Search results for "Planetary Science"
showing 10 items of 4367 documents
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…
High‐resolution simulations of convective cold pools over the northwestern Sahara
2009
[1] Cooling by evaporation of convective precipitation in the deep and dry subcloud layer over desert regions can generate intense downdrafts and long-lived and extensive atmospheric density currents. The strong gusts at their leading edges can cause so-called haboob dust storms. Despite their importance for the dust cycle, the ability of state-of-the-art numerical weather prediction models to realistically simulate the associated convective cold pools has been investigated very little to date. During the first field campaign of the Saharan Mineral Dust Experiment in southern Morocco in May/June 2006, several density currents were observed. They were triggered by deep moist convection over …
Impact of Convectively Detrained Ice Crystals on the Humidity of the Tropical Tropopause Layer in Boreal Winter
2020
Deep convection detraining in the uppermost tropical troposphere is capable of transporting water vapor and ice into the tropical tropopause layer (TTL), but the impact of deep convection on the global and regional TTL water vapor budget remains uncertain. In particular, the role of convectively detrained ice crystals that remain suspended after active convection has subsided is not well understood. These ice crystals represent aging cirrus anvils detached from the convective core. We use a cloud microphysical model that tracks individual ice crystals throughout their lifetimes to quantify the impact of detrained ice on the humidity of the TTL during boreal winter. Convective influence of a…
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…
Analysis of thermally induced flows in the laboratory by geoelectrical 3-D tomography
2010
[1] Many natural bodies as well as materials inside industrial installations, such as the Earth's mantle and the glass inside melting furnaces, exchange matter through convection. These processes result from differences in temperature, density, and chemical concentration. In this analysis, we focus on the visualization of thermally driven flows in the laboratory. In nature and in industrial installations, it is difficult to measure the temperature inside the object of interest directly. We benchmark a new DC-geoelectrical 3-D tomography method for temperature measurements that allows obtaining temperature values without influencing the flow pattern. For verification of the method, we use di…
Dust mobilization due to density currents in the Atlas region: Observations from the Saharan Mineral Dust Experiment 2006 field campaign
2007
[1] Evaporation of precipitation is a ubiquitous feature of dry and hot desert environments. The resulting cooling often generates density currents with strong turbulent winds along their leading edges, which can mobilize large amounts of dust. Mountains support this process by triggering convection, by downslope acceleration of the cool air, and by fostering the accumulation of fine-grained sediments along their foothills through the action of water. For the Sahara, the world's largest dust source, this mechanism has been little studied because of the lack of sufficiently high resolution observational data. The present study demonstrates the frequent occurrence of density currents along th…
Unprecedented evidence for deep convection hydrating the tropical stratosphere
2008
[1] We report on in situ and remote sensing measurements of ice particles in the tropical stratosphere found during the Geophysica campaigns TROCCINOX and SCOUT-O3. We show that the deep convective systems penetrated the stratosphere and deposited ice particles at altitudes reaching 420 K potential temperature. These convective events had a hydrating effect on the lower tropical stratosphere due to evaporation of the ice particles. In contrast, there were no signs of convectively induced dehydration in the stratosphere.
Classification of precipitation events with a convective response timescale and their forecasting characteristics
2011
[1] The convective timescale τc, which is mainly determined by the ratio of CAPE and precipitation rate, provides a physically-based measure to distinguish equilibrium and non-equilibrium convection. A statistical analysis of this timescale, based upon observational data from radiosonde ascents, rain gauges, and radar for seven warm seasons in Germany, reveals that the equilibrium and non-equilibrium regimes can be regarded as extremes of a continuous distribution. The two regimes characterize very different interactions between the large-scale flow and convection. The quality of precipitation forecasts from a non-hydrostatic regional weather prediction model with parameterized convection d…
Geoid effects in a convecting system with lateral viscosity variations
1992
The geoid signal and the flow patterns of two-dimensional steady state convection models with exponential temperature- and depth dependent viscosity are compared with results for an equivalent stratified viscosity structure. In analogy to Richards and Hager [1989], the latter are computed by a “dynamic response” approach. The flow fields obtained with this approach are quite different from the full solution; the geoid signals are similar but the amplitudes differ significantly. The differences are analysed in the horizontal wavenumber domain and in the spatial domain. They may lead to an overestimation of the viscosity contrast of the earth's mantle derived by modeling the earth's geoid wit…
Magnetic field emergence in mesogranular-sized exploding granules observed with SUNRISE/IMaX data
2011
We report on magnetic field emergences covering significant areas of exploding granules. The balloon-borne mission SUNRISE provided high spatial and temporal resolution images of the solar photosphere. Continuum images, longitudinal and transverse magnetic field maps and Dopplergrams obtained by IMaX onboard SUNRISE are analyzed by Local Correlation Traking (LCT), divergence calculation and time slices, Stokes inversions and numerical simulations are also employed. We characterize two mesogranular-scale exploding granules where $\sim$ 10$^{18}$ Mx of magnetic flux emerges. The emergence of weak unipolar longitudinal fields ($\sim$100 G) start with a single visible magnetic polarity, occupyi…