Periods Of Minima Research Articles

Changes in the Total Solar Irradiance and climatic effects

The correlation between the averaged reconstructed March temperature record for Kyoto, Japan, and the reconstructed Total Solar Irradiance (TSI) over 660 years from 1230 to 1890 gives evidence with 98% probability that the Little Ice Age with four cold periods is forced by variations of TSI. If the correlation is restricted to the period 1650–1890, with two cold periods in the 17th and 19th century and for which two independent reconstructed March temperature records are available, the probability of solar forcing increases to 99.99%. As solar irradiance variations have a global effect there has to be a global climatic solar forcing impact. However, by how much global temperature were lower during these minima and with what amplitude TSI was varying is not accurately known. The two quantities, global temperature and TSI, are linked by the energy equilibrium equation for the Earth system. The derivation of this equation with respect to a variation of the solar irradiance has two terms: A direct forcing term, which can be derived analytically and quantified accurately from the Stefan-Boltzmann law, and a second term, describing indirect influences on the surface temperature. If a small TSI variation should force a large temperature variation, then it has to be the second indirect term that strongly amplifies the effect of the direct forcing. The current knowledge is summarized by three statements:During the minima periods in the 13th, 15/16th, 17th, and 19th centuries the terrestrial climate was colder by 0.5–1.5 °C;Indirect Top-down and Bottom-up mechanisms do not amplify direct forcing by a large amount, i.e. indirect solar forcing is of the same magnitude (or smaller) as direct solar forcing;The radiative output of the Sun cannot be lower by more than 2 Wm−2 below the measured present-day TSI value during solar cycle minimum.These three statements contradict each other and it is concluded that at least one is not correct. Which one is a wrong statement is presently not known conclusively. It is argued that it is the third statement and it is speculated that over centennial time scales the Sun might vary its radiance significantly more than observed so far during the last 40 years of space TSI measurements. To produce Maunder minimum type cold climate excursions, a TSI decrease of the order of 10 Wm−2 is advocated.

Exceptional ocean surface conditions on the SE Greenland shelf during the Medieval Climate Anomaly

Diatom inferred 2900 year long records of August sea surface temperature (aSST) and April sea ice concentration (aSIC) are generated from a marine sediment core from the SE Greenland shelf with a special focus on the interval ca. 870–1910 Common Era (C.E.) reconstructed in subdecadal temporal resolution. The Medieval Climate Anomaly (MCA) between 1000 and 1200 C.E. represents the warmest ocean surface conditions of the SE Greenland shelf over the late Holocene (880 B.C.E.(before the Common Era) to 1910 C.E.). It was characterized by abrupt, decadal to multidecadal changes, such as an abrupt warming of ~2.4°C in 55 years around 1000 C.E. Temperature changes of these magnitudes are rare on the North Atlantic proxy data. Compared to regional air temperature reconstructions, our results indicate a lag of about 50 years in ocean surface warming either due to increased freshwater discharge from the Greenland ice sheet or intensified sea ice export from the Arctic as a response to atmospheric warming at the beginning of the MCA. A cool phase, from 1200–1890 C.E., associated with the Little Ice Age, ends with the rapid warming of aSST and diminished aSIC in the early twentieth century. The results show that the periods of warm aSST and aSIC minima are coupled with solar minima suggesting that solar forcing possibly amplified by atmospheric forcing have been behind the variability of surface conditions on the SE Greenland over the last millennium. The results indicate that the SE Greenland shelf is a climatologically sensitive area where extremely rapid changes are possible and highlights the importance of the area under the present warming conditions.

Chronological constraints on Pleistocene sapropel depositions from high-resolution geochemical records of ODP Sites 967 and 968

We completed and merged an existing high-resolution X-Ray Fluorescence (XRF) data set de- rived from Ocean Drilling Program (ODP) site 968 with new data from adjacent ODP site 967. An astro- nomical age model spanning the last 1.05 Myr was constructed for the spliced record using the highly linear relation between the elemental ratio of titanium and aluminum in the sediment (Ti/Al) and insolation. This rendered detailed ages for sapropel deposition in the Eastern Mediterranean. Our results imply major revi- sions of previous sapropel age models below MIS 11, with changes of up to two precession cycles in the in- terval ~ 450-850 ka of the ODP 967 sapropel chronology. Based on the Ti/Al age model, we find that color reflectance - used as an indicator for sapropels in this interval of ODP site 967 and 968 - is highly incon- gruent with the Ti/Al proxy as well as insolation forcing during periods of minima in the 405 kyr eccentrici- ty cycle. Our findings indicate that the use of color reflectance as a proxy for so-called ghost sapropels in these intervals is not reliable. Lastly, we demonstrate the presence of a strong obliquity signal in the Ti/Al record that lags obliquity forcing by 4 0.7 kyr). This time lag is only marginally longer than the adopted 2.7 1.1 kyr for the dominantly precession-tuned age model, and is hence much shorter than the generally accepted ice sheet response time to insolation forcing. This suggests that the obliquity-bound changes in Ti/Al are not glacial controlled and most likely reflect changes in low-latitude climate oscillations, such as the mon- soon.

Aftershock sequence analysis of 19 May, 2009 earthquake of Lunayyir lava flow, northwest Saudi Arabia

Aftershock sequence of 19th May, 2009 Lunayyir earthquake (Mw 5.7) has been recorded by deploying seismic stations immediately after the occurrence of the main shock. Analysis of this sequence clarified that; the major part of cumulative seismic moment released during the first hours after the occurrence of the main shock; their orientation is north west (NW) parallel to the Red Sea axial trend along Najd faulting system; it is clustered at two depths; from 5-10 and 15-25 km beneath Lunayyir area; illustrated successive periods of maxima and minima; decayed rapidly following the relation of n(t)=37.28 t-0.6. Fault plane solutions for five large events indicate normal faulting is the major mechanism. These findings are in agreement with the north east (NE) (transform fault) trend runs crossing the Red Sea into Shield area where the activity has been initiated and travelled through the Lunayyir area. While the NW Najd faulting system runs parallel to the Red Sea axial trend and intersected with NE fault trend underlying Lunayyir area. Accordingly, it can be concluded that, the recent earthquake activities at Lunayyir lava flow area are related to the present-day Red Sea tectonics. Monitoring earthquake activities through installing permanent seismic network around the area is highly recommended. Key words: aftershock sequence, fault plane solution, stress, and Lunayyir.

THE BEHAVIOR OF THE 17 GHz SOLAR RADIUS AND LIMB BRIGHTENING IN THE SPOTLESS MINIMUM XXIII/XXIV

The current solar minimum has surprised the entire solar community because the spotless period is presently almost 2-3 years longer than the usual minima. To better understand this, we studied the variation of the solar radius and the polar limb brightening at 17 GHz, comparing the results from the minimum at the end of cycle XXIII with those of the previous one. Daily maps obtained by the Nobeyama Radioheliograph (NoRH) from 1992 through 2010 were analyzed. Whereas the variation of the solar radius at radio frequencies indicates the heating of the solar atmosphere due to solar activity, the limb brightening intensity depends on the organization of the polar magnetic field of the Sun, including the global dipole and the features formed around it. These features are more prominent during minima periods. As a common result, researchers have observed a decrease in both radius and limb brightness intensity at 17 GHz during the present minimum when compared with the previous one. The mean solar radius is 09 ± 06 smaller and the limb brightening reduced its intensity by around 20%. Both decrements are interpreted in terms of the weaker solar chromospheric activity of the present cycle. Measurement of the radius and limb brightening at 17 GHz can be used as an alternative solar activity index and should be included in the set of parameters used to predict future cycles.

Mid-term periodicities of cosmic ray intensities

Galactic cosmic ray intensities (GCRs) observed by five neutron monitors (NMs) have been used to study cosmic ray modulations between 1971 and 2007. The influence of interplanetary magnetic polarity (IMF) states has been studied for the A < 0 and A > 0 epochs. A comparison of the spectra for both positive IMF polarities indicated different solar origins. The spectra have different power amplitudes and most peaks of different locations. In addition, the differences in the cosmic ray modulations, conditions for solar activity minima and maxima periods are probably associated with the influence of drift effects. The observed differences are related to the 22-year cycle in heliospheric modulations of cosmic rays, leading to the different shapes of CR maxima and the hysteresis effect. Accordingly, drift effects dependent on the polarity of the global solar magnetic field may play a significant role in the observed differences between maxima and minima periods. The drift mechanism is enhanced during periods of low to moderate SA, i.e., around solar cycle minima, during negative polarity periods, when A < 0.

Our Astronomical Column

SPECTRUM OF NOVA PERSEI.—In the current issue of Comptes rendus (vol. cxxxii. pp. 1542–1544) M. Deslandres gives a third series of observations of the spectrum of Nova Persei as obtained at the Meudon Observatory. Since the previous communication, spectrographs of varying power have been installed for use with the two telescopes of 0.84 metre and 0.60 metre aperture, and both photographic and visual records of the spectrum obtained during the periods of minima, although unfavourable weather has considerably interfered with their continuity. In this later work special attention has been devoted to the expected detection of the principal nebular lines. M. Deslandres states that during the first stages the principal green lines present were distinctly not the nebular lines, but the lines of parhelium, λ492 and λ5015, this being well shown in a photograph taken on March 3. On a plate taken on April 17, however, the measured position of the chief green line was λ5008, but on account of breadth of line the value is of course only approximate. The star was near its minimum brightness on this date. The gradual varying intensity of this line relative to the Hβ line of hydrogen is then described, the details being in close agreement with those already published by other observers.

On solar changes of temperature and variations in rainfall in the region surrounding the Indian Ocean

The fact that the abnormal behaviour of the widened lines in the spectra of sunspots since 1894 had been accompanied by irregularities in the rainfall of India suggested the study and correlation of various series of facts which might be expected to throw light upon the subject. The conclusions already arrived at from bringing together the results of several investigations undertaken with this view may be stated as follows:— (1.) It has been found, from a discussion of the chemical origin of lines most widened in sunspots at maxima and minima periods, that there is a considerable rise above the mean temperature of the sun around the years of sunspot maximum and a considerable fall around the years of sunspot minimum.