The Coupled Effect of Mid-Tropospheric Moisture and Aerosol Abundance on Deep Convective Cloud Dynamics and Microphysics

Abstract

Abstract:The humidity of the mid troposphere has a significant effect on the development of deep convection. Dry layers (dry intrusions) can inhibit deep convection through the effect of a thermal inversion resulting from radiation and due to the reduction in buoyancy resulting from entrainment. Recent observations have shown that the sensitivity of cloud top height to changes in mid-tropospheric humidity can be larger than straightforward "parcel dilution" would lead us to expect. Here, we investigate how aerosol effects on cloud development and microphysics are coupled to the effects of mid-tropospheric dry air. The two effects are coupled because the buoyancy loss through entrainment depends on droplet evaporation, so is controlled both by the environmental humidity and by droplet sizes, which are, in turn, controlled in part by the aerosol size distribution. Previous studies have not taken these microphysical effects into account. Cloud development and microphysics are examined using a 2-D non-hydrostatic cloud model with a detailed treatment of aerosol, drop, and ice-phase hydrometeor size spectra. A moderately deep mixed-phase convective cloud that developed over the High Plains of the United States is simulated. We find that a dry layer in the mid troposphere leads to a reduction in cloud updraft strength, droplet number, liquid water content and ice mass above the layer. The effect of the dry layer on these cloud properties is greatly enhanced under elevated aerosol conditions. In an environment with doubled aerosol number (but still realistic for continental conditions) the dry layer has about a three-times larger effect on cloud drop OPEN ACCESSAtmosphere 2011, 2 223 number and 50% greater effect on ice mass compared to an environment with lower aerosol. In the case with high aerosol loading, the dry layer stops convective development for over 10 min, and the maximum cloud top height reached is lower. However, the effect of the dry layer on cloud vertical development is significantly reduced when aerosol concentrations are lower. The coupled effect of mid-tropospheric dry air and aerosol on convective development is an additional way in which long term changes in aerosol may impact planetary cloud processes and climate.

On the Relative Sensitivity of a Tropical Deep Convective Storm to Changes in Environment and Cloud Microphysical Parameters

“…The convective thermodynamic and dynamic (e.g., shear) environment is known to strongly influence the development of moist convection (Stevens 2005;Sherwood 2010; Sherwood et al 2010;de Rooy et al 2013;Kim et al 2014;Virman et al 2018). These sensitivities have been examined from an observational perspective (Johnson and Lin 1997;Holloway andNeelin 2009, 2010;Tobin et al 2012;Masunaga 2012Masunaga , 2013Kumar et al 2014;Pereira de Oliveira and Oyama 2015;Bergemann and Jakob 2016;Hannah et al 2016;Schiro et al 2016;Yuan 2016;Chen et al 2017;Stevens et al 2017;Virman et al 2018), as well as via the use of high-resolution numerical models (Crook 1996;Derbyshire et al 2004;Mapes 2004;Raymond and Sessions 2007;Eitzen and Xu 2008;Wandishin et al 2008;Kuang 2010;Tulich and Mapes 2010;Cui et al 2011;Kirshbaum 2011;Hagos and Leung 2012;Böing et al 2012a,b;Hohenegger and Stevens 2013;Sessions et al 2015;Takemi 2015;Hernandez-Deckers and Sherwood 2016;Hannah 2017;Tsai and Wu 2017;Wang and Sobel 2017). Cloud microphysical processes have also bee...…”

Cold Pool and Precipitation Responses to Aerosol Loading: Modulation by Dry Layers

“…For instance, Khain et al (2008) found that precipitation associated with deep convection increased with increasing aerosol concentrations for high humidity but decreased for low humidity because of enhanced hydrometeor evaporation. Cui et al (2011) demonstrated that the development of a single convective cloud was more strongly impacted by aerosol loading when a midlevel dry layer was present compared to conditions with higher midlevel humidity. Storer et al (2010) found that aerosol impacts on deep convection were greater for lower convective available potential energy (CAPE), which indicates that the ability of aerosols to influence deep convective precipitation depends on the strength of the dynamical forcing and, by extension, the storm organization.…”

“…Although multiple studies have investigated aerosol impacts on deep convection under different environmental humidity profiles (e.g., Khain et al 2005;Tao et al 2007;Khain et al 2008;Lee 2011;Cui et al 2011), none of these have investigated the importance of the vertical location of the dryness. Yet, the altitude of dry layers has previously been shown to play an important role in accumulated convective precipitation, cloud-top height, cold pool characteristics, and storm morphology (Brown and Zhang 1997;Gilmore and Wicker 1998;Ridout 2002;Grant and van den Heever 2014, hereafter GvdH14).…”

Evaluating uncertainty in convective cloud microphysics using statistical emulation

“…[]. MAC3 has been used to simulate and evaluate a variety of convective clouds and cloud properties, such as warm rain in shallow cumulus [ Blyth et al ., ], secondary ice production [ Huang et al ., ], aerosol effect [ Cui and Carslaw , ; Cui et al ., ], aerosol‐cloud‐precipitation interaction [ Cui et al ., ], and the coupled effect of aerosol and moisture [ Cui et al ., ].…”