scholarly journals Extensive layer clouds in the global electric circuit: their effects on vertical charge distribution and storage

2020 ◽  
Vol 476 (2238) ◽  
pp. 20190758
Author(s):  
R. Giles Harrison ◽  
Keri A. Nicoll ◽  
Evgeny Mareev ◽  
Nikolay Slyunyaev ◽  
Michael J. Rycroft
Keyword(s):  
Current Flow ◽  
Positive Charge ◽  
Electric Circuit ◽  
Cloud Base ◽  
Global Electric Circuit ◽  
Fair Weather ◽  
Cloud Droplets ◽  
Global Circuit ◽  
Lower Cloud ◽  
Negative Surface

A fair-weather electric field has been observed near the Earth's surface for over two centuries. The field is sustained by charge generation in distant disturbed weather regions, through current flow in the global electric circuit. Conventionally, the fair-weather part of the global circuit has disregarded clouds, but extensive layer clouds, important to climate, are widespread globally. Such clouds are not electrically inert, becoming charged at their upper and lower horizontal boundaries from vertical current flow, in a new electrical regime—neither fair nor disturbed weather; hence it is described here as semi-fair weather . Calculations and measurements show the upper cloud boundary charge is usually positive, the cloud interior positive and the lower cloud boundary negative, with the upper charge density larger, but of the same magnitude (∼nC m −2 ) as cloud base. Globally, the total positive charge stored by layer clouds is approximately 10 5  C, which, combined with the positive charge in the atmospheric column above the cloud up to the ionosphere, balances the total negative surface charge of the fair-weather regions. Extensive layer clouds are, therefore, an intrinsic aspect of the global circuit, and the resulting natural charging of their cloud droplets is a fundamental atmospheric feature.

scholarly journals Cloud base height and cosmic rays

2011 ◽  
Vol 467 (2134) ◽  
pp. 2777-2791 ◽  
Author(s):  
R. Giles Harrison ◽  
Maarten H. P. Ambaum ◽  
Michael Lockwood
Keyword(s):  
Cosmic Rays ◽  
Current Flow ◽  
Pure Water ◽  
Electric Circuit ◽  
Cosmic Ray ◽  
Horizontal Layer ◽  
Electrical Circuit ◽  
Cloud Base ◽  
Global Circuit ◽  
Cloud Base Height

Cosmic rays modify current flow in the global atmospheric electrical circuit. Charging at horizontal layer cloud edges has been observed to be consistent with global circuit vertical current flow through the cloud, which can modify the properties of small and pure water droplets. Studies have been hampered by the absence of cloud edge observations, hence cloud base height information is investigated here. Cloud base height measured at the Lerwick Observatory, Shetland, UK, is analysed using threshold tests and spectral analysis. The cloud base height distributions for low cloud (cloud base less than 800 m) are found to vary with cosmic ray conditions. Further, 27 day and 1.68 year periodicities characteristic of cosmic ray variations are present, weakly, in the cloud base height data of stratiform clouds, when such periodicities are present in neutron monitor cosmic ray data. These features support the idea of propagation of heliospheric variability into layer clouds, through the global atmospheric electric circuit.

scholarly journals On the role of non-electrified clouds in the Global Electric Circuit

2014 ◽  
Vol 14 (7) ◽  
pp. 9815-9847 ◽  
Author(s):  
A. J. G. Baumgaertner ◽  
G. M. Lucas ◽  
J. P. Thayer ◽  
S. A. Mallios
Keyword(s):  
Cloud Cover ◽  
Electric Circuit ◽  
Time Averaging ◽  
Global Electric Circuit ◽  
Fair Weather ◽  
Cloud Data ◽  
Limited Mobility ◽  
Current Divergence ◽  
High Clouds

Abstract. Non-electrified clouds in the fair-weather part of the Global Electric Circuit (GEC) reduce conductivity because of the limited mobility of charge due to attachment to cloud water droplets, effectively leading to a loss of ions. A high-resolution GEC model, which numerically solves the Poisson equation, is used to show that in the fair-weather region currents partially flow around non-electrified clouds, with current divergence above the cloud, and convergence below the cloud. An analysis of this effect is presented for various types of non-electrified clouds, i.e. for different altitude extents, and for different horizontal dimensions, finding that the effect is most pronounced for high clouds with a diameter below 100 km. Based on these results, a method to calculate column and global resistance is developed that can account for all cloud sizes and altitudes. The CESM1(WACCM) Earth System Model as well as ISCCP cloud data are used to calculate the effect of this phenomenon on global resistance. From CESM1(WACCM), it is found that when including non-electrified clouds in the fair-weather estimate of resistance the global resistance increases by up to 73%, depending on the parameters used. Using ISCCP cloud cover leads to an even larger increase, which is likely to be overestimated because of time-averaging of cloud cover. Neglecting current divergence/convergence around small clouds overestimates global resistance by up to 20%, whereas the method introduced by previous studies underestimates global resistance by up to 40%. For global GEC models, a conductivity parametrization is developed to account for the current divergence/convergence phenomenon around non-electrified clouds. Conductivity simulations from CESM1(WACCM) using this parametrization are presented.

scholarly journals The effects of heating by transported dust layers on cloud and precipitation: a numerical study

2007 ◽  
Vol 7 (13) ◽  
pp. 3497-3505 ◽  
Author(s):  
Y. Yin ◽  
L. Chen
Keyword(s):  
Mineral Dust ◽  
Numerical Study ◽  
Cloud Model ◽  
Cloud Condensation Nuclei ◽  
Dust Particles ◽  
Cloud Base ◽  
Cloud Droplets ◽  
Cloud Optical Depth ◽  
Mineral Aerosols ◽  
Lower Cloud

Abstract. There have been numerous recent publications showing that mineral dust might be a good absorber for solar radiation in addition to its capability to act as cloud condensation nuclei (CCN) and ice forming nuclei (IFN), and could lead to reduced cloud cover and precipitation in the region where it is present. This effect is investigated using a dynamic cloud model with detailed microphysics of both warm and ice phase processes. The model is initialized using measured size distributions and concentrations of mineral dust particles. Our results show that when dust appears at the cloud-base height and below 3 km, where the temperature is warmer than −5°C, the heating induced by the presence of dust layers can inhibit the formation of cloud droplets and suppresses the development of precipitation, leading to lower cloud optical depth and albedo. On the other hand, when the dust layers are located at altitudes with temperature colder than −5°C, or above the −5°C level, mineral aerosols can act as effective ice nuclei, intensify the ice-forming processes, and may enhance the development of cloud and precipitation. It is also found that the heating effect is more pronounced in continental clouds than in maritime clouds.

scholarly journals Measuring Global Signals in the Potential Gradient at High Latitude Sites

2021 ◽  
Vol 8 ◽  
Author(s):  
José Tacza ◽  
Keri A. Nicoll ◽  
Edith L. Macotela ◽  
Marek Kubicki ◽  
Anna Odzimek ◽  
...  
Keyword(s):  
High Latitude ◽  
Potential Gradient ◽  
Electric Circuit ◽  
Weather Conditions ◽  
Electrical Circuit ◽  
Global Electric Circuit ◽  
Fair Weather ◽  
Wind Speeds ◽  
Gradient Measurements ◽  
Seasonal Analysis

Previous research has shown that the study of the global electrical circuit can be relevant to climate change studies, and this can be done through measurements of the potential gradient near the surface in fair weather conditions. However, potential gradient measurements can be highly variable due to different local effects (e.g., pollution, convective processes). In order to try to minimize these effects, potential gradient measurements can be performed at remote locations where anthropogenic influences are small. In this work we present potential gradient measurements from five stations at high latitudes in the Southern and Northern Hemisphere. This is the first description of new datasets from Halley, Antarctica; and Sodankyla, Finland. The effect of the polar cap ionospheric potential can be significant at some polar stations and detailed analysis performed here demonstrates a negligible effect on the surface potential gradient at Halley and Sodankyla. New criteria for determination of fair weather conditions at snow covered sites is also reported, demonstrating that wind speeds as low as 3 m/s can loft snow particles, and that the fetch of the measurement site is an important factor in determining this threshold wind speed. Daily and seasonal analysis of the potential gradient in fair weather conditions shows great agreement with the “universal” Carnegie curve of the global electric circuit, particularly at Halley. This demonstrates that high latitude sites, at which the magnetic and solar influences can be present, can also provide globally representative measurement sites for study of the global electric circuit.

scholarly journals Comparisons of CCN with Supercooled Clouds

2010 ◽  
Vol 67 (9) ◽  
pp. 3006-3018 ◽  
Author(s):  
James G. Hudson ◽  
Stephen Noble ◽  
Vandana Jha
Keyword(s):  
Droplet Size ◽  
Cloud Condensation Nuclei ◽  
Correlation Coefficients ◽  
Cloud Droplet ◽  
Liquid Water Content ◽  
Cloud Microphysics ◽  
Cloud Base ◽  
Cloud Droplets ◽  
Lower Cloud ◽  
Droplet Sizes

Abstract More than 140 supercooled clouds were compared with corresponding out-of-cloud cloud condensation nuclei (CCN) measurements. In spite of significant differences in altitude, temperature, distances from cloud base, updraft velocity (W), entrainment, and so on, the correlation coefficients (R) between droplet and CCN concentrations were substantial although not as high as those obtained in warm clouds with less variability of nonaerosol influences. CCN at slightly lower altitudes than the clouds had higher R values than CCN measured at the same altitude. Ice particle concentrations appeared to reduce droplet concentrations and reduce R between CCN and droplet concentrations, but only above 6-km altitude and for temperatures below −20°C. Although higher CCN concentrations generally resulted in higher droplet concentrations, increases in droplet concentrations were generally less than the increases in CCN concentrations. This was apparently due to the expected lower cloud supersaturations (S) when CCN concentrations are higher as was usually the case at lower altitudes. Cloud supersaturations showed more variability at higher altitudes and often very high values at higher altitudes. The use of liquid water content rather than droplet concentrations for cloud threshold resulted in higher R between CCN and droplet concentrations. The same R pattern for cumulative droplet–CCN concentrations as a function of threshold droplet sizes as that recently uncovered in warm clouds was found. This showed R changing rapidly from positive values when all cloud droplets were considered to negative values for slightly larger droplet size thresholds. After reaching a maximum negative value at intermediate droplet sizes, R then reversed direction to smaller negative or even positive values for larger cloud droplet size thresholds. This R pattern of CCN concentrations versus cumulative droplet concentrations for increasing size thresholds is consistent with adiabatic model predictions and thus suggests even greater CCN influence on cloud microphysics.

scholarly journals On the role of clouds in the fair weather part of the global electric circuit

2014 ◽  
Vol 14 (16) ◽  
pp. 8599-8610 ◽  
Author(s):  
A. J. G. Baumgaertner ◽  
G. M. Lucas ◽  
J. P. Thayer ◽  
S. A. Mallios
Keyword(s):  
Cloud Cover ◽  
Climate Model ◽  
Electric Circuit ◽  
Time Averaging ◽  
Global Electric Circuit ◽  
Fair Weather ◽  
Cloud Data ◽  
Limited Mobility ◽  
Current Divergence ◽  
Community Earth System Model

Abstract. Clouds in the fair weather return path of the global electric circuit (GEC) reduce conductivity because of the limited mobility of charge due to attachment to cloud water droplets, effectively leading to a loss of ions. A high-resolution GEC model, which numerically solves the current continuity equation in combination with Ohm's law, is used to show that return currents partially flow around clouds, with current divergence above the cloud and convergence below the cloud. An analysis of this effect is presented for various types of clouds, i.e., for different altitude extents and for different horizontal dimensions, finding that the effect is most pronounced for high clouds with a diameter below 100 km. Based on these results, a method to calculate column and global resistance is developed that can account for all cloud sizes and altitudes. The CESM1(WACCM) (Community Earth System Model – Whole Atmosphere Community Climate Model) as well as ISCCP (International Satellite Cloud Climatology Project) cloud data are used to calculate the effect of this phenomenon on global resistance. From CESM1(WACCM), it is found that when including clouds in the estimate of resistance the global resistance increases by up to 73%, depending on the parameters used. Using ISCCP cloud cover leads to an even larger increase, which is likely to be overestimated because of time averaging of cloud cover. Neglecting current divergence/convergence around small clouds overestimates global resistance by up to 20% whereas the method introduced by previous studies underestimates global resistance by up to 40%. For global GEC models, a~conductivity parameterization is developed to account for the current divergence/convergence phenomenon around clouds. Conductivity simulations from CESM1(WACCM) using this parameterization are presented.

scholarly journals Differences between Nonprecipitating Tropical and Trade Wind Marine Shallow Cumuli

2016 ◽  
Vol 144 (2) ◽  
pp. 681-701 ◽  
Author(s):  
Virendra P. Ghate ◽  
Mark A. Miller ◽  
Ping Zhu
Keyword(s):  
Surface Fluxes ◽  
Cloud Base ◽  
Trade Wind ◽  
Cumulus Clouds ◽  
Wind Speeds ◽  
Lower Cloud ◽  
Observational Site ◽  
Velocity Scale ◽  
Atmospheric Radiation Measurement ◽  
The Mean

Abstract Marine nonprecipitating cumulus topped boundary layers (CTBLs) observed in a tropical and in a trade wind region are contrasted based on their cloud macrophysical, dynamical, and radiative structures. Data from the Atmospheric Radiation Measurement (ARM) observational site previously operating at Manus Island, Papua New Guinea, and data collected during the deployment of ARM Mobile Facility at the island of Graciosa, in the Azores, were used in this study. The tropical marine CTBLs were deeper, had higher surface fluxes and boundary layer radiative cooling, but lower wind speeds compared to their trade wind counterparts. The radiative velocity scale was 50%–70% of the surface convective velocity scale at both locations, highlighting the prominent role played by radiation in maintaining turbulence in marine CTBLs. Despite greater thicknesses, the chord lengths of tropical cumuli were on average lower than those of trade wind cumuli, and as a result of lower cloud cover, the hourly averaged (cloudy and clear) liquid water paths of tropical cumuli were lower than the trade wind cumuli. At both locations ~70% of the cloudy profiles were updrafts, while the average amount of updrafts near cloud base stronger than 1 m s−1 was ~22% in tropical cumuli and ~12% in the trade wind cumuli. The mean in-cloud radar reflectivity within updrafts and mean updraft velocity was higher in tropical cumuli than the trade wind cumuli. Despite stronger vertical velocities and a higher number of strong updrafts, due to lower cloud fraction, the updraft mass flux was lower in the tropical cumuli compared to the trade wind cumuli. The observations suggest that the tropical and trade wind marine cumulus clouds differ significantly in their macrophysical and dynamical structures.

scholarly journals A 3-D RBF-FD solver for modeling the atmospheric global electric circuit with topography (GEC-RBFFD v1.0)

2015 ◽  
Vol 8 (10) ◽  
pp. 3007-3020 ◽  
Author(s):  
V. Bayona ◽  
N. Flyer ◽  
G. M. Lucas ◽  
A. J. G. Baumgaertner
Keyword(s):  
Numerical Model ◽  
Differential Operators ◽  
Lower Boundary ◽  
Elliptic Partial Differential Equation ◽  
Electric Circuit ◽  
Global Electric Circuit ◽  
Mesh Free ◽  
Conductivity Profile ◽  
The Right ◽  
Upper Boundary

Abstract. A numerical model based on radial basis function-generated finite differences (RBF-FD) is developed for simulating the global electric circuit (GEC) within the Earth's atmosphere, represented by a 3-D variable coefficient linear elliptic partial differential equation (PDE) in a spherically shaped volume with the lower boundary being the Earth's topography and the upper boundary a sphere at 60 km. To our knowledge, this is (1) the first numerical model of the GEC to combine the Earth's topography with directly approximating the differential operators in 3-D space and, related to this, (2) the first RBF-FD method to use irregular 3-D stencils for discretization to handle the topography. It benefits from the mesh-free nature of RBF-FD, which is especially suitable for modeling high-dimensional problems with irregular boundaries. The RBF-FD elliptic solver proposed here makes no limiting assumptions on the spatial variability of the coefficients in the PDE (i.e., the conductivity profile), the right hand side forcing term of the PDE (i.e., distribution of current sources) or the geometry of the lower boundary.

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