A global context for megadroughts in monsoon Asia during the past millennium

Proxy reconstructions of precipitation from central India, north-central China, and southern Vietnam reveal a series of monsoon droughts during the mid 14th–15th centuries that each lasted for several years to decades. These monsoon megadroughts have no analog during the instrumental period. They occurred in the context of widespread thermal and hydrologic climate anomalies marking the onset of the Little Ice Age (LIA) and appear to have played a major role in shaping significant regional societal changes at that time. New tree ring-width based reconstructions of monsoon variability suggest episodic and widespread reoccurrences of monsoon megadroughts continued throughout the LIA. Although the El-Niño Southern Oscillation (ENSO) plays an important role in monsoon variability, there is no conclusive evidence to suggest that these megadroughts were associated with anomalous sea surface temperature anomalies that were solely the result of ENSO-like variability in the tropical Pacific. Instead, the causative mechanisms of these megadroughts may reside in protracted changes in the synoptic-scale monsoon climatology of the Indian Ocean. Today, the intra-seasonal monsoon variability is dominated by ‘active’ and the ‘break’ spells – two distinct oscillatory modes of monsoon that have radically different synoptic scale circulation and precipitation patterns. We suggest that protracted locking of the monsoon into the “break-dominated” mode – a mode that favors reduced precipitation over the Indian sub-continent and SE Asia and enhanced precipitation over the equatorial Indian Ocean, may have caused these exceptional droughts. Impetus for periodic locking of the monsoon into this mode may have been provided by cooler temperatures at the extratropical latitudes in the Northern Hemisphere which forced the mean position of the Inter-Tropical Convergence Zone (ITCZ) further southward in the Indian Ocean.     

Horizontal and vertical winds and temperatures in the equatorial thermosphere: Measurements from Natal,Brazil during August–September 1982

Fabry-Perot interferometer measurements of Doppler shifts and widths of the 630.0 nm nightglow line have been used to determine the neutral winds and temperatures in the equatorial thermosphere over Natal, Brazil during August–September 1982. During this period, in the early night (2130 U.T.) the average value of the horizontal wind vector was 95 m s^?1 at 100° azimuth, and the temperature varied from a low of 950 K during geomagnetically quiet conditions to a high of ~ 1400 K during a storm (6 September). The meridional winds were small, ?, 50 m s^?1, and the eastward zonal winds reached a maximum value 1–3 h after sunset, in qualitative agreement with TGCM predictions. On 26 August, an observed persistent convergence in the horizontal meridional flow was accompanied by a downward vertical velocity and an increase in the thermospheric temperature measured overhead. Oscillations with periods of 40–45 min in both the zonal and vertical wind velocities were observed during the geomagnetic storm of 6 September, suggesting gravity wave modulation of the equatorial thermospheric flow.     

On the formation of the rings of saturn

It is shown in this paper that a satellite which revolves round a primary in a circular orbit in tied revolution and which spirals within Roche's limit must form by its disintegration a ring of ellipse-like cross-section which is more than 11 times larger than the original spherical diameter of the disintegrating body. The individual particles have elliptic orbits with small eccentricities and revolve in different planes at small inclinations to each other. By inelastic collisions of particles in differently inclined orbits the original considerable thickness of the ring is very greatly reduced.

Applied to the system of Saturn it is assumed that the Rings A and B are formed by disintegration of two different satellites. It can be shown that the satellite A had an original diameter of 1721 km and a density of 0.95 g/cm³, the satellite B a diameter of 2463 km and a density of 1.95.

Thus the hypothesis of G. P. Kuiper, that the rings of Saturn are composed of H²O-snow contaminated by silicate dust (as Jupiter III), seems to fit very well.     

Spectroscopic characterisation and crystal field calculations of varicoloured kyanites from Loliondo, Tanzania

Orange, ochre-coloured, light green and dark blue varieties of kyanite, ideally Al₂SiO₅, from Loliondo, Tanzania, have been characterised by electron microprobe analysis and polarised infrared and optical absorption spectroscopy. All colour varieties show elevated Fe contents of 0.39 to 1.31 wt.% FeO, but Ti contents only in the range of the EMP detection limit. Orange and ochre-coloured crystals have Mn contents of 0.23 and 0.06 wt.% MnO, respectively, the dark blue kyanite contains 0.28 wt.% Cr₂O₃, while the light green sample is nearly free from transition metal cations other than Fe. Polarised infrared spectra reveal OH defect concentrations of 3 to 17 wt.ppm H₂O with structural OH defects partially replacing the O_B (O2) oxygen atoms. Polarised optical absorption spectra show that the colour of all four varieties is governed by crystal field d-d transitions of trivalent cations, i.e. Fe³⁺ (all samples), Mn³⁺ (orange and ochre) and Cr³⁺ (blue kyanite), replacing Al in sixfold coordinated triclinic sites of the kyanite structure. Intervalence charge transfer, the prevalent colour-inducing mechanism in ‘usual’ (Cr-poor) blue kyanites, seems to play a very minor, if any, role in the present samples. Crystal field calculations in both a ‘classic’ tetragonal and in the semiempirical Superposition Model approach, accompanied by distance- and angle-least-squares refinements, indicate that Fe³⁺ preferably occupies the Al4 site, Cr³⁺ prefers the Al1 and Al2 sites, and Mn³⁺ predominantly enters the Al1 site. In each case specific local relaxation effects were observed according to the crystal chemical preferences of these transition metal cations. Furthermore, the high values obtained in the calculations for the interelectronic repulsion parameter Racah B correspond to a high ionic contribution to Me³⁺–O bonding in the kyanite structure. In the particular case of the blue sample, band positions specifically related to the high Racah B value enable this ‘unusual’ type of blue colouration of kyanite solely due to Cr³⁺ cations.     

Geochemical and petrological characteristics of Eppawala phosphate deposits,Sri Lanka

The apatite-bearing carbonate rocks at Eppawala, Sri Lanka occur as massive, discontinuous bodies in a Precambrian, high-grade metamorphic terrain, which weather to form economically important phosphate deposits. The ore bodies at Eppawala contain =42% P ₂O ₅, and citric acid solubility of different components varies from 4 to 6%. The parent rocks are mainly made up of calcite, dolomite and apatite, with lesser amounts of ilmenite, magnetite, pyrite, forsterite, phlogopite, enstatite, magnesite, diopside, tremolite and spinel. Most of minerals show an euhedral habit, with a wide range of crystal sizes (from a few millimetres to several decimetres). The Eppawala rocks are characterised by low silica (=0.41%), high phosphorous (=10.58%) and high strontium content (2,960–6,819 ppm). Concentrations of light rare-earth elements in these rocks are comparably higher than those of marbles. The REE fractionation of these rocks is pronounced, and La/Yb ratios vary between 14 and 43. Both apatite and calcite show markedly elevated strontium levels (=0.6%). The d ¹³C _PDB and d ¹⁸O _SMOW values of the carbonates are in the range of –3.4 to –2.2 and 7.7 to 16.4‰ respectively. The euhedral habit, as well as the presence of major quantities of apatite and considerable amounts of iron-bearing minerals suggest that the ore host rock has genetic links to an igneous source rather than to an intensely metamorphosed limestone. The higher light REE contents of the rocks, compared to marbles, also argue against a metamorphic or sedimentary origin. The Sr/Mn and Ce/La ratios in the apatite are ~40 and ~2 respectively, suggesting that they were formed in a carbonatite magma. The markedly increased REE concentrations in the bulk chemistry of the rocks have been shown to be mainly controlled by the content of phosphate minerals. Compared to most carbonatites, the Eppawala rocks are generally depleted in selected trace elements, particularly Ba, Nb, Th, V, U and Zr. This depletion may be due to either a primary infertility of the parent magma with regard to such trace elements, or it is a result of fractional crystallisation during the rock formation. The stable isotope ratios do not plot within the defined "mantle carbonatite box", but still lie within the broader range of carbonatitic rocks. With these data at hand, it can be readily argued that the mode of occurrence, petrography and geochemistry of the Eppawala apatite-bearing carbonates provide conclusive evidence of their carbonatitic origin.     

Avoiding deforestation in Panamanian protected areas: An analysis of protection effectiveness and implications for reducing emissions from deforestation and forest degradation

Reducing greenhouse gas emissions from deforestation and forest degradation (REDD) is likely to be central to a post-Kyoto climate change mitigation agreement. As such, identifying conditions and factors that will shape the success or failure of a reduced deforestation scheme will provide important insights for policy planning. Given that protected areas (PAs) are a cornerstone in forest conservation, we draw on interviews and secondary data to analyze the effects of available PA resources, governance ability, the level of community involvement, and provincial deforestation rates on land-cover change in nine PAs in Panama. Our results illustrate that coupling surveillance measures with greater funding and strong governance are paramount to reducing deforestation. Alone, however, these factors are insufficient for forest protection. We argue that conservation approaches that complement effective surveillance with community participation and equitable benefit sharing will address the wider issues of leakage and permanence.     

A proxy record of winter temperatures since 1836 from ice freeze-up/breakup in lake N?sij?rvi, Finland

One obstacle on the way to a comprehensive spatial reconstruction of regional temperature changes over the past centuries is the sparseness of long winter temperature records. This paper reconstructs a proxy record of April and November–December temperatures in south-central Finland for the interval from 1836 to 1872 from breakup and freeze-up dates and ice-cover duration of a lake. Emphasis is on detecting the suitable winter months and quantifying the calibrations with measured temperatures (1873–2002). The calibration slope for the breakup date (0.158°C/day) is larger than for freeze-up date (0.119°C/day) or duration (0.090°C/day). A comparison with results from other proxy records shows that the slope may depend also on the geographical site. Trend analyses of the full temperature records (1836–2002) indicate the existence of minor change-points at around 1867 (April temperature) and 1874 (November–December temperature), with warming rates thereafter of 1.67°C per century (April) and 1.16°C per century (November–December). Spectral analyses reveal peaks in the band between 2 and 5?year period, which may point to influences of the North Atlantic Oscillation, and less power in the decadal band (up to 42?year period).