The Köppen climate classification divides Earth climates into five main climate groups, with each group being divided based on patterns of seasonal precipitation and temperature. The five main groups are A (tropical), B (arid), C (temperate), D (continental), and E (polar). Each group and subgroup is represented by a letter. All climates are assigned a main group. All climates except for those in the E group are assigned a seasonal precipitation subgroup. For example, Af indicates a tropical rainforest climate. The system assigns a temperature subgroup for all groups other than those in the A group, indicated by the third letter for climates in B, C, D, and the second letter for climates in E. Other examples include: Cfb indicating an oceanic climate with warm summers as indicated by the ending b., while Dwb indicates a semi-monsoonal continental climate, also with warm summers. Climates are classified based on specific criteria unique to each climate type.