Analysis of Upwelling Events in the Southern South China Sea Using Multi-Mission Satellite Altimeter

Upwelling is a vital ocean behaviour, especially for the Fisheries Industry, where upwelling will help to detect fish ground at a particular ocean area. However, the study of upwelling is minimal and not well understood due to some reasons and constraints, such as limited observation. Upwelling lacks a comprehensive in-situ observation system where it relies on limited information collected from the ground-truthing execution such as ships, buoys, and current meter. This study aims to analyse the upwelling pattern in the southern region of the South China Sea by using a multi-mission satellite altimeter. In order to derive the physical oceanography that involves upwelling, such as sea surface height (SSH), Mean Dynamic Topography (MDT), and the Sea Level Anomaly (SLA), the Radar Altimeter Database System is used. Five Satellite Altimeter mission is used in this study, which is JASON-2, JASON-3, CYROSAT2, SARAL, SENTINAL3A from 2013 to 2017. Validation is made using a statistical method showing a good correlation between Altimetry data and Tidal Data at tide gauge, which is 0.84 to 0.97, respectively. Also, monthly altimetry derived Geostrophic Current was assessed by analysing the current pattern where it shows a similarity with a previous study where the current velocity is 0.5ms-1 to 2ms-1. From the result, eddies can be seen in the seasonal and monthly Absolute Geostrophic Ocean Current (AGOC) map, indicating the present presence of upwelling. In conclusion, this study will benefit other researchers in terms of both upwelling and eddy studies.

Assessing the Potential of Upcoming Satellite Altimeter Missions in Operational Flood Forecasting Systems

This study investigates the potential of observations with improved frequency and latency time of upcoming altimetry missions on the accuracy of flood forecasting and early warnings. To achieve this, we assessed the skill of the forecasts of a distributed hydrological model by assimilating different historical discharge time frequencies and latencies in a framework that mimics an operational forecast system, using the European Ensemble Forecasting system as the forcing. Numerical experiments were performed in 22 sub-basins of the Tocantins-Araguaia Basin. Forecast skills were evaluated in terms of the Relative Operational Characteristics (ROC) as a function of the drainage area and the forecasts’ lead time. The results showed that increasing the frequency of data collection and reducing the latency time (especially 1 d update and low latency) had a significant impact on steep headwater sub-basins, where floods are usually more destructive. In larger basins, although the increased frequency of data collection improved the accuracy of the forecasts, the potential benefits were limited to the earlier lead times.

Study of the Overflow Transport of the Nordic Sea

Changes in the climate system over recent decades have had profound impacts on the mean state and variability of ocean circulation, while the Nordic Sea overflow has remained stable in volume transport during the last two decades. The changes of the overflow flux depend on the pressure difference at the depth of the overflow outlet on both sides of the Greenland-Scotland Ridge (GSR). Combining satellite altimeter data and the reanalysis hydrological data, the analysis found that the barotropic pressure difference and baroclinic pressure difference on both sides of the GSR had a good negative correlation from 1993 to 2015. Both are caused by changes in the properties of the upper water, and the total pressure difference has no trend change. The weakening of deep convection can only change the temperature and salt structure of the Nordic Sea, but cannot reduce the mass of the water column. Therefore, the stable pressure difference drives a stable overflow. The overflow water storage in the Nordic Sea is decreasing, which may be caused by the reduction of local overflow water production and the constant overflow flux. When the upper interface of the overflow water body in the Nordic Sea is close to or below the outlet depth, the overflow is likely to greatly slow down or even experience a hiatus in the future, which deserves more attention.

Directional wave buoy data measured near Campbell Island, New Zealand

The New Zealand Defence Force (NZDF) has established a permanent wave observation station near Campbell Island, south of New Zealand (52 45.71 S, 169 02.54E). The site was chosen for logistical convenience and its unique location adjacent to the highly energetic Southern Ocean; allowing instrumentation typically deployed on the continental shelf to be used in this rarely observed southern environment. From February 2017, a Triaxys Directional Wave Buoy was moored in 147 m depth, some 17 km to the south of the island, with satellite telemetry of the 2D wave spectra at 3-hourly intervals. To date there have been three deployments on locations, yielding some 784 days of data. Validation of the measured significant wave height against co-located satellite altimeter observations suggests that the predominant wave directions are not attenuated by the island. The data provide a valuable record of the detailed wave spectral characteristics from one of the least-sampled parts of the Global Ocean.

Global Wind and Wave Climate Based on Two Reanalysis Databases: ECMWF ERA5 and NCEP CFSR

In the present work, the global wind and wave climate is studied on the basis of two well-known reanalysis products, namely ERA5 and CFSR-W (WW3 hereafter). Several statistical features of the datasets are assessed, such as seasonal variability, quantiles of the probability distribution, monthly, annual and inter-annual variability, and several error metrics. The time span covers a period of 31 years (1979–2009), a fact that assures that most of the long-scale features are equally present in both datasets. The analysis performed is depicted both on a global and regional scale. The results are also assessed by means of a global satellite altimeter dataset.

Ocean Tides near Hawaii from Satellite Altimeter Data. Part I

Sufficient and accurate tide data are essential for analyzing physical processes in the ocean. A method is developed to spatially fit the tidal amplitude and phase lag data along satellite altimeter tracks near Hawaii and construct reliable cotidal charts by using the Chebyshev polynomials. The method is completely dependent on satellite altimeter data. By using the cross-validation method, the optimal orders of Chebyshev polynomials are determined and the polynomial coefficients are calculated by the least squares method. The tidal amplitudes and phase lags obtained by the method are compared with those from the Finite Element Solutions 2014 (FES2014), National Astronomical Observatory 99b (NAO.99b), and TPXO9 models. Results indicate that the method yields accurate results as its fitting results are consistent with the harmonic constants of the three models. The feasibility of this method is also validated by the harmonic constants from tidal gauges near Hawaii.

Cross-Calibrations of the HY-2B Altimeter Using Jason-3 Satellite During the Period of April 2019–September 2020

In 2018, the Haiyang-2B (HY-2B) satellite altimeter was sent to orbit as a follow-up mission of the HY-2A satellite altimeter. The performance of the HY-2B system over the global oceans is considered to be critical. However, its performance is not fully known at the present time. In the present study, the first global quality assessment of the HY-2B Geophysical Data Record (GDR) was presented using comparison and crossover analysis processes of the main parameters and sea level anomalies (SLAs) with Jason-3 GDR data. This study’s assessment results demonstrated that the editing proportion of unqualified data for the HY-2B was 2.67%, which was at a similar level as the Jason-3 (2.86%). In addition, this study’s assessment results of the HY-2B key parameters (mainly the backscatter coefficients, significant wave heights, sea state bias, wet troposphere delays, and ionosphere delays) showed good agreement with the Jason-3, and there were no abnormal trends observed. The mean and standard deviations (STDs) were determined to be (0.21 ± 6.70) cm and (−3.4 ± 6.25) cm for the SLA differences at the self-crossover points of the HY-2B and dual-crossover points between the HY-2B and Jason-3 satellites, respectively. In addition, the SLA crossover analysis results indicated that the accuracy of the sea surface heights for the HY-2B was close to that of the Jason-3 satellite. The spatial distributions of the SLA differences showed no significant errors in the geographic characteristics. The SLA measurements were assessed using a wavenumber spectra method. The obtained results suggested that the power spectrum of the SLAs of the HY-2B satellite followed the regular patterns of the traditional Jason-3 altimeter. Furthermore, based on the spectrum analysis results, it was revealed that the noise level of the HY-2B was lower than that of the Jason-3, indicating a good overall performance of the HY-2B.