Retard saisonnier

Seasonal lag is the phenomenon whereby the date of maximum average air temperature at a geographical location on a planet is delayed until some time after the date of maximum insolation (i.e. the summer solstice). This also applies to the minimum temperature being delayed until some time after the date of minimum insolation. Cultural seasons are often aligned with annual temperature cycles, especially in the agrarian context. Peak agricultural growth often depends on both insolation levels and soil/air temperature. Rainfall patterns are also tied to temperature cycles, with warmer air able to hold more water vapor than cold air. In most Northern Hemisphere regions, the month of February is usually colder than the month of November despite February having significantly later sunsets and more daylight overall. Conversely, the month of August is usually hotter than the month of May despite August having later sunrises, increasingly earlier sunsets, and less daylight overall. In all cases, the change in average air temperature lags behind the more consistent change in daylight patterns - delaying the perceived start of the next season for a month or so. An analogous temperature lag phenomenon occurs in diurnal temperature variation, where maximum daily temperature occurs after noon (maximum insolation). Both effects are manifestations of the general physical phenomenon of thermal inertia. Earth's seasonal lag is largely caused by the presence of large amounts of water, which has a high latent heat of freezing and of condensation. The length of seasonal lag varies between different climates. Extremes range from as little as 15-20 days for polar regions in summer and continental interiors, for example Fairbanks, Alaska, where annual average warmest temperatures occur in early July, and August is notably cooler than June, to 2-3 months in oceanic locales, whether in low latitudes, as in Miami, Florida or higher latitudes as in the Kuril Islands (where at Simushir annual average temperatures peak in late August), and at Cape Sable Island in Nova Scotia, Canada, where (by a slight margin) September is actually the year's warmest month on average.