The role of soil moisture on summer atmospheric circulation climatology in the Northern Hemisphere

Soil moisture strongly modulates heat waves and droughts by altering land-atmosphere feedbacks, yet its influence on large-scale circulation remains inadequately quantified. Using large-ensemble simulations with the state-of-the-art climate model EC-Earth 3, we demonstrate that interactive soil moisture has a substantial impact on Northern Hemisphere summer circulation climatology. Two experiments were conducted: a fully interactive simulation and one with prescribed soil moisture states. The results reveal pronounced circulation shifts. Relative to the prescribed case, the interactive experiment drives a poleward displacement of the subtropical jets. It strengthens the polar front jet and enhances land-atmosphere coupling, amplifying wave amplitudes over land by ~24%. Interactive soil moisture raises mean summer surface temperatures by up to +1.5 K and extremes by +3.0 K. These findings demonstrate that soil moisture fluctuations can modify mean atmospheric circulation, with important implications for future summer climate projections.