Welcome everyone to the first lecture in
Mesmetoden and Phärnekönen. So for lecture one I'm going to try and make two about 10 minute long
videos and we're going to talk about ocean the scales of ocean processes and how they influence
measurement methods. Basically we're going to go through a bunch of different examples of
the scales of ocean processes in the ocean that we might be interested in measuring.
So one thing I want to point out is that unfortunately with this recording equipment
you can't see my cursor so when I want to highlight something I'm going to try and use a
kind of like a marker. So for example here I want to point out that this plot shows on the y-axis
the time scale so I'll do something like this or underline or just so you know what's
and then of course it'll might end up making strange shapes and things but just try and
I'll just try and make it as simple as possible to make it easy for you to follow.
So this this plot that we see is probably one that you're already familiar with or you become
very well familiar with as you go through your studies. On the y-axis as I said is the time
scale ranging from seconds or hundreds of seconds or tens of seconds up to tens of thousands of
years and on the x-axis here we have the horizontal scales generally also maybe vertical scales
ranging from millimeters up to tens of thousands of kilometers and these little bubbles show
different processes mainly physical processes that happen in the ocean and how they and what
kind of scales they fall into. So for example at the higher end we have climate change which is
a very large scale process over many many years of course thousands or tens of thousands of years
and then as we go down down these temporal and spatial scales we get to to eddies and fronts
for example so they cover quite a range but you have eddies that are hundreds of kilometers
in size and last for for months or or you maybe even up to a year and then you have
fronts which are down below one or ten kilometers here
and that lasts maybe a much shorter period on the order of weeks and you have many different
processes here internal waves surface gravity waves and as we get further and further down we
get into the area of energy dissipation or turbulence molecular processes where we actually
get energy dissipation and so that's what's kind of the key point of this this figure is
this transport of energy that can go in both directions from so it can be transferred from
large scale processes down to small scale processes but can also go in the other direction
from smaller scale processes to large scale processes so one example of the downscale of
energy is the generation by internal tides here at this kind of scale of internal waves
which then in turn may break at some point and in through vertical turbulent mixing
mix and dissipate energy away and in the other direction you may have eddies these mesoscale
eddies which form and if you have two two coming together they may form at an even larger scale
eddy so here's an example of a very large scale large spatial scale with a large temporal scale
process which is global circulation or basin scale circulation and you're kind of probably
familiar with these kind of maps as well and here we have for example the Gulf Stream heading north
where it gradually cools as it enters the Arctic Ocean
maybe through convection then we have the the cold water as the water cools it sinks
and we have the return flow through the Denmark Strait forming the northern end of the Amok
circulation but what we now know is that although this picture is very representative it doesn't
capture all the details it doesn't capture all the scales and for example the Gulf Stream
in particular is not so easy so well represented by a straight line as shown here instead it's a
very dynamic system full of instabilities and formation leading to the formation of eddies and
meandering of the stream along its path so the figure on the right we can see that as a drawing
so first we you sort of imagine this originally we had this smooth stream in the in the last slide
now we start to see meandering of the the current due to instabilities here we go
which in turn as these meanders evolve they eventually lead to the spin-off of of eddies
these mesoscale eddies which for example one here and as well in the vertical there is also
a lot of variability so here we see on on the bottom left part a section through the Gulf Stream
with depth on the y-axis and distance on the x on the distance offshore on the on the x-axis
and we can see the variability in both
vertical and horizontal scales and the image above is a satellite image showing basically the
same idea as the the drawing on the right and again here's the main path of the Gulf
Stream coming through and we see all this variability in the this would be surface sea
surface temperature so warmer water would be warmer colors red and orange and colder water would be
green and blue and we can see the meander of the Gulf Stream here and the formation of eddies
as they spin off for example here and also what's very interesting here is the change in
temperature so as this Gulf Stream moves northward it is cooling to get a real idea of
how much variability there really is in something like the Gulf Stream or in the ocean in general
there are some great modeling efforts and output that you can look at this is one example based on
the MIT GCM model put together by NASA the link you'll find in the slides and you can really
explore this visualization for hours if you're interested it's really quite amazing and so here's
a little clip showing what's called the perpetual ocean what they call the perpetual ocean showing
all the different or up to down to a certain scale at least the variability in the ocean
again over here we see the Gulf Stream moving moving northward along the course
coast of North America and the meandering that occurs in the eddies that form as it spins off
but it is of course not the only area that this happens so throughout the ocean we see
many mesoscale eddies and strong currents that are meandering as they flow
there's the agulas currents and eddies off the tip of South Africa
you
as i say we could keep watching that probably for hours but we'll i'll leave it at that and
please once you download the slides or if you already have please go check out the website
that i've linked it's actually not i was showing the youtube station but the link is to the
the data source and they have more videos there and links also to the youtube channel
so this concludes the first video of lecture one and the next video will continue with some more
examples as we move down the the plot on the left as we get into smaller time scales and
smaller spatial scales