Tutorial - Fourier Space Representation-1 — Lesson 5

This lesson covers the concept of Fourier Space and its representation through various examples. The lesson begins with an explanation of velocity fields in a box of size pi pi and how to derive the Fourier modes for this field. The instructor then moves on to discuss the concept of Fourier transform and how to compute it for different fields. The lesson also delves into the calculation of kinetic energy and enstrophy for each mode. The instructor further explains the concept of a 2D-3C field, which is a 2D field with three components. The lesson concludes with an explanation of how to compute helicity and the difference between positive and negative helicity.

Video Highlights

02:06 - Discussion on Fourier modes and Fourier transform
05:00 - Explanation of the concept of amplitude in Fourier modes
08:54 - Introduction to the concept of kinetic energy and modal kinetic energy
10:25 - Discussion on the direction of the velocity field in Fourier space
15:44 - Introduction to the concept of Quasi 2D field
19:52 - Explanation of the concept of helicity in Fourier modes

Key Takeaways

- Fourier Space is a mathematical tool used to analyze functions or signals with respect to frequency, rather than time.
- Fourier modes are the amplitudes of the Fourier transform of a field.
- The kinetic energy of a mode, also known as modal kinetic energy, can be calculated using the formula half of ux square plus uy square.
- A 2D-3C field is a 2D field with three components, which can be used to represent more complex configurations.
- Helicity, a measure of the 'twist' of a field, can be computed using the formula half u dot omega star real part.