Teleconnection Patterns along the Asian Jet Associated with Different Combinations of Convection Oscillations over the Indian Continent and Western North Pacific during Summer

A zonal teleconnection has been found along the Asian jet over the Eurasian continent during summer.In this study,the authors investigated circulation anomalies in the extratropics,in particular for the zonal teleconnection,under different combinations of subtropical convection anomalies over the northern Indian continent (IND) and the western North Pacific (WNP).The outof-phase configuration (i.e.,stronger (weaker) IND convection and weaker (stronger) WNP convection) was found to be more common than the in-phase configuration (i.e.,stronger (weaker) IND convection and stronger (weaker) WNP convection),which is consistent with previous results.Composite results indicated that circulation anomalies for out-of-phase configurations of 30-60-day convection oscillations are much stronger in the middle latitudes than those for in-phase configurations.In addition,zonal teleconnection patterns are predominant for the out-of-phase configurations,particularly for the configuration of strong IND convection and weak WNP convection;however,they are either weak or obscure for the in-phase configurations.These results suggest that the zonal teleconnection pattern along the Asian jet is dependent on different combinations of the IND and WNP subtropical convection anomalies.     

Duration and extent of lunar volcanism: Comparison of 3D convection models to mare basalt ages

It is widely accepted that lunar volcanism started before the emplacement of the mare fills ( b.p.) and lasted for probably more than 3.0 Ga. While the early volcanic activity is relatively easy to understand from a thermal point of view, the late stages of volcanism are harder to explain, because a relatively small body like the Earth's Moon is expected to cool rapidly and any molten layer in the interior should solidify rather quickly. We present several thermal evolution models, in which we varied the boundary conditions at the model surface in order to evaluate the influence on the extent and lifetime of a molten layer in the lunar interior. To investigate the influence of a top insulating layer we used a fully three-dimensional spherical shell convection code for the modelling of the lunar thermal history. In all our models, a partial melt zone formed nearly immediately after the simulation started (early in lunar history), consistent with the identification of lunar cryptomare and early mare basalt volcanism on the Moon. Due to the characteristic thickening of the Moon's lithosphere the melt zone solidified from above. This suggests that the source regions of volcanic rock material proceeded to increasing depth with time. The rapid growth of a massive lithosphere kept the Moon's interior warm and prevented the melt zone from fast freezing. The lifetimes of the melt zones derived from our models are consistent with basalt ages obtained from crater chronology. We conclude that an insulating megaregolith layer is sufficient to prevent the interior from fast cooling, allowing for the thermal regime necessary for the production and eruption of young lava flows in Oceanus Procellarum.     

A simple model for solar isorotational contours

The solar convective zone, or SCZ, is nearly adiabatic and marginally convectively unstable. But, the SCZ is also in a state of differential rotation, and its dynamical stability properties are those of a weakly magnetized gas. This renders it far more prone to rapidly growing rotational baroclinic instabilities than a hydrodynamical system would be. These instabilities should be treated on the same footing as convective instabilities. If isentropic and isorotational surfaces coincide in the SCZ, the gas is marginally (un)stable to both convective and rotational disturbances. This is a plausible resolution for the instabilities associated with these more general rotating convective systems. This motivates an analysis of the thermal wind equation in which isentropes and isorotational surfaces are identical. The characteristics of this partial differential equation correspond to isorotation contours, and their form may be deduced even without precise knowledge of how the entropy and rotation are functionally related. Although the exact solution of the global SCZ problem in principle requires this knowledge, even the simplest models produce striking results in broad agreement with helioseismology data. This includes horizontal (i.e. quasi-spherical) isorotational contours at the poles, axial contours at the equator and approximately radial contours at mid-latitudes. The theory does not apply directly to the tachocline, where a simple thermal wind balance is not expected to be valid. The work presented here is subject to tests of self-consistency, among them the prediction that there should be a good agreement between isentropes and isorotational contours in sufficiently well-resolved large-scale numerical magnetohydrodynamics simulations.     

On the Excitation Mechanism of Solar Five-minute Oscillations

The excitation mechanism of solar five-minute oscillations is studied in the present paper. We calculated the non-adiabatic oscillations of low- and intermediate-degree (l = 1 − 25) g4-p39 modes for the Sun. Both the thermodynamic and dynamic couplings are taken into account by using our non-local and time-dependent theory of convection. The results show that all the lowfrequencyf- and p-modes with periods P > 5.4 min are pulsationally unstable, while the coupling between convection and oscillations is neglected. However, when the convection coupling is taken into account, all the g- and low-frequency f- and p-modes with periods longer than 16 minutes (except the low-degree p1-modes) and the high frequency p-modes with periods shorter than 3 minutes become stable, and the intermediate-frequency p-modes with period from 3 to 16 minutes are pulsationally unstable. The pulsation amplitude growth rates depend only on the frequency and almost do not depend on l. They achieve the maximum at ν 3700 μHz (or P 270 sec). The coupling between convection and oscillations plays a key role for stabilization of low-frequency f- and p-modes and excitation of intermediate-frequency p-modes. We propose that the solar 5-minute oscillations are not caused by any single excitation mechanism, but they are resulted from the combined effect of “regular” coupling between convection and oscillations and turbulent stochastic excitation. For low- and intermediatefrequency p-modes, the coupling between convection and oscillations dominates; while for high-frequency modes, stochastic excitation dominates.     

RegCM3模式在西北地区的应用研究Ⅱ:区域选择及参数化方案的敏感性

通过数值模拟方法,研究了降水对区域尺度、积云对流参数化等的敏感性.结果表明:由于较小区域尺度的模式内部场和大尺度分析场激发的外强迫之间有更强的束缚,这种束缚使得内外强迫更容易达到一致.小区域尺度模拟的降水型比大的区域尺度的模拟更好,但同时,大的区域尺度消弱了由于模式侧边界效应产生的虚假动力效应,模拟的降水在量值上更加接近于观测值.因此,进行区域气候模拟时,须根据需要对模式区域进行仔细的选择.结果同时表明,由于Grell方案倾向于模拟更多的对流降水,因此Kuo-Anthes方案对西北地区降水型和量值的模拟比Grell方案更接近于实际.由于地形对于降水的重要意义,在复杂地形下进行区域气候模拟时有必要在模式中仔细描述地形.     

ASYMMETRIC DISTRIBUTION OF CONVECTION ASSOCIATED WITH TROPICAL CYCLONES MAKING LANDFALL ON THE EAST CHINA COAST

The asymmetric distribution of convection associated with tropical cyclones making landfall on the east China coast is studied with black-body temperature (TBB) data from Fengyun-2 (FY-2) geostationary weather satellite. The convection in various quadrants of the TCs is examined for the period of -24 to 6 h relative to landfall. The convection to the southern side of the TCs was much more intense than that to the northern side during the whole landfall period. The convection to the western side of the TCs was stronger than that to the eastern side for the time -8 h before and at the landfall. After landfall, the situation reverses. The asymmetric convection of the TCs was partly due to the vertical wind shear and storm motion, and partly because the process of landfall restrained the convection in relevant quadrants. Besides, the orographic uplift along the east of China was favorable to the enhancement of convection in the eastern side of the TCs. From the characteristics of convective asymmetry of the TCs landing on the south and east of China, it is known that their main difference might be the included angle between the TC path and the coastline as well as the terrain along the coast.     

Archean plate tectonics, rise of Proterozoic supercontinentality and onset of regional, episodic stagnant-lid behavior

Intense devolatilization and chemical-density differentiation attended late-stage accretion of the primitive Earth; it lessened after crystallization of a magma mush ocean during continued cooling. By 4.3Ga, shallow seas were present, so surface temperatures had fallen far below the 1300, 1120, and 950°C low-pressure solidi of peridotite, basalt, and granite, respectively. At temperatures less than about half their solidi, such materials existed as lithosphere in the near-surface Hadean realm. Stagnant-lid convection probably did not occur because massive heat transfer necessitated vigorous crust–mantle overturn in the early, hot Earth. Instead, bottom-up mantle convection, including voluminous plume ascent, efficiently rid the planet of heat, but lessened over time. Plate thickening and broadening is reflected in the post-Hadean rock record. Stages of geologic evolution included: (a) 4.5–4.4Ga, early, chaotic magma mush ocean overturn and ephemeral lithospheric platelets; (b) 4.4–2.7Ga, growth of oceanic and diminutive continental plates, obliterated by return mantle flow prior to 4.0Ga, but the latter enlarging and gradually accumulating as largely submarine, sutured, sialic crust-capped lithospheric collages; (c) 2.7–1.0Ga, progressive assembly of old shields and younger orogenic belts into supercratonal plates characterized by continental freeboard, sedimentary differentiation, and episodic glaciation during transpolar drift, as well as onset of regionally, temporally limited stagnant-lid convection beneath supercontinents; (d) 1.0Ga-present, modern, laminar-flowing asthenospheric cells capped by giant, stately moving plates. Restriction of komatiitic lavas to the Archean, and of multicycle sediments, most ophiolite complexes ± alkaline igneous rocks, and high-pressure and ultrahigh-pressure metamorphic belts to progressively younger Proterozoic–Phanerozoic orogens reflects increasingly negative buoyancy of the cooler oceanic lithosphere. Attending supercontinent assembly, density instabilities of thickening oceanic plates increasingly began to dominate overturn of the suboceanic mantle as cold, top-down convection. Scales and dynamics of hot asthenospheric upwelling versus lithospheric foundering and asthenospheric return flow (bottom-up versus top-down) changed gradually over geologic time in response to planetary thermal relaxation.     

洋壳俯冲过程中的地幔楔上升对流：来自芝麻坊石榴子石二辉橄榄岩早期变质的证据

苏鲁超高压变质地体中发现了大量包裹在超高压（UHP）变质片麻岩和混合岩中的造山带石榴橄榄岩。根据它们的野外产出特征和全岩地球化学成分,其中一部分石榴橄榄岩的原岩来自于亏损地幔,后来被卷入俯冲陆壳并经受过俯冲陆壳产生的熔/流体的交代。但是,对这些岩石早期的亏损过程尚缺乏清晰的认识。本文报道了东海芝麻坊石榴子石二辉橄榄岩早期变质演化的新证据。根据详细的变质反应结构观察和矿物成分研究,芝麻坊石榴子石二辉橄榄岩在经历高压低温俯冲带型超高压变质之前经历了至少两期变质演化。其原岩矿物组合由石榴子石变斑晶的高Ca-Cr核部及其中包裹的高Mg单斜辉石、高Al-Cr斜方辉石和高Mg-Ni橄榄石所记录;指示芝麻坊石榴子石二辉橄榄岩的原岩为高温-高压的富集石榴子石二辉橄榄岩。第二期矿物组合为包裹在低Cr变斑晶石榴子石幔部和细粒新生石榴子石核部的大量富Al铬铁矿和高Mg低Ni橄榄石以及少量高Mg斜方辉石。该期组合未发现单斜辉石,表明岩石随后被转变为高温低压的难熔尖晶石方辉橄榄岩或尖晶石纯橄岩。芝麻坊石榴子石二辉橄榄岩的早期变质演化记录了它们被卷入大陆板片俯冲带之前的地幔楔上升对流过程。笔者认为芝麻坊石榴子石二辉橄榄岩的原岩来源于早期俯冲大洋板片之上的深部高温富集地幔楔,洋壳俯冲过程中的地幔楔对流导致其上升到弧后或岛弧之下的地幔楔浅部,减压部分熔融使原本富集的石榴子石二辉橄榄岩转化为难熔的尖晶石方辉橄榄岩或尖晶石纯橄岩。     

A possible mechanism of inversion of the vertical lithosphere movements in the back-arc basins of the West Pacific region

We present results of the study of a three-layer tectonosphere model of the West Pacific Transition Zone based on modeling of a piecewise inhomogeneous medium caused by local density reduction of the asthenosphere, whose viscosity decreases due to fluid accumulation. We used the viscous liquid motion equation in the Stokes approximation. It was shown that the anomalous asthenosphere in the back-arc basins can move as a convective cell with an uprising flow in the zone of maximum density reduction and extension of the lithosphere above it. At the initial stages, this process causes formation of the central crustal uplift, which is transformed into a system of depressions as the asthenosphere viscosity decreases to values of the order of 4.0 × 10¹⁹ Pa s and lower. The modeling results satisfactorily agree with the reconstructions of the Cretaceous Cenozoic lithotectonic evolution of the Okhotsk Sea region.     

短波辐射对东北冷涡强对流影响的模拟分析

针对短波辐射对东北冷涡强对流的可能影响,应用MM5模式对2002年7月12日东北冷涡诱发的强风暴个例进行了数值模拟试验.发现在东北冷涡天气尺度环流背景下,大气接收的短波辐射通过激发中尺度环流影响强对流的发生时间,而不是通过影响不稳定能量的积累触发强对流;地面短波辐射对对流层低层大气的加热作用是触发本次东北冷涡强对流的重要条件.地面短波辐射加热在对流层低层产生中尺度辐合扰动及对流不稳定层结共同促使了对流的爆发和维持.