The submitted manuscript presents observational data from a cruise

that took place offshore Namibia during November-December 2016. The

dataset contains velocities inferred through 1) the boat ADCP, 2) 2

scanfish transects, 3) drifters (two releases of 12 drifters) and

estimates of temperature through remote sensing in the region.  The

region is an upwelling system where dominant Northward winds drive a

northward current with upwelling along the coast of Namibia.

The paper reports on a cold filament surface (visible on remote

sensing SST maps), formed “a priori” with upwelled cold water, and

then tracks its evolution within the regional mesoscale eddy field.

 Mesoscale upwelling filaments are common in eastern boundary currents

 --- a.k.a. squirts and jets".  This example is identifiable for

 nearly a month, and it at first is seen to extend several hundred

 kilometers offshore.

Surface maps are shown for SST, SLA, the calculated geostrophic

velocity calculated from it, and multiple drifter tracks.  In the core

of the filament the principal motion is a jet going offshore.

Sections across the filament are shown for T, S, buoyancy frequency,

horizontal velocity, and Rossby number.  The Rossby number is not

small, but there is no evident secondary circulation.

Kinetic energy wavenumber spectra are calculated from four long ship

tracks.  A fuss is made over the spectra being somewhat steeper at

smaller wavenumbers and less steep at larger ones (down to a wavelength

of 200 m).  This is consistent with previous experience.  The

horizontal velocity is mostly rotational at smaller wavenumbers,

consistent with geostrophic balance, and nearly equipartitioned with

its divergent component at larger wavenumbers, the latter consistent

with partly ageostrophic submeoscale motions or a modest presence of

inertia-gravity waves.

Links to dynamics are attempted through calculations of Rossby number,

Richardson number, and estimates of Ertel potential vorticity (but

only with along-track gradients).  The stated context is to identify

submesoscale instabilities of several types.  In my view this is not

very conclusive.  Patchy values of possible exceedance of stability

thresholds are found, especially in the surface boundary layer where

we can expect small-scale turbulence to be active, but otherwise there

seems to be no systematic pattern.  The authors claim stronger

confirmation of instabilities than I think is justified.

I view this paper as largely confirmatory of present understandings of

mesoscale near-boundary upwelling filaments.  It does establish the

mesoscale flow structure and density field during a several-week phase

of relaxation after what was probably the peak offshore excursion of

the filament.  It also establishes that this event occurs in

conjunction with smaller-scale fields suggestive of forward energy

cascade toward viscous dissipation, again more or less as expected.

It's hard to say that anything new was discovered, and partly this

should be understood as illustrating the difficulty of connecting

mesoscale and smaller-scale phenomena with the sampling methods

employed here.