Ground-level atmospheric electricity of mid-latitude Nimbostratus and Stratus cloud at Swider station, Poland

<p>We present main results of our analysis of the ground-level atmospheric electricity under  Nimbostratus and Stratus clouds at mid-latitude Geophysical Observatory in Swider. Atmospheric electricity data from the Geophysical Observatory in Swider was analysed according to the calculation scheme allowing to obtain the main components of the current density in such conditions, i.e. conduction current density and precipitation or convection current, based on the basic measured parameters: electric field, Maxwell current density and total air conductivity. The atmospheric electric field and conduction current is more likely downward under Stratus cloud as is the precipitation or convection current. The electric field under Nimbostratus during snow at the ground is downward and during rain is upward and sometimes also upward precipitation current occurs during heavier rain. Mean values of electric field, conductivity, conduction and precipitation current have been obtained and an average mean current budget was calculated. Another analysis concerns the dependence of precipitation current density on the electric field at the Earth's surface in the conditions of Nimbostratus with continuous, stable precipitation, in historical cases reported as linear. The dependence of the linear regression coefficients on the value of electrical conductivity of the air was particularly investigated from the angle of the theoretical results of the work of Ette and Oladiran (1980).</p>

A radiative transfer module for calculating photolysis rates and solar heating in climate models: Solar-J v7.5

Solar-J is a comprehensive radiative transfer model for the solar spectrum that addresses the needs of both solar heating and photochemistry in Earth system models. Solar-J is a spectral extension of Cloud-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.8 µm region. The Cloud-J core consists of an eight-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. Cloud-J uses cloud quadrature to accurately average over correlated cloud layers. It uses the scattering phase function of aerosols and clouds expanded to eighth order and thus avoids isotropic-equivalent approximations prevalent in most solar heating codes. The spectral extension from 0.8 to 12 µm enables calculation of both scattered and absorbed sunlight and thus aerosol direct radiative effects and heating rates throughout the Earth's atmosphere.The Solar-J extension adopts the correlated-k gas absorption bins, primarily water vapor, from the shortwave Rapid Radiative Transfer Model for general circulation model (GCM) applications (RRTMG-SW). Solar-J successfully matches RRTMG-SW's tropospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. We compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud, both models use the same physical properties, and we find a systematic low bias of about 3 % in planetary albedo across all solar zenith angles caused by RRTMG-SW's two-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG-SW's three different parameterizations are as large as about 20–40 % depending on the solar zenith angles and occur throughout the atmosphere.Effectively, Solar-J has combined the best components of RRTMG-SW and Cloud-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth's atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields – all have comparably small errors. More accurate solutions with Solar-J come with increased computational costs, about 5 times that of RRTMG-SW for a single atmosphere. There are options for reduced costs or computational acceleration that would bring costs down while maintaining improved fidelity and balanced errors.

A Radiative Transfer Module for Calculating Photolysis Rates and Solar Heating in Climate Models: Solar-J 7.5

Solar-J is a comprehensive model for radiative transfer over the solar spectrum that addresses the needs of both photochemistry and solar heating in Earth system models. Solar-J includes an 8-stream scattering, plane-parallel radiative transfer solver with corrections for sphericity. It uses the scattering phase function of aerosols and clouds expanded to 8th order and thus makes no isotropic-equivalent approximations that are prevalent in most solar heating codes. It calculates both chemical photolysis rates and the absorption of sunlight and thus the heating rates throughout the Earth's atmosphere. Solar-J is a spectral extension of Fast-J, a standard in many chemical models that calculates photolysis rates in the 0.18–0.85 μm region. For solar heating, Solar-J extends its calculation out to 12 μm using correlated-k gas absorption bins in the infrared from the shortwave Rapid Radiative Transfer Model for GCM applications (RRTMG-SW). Solar-J successfully matches RRTMG's atmospheric heating profile in a clear-sky, aerosol-free, tropical atmosphere. We compare both codes in cloudy atmospheres with a liquid-water stratus cloud and an ice-crystal cirrus cloud. For the stratus cloud both models use the same physical properties, and we find a systematic low bias in the RRTMG-SW of about 3 % in planetary albedo across all solar zenith angles, caused by RRTMG-SW's 2-stream scattering. Discrepancies with the cirrus cloud using any of RRTMG's three different parameterizations are larger, less systematic, and occur throughout the atmosphere. Effectively, Solar-J has combined the best components of RRTMG and Fast-J to build a high-fidelity module for the scattering and absorption of sunlight in the Earth's atmosphere, for which the three major components – wavelength integration, scattering, and averaging over cloud fields all have comparably small errors. More accurate solutions come with increased computational costs, about 5x that of RRTMG, but there are options for reduced costs or computational acceleration that would bring costs down while maintaining balanced errors across components and improved fidelity.

CCN and Vertical Velocity Influences on Droplet Concentrations and Supersaturations in Clean and Polluted Stratus Clouds

Cloud microphysics and cloud condensation nuclei (CCN) measurements from two marine stratus cloud projects are presented and analyzed. Results show that the increase of cloud droplet concentrations Nc with CCN concentrations NCCN rolls off for NCCN at 1% supersaturation (S)N1% above 400 cm−3. Moreover, at such high concentrations Nc was not so well correlated with NCCN but tended to be more closely related to vertical velocity W or variations of W (σw). This changeover from predominate Nc dependence on NCCN to Nc dependence on W or σw is due to the higher slope k of CCN spectra at lower S, which is made more relevant by the lower cloud S that is forced by higher NCCN. Higher k makes greater influence of W or σw variations than NCCN variations on Nc. This changeover at high NCCN thus seems to limit the indirect aerosol effect (IAE). On the other hand, in clean-air stratus cloud S often exceeded 1% and decreased to slightly less than 0.1% in polluted conditions. This means that smaller CCN [those with higher critical S (Sc)], which are generally more numerous than larger CCN (lower Sc), are capable of producing stratus cloud droplets, especially when they are advected into clean marine air masses where they can induce IAE. Positive correlations between turbulence σw and NCCN are attributed to greater differential latent heat exchange of smaller more numerous cloud droplets that evaporate more readily. Such apparent CCN influences on cloud dynamics tend to support trends that oppose conventional IAE, that is, less rather than greater cloudiness in polluted environments.