The sensitivity of ocean phytoplankton (chlorophyll-a concentration) to deposition of atmospheric inorganic nitrogen compounds over Japan Sea was investigated using a 3-D lower trophic-marine ecosystem model (COCO-NEMURO) combined with an atmospheric regional chemical transport model (WRF-CMAQ). The monthly mean values for the wet and dry deposition of inorganic nitrogen compounds including gases (HNO₃ and NH₃) and aerosol particles (NO₃^－ and NH₄^＋) over the Japan Sea were determined using the WRF-CMAQ. The results indicated that the total flux of inorganic nitrogen compounds was in the range of 82–302 μmol/m²/day and wet deposition was dominant in all season. These values were input into the ocean surface in NEMURO as a new nitrogen nutrient source from atmosphere. The annual average of surface chlorophyll-a concentration over Japan Sea was increased from 0.26 to 0.35 mg/m³. The chlorophyll-a concentration in summer season was ~2.1, while that in winter season was ~1.1, times higher than that without atmospheric inorganic nitrogen compounds deposition, indicating that the atmospheric deposition of inorganic nitrogen compounds significantly influence surface chlorophyll-a concentration in summer season.

Aerosols can alter cloud microphysical and dynamical properties through complex aerosol-cloud-precipitation interaction processes. As aerosols increase, precipitation is suppressed and lifetime of cloud is extended (lifetime effect), whereas largely developed clouds are expected to develop more (invigoration). This aerosol to precipitation feedback process has been extensively studied, whereas not many have been done for heavy rainfall cases in Japan. The objective of the study is to evaluate the impacts of cloud condensation nuclei (CCN) changes on precipitation during the Kanto-Tohoku heavy rainfall by using numerical simulations and idealized sensitivity tests. Three CCN spectra (relationship between supersaturation and number of aerosols activated to form cloud droplets) were prepared for the tests, reflecting two orders of magnitude variations in CCN number concentrations. Both lifetime and invigoration effects were inferred for the light and heavy precipitation areas, respectively. Due to the invigoration, the one and two orders of magnitude increase in CCN numbers resulted in enhancement of heavy precipitations (both areas and amounts) by approximately 60–80% and 80–100%, respectively.