自由落体东偏南偏的讨论

本文在计算和讨论自由落体的东偏和南偏时,考虑了惯性离心力和科里奥利力．结果表明：由惯性离心力引起的南偏要比科里奥利力引起的南偏大的多．而落体的东偏则主要是由科里奥利力引起的．     

Reduced methane growth rate explained by decreased Northern Hemisphere microbial sources

Atmospheric methane (CH(4)) increased through much of the twentieth century, but this trend gradually weakened until a stable state was temporarily reached around the turn of the millennium, after which levels increased once more. The reasons for the slowdown are incompletely understood, with past work identifying changes in fossil fuel, wetland and agricultural sources and hydroxyl (OH) sinks as important causal factors. Here we show that the late-twentieth-century changes in the CH(4) growth rates are best explained by reduced microbial sources in the Northern Hemisphere. Our results, based on synchronous time series of atmospheric CH(4) mixing and (13)C/(12)C ratios and a two-box atmospheric model, indicate that the evolution of the mixing ratio requires no significant change in Southern Hemisphere sources between 1984 and 2005. Observed changes in the interhemispheric difference of (13)C effectively exclude reduced fossil fuel emissions as the primary cause of the slowdown. The (13)C observations are consistent with long-term reductions in agricultural emissions or another microbial source within the Northern Hemisphere. Approximately half (51?±?18%) of the decrease in Northern Hemisphere CH(4) emissions can be explained by reduced emissions from rice agriculture in Asia over the past three decades associated with increases in fertilizer application and reductions in water use.     

北半球斜上抛体的运动方程

给出了同时考虑地球自转和空气阻力两种影响并当空气阻力与抛体速度的一次方成正比时北半球斜上抛体运动方程的精确解。     

High-resolution record of Northern Hemisphere climate extending into the last interglacial period

Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 degrees C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.     

Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data

A number of reconstructions of millennial-scale climate variability have been carried out in order to understand patterns of natural climate variability, on decade to century timescales, and the role of anthropogenic forcing. These reconstructions have mainly used tree-ring data and other data sets of annual to decadal resolution. Lake and ocean sediments have a lower time resolution, but provide climate information at multicentennial timescales that may not be captured by tree-ring data. Here we reconstruct Northern Hemisphere temperatures for the past 2,000 years by combining low-resolution proxies with tree-ring data, using a wavelet transform technique to achieve timescale-dependent processing of the data. Our reconstruction shows larger multicentennial variability than most previous multi-proxy reconstructions, but agrees well with temperatures reconstructed from borehole measurements and with temperatures obtained with a general circulation model. According to our reconstruction, high temperatures--similar to those observed in the twentieth century before 1990--occurred around ad 1000 to 1100, and minimum temperatures that are about 0.7 K below the average of 1961-90 occurred around ad 1600. This large natural variability in the past suggests an important role of natural multicentennial variability that is likely to continue.     

Evidence from U-Th dating against Northern Hemisphere forcing of the penultimate deglaciation

Milankovitch proposed that summer insolation at mid-latitudes in the Northern Hemisphere directly causes the ice-age climate cycles. This would imply that times of ice-sheet collapse should correspond to peaks in Northern Hemisphere June insolation. But the penultimate deglaciation has proved controversial because June insolation peaks 127 kyr ago whereas several records of past climate suggest that change may have occurred up to 15 kyr earlier. There is a clear signature of the penultimate deglaciation in marine oxygen-isotope records. But dating this event, which is significantly before the 14C age range, has not been possible. Here we date the penultimate deglaciation in a record from the Bahamas using a new U-Th isochron technique. After the necessary corrections for alpha-recoil mobility of 234U and 230Th and a small age correction for sediment mixing, the midpoint age for the penultimate deglaciation is determined to be 135 +/- 2.5 kyr ago. This age is consistent with some coral-based sea-level estimates, but it is difficult to reconcile with June Northern Hemisphere insolation as the trigger for the ice-age cycles. Potential alternative driving mechanisms for the ice-age cycles that are consistent with such an early date for the penultimate deglaciation are either the variability of the tropical ocean-atmosphere system or changes in atmospheric CO2 concentration controlled by a process in the Southern Hemisphere.     

Precipitation variability in central Himalayas and its relation to Northern Hemisphere temperature

Agriculture, industry and hydroelectric power in south Asia are heavily dependent on the performance of the summer (June to September) monsoon rainfall, which provides 75—90% of the annual rainwater over most parts of the area. A weak monsoon year generally corresponds to low crop yields. And strong monsoon usually produces abundant crops, although too much rainfall may produce devastating floods. However, modeling efforts to forecast the monsoon have met with only moderate success[1]. Prev…     

Role of Ferrel cell in daily variability of Northern Hemisphere Annular Mode

The Northern Hemisphere Annular Mode(NAM) represents the zonally symmetric planetary-scale atmospheric mass fluctuations between middle and high latitudes, whose variations have shown a large impact on other components of the climate system. Previous studies have indicated that the NAM is correlated with the Ferrel cell in their monthly or longer timescale variability.However, there have been few studies investigating their connections at daily timescale, though daily variability of NAM has been suggested to be an important component and has significant implication for weather forecast. The results from this study demonstrate that variability of the Ferrel cell leads that of the NAM by about 1–2 days. This statistically identified temporal phase difference between NAM and Ferrel cell variability can be elucidated by meridional mass redistribution. Intensified(weakened)Ferrel cell causes anomalously smaller(larger) poleward mass transport from the middle to the high latitudes,resulting in an increase(a decrease) in mass in the middle latitudes and a decrease(an increase) in the high latitudes.As a consequence, anomalously higher(lower) poleward pressure gradient forms and the NAM subsequently shifts to a positive(negative) phase at a time lag of 1–2 days. The findings here would augment the existing knowledge for better understanding the connection between the Ferrel Cell and the NAM, and may provide skillful information for improving NAM as well as daily scale weather prediction.     

Recent Northern Hemisphere tropical expansion primarily driven by black carbon and tropospheric ozone

Observational analyses have shown the width of the tropical belt increasing in recent decades as the world has warmed. This expansion is important because it is associated with shifts in large-scale atmospheric circulation and major climate zones. Although recent studies have attributed tropical expansion in the Southern Hemisphere to ozone depletion, the drivers of Northern Hemisphere expansion are not well known and the expansion has not so far been reproduced by climate models. Here we use a climate model with detailed aerosol physics to show that increases in heterogeneous warming agents--including black carbon aerosols and tropospheric ozone--are noticeably better than greenhouse gases at driving expansion, and can account for the observed summertime maximum in tropical expansion. Mechanistically, atmospheric heating from black carbon and tropospheric ozone has occurred at the mid-latitudes, generating a poleward shift of the tropospheric jet, thereby relocating the main division between tropical and temperate air masses. Although we still underestimate tropical expansion, the true aerosol forcing is poorly known and could also be underestimated. Thus, although the insensitivity of models needs further investigation, black carbon and tropospheric ozone, both of which are strongly influenced by human activities, are the most likely causes of observed Northern Hemisphere tropical expansion.     

2010年夏季北半球气温异常偏高现象及其成因

利用常规气象观测资料、NCEP/NCAR再分析资料,对2010年夏季6-8月北半球异常高温现象进行了分析.结果表明,夏季北半球大部分地方地面气温偏高,局部地区气温异常偏高,地而气温距平值达+6℃;北半球对流层平均气温正距平值达近30年以来最大值,并且各月平均气温异常偏高的区域,在对流层各层次都表现为一致的偏高;北半球对...     

Northern Hemisphere forcing of climatic cycles in Antarctica over the past 360,000 years

The Milankovitch theory of climate change proposes that glacial-interglacial cycles are driven by changes in summer insolation at high northern latitudes. The timing of climate change in the Southern Hemisphere at glacial-interglacial transitions (which are known as terminations) relative to variations in summer insolation in the Northern Hemisphere is an important test of this hypothesis. So far, it has only been possible to apply this test to the most recent termination, because the dating uncertainty associated with older terminations is too large to allow phase relationships to be determined. Here we present a new chronology of Antarctic climate change over the past 360,000 years that is based on the ratio of oxygen to nitrogen molecules in air trapped in the Dome Fuji and Vostok ice cores. This ratio is a proxy for local summer insolation, and thus allows the chronology to be constructed by orbital tuning without the need to assume a lag between a climate record and an orbital parameter. The accuracy of the chronology allows us to examine the phase relationships between climate records from the ice cores and changes in insolation. Our results indicate that orbital-scale Antarctic climate change lags Northern Hemisphere insolation by a few millennia, and that the increases in Antarctic temperature and atmospheric carbon dioxide concentration during the last four terminations occurred within the rising phase of Northern Hemisphere summer insolation. These results support the Milankovitch theory that Northern Hemisphere summer insolation triggered the last four deglaciations.     

Southern Hemisphere mean zonal wind in upper troposphere and East Asian summer monsoon circulation

1 Introduction Variability of the East Asian summer monsoon (EASM) has been detected by considering roles of El Nino and Southern Oscillation (ENSO) cycle, snow cover over Eurasia and Tibetan Plateau, and signals from the soil (namely, the soil temperatur…     

1998年夏季北半球斜压波活动与长江流域洪涝灾害分析

对流层上层的斜压波、高空槽对天气的变化有重要的影响。1998年夏季我国出现了大范围的天气异常，在长江流域发生了20世纪第二大的全流域性洪水，分析了1998年夏季北半球的西风急流、风暴轴、以及对流层上的斜压波活动与气候平均情况的异同，并揭示了1998年夏季北半球斜压波活动传播的主要区域、斜压波活动的持续性、斜压波向传播的速度以及斜压波传播时所具有的明显的下游效应。1998年夏季北半球的波包 次数共有11次，与夏季气候状况相比属于正常偏多，其中5月和8月的波包活动次数稍多。但更为明显的一个特点就是在7月中旬到8月上旬大西洋－欧洲的斜压波包活动比往年集中频繁，而且持续时间偏长， 为造成我国异常梅雨天气和长江流域洪涝灾害的乌拉尔阻塞高压的发展和维持提供了能量支持，同时为长江流域以及同期我国东北的大范围降雨提供了有利的水汽输送条件。最后分析了地面气旋生成与斜压波、高空槽之间的联系，指出在大多数向东部发展的高空槽的槽前，地面上有对应气旋地生成。     

Reconstruction of the Northern Hemisphere temperature from 1500 to 1949 by optimal regional averaging method

The rareness and inhomogeneity of the data points cause difficulties in the reconstruction of past average temperature. Optimal regional averaging is a method that can overcome these difficulties and obtain the average temperature of target area by means of optimal weights using limited temperature data. In this paper, the average temperature in the Northern Hemisphere is calculated by the optimal regional averaging method using two types of data： temperature data from Climatic Research Unit from 1901 to 2000 and maximum latewood density dataset of tree from 1500 to 1949. Five, ten, fifteen data points from CRU and forty data points from MXD are used in our research. The results show that even with the relatively less data used in this reconstruction, the method allows the reconstruction of the average temperature of the Northern Hemisphere more accurately, which provides the temperature information for palaeoclimate reconstruction.     

北半球不同强度、生命期阻塞高压的变化特征及其对温度的影响

分析了1968-2010年北半球阻塞高压频发区不同强度、生命期阻高的变化特征,从阻高强度和阻高生命期两方面分析阻高多发年、少发年与北半球地表温度的关系,结果显示:北半球的3个阻高频发区中,大西洋地区阻高出现总次数最多,太平洋地区次之,欧亚区最少;从阻高强度来看,3个阻高频发区强阻高次数均有减少趋势,以大西洋区最为显著,弱强度阻高变化趋势不明显;对于阻高生命期,长生命期阻高发生次数在21世纪以前变化不大,但近10年增加明显,短生命期阻高发生次数只有大西洋区在减少.大西洋区强阻高中长生命期阻高占25%,而太平洋区仅为14%,阻高强度越强时,出现长生命期阻高的概率也就越大.不同强度、生命期阻高对温度的影响差异显著.3个阻高频发区的长生命期阻高多发年与少发年温度差值的负异常区主要分布在中低纬度地区,而正异常区主要在高纬度地区;大西洋区、太平洋区长生命期阻高在多发年引起中低纬度地区的降温及高纬度地区的增温比强阻高产生的影响显著.     

中国北方季风气候与内陆气候过渡地带全新世环境演变

在根据洪积扇形态和内陆湖水面变化恢复全新世以来降水量的基础上，确定了全新世及近百年来夏季风西北限的位置，并以此范围作为中国北方季风气候与内陆气候过渡地带，按照该地带中季风尾间闾的波动，内陆湖水量平衡特点及与中亚冰川物质平衡的对比进行综合分析，认为这一过渡地带的东西向迁移与全世以来全球性环境变化相对应，是中国北方环境变化的直接原因和基本内容；该地带环境以多变、易变、多灾、易灾为特点，是一个环境脆弱带。