Structures and mechanisms of the first-branch northward-propagating intraseasonal oscillation over the tropical Indian Ocean

The first-branch northward-propagating intraseasonal oscillation (FNISO) over the tropical Indian Ocean (IO) often triggers the onset of the Asian summer monsoon. In this study we investigate the structures and mechanisms associated with FNISO through the diagnosis of ERA-Interim reanalysis data for the period of 1990–2009. A composite analysis is conducted to reveal the structure and evolution characteristics of the FNISO and associated background circulation changes. It is found that the FNISO convection originates from the southwestern IO and propagates eastward. After reaching the eastern IO, the major convective branch moves northward toward the northern Bay of Bengal (BoB). Two possible mechanisms may contribute to the northward propagation of the FNISO. One is the meridional asymmetry of the background convective instability. A greater background convective instability over the northern BoB may destabilize Rossby waves and cause convection to shift northward. The other is the meridional phase leading of perturbation humidity in the planetary boundary layer (PBL). Maximum PBL moisture appears to the north of the convection center, which promotes a convectively unstable stratification ahead of the convection and leads to the northward propagation of the FNISO. A PBL moisture budget analysis reveals that anomalous zonal advection is a dominant process in contributing to the moisture asymmetry.     

Comparison of the ENEAR peculiar velocities with the PSCz gravity field

We present a comparison between the peculiar velocity field measured from the ENEAR all-sky D _n– σ catalogue and that derived from the galaxy distribution of the IRAS Point Source Catalog Redshift Survey (PSC z ). The analysis is based on a modal expansion of these data in redshift space by means of spherical harmonics and Bessel functions. The effective smoothing scale of the expansion is almost linear with redshift reaching 1500 km s⁻¹ at 3000 km s⁻¹. The general flow patterns in the filtered ENEAR and PSC z velocity fields agree well within 6000 km s⁻¹, assuming a linear biasing relation between the mass and the PSC z galaxies. The comparison allows us to determine the parameter     where Ω is the cosmological density parameter and b is the linear biasing factor. A likelihood analysis of the ENEAR and PSC z modes yields     in good agreement with values obtained from Tully–Fisher surveys.     

Rural sustainability under threat in Zimbabwe – Simulation of future land use/cover changes in the Bindura district based on the Markov-cellular automata model

Spatially explicit land use/cover models are indispensable for sustainable rural land use planning, particularly in southern African countries that are experiencing rapid land use/cover changes. Using Zimbabwe as an example, we simulated future land use/cover changes up to 2030 based on a Markov-cellular automata model that integrates Markovian transition probabilities computed from satellite-derived land use/cover maps and a cellular automata spatial filter. A multicriteria evaluation (MCE) procedure was used to generate transition potential maps from biophysical and socioeconomic data. Dynamic adjustments of transition probabilities and transition potential map thresholds were implemented in the Markov-cellular automata model through a multi-objective land allocation (MOLA) procedure. Using the normalised transition probabilities, the Markov-cellular automata model simulated future land use/cover changes (up to 2030) under the 2000 calibration scenario, predicting a continuing downward trend in woodland areas and an upward trend in bareland areas. Future land use/cover simulations indicated that if the current land use/cover trends continue in the study area without holistic sustainable development measures, severe land degradation will ensue.     

Analytic solutions for coupled linear perturbations

Analytic solutions for the evolution of cosmological linear density perturbations in the baryonic gas and collisionless dark matter are derived. The solutions are expressed in a closed form in terms of elementary functions, for arbitrary baryonic mass fraction. They are obtained assuming =1 and a time-independent comoving Jeans wavenumber, k _J. By working with a time variable ln( t ^2/3), the evolution of the perturbations is described by linear differential equations with constant coefficients. The new equations are then solved by means of Laplace transformation, assuming that the gas and dark matter trace the same density field before a sudden heating epoch. In a dark matter-dominated Universe, the ratio of baryonic to dark matter density perturbation decays with time roughly as exp(5 /4) t ^5/6 to the limiting value 1/[1+( k k _J)²]. For wavenumbers the decay is accompanied by oscillations with a period in . In comparison, as increases in a baryonic matter-dominated Universe, the ratio approaches 1( k k _J)² for k k _J, and zero otherwise.     

太平洋-印度洋贯穿流南海分支在卡里马塔海峡的十年观测回顾

除印度尼西亚贯穿流之外,南海贯穿流也是太平洋向印度洋输送海水的重要分支。尽管基于数值模拟等方法的研究早已指出,南海分支在太平洋-印度洋洋际交换中有重要作用,但是直到2007年之前,南海分支在卡里马塔海峡处的观测几乎是空白。本文回顾了自2007年起,通过中印尼合作项目"南海-印度尼西亚海水交换及对鱼类季节性洄游的影响（SITE）"在卡里马塔海峡开展的近十年观测,以及在此基础上进一步开展的"印度尼西亚贯穿流海域水交换、内波和混合观测及其生态效应（TIMIT）"观测项目,并对SITE和TIMIT观测取得的成果进行了总结。     

Modelling the formation of galaxy clusters in MOND

We present time-resolved spectroscopy and photometry of the cataclysmic variable (CV) SDSS J133941.11+484727.5 (SDSS 1339) which has been discovered in the Sloan Digital Sky Survey (SDSS) Data Release 4. The orbital period determined from radial velocity studies is 82.524(24) min, close to the observed period minimum. The optical spectrum of SDSS 1339 is dominated to 90 per cent by emission from the white dwarf (WD). The spectrum can be successfully reproduced by a three-component model (white dwarf, disc, secondary) with   T _WD=12 500 K  for a fixed  log   g = 8.0, d = 170 pc  , and a spectral type of the secondary later than M8. The mass-transfer rate corresponding to the optical luminosity of the accretion disc is very low,  ≃ 1.7 × 10⁻¹³ M_⊙ yr⁻¹  . Optical photometry reveals a coherent variability at 641 s with an amplitude of 0.025 mag, which we interpret as non-radial pulsations of the white dwarf. In addition, a long-period photometric variation with a period of either 320 or 344 min and an amplitude of 0.025 mag is detected, which bears no apparent relation with the orbital period of the system. Similar long-period photometric signals have been found in the CVs SDSS J123813.73−033933.0, SDSS J204817.85−061044.8, GW Lib and FS Aur, but so far no working model for this behaviour is available.