A MATHEMATICAL MODEL OF MIGRATION AND EXPANSION OF MEANDER LOOPS

This article presents a mathematical model of the plane evolution of alluvial meandering streams,through downstream migration and lateral expansion of meander loops.Under the conditions prevailing in natural streams,the channel centerlines follow sine-generated curves,with an assumed steady-state turbulent and subcritical flow,of large width-to-depth ratio（≥ 15,for example） and small Froude number（Fr ）.The plane deformation of the channel is caused by the action on the banks of the convective vertically-averaged meandering flow.The growth（migration and expansion） of meander loops is attributed to the regime-trend.The computational results of the model show that the obtained migration and expansion patterns of the meander loops are in good agreement with those of observations and measurements in similar meandering streams.

The development process of a temperate montane peatland and its controlling factors since the middle Holocene

Peatlands are some of the largest carbon reservoirs in terrestrial ecosystems and play a key role in the global carbon cycle.Understanding peatland development,carbon accumulation processes,and the peatland response to varying forcing factors over different temporal and spatial scales helps reveal the underlying processes and general patterns of these ecosystems.To assess the role of climate and local conditions in peatland development,the basal samples from 23 peat cores and three well dated long peat cores were used to explore peatland initiation,lateral expansion,and carbon accumulation rate in the Baijianghe peatland located in the Changbai Mountains,Northeast China.Our results reveal that the Baijianghe peatland was initiated from forest conditions at 7.9 cal.kyr BP and then expanded laterally by paludification.The rapid expansion between 5 and4 cal.kyr BP likely resulted from high precipitation and gentle topography.The mean carbon accumulation rates of the three long peat cores were 36.3,39.1 and 48.4 g C m^(-2)yr^(-1),respectively,which are higher than rates from the northern peatlands.Both climate and local conditions have exerted an important influence on carbon accumulation rates in the Baijianghe peatland since the middle Holocene.The carbon accumulation patterns between 5 and 1.5 cal.kyr BP were probably linked to local conditions rather than climatic settings,including topography,hydrological conditions,and plant composition.The consistently decreasing carbon accumulation rate values at all locations within the BJH peatland over the last 1.5 cal.kyr BP suggests that climate is the primary control.This study highlights the varying primary controls on the process of peatland development and reveals the important role of local conditions in carbon accumulation.

Advances in Research on Atmospheric Energy Propagation and the Interactions between Different Latitudes

Early theoretical analyses indicated that the tropics and extratropics are relatively independent due to the existence of critical latitudes.However,considerable observational evidence has shown that a clear dynamical link exists between the tropics and midlatitudes.To better understand such atmospheric teleconnection,several theories of wave energy propagation are reviewed in this paper：（1） great circle theory,which reveals the characteristics of Rossby waves propagating in the spherical atmosphere;（2） westerly duct theory,which suggests a ＂corridor＂ through which the midlatitude disturbances in one hemisphere can propagate into the other hemisphere;（3） energy accumulation-wave emanation theory,which proposes processes through which tropical disturbances can affect the atmospheric motion in higher latitudes;（4） equatorial wave expansion theory,which further explains the physical mechanisms involved in the interaction between the tropics and extratropics;and（5） meridional basic flow theory,which argues that stationary waves can propagate across the tropical easterlies under certain conditions.In addition,the progress made in diagnosing wave-flow interaction,particularly for Rossby waves,inertial-gravity waves,and Kelvin waves,is also reviewed.The meridional propagation of atmospheric energy exhibits significant annual and interannual variations,closely related to ENSO and variation in the westerly jets and tropical upper-tropospheric troughs,amongst others.