Collaborative Research: Ocean Pressure in the Arctic Derived From Satellite Gravity Observations and In Situ Pressure Measurements

这项研究将利用对深海压力、水文和大气数据以及卫星重力的现场观测，估计北冰洋海底压力、海平面和环流的大范围季节性和更长时间的变化。北冰洋中部的海平面是海洋环流的关键决定因素，因此对海冰分布和区域淡水收支有很大影响。气候变化与海冰分布变化引起的反照率变化以及北冰洋淡水和海冰出口变化引起的全球温盐环流变化有关。因此，观测海洋中的压力分布对于理解海洋环流中的可变性至关重要。目前对冰和淡水分布及其变化的看法是基于现有的水文调查和一些自动化仪器的测量。由于缺乏对淡水分布的常规的、空间上连续的测量，因此很难在任何时候构建一幅完整的锋面位置图。这项工作的科学目标和优点是改进与气候变异性有关的海洋变化指数，促进实现从空间获得大规模海洋环流和淡水分配的系统测量的目标。海底压力记录器(BPR)将部署在一个100公里的三角形阵列中，顶点位于极点、Lomonosov海脊和靠近海脊底部的位置。这些现场测量将与GRACE(重力恢复和气候实验卫星任务)对北冰洋中部深海海底压力的估计进行比较，以交叉验证这些压力反演方法。BPR还提供潮汐和其他短周期(60天)变率的测量，并将用于减少卫星测量中的混叠问题。整个盆地随时间变化的海底压力场将与测量的海底压力、沿海海平面记录和水文数据进行比较，以估计海洋环流的变化，从而评估遥感和现场测量相结合的方法的准确性。这项工作将有助于实现将海底压力的遥感测量与卫星高度计对海面高度的观测进行比较的长期目标，以便不仅估计环流变化，而且估计总的空间异常和推断的淡水和海冰含量。这项工作的结果包括现场BPR记录、推导出的潮汐分量、漂移改正、去掉潮汐后的漂移改正压力以及由GRACE估计的退潮后底部压力的空间场。这些资料将存档在北冰洋海平面观测系统和搜索数据库中，并直接提供给北冰洋海平面观测系统的协作方。为了更广泛地传播，将在网上提供根据压力得出的海平面梯度和正压输送估计数，并将其存入ARCS和搜索数据库。该项目将在三个机构之间建立合作关系：华盛顿大学和科罗拉多大学，以及喷气推进实验室，并将需要几个学科的专业知识：海洋学、大地测量学和固体地球物理。这项工作将形成华盛顿大学一名研究生的博士论文项目，以及科罗拉多大学一名研究生的博士项目的一部分，这将是将时变卫星重力观测整合到物理海洋学中的第一步。这些观测构成了海洋学的一种新的创新数据类型，对改进和更广泛地了解极地和全球海洋的环流有很大希望。

The research will estimate the large-scale seasonal and longer time variations in the Arctic Ocean bottom pressure, sea level, and circulation using in-situ observations of deep- sea pressure, hydrographic and atmospheric data, and satellite gravity. Sea level in the central Arctic Ocean is a crucial determinant of the ocean's circulation, and as such it strongly affects the sea-ice distribution and the regional freshwater budget. Climate variability is linked to changes in albedo associated with changes in sea-ice distribution and to changes in the global thermohaline circulation associated with changes in the export of Arctic Ocean freshwater and sea ice. Observing the pressure distribution in the ocean is thus central to understanding the variability in the ocean circulation. Current perspectives of the ice and freshwater distribution and their variations are based on available hydrographic surveys and measurements from a few automated instruments. The lack of routine, spatially continuous measurements of the freshwater distribution makes it difficult to construct a complete picture of frontal locations at any one time. The scientific goal and merit of this work is to improve indices of ocean change related to climate variability and to contribute to achieving the goal of obtaining systematic measurements of large-scale ocean circulation and freshwater distribution from space. Bottom pressure recorders (BPRs) will be deployed in a 100 km triangular array with vertices at the Pole, the Lomonosov Ridge, and near the foot of the ridge. These in situ measurements will be compared with GRACE (the Gravity Recovery and Climate Experiment satellite mission) estimates of deep-sea bottom pressure in the central Arctic Ocean to cross- validate these methods of pressure retrieval. BPRs also provide measurements of tides and other short period ( 60 days) variability, and will be used to reduce aliasing problems in the satellite measurements. GRACE time-dependent bottom pressure fields for the whole basin will be compared with measured bottom pressure, coastal sea level records, and hydrographic data to estimate ocean circulation changes and thereby evaluate the accuracy of the combined remote sensing, in situ measurement approach. This work will contribute to the long-term goal of comparing remote sensing measurements of bottom pressure with satellite altimeter observations of sea surface height to produce not only estimates of circulation changes but also estimates of the total steric anomaly and inferred fresh water and sea ice content. Results from this work include in situ BPR records, derived tidal constituents, drift corrections, the drift corrected pressure with tides removed, and the spatial field of bottom pressure estimates from GRACE after tide removal. These will be archived in the ARCSS and SEARCH data banks and supplied directly to those collaborating on the system of Arctic Ocean sea-level observations. For broader dissemination, pressure-derived sea-level gradient and barotropic transport estimates will made available on the Web as well as archived in the ARCSS and SEARCH data banks. This project will establish collaborations between three institutions: the Universities of Washington and Colorado, and the Jet Propulsion Laboratory, and will require expertise in several disciplines: oceanography, geodesy, and solid earth geophysics. The work, which will form the PhD thesis project of a University of Washington graduate student and part of the PhD project of a University of Colorado graduate student, will be a first step towards integrating time-variable satellite gravity observations into physical oceanography. These observations constitute a new and innovative data type for oceanography, with considerable promise for improved and broader understanding of the circulation of the polar and global oceans.