Date: 12/10/2016 20:32:53
From: ChrispenEvan
ID: 967437
Subject: Living cloud machines.
Date: 13/10/2016 04:59:01
From: mollwollfumble
ID: 967570
Subject: re: Living cloud machines.
mollwollfumble said:
tauto said:
…“Around half of all cloud seeds are thought to originate from nucleated particles, but the process of nucleation is poorly understood.”
The process of nucleation of cloud droplets is exceedingly well understood, I’ve done research work for CSIRO that delves deeply into the topic.
The process is not easy to describe in simple terms, and the recent Richard Hammond’s “Wild Weather” series got it totally and completely wrong. Let me know if you want a detailed explanation.
Looking at the article, I was too hasty. “Blue haze” above vegetation does seem to be a valid source of cloud drop nucleation, and one that has been mostly neglected until now.
Consider the atmospheric aerosols on which cloud droplets form. The key factor here is the number of small aerosol particles. Aerosols as they are presently known can be largely grouped as follows, arranged from largest to smallest.
Wind-blown dust.
Evaporated salt droplets torn by wind from wave crests.
Smoke from bushfires.
Evaporated salt droplets (jet drops) from busting bubbles in the sea.
Evaporated salt droplets (film drops) from bursting bubbles in the sea.
Carbon nanoparticles from forest fires and industrial processes.
Individual ions from cosmic rays.
It turns out that we can eliminate the first four, and the last of the particles in the above list for the simple reason that there aren’t enough of them. That leaves
Evaporated salt droplets (film drops) from bursting bubbles in the sea and carbon nanoparticles from forest fires and industrial processes. Near city and industrial environments there are more of the latter type and in the countryside more of the former type.
However, it has been claimed that up to 50% of cloud droplets form without nuclei of any kind. The new mechanism of blue haze from plants may account for some of the droplets previously thought to have no nucleus. This mechanism has been considered before, but has been though to be of minor importance.
The following table (From Seinfeld and Pandis chapter 2.7) gives the global estimation estimates for major types of aerosols in the 1980s.
Natural sources, numbers in teragrams per year.
1500 Soil dust
1300 Sea salt
130 Sulphates from biogenic gases
60 Organic matter from biogenic volatile organic carbons (this is what the CLOUD article is about)
50 Biological debris
30 Volcanic dust
30 Nitrates from NOx emissions
20 Sulphates from volcanic SO2
Antropogenic sources
190 Solphates from SO2
100 Industrial dust
90 Biomass burning
50 Nitrates from NOx emissions
10 Soot
10 Organic matter from biogenic volatile organic carbons
In the following sketch of salt aerosol generation by bubble bursting, film droplets are shown at the far left and jet droplets at the far right.
