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71.
72.
Ice Sheet-Thermohaline Circulation Interactions in a Climate Model of Intermediate Complexity 总被引:3,自引:0,他引:3
A vertically integrated dynamic ice sheet model is coupled to the atmosphere-ocean-sea ice-land surface climate model recently
developed by Wang and Mysak (2000). The background lateral (east-west) ice sheet discharge rate used by Gallee et al. (1992) is reduced and the planetary emissivity is increased (to parameterize the cooling effect of a decrease of the atmospheric
CO2 concentration), in order to build up substantial ice sheets during a glacial period and hence set the stage for ice sheet-thermohaline
circulation (THC) interactions. The following iceberg calving scheme is then introduced: when the maximum model height of
the North American ice sheet reaches a critical value (2400 m), a prescribed lateral discharged rate is imposed on top of
the background discharge rate for a finite time. Per a small prescribed discharge rate, repeated small iceberg calving events
occur, which lead to millennial-scale climate cycles with small amplitudes. These are a crude representation of Dansgaard-Oeschger
oscillations. Over one such cycle, the zonally averaged January surface air temperature (SAT) drops about 1.5°C at 72.5°N.
However, a large prescribed lateral discharge rate leads to the shut down of the THC. In this case, the January SAT drops
about 5°C at 72.5°N, the sea ice extent advances equatorward from 57.5° to 47.5°N and the net ice accumulation rate at the
grid of maximum ice sheet height is reduced from 0.24 to 0.15 m/y. Since data strongly suggest that a collapsed THC was not
a steady state during the last glacial, we restore the THC by increasing the vertical diffusivity in the North Atlantic Ocean
for a finite time. The resulting climate cycles associated with conveyor-on and conveyor-off phases have much larger amplitudes;
furthermore, the strong iceberg calving events lead to a larger loss of ice sheet mass and hence the period of the oscillations
is longer (several thousand years).
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
73.
分析1980-1987年欧洲中长期预报中心(ECMWF)每日风场、温度场格点资料及同期南海区域测站和船舶资料,讨论南海低层风场的气候特征。南海为典型的季风活动区,冬季盛行东北季风,夏季盛行西南季风。流场的季节转换表现为季风系统的交替,相应不同的季风系统,南北温度梯度有一逆转过程,南海北部是温度梯度大且发生明显逆转的海区。12°N以南海区气温全年变化极小,整个海区大气温度的季节变化不如流场变化快和显著。 相似文献
74.
Climatic effects on plankton and productivity on the Faroe Shelf 总被引:1,自引:0,他引:1
Hansen Bogi; Eliasen Solva K.; Gaard Eilif; Larsen Karin M.H. 《ICES Journal of Marine Science》2005,62(7):1224-1232
75.
Floating tephra was deposited together with ice core,snow layer,abyssal sediment,lake sediments,and other geological records.It is of great significance to interpret the impact on the climate change of volcanic eruptions from these geological records.It is the first time that volcanic glass was discovered from the peat of Jinchuan(金川)Maar,Jilin(吉林)Province,China.And it is in situ sediments from a near-source explosive eruption according to particle size analysis and identification results.The tephra were neither from Tianchi(天池)volcano eruptions,Changbai(长白)Mountain,nor from Jinlongdingzi(金龙顶子)volcano about 1 600 aBP eruption,but maybe from an unknown eruption of Longgang(龙岗)volcano group according to their geochemistry and distribution.Geochemical characters of the tephra are similar to those of Jingiongdingzi,which are poor in s.Jica,deficient in alkali,Na20 content is more than K20 content,and are similar to distribution patterns of REE and incompatible elements,which helps to speculate that they originated from the same mantle magma with rare condemnation,and from basaltic explosive eruption of Longgang volcano group.The tephra,from peat with age proved that the eruption possibly happened in 15 BC-26 AD,is one of Longgang volcano group eruption that was not recorded and is earlier than that of Jinglongdingzi about 1 600 aBP eruption.And the sedimentary time of tephra is during the period of low temperature alteration.which may be the influence of eruption toward the local climate according to the correlativity of eruption to local temperature curve of peat cellulose oxygen isotope. 相似文献
76.
基于数学和分析力学角度分别推导了航空矢量重力测量的数学模型,得到了一致的模型公式;给出了矢量模型的3个分量形式,其中垂直方向的分量就是标量重力测量的数学模型;简要介绍了我国研制成功的航空标量重力测量系统CHAGS的数据处理的过程,分析了标量重力测量中测线交叉点和重复测线的重力异常的精度;根据实测数据计算的结果表明:测线交叉点重力异常不符值的标准差约为5×10-5ms-2左右,重复测线的内符合精度优于5×10-5ms-2,达到了预期的要求。 相似文献
77.
78.
对我国西南地区河谷深厚覆盖层成因机理的新认识 总被引:2,自引:0,他引:2
近年来,在我国水能资源开发过程中,发现各河流现代河床以下普遍堆积厚达数十米甚至上百米的松散堆积物。河谷深厚覆盖层的存在,不仅严重制约了工程坝址的选择,影响相关流域水电资源的开发利用,也给坝工设计带来巨大的困难。由于深厚覆盖层埋藏于现代河床之下,其形成年代一般先于一二级阶地,有悖于河流发育演化的常理,其成因一直令人费解。首次将河谷深切和深厚堆积事件与全球气候变化、海平面升降运动、地壳运动等有机地联系起来,并提出冰期、间冰期全球海平面大幅度升降,是导致河流深切成谷并形成深厚堆积的主要原因的新观点。在此基础上,引入层序地层学原理,从理论上较好地解释了全球气候变化导致海平面和河流侵蚀基准面大幅变化,并产生河谷深切和深厚堆积的原因和过程。最后,进一步将沿河大型古滑坡的孕育和发生与河谷深切事件相联系,提出沿河大型古滑坡是在河谷深切期因前缘临空较好而形成的新观点,从而对沿河古滑坡前缘剪出口高程往往低于现代河床数十米的原因给出了较合理的解释。 相似文献
79.
80.