Aerosols (tiny particles from pollution, dust, smoke, etc.) influence cloud formation by acting as cloud condensation nuclei (CCN). One debated pathway is “aerosol convective invigoration,” where higher aerosol concentrations can strengthen updrafts, increase cloud height, and enhance precipitation in convective systems.

A key proposed mechanism is condensational (or warm-phase) invigoration:

• In very clean (low-aerosol) environments, cloud droplets form sparsely, coalesce quickly into raindrops, and reduce the total droplet surface area available for condensation.
• This can allow very high water vapor supersaturation (SS, where relative humidity exceeds 100%) to build up in strong updrafts because condensation can’t keep pace with the rising air’s cooling.
• When aerosols (especially ultrafine ones) are added, they activate into many additional small droplets. These provide more surface area, enabling rapid condensation of the excess vapor.
• The extra condensation releases more latent heat, boosting buoyancy and updraft speeds, which can invigorate the cloud’s vertical development.

This differs from “cold-phase” invigoration (involving ice processes) and has been controversial due to limited direct observations of high SS in real clouds and modeling uncertainties

Two new peer-reviewed papers central to the recent discussion on high supersaturation (SS) and aerosol convective invigoration.

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1. Springer Paper (Main Observational Study)

Title: Aircraft-observed High Supersaturation Indicates the Potential of Aerosol Convective Invigoration Effect

Journal: Advances in Atmospheric Sciences (2026)

DOI: 10.1007/s00376-026-5894-y

Published: 18 June 2026 (very recent)

Abstract/Key Points (Highlights):

• Deep convective clouds (DCCs) in the tropics were sampled during the CAMP²Ex campaign (2019, Philippines) using aircraft.
• Inferred supersaturation reached up to ~10% in the supercooled liquid zone (below 0°C), especially peaking in the −10°C to −20°C range.
• SS increased with height, stronger updrafts, and progression of droplet coalescence (which reduces droplet surface area, slowing vapor consumption).
• Higher concentrations of small droplets (indicative of more aerosols activating) were associated with lower SS — consistent with faster condensation consuming the excess vapor.
• This provides direct observational evidence that high-SS conditions (a key prerequisite) exist in real tropical DCCs, supporting the condensational (warm-phase) aerosol invigoration mechanism.

The study derives quasi-steady state SS from measured droplet spectra, updraft velocities, and microphysical properties rather than purely direct vapor sensors (direct high-SS measurements remain extremely challenging in strong updrafts).

Abstract

Deep convective clouds (DCCs) drive much of the global circulation and hydrological cycle, especially over the tropics.

Aerosols can invigorate the formation and development of DCCs by increasing the condensation efficiency of the water vapor to cloud water.

A major pathway for aerosol effects on DCCs is called condensational aerosol convective invigoration.

This suggests that adding aerosols to clean clouds at high supersaturation conditions leads to more numerous and smaller droplets.

This process reduces supersaturation and releases latent heat, invigorating the updrafts.

However, high supersaturation, a prerequisite for the invigoration, has been simulated but not observed.

Here, based on aircraft observations of the Cloud, Aerosol, and Monsoon Processes Philippines Experiment from August to October 2019, supersaturation values reaching up to 10% were observed in tropical DCCs at the supercooled zone below 0°C.

The supersaturation increased with height and with the progression of coalescence and accelerated updrafts, peaking over the −10°C to −20°C isotherm range.

Additionally, an increase in the number of small cloud droplets was associated with a decrease in supersaturation.

These observations support the potential for condensational aerosol convective invigoration.

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2. AGU/JGR Paper (Companion/Related Study)

Title: Quasi‐Steady State Supersaturation: Do High Values Derived From ESCAPE Represent Real High Supersaturations and the Potential for Condensational Invigoration

Journal: Journal of Geophysical Research: Atmospheres (2026)

DOI: 10.1029/2025JD045547

Published: Around June 10, 2026

This paper analyzes data from the ESCAPE campaign (likely U.S.-based deep convective cloud observations). It reports extreme supersaturations estimated up to 11% from 219 updraft cores, with peak in situ updrafts reaching 28 m/s.

Overall Context

• These two papers together strengthen the observational foundation for the warm-phase invigoration pathway, which had been heavily reliant on models and theory.
• They respond to prior skepticism (e.g., studies questioning whether sufficiently high SS exists in real clouds for significant invigoration to occur).
• Mechanism reminder: In clean, coalescing clouds → high SS builds up → added aerosols → more small droplets → rapid extra condensation + latent heat → stronger updrafts.
• Limitations remain: SS is often inferred/derived, measurements in the strongest convective cores are rare and difficult, and invigoration depends strongly on environmental conditions (not always observed).

Abstract

Deep convective clouds were intensively sampled during the Experiment of Sea Breeze Convection, Aerosols, Precipitation, and Environment (ESCAPE) with coordinated flights of the NRC Convair-580 and SPEC Learjet.

A total of 219 updraft core segments were sampled over coastal Texas and Louisiana under diverse meteorological conditions.

Median updraft properties included widths of ∼1 km, velocities of 4.8 m s⁻¹, droplet number concentrations of ∼400 cm⁻³, and liquid water contents of 0.9 g m⁻³.

The limitations of using the quasi-steady state approximation to derive supersaturations were explored.

Supersaturation (S_QSS) estimated from in situ observations under a quasi-steady state assumption averaged 0.4% but occasionally exceeded 2%, with values >1% (high supersaturations) identified as statistical outliers.

Two case studies illustrated the conditions linked to high supersaturations.

In a storm over the Gulf, median core S_QSS reached 2.46% in the developing stage compared to 2.17% in the mature stage under similar thermodynamic conditions.

In a storm over coastal Louisiana, S_QSS peaked near 11% within a 13.7-m s⁻¹ updraft, accompanied by predominantly supercooled liquid droplets at −13°C and exceptionally low diameter concentrations of 0.29 mm cm⁻³.

Bootstrap analysis of all sampled cores showed that high supersaturations are most probable in cold and mixed-phase regimes with moderate to strong updrafts and are strongly influenced by vertical velocity and droplet number concentrations.

While extreme supersaturations (∼10%) were rare, their occurrence underscores the need for targeted multiplatform observations to resolve their spatiotemporal variability and assess their potential role in deep convective invigoration.