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1.
Short-term variations of the elements representing the Earth's motion around the Sun and its rotation have been analyzed over the last 6000 years using 1-year steps. Their low-frequency part is compared first to the values obtained from a secular theory of the planetary long-term motion showing that they can be considered reliable enough to represent adequately the motion of the Earth over the last 5000 years. Spectral analysis of these values shows that the main periodicities are 2.67, 3.98, 5.26, 5.93, 7.9, 9.8, 11.9, 14.7, 15.8, 29, 42, 61, 122, 165 and 250 years for the eccentricity as well as for the climatic precession, with an additional component at around 930 years for the eccentricity and around 840 years for the climatic precession. Periodicities at 2.67, 3.8, 5.9, 8.0, 9.3, 11.9, 14.7, 18.6, 29, 135, 250 and 840 yr are also shown for the obliquity. Spectral analyses of the daily July mid-month insolation at 65°N show essentially the same periodicities as the climatic precession and the obliquity, i.e. 2.67, 3.98, 5.92, 8.1, 11.9, 15.7, 18.6, 29, 40, 61 and around 900 years. Finally a wider analysis of the insolation pattern was performed related to the large periodicity band of the insolation time series for the solstices and the equinoxes for 7 different latitudes. In equatorial latitudes the insolation variance is largely explained by precession. But precession dominates everywhere with the obliquity signal being stronger at polar latitudes at the solstices. The amplitudes of the insolation change at these frequencies is of the order of 0.2 Wm–2 at the maximum.
Offprint requests to: A Berger 相似文献
2.
EMD analysis of solar insolation 总被引：7，自引：0，他引：7
Summary A new time series analysis technique, Empirical Mode Decomposition (EMD), which has been successfully applied to nonlinear
and nonstationary data, is used to examine paleoclimate cycles in the Pleistocene (1 Ma bp–20 Ka bp). The purpose of this
study is to improve knowledge of the climatic significance of solar insolation. The results show that the eccentricity band
signal is much larger than previously estimated, having an amplitude of about 1% of solar irradiance which is comparable to
the amplitude of the precession and obliquity band signals. This finding implies the need to reconsider the role of solar
radiation on the formation and maintenance of quaternary ice sheet cycles. 相似文献
3.
George C. Reid 《Climatic change》1997,37(2):391-405
Spacecraft measurements of the sun's total irradiance since 1980 have revealed a long-term variation that is roughly in phase with the 11-year solar cycle. Its origin is uncertain, but may be related to the overall level of solar magnetic activity as well as to the concurrent activity on the visible disk. A low-pass Gaussian filtered time series of the annual sunspot number has been developed as a suitable proxy for solar magnetic activity that contains a long-term component related to the average level of activity as well as a short-term component related to the current phase of the 11-year cycle. This time series is also assumed to be a proxy for solar total irradiance, and the irradiance is reconstructed for the period since 1617 based on the estimate from climatic evidence that global temperatures during the Maunder Minimum of solar activity, which coincided with one of the coldest periods of the Little Ice Age, were about 1 °C colder than modern temperatures. This irradiance variation is used as the variable radiative forcing function in a one-dimensional ocean–climate model, leading to a reconstruction of global temperatures over the same period, and to a suggestion that solar forcing and anthropogenic greenhouse-gas forcing made roughly equal contributions to the rise in global temperature that took place between 1900 and 1955. The importance of solar variability as a factor in climate change over the last few decades may have been underestimated in recent studies. 相似文献
4.
Summary In this study, trends of annual and seasonal surface air temperature time series were examined for 20 stations in Greece for the period 1955–2001, and satellite data for the period 1980–2001. Two statistical tests based on the least square method and one based on the Mann-Kendall test, which is also capable of detecting the starting year of possible climatic discontinuities or changes, were used for the analysis. Greece, in general, shows a cooling trend in winter for the period 1955–2001, whereas, summer shows an overall warming trend, however, neither is statistically significant. As a result, the overall trend of the annual values is nearly zero. Comparison with corresponding trends in the Northern Hemisphere (NH) shows that temperatures in Greece do not follow the intense warming trends. Satellite data indicate a remarkable warming trend in mean annual, winter and summer in Greece for the period 1980–2001, and a slight warming trend in annual, spring and autumn for the NH. Comparison with the respective trends detected in the surface air temperature for the same period (1980–2001) shows they match each other quite well in both Greece and the NH. The relationship between temperature variability in Greece and atmospheric circulation was also examined using correlation analysis with three circulation indices: the well-known North Atlantic Oscillation Index (NAOI), a Mediterranean Oscillation Index (MOI) and a new Mediterranean Circulation Index (MCI). The MOI and MCI indices show the most interesting correlation with winter temperatures in Greece. The behaviour of pressure and the height of the 500hPa surface over the Mediterranean region supports these results. 相似文献
5.
Sensitivity experiments with a simple water-balance model were used to constrain the possible climatic causes of distinct Holocene patterns of lake-level variation in different regions of Europe. Lakes in S Sweden were low at 9 ka, high around 6.5 ka, low again around 4 ka and are high now. Lakes in Estonia show similar but weaker trends. Lakes in S France were highest around 9 ka, lowest around 4 ka, intermediate now. Lakes in Greece were also high around 9 ka but continued rising until 7.5 ka, then fell gradually from 5 ka with a brief high phase around 3 ka, and are low now. The model was forced with insolation anomalies deduced from orbital variations, temperature anomalies inferred from the pollen record and cloudiness anomalies derived from changes in the position of the subtropical anticyclone (inferred from reconstructed changes in the equator-to-pole temperature gradient), in order to evaluate the effects of resultant evaporation changes on catchment water balance. The resulting simulated changes in runoff (precipitation minus actual evapotranspiration) were slight, and frequently opposite to the observed trends. Larger changes in precipitation are plausible and are required to explain the data. The required precipitation increase in N Europe from 9 ka (low) to 6 ka (high) is suggested by GCM experiments to have been a consequence of interacting insolation and residual ice-sheet effects on the atmospheric circulation over the North Atlantic. The explanation of other observed changes, including the drying trend during the Holocene in S Europe, has not been provided by GCM experiments to date. Explanations may lie in changes in mesoscale circulation, sea-surface temperature patterns and the coupling between these phenomena that may not follow orbital changes in any simple way.
Correspondence to: SP Harrison 相似文献
6.
We have examined the climatic variance in a series of deep-water oxygen-isotope records which range in length from 0.3 to 130 million years and have temporal resolutions between one thousand and 10 million years. These variations in 18O are interpreted as a generalized index of temperature change in high latitudes. Over five frequency decades the relation between log (variance density) and log (frequency) is approximately linear with a slope between –1 and –1.5. This relationship is interpreted as a background continuum of the sort postulated by Mitchell (1976) in which the spectrum is built up by layers of variance representing contributions from various processes acting within the climate system on different time scales. Our observed continuum slope is much steeper than that visualized by Mitchell. Additional variance is distributed at periods longer than about 3 million years, where it probably originates from forcing by tectonic processes; and at periods between 20,000 and 100,000 years where the Milankovitch forcing operates. Between these two regions there is a clear variance minimum which we predict will appear in the spectrum of other geological variables that are controlled by climate.A broad-band concentration of variance at periods near 30 My rises well above the background. Another concentration occurs at frequencies too low to be estimated accurately from our data. We assume this is a climatic response to the 400 My cycle of continental fragmentation and assembly. 相似文献
7.
The paleoclimatic variability at frequencies ranging from 10–4 cycle per year (cpy) to 10–5 cpy is investigated using a set of four deep-sea cores from the Atlantic, Pacific and Indian Oceans. Dominant features are the presence of orbital frequencies corresponding to mean periods of 117.7, 43.6, 24.9 and 19.3 kyr. These are statistically significant according to such advanced spectral tools as Blackman-Tukey, maximum entropy and the highly efficient Thomson technique. However, the main purpose of this paper is methodological, describing the statistical analyses of time series with modern methods in order to stress their relative power, advantages and disadvantages. The more advanced statistical methods confirm the coincidence of the dominant periods in the deep sea cores and those in the astronomical elements, including combination tones. Three frequency bands of high paleoclimatic variability centred at 15.4, 13 and 10.8 kyr are indeed also detected. These two last periods are very close to those predicted by the climatic non-linear model of Ghil and Le Treut and found by Pestiaux et al. and Yiou et al. 相似文献
8.
Progress in understanding how terrestrial ice volume is linked to Earths orbital configuration has been impeded by the cost of simulating climate system processes relevant to glaciation over orbital time scales (103–105 years). A compromise is usually made to represent the climate system by models that are averaged over one or more spatial dimensions or by three-dimensional models that are limited to simulating particular snapshots in time. We take advantage of the short equilibration time (10 years) of a climate model consisting of a three-dimensional atmosphere coupled to a simple slab ocean to derive the equilibrium climate response to accelerated variations in Earths orbital configuration over the past 165,000 years. Prominent decreases in ice melt and increases in snowfall are simulated during three time intervals near 26, 73, and 117 thousand years ago (ka) when aphelion was in late spring and obliquity was low. There were also significant decreases in ice melt and increases in snowfall near 97 and 142 ka when eccentricity was relatively large, aphelion was in late spring, and obliquity was high or near its long term mean. These glaciation-friendly time intervals correspond to prominent and secondary phases of terrestrial ice growth seen within the marine 18O record. Both dynamical and thermal effects contribute to the increases in snowfall during these periods, through increases in storm activity and the fraction of precipitation falling as snow. The majority of the mid- to high latitude response to orbital forcing is organized by the properties of sea ice, through its influence on radiative feedbacks that nearly double the size of the orbital forcing as well as its influence on the seasonal evolution of the latitudinal temperature gradient. 相似文献
9.
In this paper, the response of global monsoon to changes in orbital forcing is investigated using a coupled atmosphere–ocean general circulation model with an emphasis on relative roles of precession and obliquity changes. When precession decreases, there are inter-hemispheric asymmetric responses in monsoonal precipitation, featuring a significant increase over most parts of the Northern Hemisphere (NH) monsoon regions and a decrease over the Southern Hemisphere (SH) monsoon regions. In contrast, when obliquity increases, global monsoon is enhanced except for the American monsoon. Dynamic effects (caused by changes in winds with humidity unchanged) dominate the monsoonal precipitation response to both precession and obliquity forcing, while thermodynamic effects (caused by changes in humidity with winds unchanged) is related to the northward extension of the North African summer monsoon. During minimum precession, the seasonal cycle of tropical precipitation is advanced with respect to the maximum precession. The rainfall increase in the transitional season (April-June in the NH and October-December in the SH) is dominated by the dynamic component. From an energetics perspective, the southward (northward) cross-equatorial energy transport during April-June (October-December) corresponds to a northward (southward) shift of tropical precipitation, which results in a seasonal advance in the migration of tropical precipitation. Nonetheless, there is no significant change in the seasonal cycle in response to obliquity forcing.
相似文献10.
Long-term changes of the surface air temperature in relation to solar inertial motion 总被引：1，自引：0，他引：1
The inertial motion of the Sun around the barycentre, or centre of mass, of the Solar System has been employed as the base in searching for possible influence of the Solar System as a whole on climatic processes, especially on the changes in surface air temperature. A basic cycle of about 180–200 years and its higher harmonics up to 30 years have been found in surface air temperature of central Europe since 1753, established from 13 continuous instrumental time series. These periods correspond to the periods of solar inertial motion. In the first half of the 19th century, when the solar motion was chaotic, this temperature was about 0.75°C lower than that in the 20th (1940–50) and the 18th (1760–70) centuries. The mentioned decades of long-term temperature maxima coincide with the central decades of the ordered (trefoil) motion of the Sun. The temperatures in coastal Europe have been found to have slightly different properties, especially on a long-time scale. The periods of 35–45 years are significantly pronounced in the coastal Europe temperature spectrum. The chaotic motion of the Sun in the next decades could decrease both the solar forcing and global surface air temperature.This research was performed with support of the Grant Agency of the Czech Republic, Grant No. 205/93/0417, I. Charvátová: Prognosis of climate development in central Europe. 相似文献
11.
Several studies have shown that the use of different calendars in paleoclimate simulations can cause artificial phase shifts on insolation forcing and climatic responses. However, these important calendar corrections are still often neglected. In this paper, the phase shifts at the precession band is quantitatively assessed by converting the model data of the transient GCM climate simulation of Kutzbach et al. (Clim Dyn 30:567?C579, 2008) from the ??fixed-day?? calendar to the ??fixed-angular?? calendar with a new and efficient approach. We find that insolation has a big phase shift in September?COctober?CNovember (SON) when the vernal equinox (VE) is fixed to March 21. At high latitude, the phase bias is up to 60° (about 3650?years). The insolation phase bias in SON in Southern Hemisphere (SH) is especially important because it can influence the timing of the SH summer monsoon response due to the large heat capacity of ocean. The calendar correction has minor effect (±2°) on the phase relationships between forcing and precipitation responses of the six global summer monsoons studied in Kutzbach et al. (2008). After correcting the calendar effect, especial on SH ocean temperature, the new phase wheel results are more similar for both hemispheres. The results suggest that the calendar effect should be corrected before discussing the dynamics between orbital forcing and climatic responses in phase studies of transient simulations. 相似文献
12.
Simulation of the evolutionary response of global summer monsoons to orbital forcing over the past 280,000 years 总被引：3，自引：2，他引：1
We describe the evolutionary response of northern and southern hemisphere summer monsoons to orbital forcing over the past
280,000 years using a fully coupled general circulation ocean-atmosphere model in which the orbital forcing is accelerated
by a factor of 100. We find a strong and positive response of northern (southern) summer monsoon precipitation to northern
(southern) summer insolation forcing. On average, July (January) precipitation maxima and JJA (DJF) precipitation maxima have
high coherence and are approximately in phase with June (December) insolation maxima, implying an average lag between forcing
and response of about 30° of phase at the precession period. The average lag increases to over 40° for 4-month precipitation
averages, JJAS (DJFM). The phase varies from region to region. The average JJA (DJF) land temperature maxima also lag the
June orbital forcing maxima by about 30° of phase, whereas ocean temperature maxima exhibit a lag of about 60° of phase at
the precession period. Using generalized measures of the thermal and hydrologic processes that produce monsoons, we find that
the summer monsoon precipitation indices for the six regions all fall within the phase limits of the process indices for the
respective hemispheres. Selected observational studies from four of the six monsoon regions report approximate in-phase relations
of summer monsoon proxies to summer insolation. However other observational studies report substantial phase lags of monsoon
proxies and a strong component of forcing associated with glacial-age boundary conditions or other factors. An important next
step will be to include glacial-age boundary condition forcing in long, transient paleoclimate simulations, along with orbital
forcing. 相似文献
13.
We note that orbital (Milankovitch) variations, in particular the precession of the equinoxes, can lead to profound variations in the flux of heat from the tropics to higher latitudes. The mechanism involves changing the intensity of the Hadley circulation by varying the maximum displacement from the equator of the zonally averaged surface temperature maximum in summer. The precession of the equinoxes causes this quantity to vary by more than a factor of 2. The intensity of the Hadley circulation has a major influence on the heat fluxes in the winter hemisphere. Summer heat fluxes are generally small. Although the precession cycle is characterized by periods in the neighborhood of 20000 years, the variations are modulated by the eccentricity whose variation is dominated by periods in the neighborhood of 100000 years and 400000 years. We show how the fact that both small and large heat fluxes lead to low snowfall (and, hence, small glacial accumulation) causes the demodulation of the heat flux leading to dominant eccentricity periods in the resulting glaciation. 相似文献
14.
An analysis of the time scales of variability in centuries-long enso-sensitive records in the last 1000 years 总被引：2，自引：0，他引：2
We document the characteristic time scales of variability for seven climate indices whose time-dependent behavior is sensitive to some aspect of the El Niño/Southern Oscillation (ENSO). The ENSO sensitivity arises from the location of these long-term records on the periphery of the Indian and Pacific Oceans. Three of the indices are derived principally from historical sources, three others consist of tree-ring reconstructions (one of summer temperature, and the other two of winter rainfall), and one is an annual record of oxygen isotopic composition for a high-elevation glacier in Peru. Five of the seven indices sample at least portions of the Medieval Warm Period (~ A.D. 950 to 1250).Time series spectral analysis was used to identify the major time scales of variability among the different indices. We focus on two principal time scales: a high frequency band (~ 2–10 yr), which comprises most of the variability found in the modern record of ENSO activity, and a low frequency band to highlight variations on decadal to century time scales (11 <P < 150 yr). This last spectral band contains variability on time scales that are of general interest with respect to possible changes in large-scale air-sea exchanges. A technique called evolutive spectral analysis (ESA) is used to ascertain how stable each spectral peak is in time. Coherence and phase spectra are also calculated among the different indices over each full common period, and following a 91-yr window through time to examine whether the relationships change.In general, spectral power on time scales of ~ 2–6 yr is statistically significant and persists throughout most of the time intervals sampled by the different indices. Assuming that the ENSO phenomenon is the source of much of the variability at these time scales, this indicates that ENSO has been an important part of interannual climatic variations over broad areas of the circum-Pacific region throughout the last millennium. Significant coherence values were found for El Niño and reconstructed Sierra Nevada winter precipitation at ~ 2–4 yr throughout much of their common record (late 1500s to present) and between 6 and 7 yr from the mid-18th to the early 20th century.At decadal time scales each record generally tends to exhibit significant spectral power over different periods at different times. Both the Quelccaya Ice Cap
18O series and the Quinn El Niño event record exhibit significant spectral power over frequencies ~ 35 to 45 yr; however, there is low coherence between these two series at those frequencies over their common record. The Sierra Nevada winter rainfall reconstruction exhibits consistently strong variability at periods of ~ 30–60 yr. 相似文献
15.
Streamflows have a direct dependence on precipitation and these are directly linked to the climate. Then, in this paper the temporal climatic variability in the Río de la Plata Basin is analysed through the changes in the river's discharges. These are the reflection of the climatic inputs areally integrated, and in consequence, contain more information on climate variability than that provided by the scarce punctual records of precipitation and temperature. The time series of streamflows correspond to monthly and annual means in stations selected in the basin for the period 1931–1992. However, in the present paper, the period 1901–1992 was considered in all cases whenever possible. The following changes and tendencies in the flow series were detected: 1. An important change of tendency between 1970 and 1972, and another not so significant before that date were detected in 1917–1918 and 1943–1944. 2. The jumps in the means in several sub-periods were detected using different methods. They showed jumps mainly in the period 1970–1972 in the annual streamflows series. The jumps in the annual streamflow series consist of an abrupt change in climatic variables affecting temporarily the averages of such variables during a certain period of time (years). The results are consistent with the conclusions obtained by other authors for the same region, both in precipitation and in the general circulation of the atmosphere. Keeping in mind this analysis of the series of streamflows, indicators of normal variability of tendencies relative to natural regional causes were detected, although the local causes were not anthropogenically analysed, and so no other manifestations of randomless in the zone of the Basin under study because of the lacking of data. 相似文献
16.
The paleoclimatic variability at frequencies ranging from 10–4 cycle per year (cpy) to 10–3 cpy is investigated using a set of three deep-sea cores from the Indian Ocean. Three frequency bands of high paleoclimatic variability are first defined using upper and lower limits of the significant spectral power concentrations: the bands are centered around the spectral maxima located at 10.3, 4.7, and 2.5 kyr. The localisation of spectral lines is then refined by high-resolution spectral analysis.Some of the resulting lines have frequencies which are close to those previously detected in other paleoclimatic records, including the precessional peak at 19 kyr. Additional lines are also in good correspondence with the response of a nonlinear climatic oscillator forced by insolation variations, including peaks at 13 kyr, 10.4 kyr and 9.4 kyr. This correspondence suggests orbital forcing. Moreover for the Indian Ocean which is influenced by the monsoon circulation, it is plausible that the precessional contribution of the forcing interact strongly with the precipitation-temperature feedback used in the model, thus emphasizing the nonlinearity of the response. 相似文献
17.
Summary In this paper some statistical characteristics of air temperature variations over the Mediterranean are presented. The study is based on temperature data at stations in Marseille (1851–1985), Rome (1851–1985), Athens (1858–1985), and Jerusalem (1864–1985). First the homogeneity of temperature data for each station is examined by means of the short-cut Bartlett test. In another step, the existence of abrupt climatic changes towards warm or cold periods at all stations, with the exception of Athens is pointed out. Some statistical significant persistence of the annual and seasonal time series is also shown. Finally, the temperature fluctuations are examined and discussed in respect to possible causes where particularly the role of the Mediterranean Sea and the topography is considered.With 4 Figures 相似文献
18.
The response of monsoon circulation in the northern and southern hemisphere to 6?ka orbital forcing has been examined in 17 atmospheric general circulation models and 11 coupled ocean–atmosphere general circulation models. The atmospheric response to increased summer insolation at 6?ka in the northern subtropics strengthens the northern-hemisphere summer monsoons and leads to increased monsoonal precipitation in western North America, northern Africa and China; ocean feedbacks amplify this response and lead to further increase in monsoon precipitation in these three regions. The atmospheric response to reduced summer insolation at 6?ka in the southern subtropics weakens the southern-hemisphere summer monsoons and leads to decreased monsoonal precipitation in northern South America, southern Africa and northern Australia; ocean feedbacks weaken this response so that the decrease in rainfall is smaller than might otherwise be expected. The role of the ocean in monsoonal circulation in other regions is more complex. There is no discernable impact of orbital forcing in the monsoon region of North America in the atmosphere-only simulations but a strong increase in precipitation in the ocean–atmosphere simulations. In contrast, there is a strong atmospheric response to orbital forcing over northern India but ocean feedback reduces the strength of the change in the monsoon although it still remains stronger than today. Although there are differences in magnitude and exact location of regional precipitation changes from model to model, the same basic mechanisms are involved in the oceanic modulation of the response to orbital forcing and this gives rise to a robust ensemble response for each of the monsoon systems. Comparison of simulated and reconstructed changes in regional climate suggest that the coupled ocean–atmosphere simulations produce more realistic changes in the northern-hemisphere monsoons than atmosphere-only simulations, though they underestimate the observed changes in precipitation in all regions. Evaluation of the southern-hemisphere monsoons is limited by lack of quantitative reconstructions, but suggest that model skill in simulating these monsoons is limited. 相似文献
19.
István Matyasovszky 《Theoretical and Applied Climatology》2010,101(3-4):433-443
In order to gain further insights into stochastic behaviour of paleoclimate data, including timescales at and below Milankovitch forcing, three specific questions are discussed using δ 18O NGRIP and Vostok Deuterium content data. A comparison of ordinary and time-varying coefficients autoregressive (AR) models shows that both data sets are distinguishable from data generated by suitable low-order AR processes in contrast to earlier conclusions. A harmonic regression analysis clearly distinguishing between discrete and continuous spectra detects cycles corresponding to variations of eccentricity, obliquity and precession. Contribution of eccentricity to the total variance in the last 422,766-year Vostok data is close to, while the variance reduction delivered jointly by obliquity and precession is substantially smaller than a previous recent finding. A harmonic regression analysis with time-varying frequencies and amplitudes is also performed. This approach delivers a gain over the constant frequency model at any reasonable significance level. It is demonstrated that variations of frequencies are at least partly due to real variations and not merely to timescale uncertainties. In order to consider nonlinearity in paleoclimate data, threshold autoregressive (TAR) models are applied to time series examined. A bivariate TAR model describing simultaneous NGRIP and Vostok data exhibits three fix points and one limit cycle related to a part of Dansgaard–Oeschger events. The model selected suggests that Greenland has a primary role in the Greenland–Antarctica climate variation relationship. 相似文献
20.
Orbital forcing of the climate system is clearly shown in the Earths record of glacial–interglacial cycles, but the mechanism underlying this forcing is poorly understood. Traditional Milankovitch theory suggests that these cycles are driven by changes in high latitude summer insolation, yet this forcing is dominated by precession, and cannot account for the importance of obliquity in the Ice Age record. Here, we investigate an alternative forcing based on the latitudinal insolation gradient (LIG), which is dominated by both obliquity (in summer) and precession (in winter). The insolation gradient acts on the climate system through differential solar heating, which creates the Earths latitudinal temperature gradient (LTG) that drives the atmospheric and ocean circulation. A new pollen-based reconstruction of the LTG during the Holocene is used to demonstrate that the LTG may be much more sensitive to changes in the LIG than previously thought. From this, it is shown how LIG forcing of the LTG may help explain the propagation of orbital signatures throughout the climate system, including the Monsoon, Arctic Oscillation and ocean circulation. These relationships are validated over the last (Eemian) Interglacial, which occurred under a different orbital configuration to the Holocene. We conclude that LIG forcing of the LTG explains many criticisms of classic Milankovitch theory, while being poorly represented in climate models. 相似文献