# Tag Info

Accepted

### Similarities and differences between lava flows and fluvial geomorphology (rivers)

The similarities pretty much end at the fact that both water and lava flow downhill seeking the lowest possible level. As even the most fluid lavas flow somewhat slower than water because of their ...
• 4,260
Accepted

### Why air parcel is on a circular trajectory when considering Coriolis force

The parcel in question is not moving in a straight line. It is a particle at rest in the reference frame rotating earth. A "fixed" observer in space would see a particle moving in circles ...
• 1,145

### A problem of the 2-Layer hydrostatic model

Let's say our goal is to find $\eta$ which is the displacement of the fluid relative to its resting position at $z = H_2$. We find \begin{split} p_2 - p_1 &= \require{cancel} \...
• 1,145
Accepted

### How far can an andesitic lava flow, and what is the velocity?

During my PhD, I listed many dacite and rhyolite flows, but also included a few andesite flows for comparison. Here are a few interesting examples, first of andesite flows that have been observed ...
• 7,933

### How far can an andesitic lava flow, and what is the velocity?

Andesitic lava is viscous, compared to basaltic lava. Andesitic lava flows at a rate of a few kilometers per hour, whereas basaltic lava can flow up to 10 km/h. Because of their viscosity, andesitic ...
• 24.7k

### Hydrology- flow accumulation

The flow accumulation algorithm essentially determines the upstream contributing area of every grid cell; in other words, what area or how many other cells will drain into a given cell. The flow ...
• 751
Accepted

### Deriving shallow water equations: why is the vertical velocity equal to the material derivative of the surface level?

This is a statement of the kinematic free surface boundary condition: there can be no normal flow through the boundary, only tangential flow along it. Equivalently, the normal velocity (relative to ...
Accepted

### What is the simplest meteorological model to operate?

I think you are asking a question with a variety of different constraints. I'll tackle a couple of them. What is the simplest atmospheric model to operate? That would be the Zero-dimensional ...
• 8,799

### Similarities and differences between lava flows and fluvial geomorphology (rivers)

In terms of rheology, there is a key difference between water and lava: water is a Newtonian fluid, lava isn't. In early volcanology days, there has been attempts to model lava as a Newtonian fluid (...
• 7,933
Accepted

### Why are there different Notations of Vorticity Equation?

The first equation is presented when the vector identities are not used. That is when students may not have knowledge of advanced vector algebra, for example, curls, dot and cross products, ...

### Does air in the atmosphere get friction due to the planet's rotation?

The short answer is yes. Whenever a fluid moves against something else it will experience friction, it's a function of fluid dynamics. The atmosphere is a weakly viscous fluid, but friction is ...
• 24.7k
Accepted

### Why is one term missing in the derivation of continuity equation in isentropic coordinates?

Potential temperature is conserved considering adiabatic processes and thus: $\text{d} \theta/\text{d}t = 0$. Otherwise the term needs to be retained. On page 84 (just below figure 4.3) they say that ...
• 1,145
Accepted

### How is centrifugal force identified in equations of fluid motion in the rotating reference system of earth?

I wonder why there is no centrifugal force, however, the apparent force in a rotating system should be the sum of Coriolis and centrifugal force. There is a centrifugal acceleration in those ...
• 23.6k
Accepted

### At what point are water droplets too small to make a rainbow?

Some time ago I posted this answer about how rainbows are formed, and the Wikipedia link Trond Hansen posted mentions droplet size relative to the wavelength of light. For a rainbow to form, the ...
• 2,187

### Does air in the atmosphere get friction due to the planet's rotation?

Since you say "due solely to the planet's rotation", the best answer might be "No." The atmosphere rotates as a body with the planet. The interplanetary medium is so diffuse there ...
• 213
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• 8,799
Accepted

### Is COMSOL Multiphysics good for subduction CFD modelling? Are there alternatives?

numerical modelling is a vast field and the tool to address your problem depends strongly on ... your problem and your approach! Are you a master student? a PhD student with very short time to wrap up ...
• 461
Accepted

### How can speed of geostrophic wind change when forces are always perpendicular to speed?

You're confusing time-dependent and time independent equations: The time-dependent model tells you how $\vec U$ will evolve, it doesn't have to evolve into a steady-state. The steady, time-independent ...

### Is it meaningful to assume static pressure to be constant along a streamline?

If you assume both hydrostatic and pure geostrophic balance, that is a valid assumption. In Einstein notation, $$u_i=-\frac{1}{f \rho}\frac{\partial P}{\partial x_j}\epsilon_{ij3}$$ If we look at ...
• 8,799
Accepted

### What is the relationship between air pressure and temperature?

Or if the math of the other answers is a bit complex, in a broad sense, the balancing relationship is: $$\frac{\mathrm{density} \cdot \mathrm{temperature}}{\mathrm{pressure}} = \mathrm{constant}$$ For ...
• 8,768
Accepted

### Why does relative vorticity in spherical coordinates have an extra term as compared to the usual cartesian derivation?

The best way to see this extra term is to consider a bug moving along a latitude circle at constant speed $|u|$ in a constant direction arounf the poles. If the bug is moving along a geodesic then ...
• 3,831
1 vote

### Manning's N vs. Drag Coefficient Cd values for NLCD land cover classes

I think you are confusing terminologies. The Manning N values are representations of surface roughness that is used in the Manning equation, as it is applied to fluid flow in an a open or a closed ...
• 24.7k
1 vote

### What is the relationship between air pressure and temperature?

Compression and expansion of an ideal gas is an adiabatic process, i.e. the entropy $\rm (P\rho^{-\gamma}) = const$, where $\gamma$ is the adiabatic constant. You can rearrange this using the ideal ...
1 vote

### Vertical air speed

That's... a pretty specific question. Well, we start with making assumptions. Let's write the continuity equation with the Boussinesq approximation: \frac{\partial \omega}{\partial P}=-\frac{\...
• 8,799

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