## Mean free path

The average distance a molecule travels in the gas before collision is called the mean free path. To obtain an estimate of the mean free path imagine the background gas particles to be stationary. Take our test molecule of radius r0 to be moving through the lattice of fixed points used in the last subsection. A collision between our prototype molecule and a background molecule will occur when their centers are within 2r0 of each other (Figure 2.2). We can think of the test molecule having...

## Kz Kz0 fZ Paz Pezdz Jz0

Substituting the hydrostatic equation, dp dz - p g, and the ideal gas equation of state,p pRT, yields K(z) - K(z0) -R fP(Ta - Te)d(lnp). (7.6) The result is that the kinetic energy of a parcel is proportional to the area in the closed loop defined by doubly intersecting environmental and adiabatic curves in a T-lnp diagram It is worth remembering that the above derivation is valid for both dry and moist adiabatic processes. As the parcel rises adiabatically, its kinetic energy goes up, if there...

## The thermodynamic equation

In this chapter we derive two of the fundamental equations of atmospheric science, the equation of continuity and the thermodynamic equation. The equation of continuity expresses the conservation of mass in the form of a partial differential equation, the form needed to implement it in numerical simulations or forecasts. The thermodynamic equation expresses the combined First and Second Laws of Thermodynamics into a similar form. But before we come to these important formulas we need some...

## Photochemistry

Further examples of endothermic reactions include the photochemical reactions. In this case the additional source of energy necessary for the endothermic reaction to proceed is solar radiation which can break the chemical bonds of atmospheric species. In this book we will consider only one photochemical process photodissociation.1 Physics refresher Solar radiation consists of electromagnetic waves. Electromagnetic radiation has a dual wave-particle nature. This means that electromagnetic...