1
Course outline
The course is organized into two, 1½-hour lectures during the morning with 3-hour
practicals during the afternoon. The morning lectures discuss specific processes, and the
topics of the afternoon practicals are linked to the lectures as much as possible. A list of
the lectures and practicals, with a brief summary of their topics, follows.
Day 1 (introduction & observations)
Lecture 1a); Introduction & observations (McCreary): Overview of the phenomena and
processes discussed in the course.
Lecture 1b); Observations (Shankar): Overview of circulations and major currents in the
NIO, and their underlying dynamics. Remarks on the nature of geophysical fluid flows.
Practical (Suprit Kumar, Girishkumar): Introduction to Ferret, followed by an application
related to the morning lecture.
Day 2 (ocean models & waves)
Lecture 2a); Ocean models (McCreary): A hierarchy of models have been used to study
the ocean. The more-complex models simulate observations most realistically, whereas
the simpler systems are useful for identifying specific processes. Models discussed are
ocean general circulation models (OGCMs), the linear, continuously stratified (LCS) model,
and a variety of layer models.
Lecture 2b); Wave radiation (McCreary): Types of waves (gravity, Kelvin, and Rossby
waves), their dispersion relations, and phase and group speeds. These waves are very
apparent in the NIO. Their presence means that wind forcing in one region of the NIO can
affect remote regions often thousands of kilometres away.
Practical (Suprit Kumar, Girishkumar): Filtering altimeter data and model output to isolate
the waves discussed in the morning lectures.
Day 3 (interior ocean)
Lecture 3a); Interior Ocean I (McCreary): How does the interior ocean respond to wind
forcing in the interior ocean? Topics covered include: Ekman drift, Ekman pumping,
radiation of Rossby waves, and adjustment to Sverdrup balance.
Lecture 3b); Interior Ocean II (McCreary): Continuation of Part 1.
Practical (Suprit Kumar, Girishkumar): Response to interior Ekman pumping over the Bay.
Run the LCS model with the coastal and equatorial response filtered out. (Arnab already
has these simulations in place for a 0.1° version of the LCS model.) Students then
analyze this response in the interior-ocean practical. (They can analyze the coastal and
equatorial-ocean responses later in their respective practicals.)
2
Day 4 (coastal ocean)
Lecture 4a); Coastal Ocean I (McCreary): How does the coastal ocean respond to
alongshore winds? In addition to gravity and Rossby waves, coastal Kelvin waves are
excited by the wind. Vertical propagation of Kelvin waves. When there is a continental
shelf, shelf waves are also generated.
Lecture 4b); Coastal Ocean II (McCreary, Amol): Continuation of Part 1. Observations and
modelling of coastal currents.
Practical (Amol, Mukherjee): Analyses that illustrate wave propagation around the
perimeter of the Bay and along the west coast of India. Part of this practical will be
analysis of LCS results with non-coastal responses filtered out. Another part could be
analysis of tide-gauge and altimeter data.
Day 5 (equatorial ocean)
Lecture 5a); Equatorial Ocean I (McCreary): What are equatorially trapped waves, and
how do they differ from off-equatorial waves? In addition to gravity and Rossby waves,
there is an equatorial Kelvin wave and a Yanai wave. How does the equatorial ocean
respond to wind forcing? Vertical propagation of equatorial Kelvin, Yanai, and Rossby
waves.
Lecture 5b); Equatorial Ocean II (McCreary): Continuation of Part 1.
Practical (Chatterjee, Amol): Analyses of altimeter data and/or LCS/MOM outputs that
illustrate aspects of equatorial currents. Possible analyses are: 1) Wyrtki Jets, showing
their semiannual nature; 2) obtaining meridional sections that show vertical phase
propagation of Rossby-like features (the WJs appear to part of this vertical propagation);
and 3) isolation of equatorially forced circulations in the Bay and AS.
Day 6, Saturday (small-scale instabilities & mixed-layer processes)
Lecture 6a); Small- scale instabilities (McCreary): Small-scale instabilities include
convective overturning and Kelvin-Helmholtz instability. Mile's famous requirement for the
existence of KH instability (Ri < 0.25) is derived. These instabilities are important for
generating turbulence in the surface mixed layer. KH instability is also important for
subsurface mixing (e.g., for the breaking of internal waves).
Lecture 6b); Mixed layer (Shankar): The discussion of small-vertical scale instabilities
leads naturally into mixed-layer processes and models.
Practical (Vijith): Use Ferret to contrast mixed layers and their variability in the Bay of
Bengal and Arabian Sea. We could analyze output from an OGCM solution, or data from
CTDs, the Chatterjee et al. (2012) climatology, and maybe Argo floats.
Day 7 (biophysics)
3
Lecture 7a); Biophysics I (McCreary): Introduction to biophysical phenomena and
processes in the NIO. A major conclusion is that ocean physics is critical: Unless ocean
physics (in particular, the mixed-layer thickness) is accurately modelled, biological activity
cannot be accurately simulated.
Lecture 7b); Biophysics II (Vijith): A specific example of the impact of physics on biology,
namely, the impact of the large-scale WICC on the NEAS ecosystem.
Practical (Vijith): Discussion and plotting of TOPAZ results.
Day 8 (large-scale instabilities & eddies and fronts)
Lecture 8a); Large-scale instabilities (McCreary): Large-scale instabilities include
barotropic and baroclinic instability. The familiar requirement for the existence of
barotropic instability (Uyy – β must change sign) is derived. When these instabilities grow
to finite amplitude, they generate eddies and fronts.
Lecture 8b); Eddies and fronts (Francis, Aparna): Differences between 0.1° and 1/48°
OGCM solutions will be contrasted. Specific examples of the impact of eddies and fronts
on NIO circulations.
Practical (Aparna): Identification of SST fronts in observational and model data.
Day 9 (overturning circulations)
Lecture 9a); Overturning circulations I (McCreary): Two prominent overturning circulations
in the NIO are the Cross-equatorial Cell (CEC) and Subtropical Cell (STC). The CEC is
important for the NIO as it provides most of the water that upwells in the region. The STC
is important because variability in its strength (particularly, its upwelling branch) impacts
climate.
Lecture 9b); Overturning circulations II (Shankar): Two other overturning cells with their
descending branches in the Arabian Sea generate Persian-Gulf water (PGW) and RedSea water (RSW).
Practical (Amol, Suprit Kumar, and Girishkumar): Identify overturning cells in models using
Ferret.
Day 10 (intraseasonal variability)
Lecture 10a); Intraseasonal variability I (Jay, Amol, Mukherjee): Introduction to
instraseasonal variability (ISV) in the NIO. Analyses of altimeter and ADCP data on the
west and east coasts of India.
Lecture 10b); Intraseasonal variability II (Amol): Theory and model simulations of
circulations along Indian coasts.
Practical (Amol, Mukherjee): Use Ferret to identify the structure of prominent intraseasonal
events in the NIO. Focus will be on analyses of altimeter data, including OSCAR currents.
4
Day 11 (South Asian Monsoon)
Lecture 11a); Description (Francis): General features of the South Asian Monsoon.
Lecture 11b); Oceans and the Monsoon (Francis): Variability of the South Asian Monsoon,
and its links to climate processes in the Indian and Pacific Oceans (EQUINOO/IOD and
ENSO).
Practical: Discussion and feedback of the course.