What is the expression for pressure distribution in a rotating tornado?

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Homework Help Overview

The problem involves determining the pressure distribution in a rotating tornado characterized by a constant angular velocity and uniform temperature. The original poster seeks to express the outward pressure distribution in relation to the central pressure, given specific conditions such as temperature and atmospheric pressure at a certain distance from the center.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the application of the ideal gas law and the pressure gradient force in the context of a rotating system. There are questions about the validity of using the equation of state for dynamic systems like tornadoes and the implications of uniform angular velocity on the pressure distribution.

Discussion Status

The discussion is ongoing, with participants exploring different aspects of the problem, including the relationship between pressure and density in a rotating frame. Some guidance has been offered regarding the use of the hydrostatic equation and considerations for air density as a function of pressure.

Contextual Notes

Participants note the need to consider the ideal gas law in relation to the pressure distribution and the potential complexities introduced by the dynamic nature of the tornado. There is an acknowledgment of the assumptions involved in modeling the tornado's behavior.

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Homework Statement


A tornado rotates with constant angular velocity ##\omega## (i.e. like a solid object would rotate) and has
a uniform temperature T. Find an expression for the outward pressure distribution in terms of the central pressure ##p_0##. Use this to calculate ##p_0## given that T = 300 K and that at 0.1 km from the centre the atmospheric pressure p = 100 kPa and wind speed V = 100 m s-1.2. The attempt at a solution
Pressure gradient force =## -\frac{1}{\rho} \nabla p##
PV=NRT
 
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Raptor112 said:
PV=NRT
In my incomplete understanding, an 'equation of state' (such as PV=NRT) describes the properties of a system near equilibrium. I don't believe it can be (at least not naively) applied to more dynamic systems (such as a tornado). If anyone has more to say on this, please do; I like to learn as well.

Raptor112 said:
Pressure gradient force =## -\frac{1}{\rho} \nabla p##
Perhaps you mean "acceleration due to pressure gradient force" (check dimensions).
Anyway you want to model the tornado as having uniform angular velocity, so can you figure what the acceleration field (i.e. the left side of this quoted equation) is? (Use symmetry when choosing coordinates.)
 
Nathanael said:
Perhaps you mean "acceleration due to pressure gradient force" (check dimensions).
Pressure gradient (PG) = rate of change of pressure with distance which is from low to high pressure.PGF is from high to low pressure. But still don't see how you get the pressure distribution?
 
If a body is rotating with radial acceleration ##\omega^2r##, it is analogous to a gravitational force acting in the negative radial direction. So, from the hydrostatic equation,

$$\frac{dp}{dr}=\rho (\omega ^2r)$$

Of course the air density ##\rho## is a function of the pressure, so you need to take that into consideration using the ideal gas law. What is the equation for the density of an ideal gas in terms of the pressure, molecular weight, and temperature?
 

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