到底什么因素引起重力加速度随纬度变化

地球表面的重力加速度大小随纬度变化、赤道圈最小、两极最小。变化过程中并不是均匀变化的，本文讨论引起这一变化的因素。

地缘人类学

人类5000年发展历史研究表明:越趋于寒带、阴霾越重的高纬度地区,民族性格越严谨、缜密;同一物种在越冷的地方个体体积越大,外形越接近球形,而这是生物在漫长进化过程中适应环境变化的结果,地球纬度对人类命运的影响较大。

Dynamic Seasonal Transition from Winter to Summer in the Northern Hemisphere Stratosphere

This study applied the modified spatial similarity coefficient method to define the seasonal transition(ST) from winter to summer in the extratropical stratosphere of the Northern Hemisphere.The features of the ST were examined using European Centre for Medium-Range Weather Forecasts(ECMWF) Interim reanalysis data;and the results showed that the time and duration of the ST,which is affected by the activity of planetary waves(PW) in the stratosphere,largely depended on the geophysical locations.This study also investigated the interannual variability of the ST and its relationship with stratospheric sudden warming(SSW) and the quasi-biennial oscillation(QBO).It was shown that the late-onset SSW events(after 22 January) are close to the start of the ST.An easterly(westerly) QBO hastens(delays) the onset of the ST in high and low latitudes,whereas it delays(hastens) the ST in midlatitudes.The duration of the ST is significantly affected by the QBO.The influence of SSW and the QBO have different significance in different latitudes,so they are both important and irreplaceable factors.

Comparison and Analysis of Agricultural and Forest Land Changes in Typical Agricultural Regions of Northern Mid-latitudes

The northeastern China, the United States, and the western Europe are important agricultural regions both on the global and regional scales. The westem Europe has a longer history of agricultural land development than the eastem United States. These two regions have changed from the deforestation and reclamation phase in the past to the current land abandonment and reforestation phase. Compared with the two regions, large-scale land exploitation has only been practiced in the northeastern China during the last century. After a short high-intensity deforestation and reclamation period, agricultural and forest lands are basically in a dynamic steady state. By comparing domestic and international agro-forestry development and considering the ecological environment and socio-economic bene- fits that can be derived from agro-forestry, this paper suggests that large area of reforestation would be inevitable in future though per- sistent and large agricultural demand in coming decades even more. And local reforestation at slope farmland with ecological vulner- ability should be imperative at present to avoid severer damage. At the same time, from the perspective of Land Change Science, the results demonstrate that the research on land use change in the agro-forestry ecotone is typical and critical, particularly those dealing with the analysis of spatial and temporal characteristics and the simulation of climate, hydrology, and other environmental effects.

Projections of 2.0°C Warming over the Globe and China under RCP4.5

The outputs of 17 models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) are employed to investigate the temporal and spatial features of 2.0°C warming of the surface temperature over the globe and China under the Representative Concentration Pathways (RCP) 4.5 scenario. The simulations of the period 1860-1899 in the "historical" experiment are chosen as the baseline. The simulations for the 21st century in the RCP4.5 experiment are chosen as the future project. The multi-model ensemble mean (MME) shows that the global mean temperature would cross the 2.0°C warming threshold in 2047. Warming in most of the models would cross the threshold during 2030-2060. For local warming, high-latitude areas in the Northern Hemisphere show the fastest warming over the globe. Land areas warm substantially faster than the oceans. Most of the southern oceans would not exceed the 2.0°C warming threshold within the 21st century. Over China, surface warming is substantially faster than the global mean. The area-averaged warming would cross the 2.0°C threshold in 2034. Locally, Northwest China shows the fastest warming trend, followed by Central North China and Northeast China. Central China, East China, and South China are the last to cross the 2.0°C warming threshold. The diversity of the models is also estimated in this study. Generally, the spread among the models increases with time, and there is smaller spread among the models for the areas with the faster warming.

Northern-Hemisphere Snow Cover Patterns and Formation Conditions in Winter 2007 and 2012

The Arctic sea ice minimum records appeared in the Septembers of 2007 and 2012, followed by high snow cover areas in the Northern Hemisphere winters. The snow cover distributions show different spatial patterns in these two years: increased snow cover in Central Asia and Central North America in 2007, while increased snow cover in East Asia and northwestern Europe in 2012. The high snow cover anomaly shifted to higher latitudes in winter of 2012 compared to 2007. It is noticed that the snow cover had positive anomaly in 2007 and 2012 with the following conditions: the negative geopotential height and the related cyclonic wind anomaly were favorable for upwelling, and, with the above conditions, the low troposphere and surface air temperature anomaly and water vapor anomaly were favorable for the formation and maintenance of snowfalls. The negative geopotential height, cyclonic wind and low air temperature conditions were satisfied in different locations in 2007 and 2012, resulting in different spatial snow cover patterns. The cross section of lower air temperature move to higher latitudes in winter of 2012 compared to 2007.

滴水法测量重力加速度实验及分析

在物理中,重力加速度g是一个特别重要的物理量,无论它在地面上哪个地区,其值都是不相同的。重力加速度g的大小是由物体所在地区的海拔、纬度等因素决定,随着海拔高度和地球纬度的变化而变化。在理论、科研、生产以及军事上,精确地测量它的量值,都有十分重大的意义。重力加速度g的测量方法各种各样,我所做的主要是通过学习前人的理论知识,采用简单的滴水法来测量重力加速度,并归纳和总结,提出自己的看法与体会。一、实验仪器:秒表,输液瓶及输液管,胶布,米尺,塑料瓶,铁盘。

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Plume-ridge interaction induced migration of the Hawaiian-Emperor seamounts

The history of the Hawaiian hotspot is of enduring interest in studies of plate motion and mantle flow,and has been investigated by many researchers using the detailed history of the Hawaiian-Emperor Seamount chain.One of the unexplained aspects of this history is the apparent offset of several Emperor seamounts from the Hawaii plume track.Here we show that the volcanic migration rates of the Emperor seamounts based on existing data are inconsistent with the drifting rate of the Pacific plate,and indicate northward and then southward “absolute movements”of the seamounts.Numerical modeling suggests that attraction and capture of the upper part of the plume by a moving spreading ridge led to variation in the location of the plume’s magmatic output at the surface.Flow of the plume material towards the ridge led to apparent southward movement of Meiji.Then,the upper part of the plume was carried northward until 65 Ma ago.After the ridge and the plume became sufficiently separated,magmatic output moved back to be centered over the plume stem.These changes are apparent in variations in the volume of seamounts along the plume track.Chemical and isotopic compositions of basalt from the Emperor Seamount chain changed from depleted(strong mid-ocean ridge affinity)in Meiji and Detroit to enriched(ocean island type),supporting declining influence from the ridge.Although its surface expression was modified by mantle flow and by plume-ridge interactions,the stem of the Hawaiian plume may have been essentially stationary during the Emperor period.

SuperDARN CUTLASS Finland radar observations of high-latitude magnetic reconnections under northward interplanetary magnetic field (IMF) conditions

A number of backscatter power enhancement events with ＂equatorward-moving radar auroral forms＂ in the high-latitude ionosphere were observed by SuperDARN CUTLASS Finland radar when the IMF was northward during 09：00 -10：00 UT on 26 March 2004. These events were also associated with sunward flow enhancements at each location in the Northern Hemisphere which were shown in ionospheric convections measured by the SuperDARN radars. These are typical features of high-latitude （lobe） magnetic reconnections. The durations of the velocity enhancements imply that the evolution time of the lobe reconnec- tions is about 8-16 rain from their origin at the reconnection site to their addition to the magnetotall lobe again. In additional, the Double Star TC-1 spacecraft was moving from magnetosheath into magnetosphere, and crossing the magnetopause near the subsolar region during this interval, and observed typical low-latitude magnetic reconnection signatures. This infers that the dayside high- and low-latitude reconnections may occur simultaneously.

Comparing simulated atmospheric carbon dioxide concentration with GOSAT retrievals

Satellite observations of atmospheric carbon dioxide （CO2） provide a useful way to improve the understanding of global carbon cycling. In this paper, we present a comparison between simulated CO2 concentrations from an inversion model of the CarbonTracker Data Assimilation System （CTDAS） and satellite-based CO2 measurements of column-averaged dry air mole fraction （denoted XCO2） derived from version 3.3 Atmospheric CO2 Observations from Space retrievals of the Greenhouse Gases Observing SATellite （ACOS-GOSAT） L2 data products. We examine the differences of CTDAS and GOSAT to provide important guidance for the further investigation of CTDAS in order to quantify the corre- sponding flux estimates with satellite-based CO2 observations. We find that the mean point-by-point difference （CTDAS-GOSAT） between CTDAS and GOSAT XCO2 is -0.11 4-1.81 ppm, with a high agreement （correlation r = 0.77, P 〈 0.05） over the studied period. The latitudinal zonal variations of CTDAS and GOSAT are in general agreement with clear seasonal fluctuations. The major exception occurs in the zonal band of 0°-15°N where the difference is approximately 4 ppm, indicating that large uncertainty may exist in the assimilated CO2 for the low- latitude region of the Northem Hemisphere （NH）. Additionally, we find that the hemispherical/continental differences between CTDAS and GOSAT are typically less than 1 ppm, but obvious discrepancies occur in different hemispheres/continents, with high consistency （point-by-point correlation r = 0.79, P 〈 0.05） in the NH and a weak correlation （point-by-point correlation r = 0.65, P 〈 0.05） in the Southern Hemisphere. Overall, the difference of CTDAS and GOSAT is small, and the comparison of CTDAS and GOSAT will further instruct the inverse modeling of CO2 fluxes using GOSAT.