What atmospheric condition must exist for the Bergeron process to induce precipitation year-round in the middle latitudes?

The Bergeron process, which describes how precipitation forms in cold clouds within the middle latitudes, relies fundamentally on the presence of ice crystals in the upper parts of these clouds. In this process, water vapor sublimates directly onto ice crystals when temperatures are below freezing, causing these crystals to grow. As they gain mass, they eventually become heavy enough to overcome air resistance and fall to the ground as precipitation, typically in the form of snow or ice.

For the Bergeron process to induce precipitation consistently throughout the year in the middle latitudes, it is essential to have ice crystals present. This is because the freezing temperatures necessary for ice formation are more commonplace in the upper atmosphere, particularly at higher latitudes and altitudes. If ice crystals are absent, the process cannot initiate, and therefore, precipitation would not happen as reliably. The effectiveness of this process is diminished if other atmospheric conditions, such as warm temperatures preventing ice formation or lack of humidity, are present. Thus, the presence of ice crystals is a critical factor for this precipitation mechanism to operate efficiently year-round in those regions.