Search results for "Cloud"

2021

Abstract. The formation of ice in clouds is an important processes in mixed-phase and ice-phase clouds. Yet, the representation of ice formation in numerical models is highly uncertain. In the last decade, several new parameterizations for heterogeneous freezing have been proposed. However, it is currently unclear what the effect of choosing one parameterization over another is in the context of numerical weather prediction. We conducted high-resolution simulations (Δx=250 m) of moderately deep convective clouds (cloud top ∼-18 ∘C) over the southwestern United Kingdom using several formulations of ice formation and compared the resulting changes in cloud field properties to the spread of an…

Sensitivities of Amazonian clouds to aerosols and updraft speed

2017

Abstract. The effects of aerosol particles and updraft speed on warm-phase cloud microphysical properties are studied in the Amazon region as part of the ACRIDICON-CHUVA experiment. Here we expand the sensitivity analysis usually found in the literature by concomitantly considering cloud evolution, putting the sensitivity quantifications into perspective in relation to in-cloud processing, and by considering the effects on droplet size distribution (DSD) shape. Our in situ aircraft measurements over the Amazon Basin cover a wide range of particle concentration and thermodynamic conditions, from the pristine regions over coastal and forested areas to the southern Amazon, which is highly poll…

The ACRIDICON-CHUVA campaign: Studying tropical deep convective clouds and precipitation over Amazonia using the new German research aircraft HALO

2016

Abstract Between 1 September and 4 October 2014, a combined airborne and ground-based measurement campaign was conducted to study tropical deep convective clouds over the Brazilian Amazon rain forest. The new German research aircraft, High Altitude and Long Range Research Aircraft (HALO), a modified Gulfstream G550, and extensive ground-based instrumentation were deployed in and near Manaus (State of Amazonas). The campaign was part of the German–Brazilian Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems–Cloud Processes of the Main Precipitation Systems in Brazil: A Contribution to Cloud Resolving Modeling and to the GPM (Global Precipitatio…

Observed and Simulated Variability of Droplet Spectral Dispersion in Convective Clouds Over the Amazon

2021

In this study, the variability of the spectral dispersion of droplet size distributions (DSDs) in convective clouds is investigated. Analyses are based on aircraft measurements of growing cumuli near the Amazon basin, and on numerical simulations of an idealized ice‐free cumulus. In cleaner clouds, the relative dispersion ϵ, defined as the ratio of the standard deviation to the mean value of the droplet diameter, is negatively correlated with the ratio of the cloud water content (qc) to the adiabatic liquid water content (qa), while no strong correlation between ϵ and qc/qa is seen in polluted clouds. Bin microphysics numerical simulations suggest that these contrasting behaviors are associ…

Numerical sensitivity studies on the impact of aerosol properties and drop freezing modes on the glaciation, microphysics, and dynamics of clouds

2006

[1] Numerical simulations were performed to investigate the effects of drop freezing in immersion and contact modes for a convective situation. For the description of heterogeneous drop freezing, new approaches were used considering the significantly different ice nucleating efficiencies of various ice nuclei. An air parcel model with a sectional two-dimensional description of the cloud microphysics was employed. Sensitivity studies were undertaken by varying the insoluble particle types as well as the soluble fraction of the aerosol particles showing the effects of these parameters on drop freezing and their possible impact on the vertical cloud dynamics. The soluble fraction ɛ decides whe…

Definition of "banner clouds" based on time lapse movies

2007

Abstract. Banner clouds appear on the leeward side of a mountain and resemble a banner or a flag. This article provides a comprehensive definition of "banner clouds". It is based primarily on an extensive collection of time lapse movies, but previous attempts at an explanation of this phenomenon are also taken into account. The following ingredients are considered essential: the cloud must be attached to the mountain but not appear on the windward side; the cloud must originate from condensation of water vapour contained in the air (rather than consist of blowing snow); the cloud must be persistent; and the cloud must not be of convective nature. The definition is illustrated and discussed …

The impact of overshooting deep convection on local transport and mixing in the tropical upper troposphere/lower stratosphere (UTLS)

2015

Abstract. In this study we examine the simulated downward transport and mixing of stratospheric air into the upper tropical troposphere as observed on a research flight during the SCOUT-O3 campaign in connection to a deep convective system. We use the Advanced Research Weather and Research Forecasting (WRF-ARW) model with a horizontal resolution of 333 m to examine this downward transport. The simulation reproduces the deep convective system, its timing and overshooting altitudes reasonably well compared to radar and aircraft observations. Passive tracers initialised at pre-storm times indicate the downward transport of air from the stratosphere to the upper troposphere as well as upward tr…

Modeling of biomass smoke injection into the lower stratosphere by a large forest fire (Part I): reference simulation

2006

Abstract. Wildland fires in boreal regions have the potential to initiate deep convection, so-called pyro-convection, due to their release of sensible heat. Under favorable atmospheric conditions, large fires can result in pyro-convection that transports the emissions into the upper troposphere and the lower stratosphere. Here, we present three-dimensional model simulations of the injection of fire emissions into the lower stratosphere by pyro-convection. These model simulations are constrained and evaluated with observations obtained from the Chisholm fire in Alberta, Canada, in 2001. The active tracer high resolution atmospheric model (ATHAM) is initialized with observations obtained by r…

2015

Abstract. A recent parcel model study (Reutter et al., 2009) showed three deterministic regimes of initial cloud droplet formation, characterized by different ratios of aerosol concentrations (NCN) to updraft velocities. This analysis, however, did not reveal how these regimes evolve during the subsequent cloud development. To address this issue, we employed the Active Tracer High Resolution Atmospheric Model (ATHAM) with full microphysics and extended the model simulation from the cloud base to the entire column of a single pyro-convective mixed-phase cloud. A series of 2-D simulations (over 1000) were performed over a wide range of NCN and dynamic conditions. The integrated concentration …

A Theoretical Study of the Wet Removal of Atmospheric Pollutants. Part III: The Uptake, Redistribution, and Deposition of (NH4)2SO4Particles by a Con…

1988

Abstract Our model for the scavenging of aerosol particles has been coupled with the two-dimensional form of the convective cloud model of Clark and Collaborators. The combined model was then used to simulate a convective warm cloud for the meteorological situation which existed at 1100 LST 12 July 1985 over Hawaii; assuming an aerosol size distribution of maritime number concentration and of mixed composition with (NH4)2SO4 as the soluble compound. A shallow model cloud developed 26 min after the onset of convection leading to moderate rain which began after 45 min and ended after 60 min. Various parameters which characterize the dynamics and micophysics of the cloud, as well as the scaven…