{
  "abstract": "Current in situ measurements of water vapor supersaturation ( S v ) with respect to liquid water at cloud base are highly uncertain due to instrumental limitations. Consequently, S v is commonly estimated using cloud microphysical models and parameterizations. Here, we derive S v at warm cumulus cloud base from in situ measurements through calculations of the energy and water vapor budgets associated with cloud formation. The derived S v provides a thermodynamic analogue to the supersaturation established in a cloud condensation nuclei (CCN) chamber, enabling direct comparison with independently measured CCN activation spectra below cloud base. To this end, we formulate the energy budget of a saturated rising air parcel at cloud base and treat the transition between saturated thermodynamic states locally as quasi-isobaric. Under these conditions, the latent heat ( Q ) released during condensational droplet growth is determined by the corresponding sensible enthalpy difference between the saturated-vapor and water vapor–liquid states. According to the first law of thermodynamics, Q is partitioned between the change in internal energy (Δ U ) and water vapor expansion work ( W s ). Within this diagnostic framework, part of the condensational energy is, therefore, spent on W s , reducing the amount of liquid water formed relative to the limiting case in which the entire condensational energy contributes to droplet growth. Accordingly, the cloud supersaturation ( S c ) is diagnostically partitioned into liquid-phase ( S l ) and vapor-phase ( S v ) components based on the fractions of Q associated with Δ U and W s , respectively. This framework enables the derivation of S v from airborne cloud-base measurements through thermodynamic constraints on condensational energy partitioning. Here we use airborne measurements collected in growing convective cumuli over the Amazon Basin during the ACRIDICON-CHUVA campaign. Our results demonstrate that the derived cloud droplet number concentration as a function of S v agrees, within measurement uncertainties, with S v activation spectra of CCN measured below cloud base.",
  "abstract_shown": true,
  "affiliations": [
    "Southern Cross University (Lismore, Australia)"
  ],
  "article_type": null,
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Ramon C. Braga",
      "orcid": "0000-0002-7053-2534"
    },
    {
      "name": "Manfred Wendisch",
      "orcid": "0000-0002-4652-5561"
    },
    {
      "name": "Rachel Albrecht",
      "orcid": "0000-0003-0582-6568"
    },
    {
      "name": "Daniel Harrison",
      "orcid": "0000-0001-8353-6107"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/fzdktrd3g6rf5.bib",
  "cited_by": 0,
  "doi": "10.5194/acp-26-14769-2026",
  "fulltext_url": null,
  "id": "fzdktrd3g6rf5",
  "issns": [
    "1680-7324"
  ],
  "landing_url": "https://acp.copernicus.org/articles/26/14769/2026/",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2306|Atmospheric aerosols and clouds"
    ]
  ],
  "openalex": "W7129569032",
  "pdf_url": "https://acp.copernicus.org/articles/26/14769/2026/acp-26-14769-2026.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-20",
  "publisher": "Copernicus GmbH",
  "ris": "https://research.draconitic.com/paper/fzdktrd3g6rf5.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:20:34Z",
      "native_id": "10.5194/acp-26-14769-2026",
      "source": "crossref",
      "url": "https://acp.copernicus.org/articles/26/14769/2026/"
    }
  ],
  "subjects": [
    {
      "field": "earth",
      "origin": "openalex:2306|Atmospheric aerosols and clouds",
      "subfield": "climate"
    }
  ],
  "title": "A new method to derive water vapor supersaturation at cumulus cloud base from in situ measurements",
  "title_text": "A new method to derive water vapor supersaturation at cumulus cloud base from in situ measurements",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:20:34Z",
  "url": "https://research.draconitic.com/paper/fzdktrd3g6rf5",
  "venue": "Atmospheric Chemistry and Physics",
  "versions": [
    {
      "doi": "10.5194/egusphere-2026-795",
      "pid": null,
      "relation": "preprint",
      "title": null,
      "venue": null
    }
  ]
}