Sentences with phrase «ice nuclei»

These studies concern the formation of ice nuclei in supercooled vapours at low temperatures.

We examined the the April 8 case (flight 16), when the average ice nucleus concentration that was measured above the boundary layer substantially exceeded the average ice number concentration within the cloud layer, and the predominant ice habit was dendritic, which is a slow - falling crystal type.

In addition, naturally occurring bacteria found in decayed leaf litter can serve as ice nuclei at temperatures of less than about − 4 °C (24.8 °F).

These studies concern the formation of ice nuclei in supercooled vapours at low temperatures.

As a result, liquid water cooled below 0 °C (32 °F) can often remain liquid at subfreezing temperatures because of the absence of effective ice nuclei.

While in the air, he tested the samples to see whether he could make the dust particles in them create ice nuclei again, inside his instrument.

«Dust particles have been shown to be efficient ice nuclei, which may influence the monsoon by changing clouds» properties,» Jin said.

Methods: Scientists have known since the 1940s that seeding with silver and lead iodide can produce artificial ice nuclei in cirrus clouds.

Except for true ice crystals, which are effective at 0 °C, all other ice nuclei become effective at temperatures below freezing.

When ice nuclei are present, heterogeneous ice nucleation can occur at warmer temperatures.

In a process called cloud seeding, silver iodide, with effective ice - nucleating temperatures of less than − 4 °C, has been used for years in attempts to convert supercooled water to ice crystals in regions with a scarcity of natural ice nuclei.

Several studies were able to roughly reproduce the observed ice distributions, but only by invoking novel mechanisms for ice formation or by including sources of ice nuclei not confirmed by the measurements.

In contrast to cloud condensation nuclei, the most effective ice nuclei are hydrophobic (having a low affinity for water) with molecular spacings and a crystallographic structure close to that of ice.

The ability to essentially re-create in the aircraft what the researchers believed was happening out in the cloud further confirmed that the dust particles were creating ice nuclei.

The presence of cloud condensation and ice nuclei in air parcels is tested by using cloud chambers in which controlled temperatures and relative humidities are specified.

However, past studies of such Arctic mixed - phase clouds have been unable to explain the measured abundance of ice crystals larger than 100 micrometers in maximum dimension (the size range where measurements are available), given observed environmental conditions and the measured concentrations of ice nuclei that could be entrained into the observed shallow cloud layers from aloft.

Over a third of the ice nuclei generated contained lead, suggesting it is a highly - efficient nucleator.

The team found there were much fewer of these ice nuclei than there were actual ice crystals in the clouds.

Ice nuclei, a type of aerosol particle in the atmosphere, form the ice crystals in mixed - phase clouds.

Wikipedia «Ice Nucleus.»

A recent Science paper (open link here), doesn't quite answer that question, but does provide a strong indicator by measuring the residues from the ice nuclei from which cirrus clouds form.

The paper, Clarifying the Dominant Sources and Mechanisms of Cirrus Cloud Formation, D, J. Cziczo, et al. find that most of the ice nuclei form around mineral dust.

Aerosols that are effective for the conversion of water vapour to ice crystals are referred to as ice nuclei.

While cloud condensation nuclei are always readily available in the atmosphere, ice nuclei are often scarce.

Examples of cloud condensation nuclei include sodium chloride (NaCl) and ammonium sulfate -LRB-[NH4] 2 SO2), whereas the clay mineral kaolinite is an example of an ice nuclei.

Ice nuclei are of three types: deposition nuclei, contact nuclei, and freezing nuclei.

In the absence of any ice nuclei, the freezing of supercooled water droplets of a few micrometres in radius, in a process called homogeneous ice nucleation, requires temperatures at or lower than − 39 °C (− 38 °F).

Thus, the entrainment source of ice nuclei was relatively large (compared to previous case studies) and the sedimentation sink of ice crystals was small.

Including aggregation, in addition to quadrupled ice nucleus concentrations aloft or an ice nucleus reservoir below, allowed the simulations to roughly match the in situ properties when assuming the presence of low - density dendrites and their aggregates (Fig. 2).

Simulations include possible quadrupled ice nucleus concentration aloft (top two rows; see paper for details) or near - surface ice nucleus reservoir (bottom two rows).

We also note that agreement between observed and simulated ice crystal number concentrations in our study required the concentration of entrained ice nuclei to be much greater than the number concentration of ice crystals, which conflicts with studies that indicate that entrained ice nucleus concentrations are equal to in - cloud ice crystal concentrations.

However, we caution that these results do not imply that the ice formation problem is solved because several unique conditions favored agreement between simulated and observed ice crystal number concentrations in this case: overlying ice nucleus concentrations much greater than in - cloud ice crystal concentrations, very slow - falling ice crystals, and the possible presence of an ice nucleus reservoir below a decoupled surface layer.

The aircraft also made in situ measurements of cloud microphysics and ice nuclei, as well as meteorological state parameters and radiative fluxes, which were important study inputs.

With cloud tops warmer than -38 degrees Celsius, ice formation depends on aerosols that preferentially freeze at warm temperatures, referred to as ice nuclei.

We found that without crystal aggregation, our simulations using low - density dendrites were able to predominantly match the in situ measurements, but this rough match required either increasing the overlying ice nucleus concentration fourfold or assuming a reservoir of ice nuclei from the surface layer to be entrained from the underlying, decoupled surface layer (both conceivable; see paper for details).

Simulations include possible quadrupled ice nucleus concentration aloft (top four panels; see paper for details) or a possible ice nucleus reservoir in the surface layer (bottom four panels).

On the other hand, if some of the anthropogenic aerosols act as ice nuclei, supercooled clouds could be converted into ice clouds by the glaciation indirect effect (Lohmann, 2002), resulting in more efficient precipitation formation.

Interactions with the hydrological cycle, and additional impacts on the radiation budget, occur through the role of aerosols in cloud microphysical processes, as aerosol particles act as cloud condensation nuclei (CCN) and ice nuclei (IN).