Northern hemisphere isotherm

In winter, the land temperature is lower than that of the ocean, so the land temperature at the same latitude is lower and the ocean temperature is higher, so the isotherm on the mainland protrudes southward (low latitude). In summer, the land temperature is higher than the ocean temperature, so the land temperature is higher and the ocean temperature is lower at the same latitude, so the isotherm on the mainland protrudes to the north (high latitude). The ocean protrudes to the south (low latitude), which is caused by the difference of thermal properties between land and ocean. The land absorbs heat quickly and dissipates heat quickly, while the ocean absorbs heat slowly and dissipates heat slowly (physical specific heat capacity), so the temperature rises quickly in summer, which is higher than that in the ocean, but the opposite is true in winter.