Seasonal and Geographical Differences in the Marine Thermal Influence on US Coastal Air Temperatures

The ocean is often thought to moderate temperatures along adjacent coastlines, but its influence varies by region, season, and time of day. This study quantifies the ocean’s influence on coastal air temperatures along the East and West Coasts of the United States using a ten-year record of land-based weather observations and satellite derived sea surface temperatures. By calculating ocean-land temperature differences and estimating temperature advection, we identify distinct seasonal and geographical differences in marine thermal influence. Generally, the ocean has a moderating influence on daily average coastal air temperatures, warming in winter and cooling in summer. However, this does not hold at all latitudes. On the East Coast south of 35°N, warm coastal ocean waters have a year round warming influence on nighttime temperatures that exceeds the cooling influence on daytime temperatures, resulting in a net warming effect on daily average coastal air temperatures. In contrast, the west coast is more uniform latitudinally, with oceans providing a generally cooling influence on coastal land temperatures, but more variable between nearby stations, likely due to topography. These findings challenge the assumption that the ocean uniformly cools coastal regions in warmer months and highlight the need to consider spatial, seasonal, and daily dynamics in adaptation strategies for coastal heat hazards.