Improving ocean tides by constraining the dynamic HAMTIDE model with altimetry an GRACE data

通过同化测高和GRACE数据提供的潮汐信息来改进全球海潮模型的拟议努力是SPP 1257“Massentransporte und Massenverteilungen im System Erde”的核心问题，也是改进GRACE和GOCE重力场建模（以避免混淆）所必需的。与此同时，这一努力将提高我们对潮汐在海洋环流中的作用的认识。全球海潮模型描述短期海洋质量变化，量化陆地台站的负荷效应，解释地球自转中观察到的部分变化，并需要用于校正测高海面高度以及GRACE和GOCE重力场建模（去混叠）。同样重要的是，潮汐摩擦，主要是在浅海，有助于混合海洋，并施加影响的角动量，从而对一天的长度。此外，正压潮流与地形相互作用产生的内波阻力也会导致深海内潮的产生。这种将机械能转化为内潮的过程，对于深海混合维持一般海洋环流（接近稳态过程）十分重要。潮汐的其他重要特征是它们对固体地球变形（负载和自吸引效应）和重力场变化的影响，从而对卫星轨道的变化产生影响。因此，提高我们对海洋潮汐的理解，扩大我们对潮流、潮汐能转移或耗散的认识，对物理海洋学和大地测量界来说都是一个O（1）问题。改进的海洋潮汐的估计，超出了我们可以从经验潮汐模型，可以通过约束观测到的潮汐信息的动力学潮汐模型。该项目中使用的数据同化模型HAMTIDE已经证明很有价值，能够在DAROTA的头两个供资期间模拟海潮。高质量的动力学解是通过一种有效的方法获得的，通过这种方法，模型受到表面潮汐信息（由测高以及推断潮流的数据定义的水位）的约束。结果可用于探测表面-内部潮汐转换的速率和产生地点，寻找潮汐引起的垂直混合区域，从而对气候产生影响，即，卫星信号与气候变化的重要联系。在下一阶段，重力测量（GRACE、GOCE）和测高（T/P、ICESat、CRYOSAT 2）数据将同时用作同化过程中的约束条件。这不仅将改善可利用测高技术的低、中纬度地区的潮汐估算，而且将改善需要更好潮汐模型以改善重力场反演的高纬度地区的潮汐估算。这种数据同化的第一个结果（具有粗分辨率和很少的重力测量数据）是非常有希望的。研究结果将用于更好地了解潮汐消散（另见标题页上的图和所附文件草稿Taguchi、Stammer和Zahel，2010年）。结果同样将与所有最先进的全球潮汐模型进行相互比较，作为拟议工作的一部分。

The proposed effort of improving global ocean tide models through the assimilation of tidal information available from altimetry and GRACE data is of central concern for the SPP 1257 “Massentransporte und Massenverteilungen im System Erde” and is necessary to improve GRACE and GOCE gravity field modeling (to avoid aliasing). At the same time the effort will improve our knowledge about the role of tide in the general circulation of the ocean. Global ocean tide models describe short term ocean mass variations, quantify loading effects for stations on land, explain parts of the variations observed in Earth rotation, and are required for correcting altimetric sea surface heights and for GRACE and GOCE gravity field modeling (dealiasing). Equally important, tidal friction, mainly in the shallow seas, contribute to mixing the ocean, and exerts influence on the angular momentum and hence on the length of the day. Moreover, the internal wave drag caused by interaction of barotropic tidal currents with topography induces generation of the internal tides in the deep ocean. Such conversion of the mechanical energy into the internal tides is important for the abyssal ocean mixing to maintain the general ocean circulation (nearly steady-state process). Other important features of the tides are their influence on the solid Earth deformation (loading and self-attraction effect) and on the variation of the gravitational fields, consequently on the variation of the satellite orbits. Improving our understanding of ocean tides and expanding our insight into tidal currents, tidal energy transfer or dissipation is therefore an O(1)-problem to physical oceanography and the geodetic community alike. Improved estimates of ocean tides, beyond what we can learn from empirical tide models, can be obtained by constraining dynamical tide models by observed tidal information. The dataassimilative model HAMTIDE, which is used in this project, has already proven valuable and capable of modelling ocean tides during the first two funding periods of DAROTA. The high quality of the dynamical solution is obtained through an effective method by which the model is being constrained by surface tide information (water elevation defined by the altimetry as well as data inferring tidal currents). Results can be used for detecting rates and generation sites of the surface-to-internal tide conversion, finding regions of the tidally induced vertical mixing, and consequently influence on the climate, i.e., an important link from satellite signals to climate variations. In the next phase, the gravimetry (GRACE, GOCE) and altimetry (T/P, ICESat, CRYOSAT2) data will be used simultaneously as constraints in the assimilation process. This will improve tidal estimates not only in low and mid-latitudes where altimetry is available, but also in high latitudes where better tide models are needed to improve gravity field retrievals. The first result of this kind of data assimilation (with coarse resolution and few gravimetry data) is highly promising. Results will be used for an improved understanding of tidal dissipation (see also the figure on the title page and the attached draft paper Taguchi, Stammer and Zahel, 2010). Results will likewise be intercompared with all state of the art global tide models as part of the proposed effort.