Influence of coastal upwelling on the surface current in the Bay of Bengal using HF radar and satellite observations

2021 ◽  
Author(s):  
Shouvik Dey ◽  
Sourav Sil ◽  
Samiran Mandal
Keyword(s):  
Coastal Upwelling ◽  
Surface Current ◽  
Hf Radar ◽  
Second Phase ◽  
Biological Productivity ◽  
Maximum Peak ◽  
Current Observation ◽  
Ekman Layers ◽  
Ocean Surface Current ◽  
Upwelling Index

<p>Coastal Upwelling is a phenomenon in which cold and nutrient-enriched water from the Ekman layers reaches the surface enhancing the biological productivity of the upwelling region. In this work, an attempt is made to understand the influence of coastal upwelling on surface current variations during May 2018 to August 2018, when HF radar current observation (source: NIOT, India) is available. The wind-based Upwelling Index(UI<sub>wind</sub>) showed coastal upwelling throughout the study period. But the SST based upwelling index (UI<sub>sst</sub>) showed upwelling occurred only from May to the first week of June. Cross-shore components of HF radar-derived ocean surface current (CSSC)  showed strong similarity with UI<sub>sst</sub>. The first phase of upwelling from UI<sub>sst</sub> is observed to start on 5<sup>th</sup> May and lasts till 14<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km. Then, there is a break period for about three days and after that, the second phase of upwelling starts on 17<sup>th</sup> May and lasts till 25<sup>th</sup> May with a maximum peak on around 20<sup>th</sup> May, but this time the horizontal extension is ~100 km which is much larger than during the first phase. A strong positive (from coast to offshore) CSSC is observed to start on around 5<sup>th</sup> May and lasts till 13<sup>th</sup> May with a maximum peak on around 10<sup>th</sup> May and having a horizontal extension of ~40 km, as observed from UIsst. A reversal of CSSC (towards coast) is noted on 14<sup>th</sup> May when the break of coastal upwelling is evident from UI<sub>sst</sub>. The CSSC then again started intensifying 15<sup>th</sup> May onwards and continued for ten days till 25<sup>th</sup> May, similar to UI<sub>sst</sub>.  The horizontal extension of the upwelling signature in the second phase of upwelling is ~70 km. Therefore, a 7-10 days of the coastal upwelling and its horizontal extension are identified in this study. This study suggests the use of high resolution (~6 km) HF radar current observation on the monitoring of coastal upwelling processes.</p>

Detecting Subtle Seasonal Transitions of Upwelling in North-Central Chile

2015 ◽  
Vol 45 (3) ◽  
pp. 854-867 ◽  
Author(s):  
David A. Rahn ◽  
Benjamín Rosenblüth ◽  
José A. Rutllant
Keyword(s):  
Wind Stress ◽  
Large Scale ◽  
Coastal Upwelling ◽  
Southern Oscillation ◽  
Biological Productivity ◽  
Wind Stress Curl ◽  
Two Phase ◽  
North Central ◽  
Central Chile ◽  
Upwelling Index

AbstractBiological productivity in the ocean along the Chilean coast is tied to upwelling that is primarily forced by equatorward wind stress and wind stress curl on the ocean surface. Southerly alongshore flow is driven by the southeast Pacific (SEP) anticyclone, and its intensity and position vary on a range of time scales. Variability of the SEP anticyclone has been linked to large-scale circulations such as El Niño–Southern Oscillation and the Madden–Julian oscillation. The actual timing, duration, and nature of the seasonal meridional drift of the SEP anticyclone are associated with the onset, demise, and strength of the local upwelling season. Seasonal variation is especially marked at the Punta Lavapié (37°S) upwelling focus, where there is a clear upwelling season associated with a change of the cumulative upwelling index (CUI) slope between positive and negative. The Punta Lengua de Vaca (30°S) focus typically exhibits upwelling year-round and has less distinct transitions, making it more difficult to identify an enhanced upwelling season. A two-phase linear regression model, which is typically used to detect subtle climate changes, is applied here to detect seasonal changes in CUI at Punta Lengua de Vaca. This method objectively finds distinct transitions for most years. The spring-to-summer transition is more readily detected and the slackening of the upwelling-favorable winds, warmer waters, and longer wind strengthening–relaxation cycles change the coastal upwelling ecosystem. While the spring-to-summer transition at Punta Lengua de Vaca could be influenced by large-scale circulations, the actual dates of transition are highly variable and do not show a clear relationship.

Measuring Antenna Patterns for Ocean Surface Current HF Radars with Ships of Opportunity

2014 ◽  
Vol 31 (7) ◽  
pp. 1564-1582 ◽  
Author(s):  
Brian M. Emery ◽  
Libe Washburn ◽  
Chad Whelan ◽  
Don Barrick ◽  
Jack Harlan
Keyword(s):  
Surface Current ◽  
Ocean Surface ◽  
Radar Data ◽  
Direction Finding ◽  
Antenna Pattern ◽  
Hf Radar ◽  
Ocean Current ◽  
Identification System ◽  
Screening Methods ◽  
Ocean Surface Current

Abstract HF radars measure ocean surface currents near coastlines with a spatial and temporal resolution that remains unmatched by other approaches. Most HF radars employ direction-finding techniques, which obtain the most accurate ocean surface current data when using measured, rather than idealized, antenna patterns. Simplifying and automating the antenna pattern measurement (APM) process would improve the utility of HF radar data, since idealized patterns are widely used. A method is presented for obtaining antenna pattern measurements for direction-finding HF radars from ships of opportunity. Positions obtained from the Automatic Identification System (AIS) are used to identify signals backscattered from ships in ocean current radar data. These signals and ship position data are then combined to determine the HF radar APM. Data screening methods are developed and shown to produce APMs with low error when compared with APMs obtained with shipboard transponder-based approaches. The analysis indicates that APMs can be reproduced when the signal-to-noise ratio (SNR) of the backscattered signal is greater than 11 dB. Large angular sectors of the APM can be obtained on time scales of days, with as few as 50 ships.

scholarly journals Ocean Surface Current Observation with a Dual Monopole-Cross-Loop Antenna Array

2017 ◽  
Vol 2017 ◽  
pp. 1-8 ◽  
Author(s):  
Yeping Lai ◽  
Hao Zhou ◽  
Yuming Zeng ◽  
Biyang Wen
Keyword(s):  
Antenna Array ◽  
Surface Current ◽  
Ocean Surface ◽  
Antenna System ◽  
Current Measurement ◽  
Current Profile ◽  
Current Observation ◽  
Ocean Surface Currents ◽  
Ocean Surface Current

The high-frequency radars (HFRs) receiving the sea echoes backscattered from the fluctuating ocean surface to remotely sense ocean surface currents are a popular and powerful tool in oceanic observation. Dominant error source in current measurement for HFR systems has been recognized to be the direction of arrival (DOA) determination of the sea echoes. To eliminate this error and therefore improve the performance of direction-finding HFR system in current measurement, we have investigated a dual monopole-cross-loop (MCL) antenna array in current observation. Simulations indicated that the dual MCL antenna array has a better performance than the conventional single MCL antenna system in current mapping, especially for the complex current profile. And comparisons of radar field data and buoy measurements suggested that the RMSE value was larger than 15 cm/s for the conventional MCL antenna. But it decreased to 12.64 cm/s for the dual MCL antenna array. Moreover, the temporal coverage rate also showed the benefit of using this antenna system in current mapping. The results demonstrated that it is advisable to adopt the dual MCL antenna array in operational applications.

Simulation of tsunami signatures in ocean surface current maps measured by HF radar

2009 ◽  
Author(s):  
Anna Dzvonkovskaya ◽  
Klaus-Werner Gurgel ◽  
Thomas Pohlmann ◽  
Thomas Schlick ◽  
Jiangling Xu
Keyword(s):  
Surface Current ◽  
Ocean Surface ◽  
Hf Radar ◽  
Ocean Surface Current

Surface current measurements in Terra Nova Bay by HF radar

2003 ◽  
Vol 15 (1) ◽  
pp. 55-62 ◽  
Author(s):  
D. FLOCCO ◽  
P. FALCO ◽  
P. WADHAMS ◽  
G. SPEZIE
Keyword(s):  
Continuous Monitoring ◽  
Ross Sea ◽  
Surface Current ◽  
Hf Radar ◽  
Dynamical Characteristics ◽  
Terra Nova Bay ◽  
Terra Nova ◽  
Ocean Surface Current ◽  
Future Work

During summer (2 December 1999–23 January 2000) an Ocean Surface Current Radar (OSCR-II) was used to provide surface current measurements within the Terra Nova Bay polynya, one of the most important coastal polynyas of the Ross Sea. This represents an important step towards a continuous monitoring of the area. Useful information is now available as a basis for future work in this field, although the two radar sites, necessary to calculate the total current vector, did not work together throughout the whole period of the experiment as one of the units was damaged. The results demonstrate the feasibility of this kind of measurement and suggest that very important dynamical characteristics of the polynya could be deduced from long term deployment of such a system.

Ocean Surface Current Measurement Using Shipborne HF Radar: Model and Analysis

2016 ◽  
Vol 41 (4) ◽  
pp. 970-981 ◽  
Author(s):  
Guanghong Chang ◽  
Ming Li ◽  
Junhao Xie ◽  
Ling Zhang ◽  
Changjun Yu ◽  
...  
Keyword(s):  
Surface Current ◽  
Ocean Surface ◽  
Current Measurement ◽  
Hf Radar ◽  
Ocean Surface Current

scholarly journals Biological productivity in the Mauritanian upwelling estimated with a triple gas approach

2012 ◽  
Vol 9 (4) ◽  
pp. 4853-4875 ◽  
Author(s):  
T. Steinhoff ◽  
H. W. Bange ◽  
A. Kock ◽  
D. W. R. Wallace ◽  
A. Körtzinger
Keyword(s):  
Coastal Upwelling ◽  
Strong Relationship ◽  
Biological Productivity ◽  
Net Community Production ◽  
Surface Ocean ◽  
Northwest Africa ◽  
Upwelled Water ◽  
Novel Approach ◽  
Different Seasons ◽  
Upwelling Index

Abstract. Due to their high biological productivity coastal upwelling regions are important for biogeochemical cycles in the ocean and for fisheries. Upwelled water is not only enriched in nutrients but also supersaturated with respect to atmospheric CO2 and N2O and undersaturated for O2. We present a novel approach to estimate carbon based net community production (NCP) using surface ocean data for CO2, O2 and N2O from three cruises to the Mauritanian upwelling region (Northwest Africa) that were conducted in different seasons. Through combination of the saturation patterns of CO2, O2 and N2O effects of air–sea gas exchange and NCP could be separated. NCP values ranges from 0.6 ± 0.1g C m−2 d−1 during times of weak upwelling to 1.6 ± 0.4 g C m−2 d−1 during strong upwelling. The estimated NCP values show a strong relationship with a wind derived upwelling index, which was used to estimate annual NCP.

scholarly journals Applying the Method of EOF Interpolation and 2dVar to Complete the Ocean Surface Current Data Obtained from HF Radar System

2018 ◽  
Vol 34 (1S) ◽  
Author(s):  
Nguyen Thi Thu Mai ◽  
Alexei Sentchev ◽  
Tran Manh Cuong
Keyword(s):  
Interpolation Method ◽  
Surface Current ◽  
Ocean Surface ◽  
Radar Data ◽  
Current Data ◽  
Surface Flow ◽  
Radar System ◽  
Hf Radar ◽  
High Frequency Radar ◽  
Ocean Surface Current

Abstract: There are now over 350 high frequency radar (HF radar) stations operating on the coast of 37 countries around the world that allow the mapping of ocean surface current. However, observation from HF radars are often interrupted (loss of data) in both space and time due to signal inference, backscatters, ocean state.Therefore, in this study, we will present a method to improve the surface current data collected from HF radar system. Firstly, the radial surface current data will be filtered intermittently, then the result is interpolated over time and space by the orthogonal experimental EOF and the 2dVar bi-directional variable interpolation. In addition, the authors have initially applied 2dVar interpolation method to the HF radar data in Vietnam and received initial positive results. The methods used in this paper promise to be effective when applied to improve surface flow data obtained from HF radar stations in Vietnam in the future.   Keywords:EOF interpolation, 2dVar, Iroise sea, HF radar, ocean surface current.

Sign in / Sign up

Export Citation Format

Share Document