A Dynamic Perspective on aerosol-vorticity-wave Interactions

Non-linear aerosol-cloud-precipitation-climate interactions depend on many parameters such as aerosol features, regional atmospheric dynamics and variability. Although there are remarkable modeling studies indicating that aerosols induce robust modifications in cloud properties, circulations and the hydrological cycle, many of the physical and dynamical processes involving in these complex interactions between aerosols and Earth's system are still poorly understood. Better understanding the contribution of aerosols with multi-scale atmospheric phenomena and their transient changes are crucial for efforts to evaluate climate predictions by next generation climate models. This study provides strong evidence of mechanistic relationships between perturbations of the oceanic Saharan air layer (OSAL) and anomalies of atmospheric circulations over the eastern tropical Atlantic/Africa. These relationships are characterized using an ensemble of daily datasets including the Modern-Era Retrospective Analysis for Research and Applications (MERRA), the Moderate Resolution Imaging Spectro-radiometer (MODIS), and the Sea-viewing Wide Field-of-View Sensor (SeaWIFS) for boreal summer season.

Our hypothesis is that perturbations in OSAL significantly interact with regional climate dynamics through African Easterly Jet- African Easterly Waves (AEJ-AEW) system. Passive/ active phases of AEWs in the northern and southern-track wave packets are associated with dipole patterns of thermal/dynamical anomalies correlated with perturbations of aerosol optical depth (AOD) in OSAL. Enhanced (suppressed) dust AOD in OSAL are significantly correlated with convective re-circulation within subsidence region of Hadley cell as well as robust mid-level dipole vorticity disturbances downstream of the AEJ core, along with strengthened (weakened) correlative low-level trade winds in northern and southern edges of the Atlantic intertropical convergence zone (ITCZ). These result three-dimensional displacements and changes in circulations and precipitation variability, especially in West African monsoon (WAM) dynamics.