Can the Elevated Heat Pump Work Without Clouds? (Invited Presentation)

The essence of the elevated heat pump (EHP) is the heating of elevated aerosol layers by absorbing solar radiation, thus heating the air column relative to the air masses around. Pollution aerosols that contain black carbon absorb solar radiation most effectively. This causes convergence and regional rising of the deep polluted air mass over land, thus promoting influx of cleaner and cooler air from the adjacent seas, thereby enhancing the monsoonal component of the circulation. The top of the polluted layer that is capable of serving the EHP mechanism is usually much higher than cloud base height, so the pollution must have transported through convective clouds that incorporated the pollution aerosols through their base, and detrained the aerosols along with the evaporation of cloud drops at higher levels. Therefore, heavy emission of pollution aerosols is a necessary but insufficient condition for the EHP to be operative, as the pollution requires a mechanism to be dispersed to the mid troposphere to heights which can rarely be reached without the mediation of convective clouds. An aerosol particle that is drawn into cloud base can be either wet scavenged to the ground by precipitation or detrained at higher levels when the cloud mixes with the ambient air and evaporates. This applies to both interstitial aerosols and those that nucleated cloud droplets. Therefore, it is expected that the aerosols would be detrained at greater heights in clouds in which precipitation initiated is delayed to greater elevations above cloud base. Higher concentrations of pollution aerosols act to delay rain initiation to greater heights. Therefore, these higher aerosol concentrations can be respectively detrained to greater heights before being deposited by precipitation that is forms yet higher. This constitutes a mechanism by which greater aerosol concentrations at the cloud base level are more effective at reaching greater heights when incorporated in convective clouds. A documentation of these processes was done by combined satellite observations of aerosols by CALIPSO and cloud microphysical properties by the NPP/VIIRS. Evidence for the existence of this process will be shown based on these observations, both on the basis of case studies and on the basis of statistics of a large number of cases.