Deep convective clouds with sustained supercooled liquid water down to -37.5 degrees C

Area of Science:

• Atmospheric Science
• Cloud Physics
• Meteorology

Background:

• Highly supercooled water (liquid water below 0°C) is known in cirrus and wave clouds but not well-studied in deep convective clouds.
• Satellite data indicate frequent occurrence of highly supercooled water in continental convective storms.
• Previous research lacked in situ measurements for supercooled water in deep convective cloud tops.

Purpose of the Study:

• To report in situ measurements of highly supercooled water in deep convective clouds.
• To quantify the amount and droplet size of liquid water at very low temperatures.
• To provide data for improving cloud process simulations and understanding climate implications.

Main Methods:

• In situ measurements using aircraft instrumentation within deep convective clouds.
• Analysis of condensed water content and droplet size distribution at sub-zero temperatures.
• Observation of phase transition from liquid to ice to infer freezing mechanisms.

Main Results:

• Most condensed water in deep convective clouds remained liquid down to -37.5°C.
• Liquid water content reached 1.8 g m⁻³, an order of magnitude higher than previously reported.
• Droplet median volume diameter was 17 micrometers.
• Ice was exclusively observed at slightly colder temperatures, suggesting homogeneous freezing.

Conclusions:

• Deep convective clouds can contain significant amounts of highly supercooled liquid water.
• These findings challenge existing assumptions about mixed-phase cloud processes.
• The data are vital for improving numerical weather prediction and climate models, particularly concerning precipitation, hail, and electrification.