Document Details
|
Document Type |
: |
Thesis |
|
Document Title |
: |
IMPACT OF LARGE-SCALE CLIMATE MODES ON THE SEA LEVEL AND SURFACE TEMPERATURE IN THE RED SEA AND GULF OF ADEN تأثير الأنماط المناخية العظمى علي منسوب سطح البحر ودرجة الحرارة السطحية في البحر الحمر وخليج عدن |
|
Subject |
: |
Faculty of Marine Sciences |
|
Document Language |
: |
Arabic |
|
Abstract |
: |
Oceanic and atmospheric teleconnection through the large-scale modes is the most striking phenomenon associated with the recent global warming. From the second part of the 20th century, there is strong observational evidence that the global warming causes the global mean sea level to rise, with concern that the rise rate will accelerate with time through the end of 21st century threatening coastal populations. Thermal expansion of the water and melting of land-locked ice are the major contributors of this rise. However, the regional sea level can differed in the trend and pattern of variability from those of global means. For that, investigating the sea-level variability in some regions requires to concentrate on the expected individual driving factors for those regions.
In general, the main reasons for sea level variations are the geological drivers, regional drivers and the large-scale drivers. Globally, the sea level climatology prominently modulated by the large-scale modes in the global oceans. At the same time, in semi-enclosed basins, the sea level variability has strong links with the global climate that governs the long-term spatial pattern and temporal variability in trends.
In the Red Sea (RS), a number of studies carry out the controlling factors of the sea level, but mainly from the local view and look for the seasonal variability using short-term data. It agrees that the local surface wind and the combine effect of evaporations and water exchange with GA govern the sea level variability. However, the SL increases in winter and decreases in summer. While this is true, there are no long-term studies on this topic associated with physical mechanisms so far; primarily because of non-availability of long-term in situ data combine with poor coverage. For that, few studies used reanalysis data to investigate this relation; nevertheless, the responsible physical mechanisms are still unclear and not yet explored. In addition, other studies used proxy data constructed from paleoclimate sources.
Motivated by the above findings we speculate that the climate variability has a significant impact on the sea level variability in the RS and GA, with seasonal and inter–annual fluctuations that can be correlated with large-scale climate modes. Taking this in our consideration, the objectives of this study includes:
(1) To investigate the multi-scale interaction in term of dominant signals that represent the footprint of large-scale climate modes on the sea level.
(2) To investigate the dominant modes and pattern of variability of sea level and the possible physical mechanism that explain the signal transferring.
Chapter 1: Focus on general introduction of study area that include geography, climatology, hydrographic feature and general ocean circulations.
Chapter 2: Deals with previous work of the sea level in the study area, followed by the impact of the large-scale climate modes on the Red Sea and Gulf of Aden as it observed on other parameters. A number of studies carry out the controlling factors of the sea level, but mainly from the local view and look for the seasonal variability using short-term data. Due to non-availability of long-term in-situ data combine with poor coverage many studies used proxy data constructed from paleoclimate sources.
Chapter 3: Describes the data and methodology followed in the work. Various sources of dataset have been used in the study. Two type of sea level SODA from 1958 to 2010 and AVISO sea level anomaly from 1993-2017. Furthermore, different reanalysis data are used to investigate the physical mechanism that includes ERA-interim SST, 2m air temperature, SLP and 10m zonal and meridional wind from ECMWF, the depth of 20° isotherm from GODAS spanning from 1993-2017, and climate modes indices. As well as the statistical methods wavelet analysis, EOF, correlation and regression analysis.
Chapter 4: Details the investigation the multi-scale interaction between the sea level in the RS and GA with the tropical large-scale climate modes in Pacific and Indian Oceans, namely Nino 3.4, SOI and IOD indices. In this analysis, we used SODA sea level data that spanning from January 1958-December 2010, which is the best available long-term gridded dataset. Study reveals the positive phase of both Nino3.4 and combine events (Nino3.4+IOD) contribute to rising the sea level in the Red Sea and Gulf of Aden. The maximum positive SLA mainly occurs in the following year during February to May and vice versa for the negative phase.
The wavelet analysis extract different periodicities semi-annual, annual, 2-7 and 11-18 years band of sea level. The Nino3.4 is in phase with semi-annual band, and it leads the annual band by 9-10 months, while the contribution of SIO and IOD in both bands are weak compared to Nino3.4. The 2-7 year band reveals that Nino3.4 and SOI lead sea level by 3 months in the Gulf of Aden, but 4 months was observed in the northern Red Sea, while 11-18 year band of both modes lead it by 3-4 months in the southern Red Sea only around 1980. The interesting result in this chapter is the observed shift of 2-7 year band to 5-7 year in the southern RS during 1990-2000, but it appears in the north by the same phase angle in the same period.
Chapter 5: Deals with the possible physical mechanism that explain the signal transferring from Pacific and Indian Oceans to the basins. In order to have precise and clear results, we used monthly mean gridded satellite altimetry SLA data obtained from AVISO, as well as ERA-interim SST, 2m air temperature, SLP and 10m zonal and meridional wind from ECMWF and profile temperature data for the thermocline depth (D20) from the GODAS. All the data spanning from January 1993-December 2017.
The time series of the SLA reveals an increasing trend about 0.0028 my-1 during the study period comparing to 0.0032 my-1 as the global mean sea level trend from 1993-2010. The first and second EOF modes together explained between 45%-55% throughout the seasons, while during winter season, they contribute equally to explain about 50% of the total variance. The PCs that associated to EOF are clearly reflects the mega events during the study period. The PC1 of SLA showed strong relation with ENSO and positive IOD while the PC2 showed weak relation to LaNina and negative IOD and seems to be modulated locally. The row SLA showed strong positive relation with ENSO and IOD during all season and strong negative relation with EAWR during winter and spring.
The unusual stronger easterlies wind that displaced north of the equator generate upwelling area of cold water near the coast of Sumatra and drive both warm surface and deep water westward. As the results of that, the SST and thermal expansion increase toward west IO and AS, rising SLA over the RS and GA. This process could explain the increasing of SLA in the basin during positive phase of MEI and IOD.
Chapter 6: Summary and conclusions that covers the entire summary of work and the main conclusions of the present study as well as a scope for future work. |
|
Supervisor |
: |
Dr. Abdullah M. Al-Subhi |
|
Thesis Type |
: |
Doctorate Thesis |
|
Publishing Year |
: |
1441 AH
2019 AD |
|
Added Date |
: |
Thursday, December 5, 2019 |
|
Researchers
| كمال الدين ابراهيم العوض | Alawad, Kamal Aldien Ibrahim | Researcher | Doctorate | |
|
Back To Researches Page
|