pyParaOcean, A System for Visual Analysis of Ocean Data: Case study: Bay of Bengal

30 May 2024


(1) Toshit Jain, Indian Institute of Science Bangalore, India;

(2) Varun Singh, Indian Institute of Science Bangalore, India;

(3) Vijay Kumar Boda, Indian Institute of Science Bangalore, India;

(4) Upkar Singh, Indian Institute of Science Bangalore, India;

(5) Ingrid Hotz, Indian Institute of Science Bangalore, India and Department of Science and Technology (ITN), Linköping University, Norrköping, Sweden;

(6) P. N. Vinayachandran, Indian Institute of Science Bangalore, India;

(7) Vijay Natarajan, Indian Institute of Science Bangalore, India.

Abstract and Intro

Ocean data

pyParaOcean: Architecture

pyParaOcean: Functionalities

Case study: Bay of Bengal

Conclusion, Acknowledgments, and References

5. Case study: Bay of Bengal

The Summer Monsoon Current (SMC) is a prominent feature of Indian ocean circulation and the SMC flows around Sri Lanka to flow into the Bay of Bengal. We use pyParaOcean to study different phenomena in the Bay of Bengal, particularly during the monsoon.

Eddies. Figure 5 is a rough schematic of the major currents and eddies in the Bay during the monsoon season. A large anticyclonic eddy (AE) located to the right of the SMC and a cyclonic eddy known as the the Sri Lanka Dome (SLD) to its left [VY98] are regular features in this region during summer. The AE has a diameter of about 500 km, located to the southeast off the coast of Sri Lanka, and is characterized by intense downwelling inside owing to its anticyclonic circulation. [VY98] proposed that the AE is formed by the interaction of the SMC and the incoming Rossby waves from Sumatra. The timeline of appearance and disappearance of the AE was documented in later work [VCMN04]. The AE starts forming in June, develops into its circular shape in July, and weakens in August, as shown in Figure 6 and the accompanying video.

Figure 6: Dissipation of a large anticylonic eddy in the Bay of Bengal through August 2020. Streamlines are seeded near detected vortex cores to show evolution of eddy profiles in 3D.

Figure 7: The Bay of Bengal between July 1, 2020 and July 31, 2020. Visualization of the flow using streamlines with uniform seeding and (≥ 35 psu) salinity isovolume rendering. (a) July 1, 2020: The AE can be seen forming around 8°N and 90°E with the SMC streamlines visible from 78°E to about 86°E. (b) July 15, 2020: The AE, 8°N and 87°E, has matured into a circular shape and moves westward towards Sri Lanka. The (≥ 35 psu) isovolume shows recirculation of high salinity waters into they Bay by AE. (c) July 31, 2020: The AE, 7°N and 84°E, reaches the eastern coast of Sri Lanka where it will start to dissipate.

Salinity transport. pyParaOcean serves as an efficient tool to analyze the effects of AE on the Bay of Bengal. Streamlines and pathlines offer visualization of circulation associated with the AE and its movement in the ocean. The field lines may be overlaid on a volume rendering of a scalar to visualize the transport caused by the eddy. Figure 7 and the accompanying video show the streamlines overlaid on a salinity volume rendering at different time steps to show the role of the AE in transport of salt. The movement of high salinity water from the Arabian sea by the SMC into the Bay of Bengal and its recirculation by the AE is well captured in this representation. Tracking surface fronts of high salinity water and highlighting the long-lived tracks helps capture an overview of significant salinity movement in the region. We observe a track that moves towards the coast of India, see Figure 4.

Downwelling. Figure 8 and the accompanying video show the use of the depth profile filter to visualize the depression of the 27◦ isotherm by the AE. The anticyclonic nature of the eddy causes a downwelling inside the eddy and pushes the relatively warmer water downward. The parallel coordinates view shows changes in temperature, salinity, and speed in the water column caused by the arrival of the eddy at the point of interest.

Experience and performance. This case study was conducted in collaboration with an oceanographer coauthor. Several observations on phenomena such as the SLD and the movement of high salinity water could be made using pyParaOcean. While our oceanographer collaborators typically use tools such as pyFerret for 2D analysis, they found the capability of pyParaOcean to be very useful. After this initial satisfying experience, we plan to work together on the study of higher resolution model output using pyParaOcean. The surface front tracking and eddy detection filters take a few minutes, while all other filters take 1-2 seconds or less. All the experiments were run on a workstation with an 8 core AMDEPYC 7262 @ 3.2 GHz CPU with 512 GB main memory and NVIDIA RTX A4000 (16 GB) GPU. The surface front computation is parallelized using the python multiprocessing library but there is scope for further improvement in runtime. The eddy detection and visualization filter can also be optimized by parallelizing some of the computation. We plan to take this up in the future.

Figure 8: The depression of the 27◦ isotherm (yellow) by the anticylonic eddy in the Bay of Bengal. A needle is dropped at 7◦N, 84◦E and the depth profile shows the temperature drop. The interactive parallel coordinates plot is used to brush-select 10 m intervals at depths of 25 m and 85 m. (a) July 1, 2020: The downwelling of the AE can be seen around 8◦N and 90◦E, at the depth of 100 m. As it forms, the AE pushes the 27◦ isotherm down. (b) July 15, 2020: The AE, 8◦N and 87◦E, can be seen moving east with the depression of the isotherm and the depth profile of temperature begins to flatten near 29◦C as the eddy moves closer to the needle. (c) July 31, 2020: The AE centre, 7◦N and 85◦E, is very close to the needle and the depression in the isotherm has moved all the way to near the east coast of Sri Lanka.

This paper is available on arxiv under CC 4.0 license.