ABSTRACT
This chapter examines how the uplift results from features of the temperature profile and the humidity profile. A lapse rate is the change of temperature with unit rise of elevation, and the rate at any particular level is given by the temperature profile, measured by radiosonde. The flow of wind past surface obstacles, and daytime heating of the ground, both induce a random stirring called turbulence. Turbulence depends on both the wind speed and the atmosphere’s lapse rate. Ideas of stability and instability are linked to the notion of feedback. Stability arises from negative feedback, where an initial impulse results in an opposite effect, offsetting the original perturbation. In contrast, instability is the result of positive feedback, where the effect aggravates the impulse. The feedback processes most relevant to weather forecasting are those acting rapidly, especially processes connected with two particular kinds of instability: (vertical) static instability and baroclinic instability.
