15. Life Cycle of Mid-Latitude Cyclones

15.1. Introduction

Before the publication of Bjerknes and Solberg [1922], the meteorological lexicon did not have cold or warm fronts, or the idea that mid-latitude cyclones evolved through a life cycle. In many different scientific disciplines one can learn about the life cycle of cells, animals, stars, etc. This advancement in meteorological knowledge did not come out of nowhere. Throughout the latter parts of the 19^th^ century and the beginning of the 20^th^, many meteorological researchers were slowly modifying the way we view the atmosphere, but it was the work of the Bergen School that solidified this evolving view.

The revelation that all mid-latitude cyclones were moving and evolving through a roughly structured life cycle had large ramifications for forecasting. With the advent of the life cycle of cyclones one could use that life cycle to predict how the low-pressure system would change based on its current state. While we have progressed and modified the simple life cycle presented in 1923, the foundations of using maps to understand how weather patterns evolved have only grown with time. This lab handout will build upon the ideas of Bjerknes and Solberg [1922] to develop a complete basic conceptual model of the life cycle of mid-latitude cyclones.

15.2. Life Cycle of Cyclones

In the time since the Bergen School published the first theories of cyclone life cycles, meteorologists have learned that it is vitally important to understand the evolution of the upper-air pattern in association with the mean sea-level pressure pattern. We will start with understanding the evolution of the characteristics of surface values of temperature and mean sea-level pressure and its association with a 500-hPa trough.