Atmospheric pressure and gravity
Atmospheric pressure and gravity
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DOI：
10.1111/j.1365-246x.1992.tb00112.x
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发表时间：
1992-06
影响因子：
2.8
通讯作者：
J. Merriam
中科院分区：
文献类型：
--
作者：
J. Merriam
本文给出了一个球形弹性地球上模型大气柱载荷的重力绿色函数，并将其用于估算全球大气压力变化对局部重力的贡献。发现绿色函数对模型大气的细节相对不敏感，但它们依赖于柱底部的温度，以及柱底部和重力站之间的相对高度差。全球压力系统对重力产生的总信号约为30 μgal，其中约90%是由重力站50公里范围内的大气产生的。距离重力站50到1000公里的区域贡献了几个微伽，地球仪的其余部分也是如此。这种模式，压力波动的相干尺度，适合于流体静力学近似的时间和空间尺度，以及重力站与海洋的距离，表明地球仪分为地方，区域和全球区。每个区域的数据要求、处理细节和计算信号的可靠性都不同。当地区域距离重力站约50公里。在这一区域内，气压随时间迅速变化，但在空间上是一致的，因此，除了锋面通过时，仅在重力场每小时观测一次的气压和温度就足以计算出准确的校正值。区域范围从局部区域的边缘延伸到几百至一千公里。来自该区域的信号很小，并且与来自中心区域的信号仅弱相干，因此需要相当稀疏的每小时压力和温度样本阵列。来自全球带的重力信号可以达到大约1 μgal。它以天为时间尺度变化，并受到海洋对压力变化的反应的影响。以前报道的意见，当地压力和重力残差之间的导纳取决于历元，频率，或网站，是最有可能由于不正确的建模。一个适当的本地，区域，温度和全球的校正可以充分考虑从大气中的重力信号，在几十个ngal的日带，约100 ngal的天，季节带，除了在极端天气条件下。局部校正的应用降低了重力残差从季节到逐时的各个波段的功率谱密度。区域、全球和温度修正降低了季节和天气带中的残余噪声，但在不到半天的时间内并不总是有效。
SUMMARY Gravity Green's functions for a column load of a model atmosphere on a spherical, elastic Earth are presented and they are used to evaluate the contribution of global atmospheric pressure variations to local gravity. The Green's functions are found to be relatively insensitive to the details of the model atmosphere, but they are dependent on the temperature at the base of the column, and on the relative height difference between the base of the column and the gravity station. The total signal that global pressure systems contribute to gravity is about 30 μgal, of which about 90 per cent is produced by the atmosphere within 50 km of the gravity station. A zone between 50 and 1000km from the gravity station contributes a couple of μgal, as does the remainder of the globe. This pattern, the coherence scale of pressure fluctuations, the time and spatial scales appropriate to the hydrostatic approximation, and the distance of the gravity station from the oceans, suggest a division of the globe into local, regional, and global zones. Data requirements, processing details, and the reliability of the computed signal are different in each zone. The local zone is within about 50 km of the gravity station. Within this zone pressure changes rapidly in time, but is spatially coherent, so that hourly observations of pressure and temperature at the gravity site alone are sufficient to compute an accurate correction, except when a front is passing through. The regional zone extends from the edge of the local zone to between several hundred and a thousand kilometres. The signal from this zone is small and is only weakly coherent with the signal from the central zone, so that a rather sparse array of hourly samples of pressure and temperature are required. The gravity signal from the global zone can reach about a μgal. It varies on a time-scale of days, and is influenced by the response of the oceans to pressure variations. Previously reported observations that the admittance between local pressure and gravity residuals depends on epoch, frequency, or site, are most probably due to incorrect modelling. A proper local, regional, temperature, and global correction can adequately account for the gravity signal from the atmosphere to within a few tens of ngal in the diurnal band, and about 100 ngal in the days to seasonal band, except during extreme weather conditions. The application of the local correction lowers the power spectral density of the gravity residuals in every band from seasonal to hourly. The regional, global, and temperature corrections lower the residual noise in the seasonal and synoptic bands, but are not consistently effective at periods less than about half a day.