- Title
- Sea level variability and mean sea level determination around Australia from satellite altimetry
- Creator
- Agha Karimi, Armin
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2019
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- This research aims at studying the sea level variability and determining the Mean Sea Surface (MSS) around Australia using satellite altimetry data in the period from 1993 to 2018. Analysing sea level variation is of a great importance due to its effects on coastal areas. Particularly, several studies have reported the acceleration in the sea level rise mainly due to the anthropogenic impacts. In this respect, determination of the sea level behaviour at the regional scale gives better understanding about the underlying threats of sea level rise on coastal regions. Accurate determination of the sea level rise around Australia, in the altimetry era, is the one of the main objectives of this study. The usability of the CryoSat-2 data to augment the existing global MSS and derive a new MSS around Australia is also analysed in this dissertation. CryoSat-2 data provides spatially denser and more accurate data in comparison to previous conventional altimetry missions. Fitting a surface to the CryoSat-2 Sea Surface Height (SSH) data may not provide a true MSS due to the presence of strong annual and semi-annual signals in the measured sea level data. A two-stage method is applied to mitigate the effect of periodic and non-periodic signals in the Sea Level Anomalies (SLAs) provided by CryoSat-2. At the first stage, the annual and semi-annual signals are removed using data from Topex/Poseidon and follow on missions. Then, the data are clustered in 0.1° x 0.1° cells and averaged to compensate for the effects of non-periodic signals. The estimated MSS provides promising result when it is compared to the MSS derived from Jason-2 and Jason-3 data, obtained in the same time span of CryoSat-2 data. The Mean Dynamic Topography (MDT) is also estimated using the MSS of CryoSat-2. It gives a consistent result when compared to global MDT models and is in good agreement with geodetic data. Additionally, the north-south tilt of Australian Height Datum (AHD) and the offset between the vertical datum of mainland and Tasmania are re-estimated using the MDT derived from CryoSat-2 data. The results show that the north-south tilt is ~27 mm/degree and the offset between AHD (Tasmania) and AHD (mainland) is highly variable depending on the locations adopted for the estimation of the offset. The sea level trend in the altimetry era is investigated considering the low frequency signals modulated by climate modes in the tropical region around Australia. Two new methods are used to estimate the sea level trend by considering the intra-decadal and decadal signals. The average sea level rise is estimated as 3.92 ± 0.15 mm/year around Australia. Apparently, the sea level rise in the tropical regions approximately doubles that in the Southern Ocean. The intra-decadal and decadal signals are traceable in the effective climate indices in the area. The time-frequency analysis of the signals in both climate indices and altimetry data shows that the intra-decadal signals, except for annual signal, are not stationary in the altimetry era. However, the decadal signal with the period of 11.17 years started to be effective from the mid-1980s and to the time. From spatial point of view, almost all of the signals are effective only in the tropical region. A few studies used linear regression and estimated biased trends due to the low frequency signal in recent years. However, the analysis shows that the sea level trend estimated using linear regression is less effected by the low frequency signal whilst the length of the time series is increasing. Therefore, in the current data sets (1993-2018), the sea level trend estimated by linear regression does not differ substantially from the trend estimated by the models where the low frequency signal is considered. The variations of the sea level contributors around Australia are investigated using different data sets. The spectral analysis of the eustatic and steric sea levels shows that the detected intra-decadal and decadal signals are mainly due to the steric sea level variations. The sea level budget closure in different regions of the study area is also investigated. The largest separation between the observed total sea level by altimetry and the summation of the contributors is in the seas of Indonesia. This can be linked to the lack of steric sea level data in this region and the leakage error in the equivalent water height derived from GRACE data.
- Subject
- sea level variation; coastal regions; sea level rise; CryoSat
- Identifier
- http://hdl.handle.net/1959.13/1407551
- Identifier
- uon:35741
- Rights
- Copyright 2019 Armin Agha Karimi
- Language
- eng
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 15 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 152 KB | Adobe Acrobat PDF | View Details Download |