ERTH 430: Fluid Dynamic in Earth Systems In-Class Exercise: Temperature Changes at a Location (for class Friday, Oct. 6) Dr. Dave Dempsey Dept. of Earth & Climate Sciences SFSU, Fall 2017

### Accounting for Observed Changes and Forecasting for a Location

1. You are standing outside. With a thermometer, you observe the air temperature to be falling. You feel a breeze blowing, and you happen to know that the air is coming from a location nearby where the temperature is colder than where you are.

1. Suppose that air parcels are conserving their temperature in this situation. How might you account for your observation that the temperature is falling, assuming that your observation is accurate?

2. What factors might affect the rate at which you observe the temperature to be falling? [Hint: I have in mind three, relatively intuitive factors.] How might mechanism causing the temperature to change where you are standing depend on these factors mathematically?

3. What kind of time derivative are you observing?

4. Write down an equation for the rate of change of temperature in your situation.

5. Explain why the mechanism that you identify in (a) above is meaningless in the context of a conservation equation.

2. On another day, you are again standing outside. With a thermometer, you observe the air temperature to be falling. You feel a breeze blowing, and you happen to know that the air is coming from a location nearby where the temperature is warmer than where you are.

1. How might you account for your observation that the temperature is falling, assuming that your observation is accurate?

3. Based on your result in (1)(d) above, briefly explain how, in principle, you might use your equation to make a forecast at a particular location.

4. How much, if any, of the foregoing might apply to fluid velocity (instead of temperature) at a location? What, if anything, would you have to change?

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