Jon Nelson

Researcher, Editor

Phone: 425-691-9905

Curriculum Vitae (

Education: PhD Physics, University of Washington, 1994




Research Interests:


To me, the two most interesting unanswered questions in cloud physics are

1) Why, fundamentally, do we see snow crystals with so many different (and often amazing) shapes?


2) How exactly do ice particles charge up thunderstorms?


About 1), when snow and ice crystals grow from the vapor in a cloud largely consisting of water droplets, the crystal shape is highly reproducible yet extremely sensitive to temperature, ranging from needle-shaped forms to stellar dendrites. And yet when there are few-to-no droplets in the cloud, the crystal shape seems to be neither reproducible nor extreme in aspect ratio. Why? Finding the answer will involve knowing the dominant crystal-growth mechanism for a given set of environmental conditions and knowing the surface parameters involved in that mechanism.  Researching this question may answer a slew of other questions such as

-        How fast do the crystal faces grow under a given set of environmental conditions?

-        How exactly does a crystal respond to changing conditions?

-        How does the crystal nucleation process affect crystal habit?

-        How do atmospheric impurities affect crystal habit and growth rates?

-        How exactly do stellar sidebranches form?

-        What conditions produce trigonal, disc-shaped, and other unusual forms?

Answering some of these questions would be of immense practical use for improving cloud modeling, and ultimately, helping to improve climate models.


Description: thunderstorm sketch computer.jpg

About 2), the evidence strongly indicates that the primary electrification mechanism involves colliding ice particles. To have a particularly high charging rate, the particles should include large rimed particles and smaller, non-rimed ice crystals, the temperature should be near -15 C, and the cloud region should have an ample supply of water droplets. The thunderstorm becomes charged when the ice particles collide and segregate, with the smaller crystals floating up high and the heavier rimed particles sinking down low. Moreover, the charging rate increases once the thunderstorm develops an electric field. But what are the primary charge carriers that get exchanged between the ice particles and why do they exchange? Answering these questions will address some more practical issues as well:

-        What is the average amount of charge transferred between an ice crystal and a rimed ice particle under a given set of environmental conditions?

-        How does this charge transfer change when an electric field is present?

-        How does the charge transfer change when the crystal size changes?

-        How does the charge transfer change when atmospheric impurities are present?

Answering these questions would help us model thunderstorms better, which ultimately may help us to better predict the occurrence of lightning and thus reduce personal and structural damage from lightning strikes.


IÕm also very curious about a seemingly forgotten question in ice physics:

3) Why does ice curve (both physically and crystallographically) when it grows as a thin layer on a surface? That is, why does surface frost curve?

Published research on this topic has been practically non-existent, with only a few papers, the latest being from the 1970s. Moreover, there appears to be no quantitative theory about the curving phenomenon. The curving arises when a thin film of water freezes on a surface, and thus an interaction between the growing ice-front and the surface substrate appears crucial; however, curving forms (though less sharp) also appear in ice growing along the top surface of large puddles, ponds, and other large open water surfaces. Understanding this curving may help us to better understand the influence a surface substrate exerts over the crystallization of ice deposits.


Current Research Projects:

1)     Isotope fractionation in vapor-grown crystals (theory)

2)     Modeling ice crystal growth from the vapor (theory)

3)     Inductive charge exchange between ice particles (theory)

4)     Film-frost and hoar-frost pattern development (observational)



See my publication list here. (