Abstract
A new empirical parameterization (EP) for multiple groups of primary biological aerosol particles (PBAPs) is implemented in the aerosol cloud model (AC) to investigate their roles as ice-nucleating particles (INPs). The EP describes the heterogeneous ice nucleation by (1) fungal spores, (2) bacteria, (3) pollen, (4) detritus of plants, animals, and viruses, and (5) algae. Each group includes fragments from the originally emitted particles. A high-resolution simulation of a midlatitude mesoscale squall line by AC is validated against airborne and ground observations. Sensitivity tests are carried out by varying the initial vertical profiles of the loadings of individual PBAP groups. The resulting changes in warm and ice microphysical parameters are investigated. Overall, PBAPs have little effect on the ice phase, especially in the convective region. In the stratiform region, increasing the initial PBAP loadings by a factor of 100 resulted in less than 60 % change in ice number concentrations. The total ice concentration is mostly controlled by various mechanisms of secondary ice production (SIP). However, when SIP is artificially prohibited in sensitivity tests, increasing the PBAP loading by a factor of 100 has no significant effect on the ice phase. Further sensitivity tests revealed that PBAPs have little effect on surface precipitation as well as on shortwave and longwave flux.
Highlights
In most climate models, the largest source of uncertainty for estimating the total anthropogenic forcing is associated with cloud-aerosol interactions (Forster et al, 2007)
The current study aims to simulate realistic concentrations of multiple groups of primary biological aerosol particles (PBAPs) ice-nucleating particles (INPs), including bacterial and fungal particles, to investigate their interactions with convective clouds observed during the Midlatitude Continental Convective Clouds Experiment field campaign (MC3E), (Jensen et al 2016), in the USA
A series of sensitivity experiments were conducted to test the impact of PBAP groups on cloud properties. 861 A mid-latitude squall line that occurred on 20 May 2011 during MC3E over the US Southern 862 Great Plains is simulated with the model
Summary
The largest source of uncertainty for estimating the total anthropogenic forcing is associated with cloud-aerosol interactions (Forster et al, 2007). (2009) had a 3-D domain of about 100 km in width, and many cloud types were present in the mesoscale convective system that was simulated Their simulations revealed that the cloud cover, domain radiative fluxes, and surface precipitation rate were significantly altered by boosting organic aerosols representing PBAPs. According to Hummel et al (2018) in shallow mixed-phase clouds (i.e., altostratus) when the cloud top temperature is below -15oC, PBAPs have the potential to influence the cloud ice phase and produce ice crystals in the absence of other INPs. 99 The quest for insights about the broader atmospheric role of PBAP INPs for cloud microphysical properties and precipitation is hampered by the limited availability of observations both of their ice nucleation activities for various species and their aerosol distributions in the real atmosphere. We examine the relative importance of various secondary ice processes in their role in mediating the PBAP effects on cloud microphysical properties, given the weakness of PBAP effects on cloud microphysical properties
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