Astronomical Parameters Research Articles

High-resolution regional simulation of last glacial maximum climate in Europe

Afully coupled atmosphere—ocean general circulationmodel is used to simulate climate conditions during the last glacial maximum (LGM). Forcing conditions include astronomical parameters, greenhouse gases, ice sheets and vegetation. A 50-yr period of the global simulation is dynamically downscaled to 50 km horizontal resolution over Europe with a regional climate model (RCM). A dynamic vegetation model is used to produce vegetation that is consistent with the climate simulated by the RCM. This vegetation is used in a final simulation with the RCM. The resulting climate is 5–10 ◦C colder than the recent past climate (representative of year 1990) over ice-free parts of Europe as an annual average; over the ice-sheet up to 40 ◦C colder in winter. The average model-proxy error is about the same for summer and winter, for pollen-based proxies. The RCM results are within (outside) the uncertainty limits for winter (summer). Sensitivity studies performed with the RCM indicate that the simulated climate is sensitive to changes in vegetation, whereas the location of the ice sheet only affects the climate around the ice sheet. The RCM-simulated interannual variability in near surface temperature is significantly larger at LGM than in the recent past climate.

27.3-day and average 13.6-day periodic oscillations in the Earth’s rotation rate and atmospheric pressure fields due to celestial gravitation forcing

Variation in length of day of the Earth (LOD, equivalent to the Earth’s rotation rate) versus change in atmospheric geopotential height fields and astronomical parameters were analyzed for the years 1962–2006. This revealed that there is a 27.3-day and an average 13.6-day periodic oscillation in LOD and atmospheric pressure fields following lunar revolution around the Earth. Accompanying the alternating change in celestial gravitation forcing on the Earth and its atmosphere, the Earth’s LOD changes from minimum to maximum, then to minimum, and the atmospheric geopotential height fields in the tropics oscillate from low to high, then to low. The 27.3-day and average 13.6-day periodic atmospheric oscillation in the tropics is proposed to be a type of strong atmospheric tide, excited by celestial gravitation forcing. A formula for a Tidal Index was derived to estimate the strength of the celestial gravitation forcing, and a high degree of correlation was found between the Tidal Index determined by astronomical parameters, LOD, and atmospheric geopotential height. The reason for the atmospheric tide is periodic departure of the lunar orbit from the celestial equator during lunar revolution around the Earth. The alternating asymmetric change in celestial gravitation forcing on the Earth and its atmosphere produces a “modulation” to the change in the Earth’s LOD and atmospheric pressure fields.

Nonthermal and thermal emission from the supernova remnant RX J1713.7-3946

A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is employed to investigate the properties of SNR RX J1713.7-3946. Observations of the non-thermal radio and X-ray emission spectra as well as the H.E.S.S. measurements of the very high energy gamma-ray emission are used to constrain the astronomical and CR acceleration parameters of the system. It is argued that RX J1713.7-3946 is a core collapse supernova (SN) of type II/Ib with a massive progenitor, has an age of ~1600 yr and is at a distance of ~1 kpc. It is in addition assumed that the CR injection/acceleration takes place uniformly across the shock surface for this kind of core collapse SNR. The theory gives a consistent description for all the existing observational data, including the non-detection of thermal X-rays and the spatial correlation of the X-ray and gamma-ray emission in the remnant. Specifically it is shown that an efficient production of nuclear CRs, leading to strong shock modification and a large downstream magnetic field strength B_d ~140 mkG can reproduce in detail the observed synchrotron emission from radio to X-ray frequencies together with the gamma-ray spectral characteristics as observed by the H.E.S.S. telescopes. The calculations are consistent with RX J1713.7-3946 being an efficient source of nuclear cosmic rays.

Modeling the 100-kyr glacial–interglacial cycles

Investigations during the last twenty-five years have demonstrated that the astronomically related 19, 23 and 41-kyr quasi-periodicities actually occur in long records of the Quaternary climate. But the same investigations identified also the largest climatic cycle as being about 100-kyr long. This cycle, the most striking feature of the Quaternary paleoclimate records, is characterized by long glacial periods followed by a short interglacial (∼ 10 to 15 kyr long). Different sources for this so-called 100-kyr cycle have been found in the astronomical parameters and in the insolation itself. The most popular astronomical one is certainly the eccentricity with the largest spectral components around 100-kyr being 94 945, 123 297, 99 590 and 131 248 years (Berger, 1978). For insolation, it is known that there is only a very weak signal around 100-kyr coming from eccentricity itself. Moreover, the 100-kyr signal in eccentricity is fading away in the upper Pleistocene, at the same time that it appears to be stronger and stronger in paleoclimate records. Therefore, eccentricity cannot be related to either the orbital forcing or to the climate response by any simple linear mechanism. Actually, the variance components centered near the 100-kyr cycle seem to be in phase with the eccentricity cycle, but its exceptional strength in the climate record demands a non-linear amplification. It was already suggested that this can be done by the ice sheet (Imbrie and Imbrie, 1980), the carbon cycle (Shackleton, 2000) and/or the ocean circulation (Imbrie et al., 1993), all arguments which imply that climate model must be used to test the origin of this 100-kyr cycle in paleoclimate records. Such a model has been developed in Louvain-la-Neuve for the Northern Hemisphere and used to perform sensitivity analyses to the astronomically-driven insolation changes and to the atmospheric CO 2 concentration over the Quaternary. Assuming a CO 2 concentration decreasing linearly from 320 ppmv at 3 Myr BP (late Pliocene) to 200 ppmv at the Last Glacial Maximum, the model simulates the intensification of glaciation around 2.75 Myr BP, the late Pliocene–early Pleistocene 41-kyr cycle, the emergence of the 100-kyr cycle around 900 kyr BP, and the glacial–interglacial cycles of the last 600 kyr ( Berger and Loutre, 2004). Simulations with different CO 2 reconstructions over the last 1 Myr have confirmed that the model can sustain the glacial–interglacial cycles of the late Pleistocene ( Berger et al., 2004). Although the model results agree pretty well with the reconstruction in phase and amplitude over the last 400 kyr, before MIS-11 it neither keeps enough ice during the interglacials nor produces the reduced amplitude of the glacial–interglacial cycles as shown in deep-sea ( Imbrie et al., 1984) and ice cores ( EPICA, 2004).

Astrochronology of the late Jurassic Kimmeridge Clay (Dorset, England) and implications for Earth system processes

The Late Jurassic Kimmeridge Clay Formation (KCF) is an economically important, organic-rich source rock of Kimmeridgian–Early Tithonian age. The main rock types of the KCF in Dorset, UK, include grey to black laminated shale, marl, coccolithic limestone, and dolostone, which occur with an obvious cyclicity at astronomical timescales. In this study, we examine two high-resolution borehole records (Swanworth Quarry 1 and Metherhills 1) obtained as part of a Rapid Global Geological Events (RGGE) sediment drilling project. Datasets examined were total organic carbon (TOC), and borehole wall microconductivity by Formation Microscanner (FMS). Our intent is to assess the rhythmicity of the KCF with respect to the astronomical timescale, and to discuss the results with respect to other key Late Jurassic geological processes. Power spectra of the untuned data reveal a hierarchy of cycles throughout the KCF with ∼ 167 m, ∼ 40 m, 9.1 m, 3.8 m and 1.6 m wavelengths. Tuning the ∼ 40 m cycles to the 405-kyr eccentricity cycle shows the presence of all the astronomical parameters: eccentricity, obliquity, and precession index. In particular, ∼ 100-kyr and 405-kyr eccentricity cycles are strongly expressed in both records. The 405-kyr eccentricity cycle corresponds to relative sea-level changes inferred from sequence stratigraphy. Intervals with elevated TOC are associated with strong obliquity forcing. The 405-kyr-tuned duration of the lower KCF (Kimmeridgian Stage) is 3.47 Myr, and the upper KCF (early part of the Tithonian Stage, elegans to fittoni ammonite zones) is 3.32 Myr. Two other chronologies test the consistency of this age model by tuning ∼ 8–10 m cycles to 100-kyr (short eccentricity), and ∼ 3–5 m cycles to 36-kyr (Jurassic obliquity). The ‘obliquity-tuned’ chronology resolves an accumulation history for the KCF with a variation that strongly resembles that of Earth's orbital eccentricity predicted for 147.2 Ma to 153.8 Ma. There is evidence for significant non-deposition (up to 1 million years) in the lowermost KCF ( baylei– mutabilis zones), which would indicate a Kimmeridgian/Oxfordian boundary age of 154.8 Ma. This absolute calibration allows assignment of precise numerical ages to zonal boundaries, sequence surfaces, and polarity chrons of the lower M-sequence.

Cosmic ray acceleration parameters from multi-wavelength observations. The case of SN 1006

The properties of the Galactic supernova remnant SN 1006 are theoretically reanalysed. Nonlinear kinetic theory is used to determine the acceleration efficiency of cosmic rays (CRs) in the supernova remnant SN 1006. The known range of astronomical parameters and the existing measurements of nonthermal emission are examined in order to define the values of the relevant physical parameters which determine the CR acceleration efficiency. It is shown that the parameter values -- proton injection rate, electron to proton ratio and downstream magnetic field strength -- are determined with the appropriate accuracy. In particular also the observed azimuthal variations in the gamma-ray morphology agree with the theoretical expectation. These parameter values, together with the reduction of the gamma-ray flux relative to a spherically symmetric acceleration geometry, allow a good fit to the existing data, including the recently detected TeV emission by H.E.S.S. SN 1006 represents the first example where a high efficiency of nuclear CR production, required for the Galactic CR sources, is consistently established.

Numerical methods applied to global solar radiation modeling – comparison with measured data

PurposeThe purpose of this paper is to predict the global solar radiation intensity in areas where meteorological stations do not exist and information on solar radiation cannot be obtained experimentally.Design/methodology/approachThe approach to achieve the objective of the paper is developing multiple regression relations between the global solar radiation intensity (the dependent variable) and geographical, geometrical, astronomical and meteorological parameters (the independent variables). The independent variables used for this purpose were selected based on their ease of measurability outside the meteorological station and without expensive equipment. The number of independent variables is arbitrarily chosen and directly affects the accuracy of predictions.FindingsLinear regression relations using one, two, three, four, five, six, and seven independent variables were developed to predict the global solar radiation intensity on horizontal surfaces. An advanced computer program based on least square analysis was used to obtain the regression coefficients. The relations having the highest correlation coefficients were selected. The study shows even when only one independent variable (declination angle) is used, the one variable regression relation predicts the global solar radiation with an accuracy that is satisfactory in most engineering applications.Originality/valueThe diversity of regression relations introduced in this paper gives the engineer such a broad freedom of choice, that knowing only an astronomical parameter of the site makes him capable of estimating the global solar radiation intensity within acceptable margins. The predicted values of global solar radiation intensity by this approach can be used for the design and performance estimation in solar applications. The statistical model developed in this research was validated when compared with the measured data in Yazd airport. The measured data used to analyze the model equations were collected in a 13‐year period. No investigation of this type exists having such degree of accuracy in geographical, geometrical, astronomical and meteorological parameters in Iran.

Explorations of Atmosphere–Ocean–Ice Climates on an Aquaplanet and Their Meridional Energy Transports

Abstract The degree to which total meridional heat transport is sensitive to the details of its atmospheric and oceanic components is explored. A coupled atmosphere, ocean, and sea ice model of an aquaplanet is employed to simulate very different climates—some with polar ice caps, some without—even though they are driven by the same incoming solar flux. Differences arise due to varying geometrical constraints on ocean circulation influencing its ability to transport heat meridionally. Without complex land configurations, the results prove easier to diagnose and compare to theory and simple models and, hence, provide a useful test bed for ideas about heat transport and its partition within the climate system. In particular, the results are discussed in the context of a 1978 study by Stone, who argued that for a planet with Earth’s astronomical parameters and rotation rate, the total meridional heat transport would be independent of the detailed dynamical processes responsible for that transport and depend primarily on the distribution of incoming solar radiation and the mean planetary albedo. The authors find that in warm climates in which there is no ice, Stone’s result is a useful guide. In cold climates with significant polar ice caps, however, meridional gradients in albedo significantly affect the absorption of solar radiation and need to be included in any detailed calculation or discussion of total heat transport. Since the meridional extent of polar ice caps is sensitive to details of atmospheric and oceanic circulation, these cannot be ignored. Finally, what has been learned is applied to a study of the total heat transport estimated from the Earth Radiation Budget Experiment (ERBE) data.

A parameter database for large scientific projects: application to the Gaia space astrometry mission

The parallel development of many aspects of a complex space science mission like Gaia, which includes numerous participants in ESA, industrial companies, and a large and active scientific collaboration throughout Europe, makes keeping track of the many design changes, instrument and operational parameters, and numerical values for the data analysis and simulations, a challenging but crucially important problem. A comprehensive, easily-accessible, up-to-date, and definitive compilation of a large range of numerical quantities is required, and the Gaia parameter database has been established to satisfy these needs. The database is a centralised repository containing, besides mathematical, physical, and astronomical constants, many satellite and subsystem design parameters. Version control provides both a ‘live’ version with the most recent parameters, as well as previous ‘reference’ versions of the full database contents. Query results are formatted by default in HTML, while an important feature is that data can also be retrieved as Java, ANSI-C, C++, Ruby, or XML structures for direct inclusion into software codes, such that all collaborating scientists can use the retrieved database parameters and values directly linked to computational routines.

Image Navigation for the FY2 Geosynchronous Meteorological Satellite

Abstract An automatic image navigation algorithm for Feng Yun 2 (FY2) spin-stabilized geosynchronous meteorological satellites was determined at the National Satellite Meteorological Center (NSMC) of the China Meteorological Administration (CMA). This paper derives the parameters and coordinate systems used in FY2 image navigation, with an emphasis on attitude and misalignment parameters. The solution to the navigation model does not depend on any landmark matching. The time series dataset of the satellite orientation with respect to the center line of the earth’s disk contains information on the two components of the attitude (orientation of the satellite spin axis) and the roll component of the misalignment. With this information, the two attitude components can be solved simultaneously, expressed as declination and right ascension (with diurnal variation in the fixed earth coordinate system) and the roll component of the misalignment (with no diurnal variation). In each spin cycle, the satellite views the sun and earth. The position of the sun is detected and used to align earth observation pixels in the scan line together with an angle subtended at the satellite by the sun and earth (β). With satellite position and attitude known, the β angle can be calculated and predicted with sufficient accuracy. Next, the image is assembled. Prediction of the β angle takes an important role in the image formation process, as imperfect β angle prediction may cause east–west shift and image deformation. In the image registration process of FY2, both the east–west shift and the image deformation are compensated for. The above-mentioned solution to the navigation model requires accurate knowledge of astronomical parameters and coordinate systems. The orbital, attitude, misalignment, and β angle parameters are produced automatically and routinely without any manual operation. Image navigation accuracy for the FY2 geosynchronous meteorological satellite approaches 5 km at the subsatellite point (SSP).

Modeling Optical Turbulence and Seeing over Mauna Kea*

Abstract Atmospheric turbulence is a primary concern for astronomers. Turbulence causes amplitude and phase fluctuations in electromagnetic waves propagating through the atmosphere, constraining the maximum telescope resolution and resulting in telescope image degradation. Astronomical parameters that quantify these effects are generically referred to as seeing. Adaptive optics (AO) is used to reduce image degradation associated with optical turbulence. However, to optimize AO, knowledge of the vertical profile of turbulence and overall (integrated) seeing is needed. In this paper, an optical turbulence algorithm is described that makes use of the information on turbulence kinetic energy provided by a planetary boundary layer scheme available in the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5). Optical turbulence data collected on Mauna Kea during the 2002 site monitoring campaign are used to validate the algorithm, which has been implemented in operational runs of MM5 at the Mauna Kea Weather Center.

On the planetary acceleration and the rotation of the Earth

We have developed a model for the Earth rotation that gives a good account (data) of the Earth astronomical parameters. These data can be compared with the ones obtained using space-base telescopes. The expansion of the universe has an impact on the rotation of planets, and in particular, the Earth. The expansion of the universe causes an acceleration that is exhibited by all planets.

Gamma-ray emission expected from Kepler’s SNR

Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties of Kepler’s SNR and, in particular, to predict the γ-eay spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical constraints for the total supernova (SN) explosion energy E sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler’s SN is a type Ia SN we determine for any given explosion energy E sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes it possible to make predictions for the expected γ-eay flux. Exploring the expected distance range we find that for a typical explosion energy E sn=1051 erg the expected energy flux of TeV γ-rays varies from 2×10−11 to 10−13 erg/(cm2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the γ-eay emission is dominated by π 0-decay γ-rays due to nuclear CRs. Therefore Kepler’s SNR represents a very promising target for instruments like H.E.S.S., CANGAROO and GLAST. A non-detection of γ-rays would mean that the actual source distance is larger than 7 kpc.

Will black holes eventually engulf the Universe?

The Babichev–Dokuchaev–Eroshenko model for the accretion of dark energy onto black holes has been extended to deal with black holes with non-static metrics. The possibility that for an asymptotic observer a black hole with large mass will rapidly increase and eventually engulf the Universe at a finite time in the future has been studied by using reasonable values for astronomical parameters. It is concluded that such a phenomenon is forbidden for all black holes in quintessential cosmological models.

Gamma-ray emission expected from Kepler's supernova remnant

Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova remnants (SNRs) is used to investigate the properties of Kepler's SNR and, in particular, to predict the gamma-ray spectrum expected from this SNR. Observations of the nonthermal radio and X-ray emission spectra as well as theoretical constraints for the total supernova (SN) explosion energy E_sn are used to constrain the astronomical and particle acceleration parameters of the system. Under the assumption that Kepler's SN is a type Ia SN we determine for any given explosion energy E_sn and source distance d the mass density of the ambient interstellar medium (ISM) from a fit to the observed SNR size and expansion speed. This makes it possible to make predictions for the expected gamma-ray flux. Exploring the expected distance range we find that for a typical explosion energy E_sn=10^51 erg the expected energy flux of TeV gamma-rays varies from 2x10^{-11} to 10^{-13} erg/(cm^2 s) when the distance changes from d=3.4 kpc to 7 kpc. In all cases the gamma-ray emission is dominated by \pi^0-decay gamma-rays due to nuclear CRs. Therefore Kepler's SNR represents a very promising target for instruments like H.E.S.S., CANGAROO and GLAST. A non-detection of gamma-rays would mean that the actual source distance is larger than 7 kpc.

Dependence of the gamma-ray emission from SN 1006 on the astronomical parameters

We use nonlinear kinetic theory to study the remnant dynamics and the particle acceleration as well as the properties of the nonthermal emission from the supernova remnant SN 1006. The known range of astronomical parameters is examined to determine whether it encompasses the existing synchrotron emission data. Given the present-day spatial extent and expansion rate of the object, it is shown that the hadronic gamma-ray flux is very sensitive to the ambient gas density and that the existing HESS upper limit requires cm-3. The strength of the amplified magnetic field downstream of the shock is about 150 μG.

Correlation of global solar radiation with common geographical and meteorological parameters for Damascus province, Syria

In this study, the effect of geographical and meteorological parameters on the monthly mean daily global solar radiation in Damascus was investigated. With measured data of global solar radiation and the relevant data of astronomical, geographical, geometrical and meteorological parameters for Damascus province, an attempt has been made to correlate the monthly mean daily global solar radiation on a horizontal surface with seven different variables; mean daily extraterrestrial solar radiation intensity I¯0, average daily ratio of sunshine duration n¯/N¯, mean daily relative humidity ϕ¯, mean daily maximum air temperature ϑ¯max, mean daily maximum dew point temperature ϑ¯d,max, mean daily atmospheric pressure P¯ and sine of the solar declination angle sin δ. A new multiple regression relation giving accurate estimates of monthly mean daily global solar radiation on a horizontal surface was suggested. It has a high coefficient of correlation R = 0.9915. The results showed that the suggested model can estimate the global solar radiation within relative errors e of −6.37% and 8.27%. The values of MBD (0.1 W/m2) and also RMSD (229 W/m2) are within acceptable ranges. The global solar radiation intensity values produced by this approach can be used in the design and estimation of the performance of solar applications. It is believed that the model developed in this work is applicable for estimating the monthly mean daily global solar radiation on a horizontal surface at any site in Damascus province, Syria.

CYCLIC FLUCTUATIONS, CLIMATIC CHANGES AND ROLE OF NOISE IN PLANKTONIC FORAMINIFERA IN THE MEDITERRANEAN SEA

The study of Planktonic Foraminifera abundances permits to obtain climatic curves on the basis of percentage ratio between tropical and temperate/polar forms. Climatic changes were controlled by several phenomena as: (i) Milankovitch's cycles, produced by variations of astronomical parameters such as precession, obliquity and eccentricity; (ii) continental geodynamic evolution and orogenic belt; (iii) variations of atmospheric and oceanic currents; (iv) volcanic eruptions; (v) meteor impacts. But while astronomical parameters have a quasi-regular periodicity, the other phenomena can be considered as "noise signal" in natural systems. The interplay between cyclical astronomical variations, the "noise signal" and the intrinsic nonlinearity of the ecologic system produces strong glacial or interglacial period according to the stochastic resonance phenomenon.

Relationships between aerosol optical depth and surface-layer extinction in the central part of the Upper Silesia industrial region over the period of 1983–1994

The subject of analysis is the aerosol optical depth (AOD) in the visible part of the solar spectrum ( τ vis ) (wavelength λ = 0.295 – 0.695 μ m ). Calculation of τ vis -values was based on pyrheliometric observation data performed from 1983 to 1994 at IEIA's station (Katowice-Załęże). This paper examines the dependence of τ vis and its relation to surface-layer extinction coefficient σ (Koschmider quotient of 3.912 and visibility V ) on meteorological and anthropological factors during the observation period. Knowledge of the relationship between columnar aerosol turbidity (which can be expressed by τ vis ) and σ allows a more precise and accurate estimation of the aerosol effect on the radiative composition of climate. This work offers some contributions to solving this problem. Therefore, the relations have been described in the form of mathematical/statistical models of AOD (based on “momentary” and mean seasonal values), in which meteorological (and astronomical) parameters as well as the amount of industry dust emission were used as independent variables to improve exactness and credibility in the models.

MAGNETOSTRATIGRAPHY OF THE HOMO -BEARING PLEISTOCENE DANDIERO BASIN (DANAKIL DEPRESSION, ERITREA)

Four magnetozones have been found in the 530 m thick profile of the Dandiero Group. The lower unit, the Bukra Sand and Gravel, extends in the R1 reversed magnetozone from 150 m below the tephra level which was used as the reference marker between the sampled sections. The normal magnetozone N1 is almost completely covered by the lacustrine and deltaic sediments of the Alat Formation, while the following reversed magnetozone contains both the Wara Sand and Gravel and the lacustrine Goreya Fm. The N2 polarity zone is completely occupied by the Aro Sand. This polarity sequence has been calibrated to the geomagnetic time scale using the Early to Middle Pleistocene age of the associated vertebrate fauna and fission-track dating. The four magnetozones were thus regarded as representing the chrons by which the Pleistocene is correlated with magnetochronology. Their three reversal boundaries provided the dates of 1.07, 0.99 and 0.78 Ma, allowing to determine average sedimentation rates close to 1 m/ky. Cyclostratigraphy of the magnetic signal, analysed by the spectral analysis of the time series across the Jaramillo and late Matuyama chrons, confirmed that value. The evidenced cyclicities were directly related to the alternating lithofacies, and both to the astronomical parameters driving the climate changes during the deposition of the Dandiero group (some five hundred thousand years). The section with the Homo site covers the Jaramillo/Matuyama boundary, and the Homo bed located 2 m below this limit is dated 0.992 Ma.