北半球Hadley环流与臭氧气候演变规律及其相互关系

 利用欧洲中心(ECMWF)1957年9月到2002年8月共540月的ERA-40的经向风和臭氧质量混合比月平均资料,通过定义一系列Hadley环流指数来分析研究Hadley环流与臭氧的气候演变规律及其相互关系.分析指出:①在定义的几个Hadley环流指数中,北半球Hadley环流强度指数(NHCI)与臭氧的相关最好,全球Hadley环流指数(HCI)次之.因此进一步运用功率谱和凝聚谱方法对NHCI与臭氧的变化做出周期分析;②南半球臭氧的时间序列与Hadley环流各指数的相关关系最好,赤道次之,北半球相对小一些;③NHCI与臭氧之间的相关关系总体表现为明显的纬度带分布,说明了不同的纬度,平均经圈环流(MMC)对臭氧的输送作用不同.④NHCI与臭氧的季节变化都十分显著,二者之间有很多显著的共振周期,最突出的约为5~6个月,1 a的共振周期是各自变化的显著周期.臭氧的变化落后于NHCI振荡,且不同的纬度带落后时间长度不同.     

北半球温带反气旋的气候统计特征

利用美国国家环境预报中心(National Centers for Environmental Prediction,NCEP)/美国国家大气研究中心(National Center for Atmospheric Research,NCAR)再分析资料,采用判定和追踪反气旋的客观方法统计分析了1948～2016年北半球冬季温带反气旋活动特征。研究发现,北半球温带反气旋主要活动在中东部的北太平洋、东北大西洋、北美的沿落基山脉东部和美国东部、欧亚的环地中海、伊朗高原、青藏高原以北且贝加尔湖以南地区。海洋上、北美洲和环地中海地区上的反气旋夏季频数最高,而伊朗高原、青藏高原以北且贝湖以南的反气旋均冬季最多。海洋上的反气旋生成区域分布较分散,且主要向偏东方向移动、发展,且具有季节变化。相比于海洋,大陆上反气旋生成的纬度较低,主要向东南方移动、发展。北美大陆上的反气旋夏季生成的较多,冬季移动范围较广。北半球反气旋年平均过程数呈缓慢上升趋势。夏季过程数最多,且从1970年开始呈上升趋势。欧亚地区的反气旋过程数最多,其次太平洋,大西洋最少,但是同一个区域的四季相差较小。反气旋的中心气压大值区的形态和高频区的分布形态相似,且中心气压有明显的季节变化。四季中冬季反气旋最强。秋冬季节是欧亚地区的反气旋最强,大西洋的最弱。春夏季大西洋的反气旋最强,欧亚地区的最弱。四季均是欧亚地区的反气旋的平均纬度较低,且冬季最低。北美地区的反气旋除秋季均是移动纬度范围最大的。反气旋数随生命史的变长而急剧下降,90%左右的反气旋的生命史在4 d内,四季均是大洋上的反气旋生命史较大陆上的长。     

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．     

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。     

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.     

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.     

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.     

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.     

北半球夏季的斜压波包个例分析

利用NCEP/NCAR再分析资料,使用局地能量诊断和三维准地转波动通量等工具分析了2002年北半球夏季的一次斜压波包过程。结果表明：波包发展的能量来源主要依靠斜压转换获得,频散项对波包的影响很小;波包进入衰减期以后,波包的东侧和南侧作为垂直方向的波动源,向下传播波动通量;向下的波通量进入对流层低层气旋范围,对气旋的维持起到重要作用。     

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...     

Statistical characteristics of the double ridges of subtropical high in the Northern Hemisphere

The generality and some climatological characteristics of the double ridge systems of subtropical high （SH） are investigated statistically by using the daily NCEP/NCAR reanalysis data from 1958 to 1998. The results show that the SH double-ridge event is a common phenomenon in the Northern Hemisphere, with the distinct seasonal and regional features, that is, the majority of SH double-ridge geneses concentrate over the eastern North India Ocean-western North Pacific as well as the central North Pacific in the period from mid-July to mid-September. Especially over the western North Pacific subtropics, the SH double-ridge events are extremely active. It is found that the life cycle of most double-ridge events of western Pacific subtropical high （WPSH） is shorter but some still last longer. The WPSH double-ridge events occur most frequently from July to September, while there is a paucity of occurrences during November-March. Also, it is shown that the WPSH double-ridge events have a strong interannual variation with a certain periodicity which possesses a remarkably abrupt change in the mid-1970s. Additionally, the relationship between the WPSH double ridges and the meridional movement of WPSH is discussed.     

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.     

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.     

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…