Live display program

B.3

Oceanography

Papers are solicited on the advances in oceanographic applications of GRACE and GRACE-FO data products, including signal interpretation and model assimilation. Other topics include, but are not limited to, the validation of data products, the studies of regional or global oceanographic processes, exploitation of GRACE and GRACE-FO data products jointly with data from other missions (such as GOCE), or other in situ oceanographic measurement systems (e.g. ARGO), etc.

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| Wed, 28 Oct, 18:00–18:45 (CET)

Offline display program

Session assets

Wednesday, 28 October 2020 | Virtual meeting room

Chairperson: Jennifer Bonin, Henryk Dobslaw

18:00–18:15 |

GSTM2020-10

Intraseasonal Variability in the Persian Gulf Revealed by GRACE and Altimetry

Christopher Piecuch, Rui Ponte, and Ichiro Fukumori

The Persian Gulf is a semi-enclosed marginal sea of the Indian Ocean. It connects to the Arabian Sea through the Gulf of Oman and the Strait of Hormuz. The Persian Gulf has a large coastal population, and is relevant economically and geopolitically, and so it is important to understand sea-level changes in the region. We use satellite observations from the Gravity Recovery and Climate Experiment (GRACE) and satellite altimetry to study intraseasonal sea level variation over the Persian Gulf during 2002-2015. We interrogate the spatial scales and forcing functions of the variation and its relation to large-scale circulation and climate over the Indian Ocean. Empirical orthogonal function analysis applied to sea level data from satellite altimetry reveals that the intraseasonal sea level variation in the Persian Gulf is dominated by a basin-wide, single-signed mode of fluctuation. Maximum covariance analysis applied to altimetry and GRACE satellite retrievals shows that these basin-wide intraseasonal sea level fluctuations are largely barotropic in nature and coupled to variations in ocean bottom pressure. To interpret the results, we develop a simple linear barotropic theory based on volume and momentum conservation. The theory describes Persian Gulf sea level in terms of freshwater flux over the region, wind stress along the Strait of Hormuz, and sea level in the Gulf of Oman. To test this theory, we perform a complex multiple linear regression using these regional freshwater flux, wind stress, and sea level as inputs, and Persian Gulf sea level as output. The regression model explains ~70% of the intraseasonal Persian Gulf sea level variance. The magnitudes and phases of the coefficients determined from the regression model are consistent with expectations from the simple theory. The Gulf of Oman sea level boundary condition shows significant lagged correlation with intraseasonal sea level upstream along the Indian Subcontinent, Maritime Continent, and equatorial Indian Ocean. This hints at a large-scale circulation and climate influence on intraseasonal sea level variation of the Persian Gulf mediated by waves propagating along equatorial and coastal waveguides. This study highlights the value of GRACE retrievals of ocean bottom pressure for understanding sea level in an understudied semi-enclosed marginal sea.

How to cite: Piecuch, C., Ponte, R., and Fukumori, I.: Intraseasonal Variability in the Persian Gulf Revealed by GRACE and Altimetry, GRACE/GRACE-FO Science Team Meeting 2020, online, 27–29 Oct 2020, GSTM2020-10, https://doi.org/10.5194/gstm2020-10, 2020.

18:15–18:30 |

GSTM2020-12

How Salty Is the Global Ocean: Weighting It All or Tasting It a Sip at a Time?

Rui Ponte, Qiang Sun, Chao Liu, and Xinfeng Liang

Global ocean mean salinity S is a key indicator of the Earth's hydrological cycle and the exchanges of freshwater between the terrestrial water and ice reservoirs and the ocean. We explore two different ways of determining how salty the ocean is: (1) use in situ salinity measurements to taste the ocean a sip at a time and obtain a sample average; (2) use space gravimetry to weigh the whole ocean including sea-ice, and then separate sea-ice effects to infer changes in liquid freshwater content and thus S. Focusing on the 2005-2019 period, we assess monthly series of S derived from five different in situ gridded products, based mostly but not exclusively on Argo data, versus a series obtained from GRACE and GRACE Follow-On data and available sea ice mass estimates.

There is little consistency in S series from the two methods for all time scales examined (seasonal, interannual, long-term trend). In situ series show larger variability, particularly at the longest scales, and are somewhat incoherent with the GRACE-derived series. In addition, there are wide spread differences among all the in situ S series, which denote their considerable sensitivity to choice of data, quality control procedures, and mapping methods. Results also suggest that in situ S values are prone to systematic biases, with most series showing increases after around 2014 that are equivalent to a drop in barystatic sea level of tens of centimeters! Estimates derived from GRACE are much smaller in magnitude and consistent with contributions of freshwater to the global mean sea level budgets, and they are thus more reliable than in situ-based S estimates. The existence of GRACE-derived estimates can serve as a consistency check on in situ measurements, revealing potential unknown biases and providing a way to cross-calibrate the latter data.

How to cite: Ponte, R., Sun, Q., Liu, C., and Liang, X.: How Salty Is the Global Ocean: Weighting It All or Tasting It a Sip at a Time?, GRACE/GRACE-FO Science Team Meeting 2020, online, 27–29 Oct 2020, GSTM2020-12, https://doi.org/10.5194/gstm2020-12, 2020.

18:30–18:45 |

GSTM2020-52

Sensitivity of Global Ocean Mass Calculations to Different Methods and Models

Don Chambers, Jennifer Bonin, and Mark Tamisiea

Global ocean mass (or barystatic sea level) is an important component of the sea level budget. It can be computed directly from the GRACE and GRACE-FO data, or it can be computed by summing contributions from the cryosphere and hydrosphere. Here, we present a sensitivity analysis of the direct computation, using both averaging of mascon solutions as well as avering kernel methods applied to the spherical harmonics. We will discuss sensitivity to various geocenter models and GIA models, as well as discuss whether scaling is required for the averaging kernel method. For the scaling tests, we will utilize a simulation that includes trend fingerprints from icesheets and glaciers. We also discuss the effect of using different averaging areas (global oceans, global oceans excluding Hudson Bay, oceans with a 300km mask).

We find consisent results between the spherical harmonic and mascon calculations within the estimated uncertainy of fits based on the residuals to the linear trend + annual sinuspid model. Trends will change by up to 0.2 mm/year if geocenter models based on GRACE and ocean moddel data are used, or up to 0.4 mm/year if SLR-based geocenter is used. Different versions of glacial isostatic models introduce trend differences of order 0.1-0.2 mm/year. These systematic errors should be considered in addition to uncertainty from least squares fits when assesing closure to the sea level budget.

How to cite: Chambers, D., Bonin, J., and Tamisiea, M.: Sensitivity of Global Ocean Mass Calculations to Different Methods and Models, GRACE/GRACE-FO Science Team Meeting 2020, online, 27–29 Oct 2020, GSTM2020-52, https://doi.org/10.5194/gstm2020-52, 2020.