Because the Stefan-Boltzmann equation (or the implications thereof) are not safe for the children of climate science?
As for your other question I'm going for "outside in" based on this article.
Title:
Contact Nucleation Linked to `Evaporation Freezing'
Authors:
Shaw, R. A.;
Durant, A. Affiliation:
AA(Department of Physics, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 United States ;
rashaw@mtu.edu), AB(Department of Physics, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 United States ; Geological Engineering and Sciences, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931 United States ;
ajdurant@mtu.edu)
Publication:
American Geophysical Union, Fall Meeting 2005, abstract #A23C-0970
Publication Date:
12/2005
Origin:
AGU AGU Keywords:
0305 Aerosols and particles (0345, 4801, 4906), 0320 Cloud physics and chemistry, 4801 Aerosols (0305, 4906), 4906 Aerosols (0305, 4801)
Abstract Copyright:
(c) 2005: American Geophysical Union
Bibliographic Code:
2005AGUFM.A23C0970S
Abstract
Ice formation in atmospheric clouds plays a fundamental role in precipitation and cloud radiative properties. Contact nucleation, an important but poorly understood heterogeneous nucleation pathway, defines the freezing of a supercooled cloud drop on contact with an ice-forming nucleus (IN), traditionally from the outside of the drop. In recent work it was shown that heterogeneous ice nucleation rates are enhanced by a form of `surface crystallization'. Here we describe additional experiments and consider the implications for contact nucleation and its relevance to ice nucleation in atmospheric clouds. Our observations suggest that the notion of contact nucleation should be generalized to include surface crystallization from particles contacting a supercooled drop from the inside out, as well as from the outside in. Specifically, (1) we challenge the existing hypothesized mechanisms for contact nucleation in light of the laboratory observations; (2) we present laboratory evidence for enhanced ice nucleation during drop evaporation; and (3) we hypothesize that this more general picture of contact nucleation can result in `evaporation freezing' in atmospheric clouds. Our observations are not consistent with the three leading hypotheses for contact nucleation which include partial solubility of the IN, incomplete adsorption upon initial contact with water, and mechanical disturbance of the water-air interface upon contact: All of these mechanisms are related in some way to the transient nature of contact between a dry IN and a supercooled water drop, which is not present in our experiments. The generalized view of contact nucleation has implications for atmospheric ice formation. For example, there are abundant observations of enhanced ice formation in regions where cloud droplets are evaporating in cumuliform, stratiform, and wave clouds, and it has been speculated that contact nucleation may be responsible for evaporation freezing. Our results lead to the hypothesis that the freezing temperature of an evaporating drop will suddenly increase once the drop surface contacts an immersed IN. This mechanism for evaporation freezing is therefore a plausible explanation for observations of high ice concentrations associated with cloud dilution and droplet evaporation.
