of chaos.
Zones of severe rainstorm activity over India—some refinements
Authors: Dhar O. N. , Nandargi Shobha
Published: February 2007

An examination of daily rainfall data and other rainstorm studies have shown that about 231 severe rainstorms affected India during the period 1880–1990. This study is an extension of the previous study made by Dhar and Nandargi. This study, with specified locations of frequent rain centres and a large sample of 231 severe rainstorms, has confirmed the existence of the four rainstorm zones found earlier and has also found small zones in south‐east Rajasthan and along the east and west coasts of India. It has also specified locations of frequent rain centres during severe rainstorms.
Climatic response of the Indian subcontinent to doubled CO2 concentrations
Authors: Bhaskaran B. , Mitchell J. F. B. , Lavery J. R. , Lal M.
Published: February 2007

Results from the United Kingdom Meteorological Office (UKMO) coupled climate model have been analysed over the Indian subcontinent in order to validate the model's performance and to assess the changes in climate and its variability in a simulation with a 1 per cent increase per year in CO2 (compound).

The model produces a reasonable simulation of present‐day climate over the Indian subcontinent. At the time of CO2 doubling, the model simulates temperature increases of the order of 1 K to 4 K over the Indian subcontinent during winter and monsoon seasons. The model‐simulated monsoon circulation shifts by 10° latitude towards the north and intensifies by approximately 10 per cent in the warmer atmosphere. The interannual variability of monsoon onset dates and intraseasonal variability of monsoon rainfall are not significantly different when the CO2 concentration doubles. However, the model simulates increased interannual variability of the monsoon rainfall and a greater number of heavy rainfall days during the monsoon.
Solar dimming and urban heating at Hong Kong
Authors: Stanhill G. , Kalma J. D.
Published: February 2007

Over the last 35 years solar radiation in Hong Kong has decreased by more than one‐third. During the same period the population doubled and the total use of fossil fuels increased more than sevenfold. A surface energy balance model was used to demonstrate the opposing effects of the decline in irradiance and the increase in anthropogenic heat production on air temperature. Differences between air temperatures measured in the city and at an upwind, unpopulated island were used to verify the simulated decrease in the urban heat‐island by day and increase at night, leading to an unchanged mean air temperature difference. The implications of these results for climate change in the rapidly urbanizing Pacific Rim region are discussed briefly.
Growing season temperatures over the former Soviet Union
Authors: Jones P. D. , Briffa K. R.
Published: February 2007

Analyses of daily mean temperatures during the growing season (days >5°C) from about 200 stations over the former Soviet Union indicate that little change has taken place in a number of growing‐season‐related variables during the last 110 years. We have considered the start (STR), end (END), duration (DUR), and the number of degree‐days above 5°C (DD). Annual average temperatures in the region have warmed by about 1°C, but this increase has been confined to the October‐to‐April period. Time series of the variables at individual stations show that there is little correlation between the start and end dates of the growing season and between the duration and the number of degree‐days in the season. Mean May‐to‐September temperatures at individual stations are shown to be highly correlated with the number of degree‐days, implying that the average of an appropriate combination of monthly temperatures can be used as a proxy for the number of degree‐days when daily data are not available. The low correlation between degree‐day counts and growing season duration in time series at all the stations is surprising given the strong spatial dependence between the 1950–1989 averages of the variables at all the stations. The results have implications for studies concerned with the impacts on growing season temperatures of future climate change.
The tropical‐subtropical semi‐annual oscillation in the upper troposphere
Authors: Shea Dennis J. , Van Loon Harry , Hurrell James W.
Published: February 2007

The tropical‐subtropical semi‐annual oscillation (TSSAO) of the zonal wind and temperature in the upper troposphere has been described by van Loon and Jenne. Their description was based on analysis of 20 Southern Hemisphere (SH) radiosonde stations and on two SH climatological atlases. This note documents further the TSSAO's climatology and its' spatial and temporal variability. This is accomplished by (i) using more radiosonde stations, in which data records span longer time periods, and (ii) using analyses from the European Centre for Medium Range Weather Forecasts for a spatially coherent picture.
Impacts of model improvements on general circulation model sensitivity to sea‐surface temperature forcing
Authors: Druyan Leonard M. , Shah Kathryn P. , Lo Kwok‐Wai K. , Marengo Jose A. , Russell Gary
Published: February 2007

The sensitivity of the 4° × 5° resolution general circulation model of the Goddard Institute for Space Studies to some basic changes in model formulation was studied by comparing parallel simulations forced by global sea‐surface temperature of June‐August 1987 and 1988. The new modelling schemes were substituted for the control model's parameterizations of moist convection, planetary boundary layer, ground hydrology, and cloud optical thickness in a series of sensitivity experiments. In addition, linear and quadratic upstream schemes for advecting tracers were tried in place of second‐order differencing. Elimination of the vertical mixing of horizontal momentum by moist convection was also tested. Impacts of the new modelling schemes on simulated circulation, temperature, and precipitation rates were inferred from pairs of simulations made by model versions that differed with respect to a single change. No discernible positive impacts were found for the new ground hydrology scheme or for changes in the determination of cloud optical thickness. Profiles of zonal wind speeds and lower tropospheric circulation patterns, both in the tropics, were more realistic when the vertical mixing of horizontal momentum was included. Major improvements in modelling the interannual variability of the planetary circulation, mid‐tropospheric temperature, and precipitation can be attributed to the salutory effects of the new moist convection, new planetary boundary layer, and the quadratic upstream scheme for advecting tracers.
Trends in air temperature and precipitation for Canada and north‐eastern USA
Authors: Gan Thian Yew
Published: February 2007

Using the univariate, non‐parametric, Kendall's test for monotonic trends from the 1949 to 1989 period, monthly maximum, minimum, average temperature, and precipitation data of some carefully selected stations in Canada and north‐eastern USA, it is found that western Canada for the past 40 years has experienced significant warming in January and March, and to a limited extent in April, May, and June, but virtually no warming trend was detected in eastern Canada and north‐eastern USA. Instead, some cooling trends were found, particularly in October. The analysis on the annual cycle of temperature data also shows the seasonal and regional nature of warming and cooling trends. Unlike temperature, no obvious trend is found in the precipitation data, but on the whole there are more stations (up to 10 per cent) with upward trends (increase in precipitation) during springs and summers. A bivariate test was used to detect a shift in the mean of precipitation series with respect to maximum temperature series but no obvious indication of such a shift was detected.
Large‐scale circulation regimes and surface climatic anomalies over the Mediterranean
Authors: Corte‐Real João , Zhang Xuebin , Wang Xiaolan
Published: February 2007

Significant relationships between atmospheric circulation anomalies, in terms of monthly mean 500 hPa geopotential height (Z500) and sea‐level pressure (SLP) over Atlantic‐Europe, and surface climatic anomalies, in terms of monthly rainfall (Rm) and monthly mean temperature (Tm), over the extended Mediterranean area, are examined statistically by canonical correlation analysis (CCA), with time lags from zero to four months.

At a confidence level of 99.99 per cent, CCA yields five pairs of patterns that describe simultaneous responses of the monthly rainfall field to anomalies of surface circulation (SLP). Between mid‐tropospheric circulation (Z500) and rainfall fields, six concurrent CCA pairs were also identified to be significant at the same confidence level. From the synoptic point view, these results seem very reasonable.

Six concurrent (hereafter lag 0) CCA pairs and one CCA pair for a lag of 1 month (hereafter lag 1) were identified for the Z500—Tm fields at the confidence level of 99 per cent. The SLP—Tm fields, also six concurrent CCA pairs and three pairs for lag 1, were found to be significant at the same confidence level. Quite similar temperature anomaly patterns are represented in the first CCA pairs of the Z500—Tm fields for both lag 0 and lag 1, and in the first lag‐1 and second lag‐0 CCA pairs of the SLP‐Tm fields; the patterns of air temperature anomalies revealed in the third CCA pair of SLP—Tm fields for lag 1, as well as in the fourth concurrent CCA pairs of the Z500—Tm and SLP—Tm fields, also resemble each other. Similar temperature anomaly patterns can be found for other CCA pairs. These similarities reveal that some slow‐changing processes in large‐scale anomalies of atmosphere are responsible for producing the same type of temperature anomalies.