Aircraft evaluation of MODIS cloud drop number concentration retrievals
<p>Cloud drop number concentration (<span class="inline-formula"><i>N</i><sub>d</sub></span>) can be retrieved through passive satellite observation. These retrievals are useful due to their wide spatial and temporal coverage. However, the accuracy...
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Copernicus Publications
2025-08-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/18/3819/2025/amt-18-3819-2025.pdf |
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| author | S. R. Passer M. K. Witte P. Y. Chuang |
| author_facet | S. R. Passer M. K. Witte P. Y. Chuang |
| author_sort | S. R. Passer |
| collection | DOAJ |
| description | <p>Cloud drop number concentration (<span class="inline-formula"><i>N</i><sub>d</sub></span>) can be retrieved through passive satellite observation. These retrievals are useful due to their wide spatial and temporal coverage. However, the accuracy of the retrieved values is not well understood. In this study, we seek to understand why the retrievals agree or disagree with in situ measurements by examining the various cloud properties that underlie the retrievals. To do so, we compare satellite <span class="inline-formula"><i>N</i><sub>d</sub></span> derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument with in situ aircraft measurements made using a phase Doppler interferometer on board three flight campaigns sampling marine stratocumulus clouds. Intercomparison of <span class="inline-formula"><i>N</i><sub>d</sub></span> values shows that the discrepancy between retrieved and in situ <span class="inline-formula"><i>N</i><sub>d</sub></span> can be <span class="inline-formula">±</span> 50 % or more. In the mean, there is evidence of an overestimation bias by MODIS retrievals, although the sample size is insufficient for statistical certainty. We find that MODIS <span class="inline-formula"><i>N</i><sub>d</sub></span> is best interpreted as representative of the mid-cloud region, as there is almost always a greater discrepancy from in situ values near the cloud top and cloud base. We also find evidence of cases where <span class="inline-formula"><i>N</i><sub>d</sub></span> is accurately retrieved but the effective radius is not, presumably due to offsetting errors in other retrieval parameters. Vertical profiles of the extinction coefficient <span class="inline-formula"><i>β</i></span>, liquid water content <span class="inline-formula"><i>L</i></span>, and effective radius <span class="inline-formula"><i>r</i><sub>e</sub></span> measured during sawtooth-pattern flight legs through the cloud top are also compared to implicit MODIS retrieval profiles. For the two cases with <span class="inline-formula"><i>N</i><sub>d</sub></span> agreement, all profiles match well. For the six cases with significant disagreement, there is no consistent underlying cause. The discrepancy originates from one of the following: (a) discrepancy in the <span class="inline-formula"><i>r</i><sub>e</sub></span> profile, (b) discrepancy in the <span class="inline-formula"><i>β</i></span> and <span class="inline-formula"><i>L</i></span> profiles, or (c) discrepancy in both.</p> |
| format | Article |
| id | doaj-art-dc90c4e6f2ff44eab2cb61a71c60897e |
| institution | Kabale University |
| issn | 1867-1381 1867-8548 |
| language | English |
| publishDate | 2025-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Measurement Techniques |
| spelling | doaj-art-dc90c4e6f2ff44eab2cb61a71c60897e2025-08-20T03:36:25ZengCopernicus PublicationsAtmospheric Measurement Techniques1867-13811867-85482025-08-01183819383110.5194/amt-18-3819-2025Aircraft evaluation of MODIS cloud drop number concentration retrievalsS. R. Passer0M. K. Witte1P. Y. Chuang2Earth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, USADepartment of Meteorology, Naval Postgraduate School, Monterey, CA, USAEarth and Planetary Sciences, University of California Santa Cruz, Santa Cruz, CA, USA<p>Cloud drop number concentration (<span class="inline-formula"><i>N</i><sub>d</sub></span>) can be retrieved through passive satellite observation. These retrievals are useful due to their wide spatial and temporal coverage. However, the accuracy of the retrieved values is not well understood. In this study, we seek to understand why the retrievals agree or disagree with in situ measurements by examining the various cloud properties that underlie the retrievals. To do so, we compare satellite <span class="inline-formula"><i>N</i><sub>d</sub></span> derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument with in situ aircraft measurements made using a phase Doppler interferometer on board three flight campaigns sampling marine stratocumulus clouds. Intercomparison of <span class="inline-formula"><i>N</i><sub>d</sub></span> values shows that the discrepancy between retrieved and in situ <span class="inline-formula"><i>N</i><sub>d</sub></span> can be <span class="inline-formula">±</span> 50 % or more. In the mean, there is evidence of an overestimation bias by MODIS retrievals, although the sample size is insufficient for statistical certainty. We find that MODIS <span class="inline-formula"><i>N</i><sub>d</sub></span> is best interpreted as representative of the mid-cloud region, as there is almost always a greater discrepancy from in situ values near the cloud top and cloud base. We also find evidence of cases where <span class="inline-formula"><i>N</i><sub>d</sub></span> is accurately retrieved but the effective radius is not, presumably due to offsetting errors in other retrieval parameters. Vertical profiles of the extinction coefficient <span class="inline-formula"><i>β</i></span>, liquid water content <span class="inline-formula"><i>L</i></span>, and effective radius <span class="inline-formula"><i>r</i><sub>e</sub></span> measured during sawtooth-pattern flight legs through the cloud top are also compared to implicit MODIS retrieval profiles. For the two cases with <span class="inline-formula"><i>N</i><sub>d</sub></span> agreement, all profiles match well. For the six cases with significant disagreement, there is no consistent underlying cause. The discrepancy originates from one of the following: (a) discrepancy in the <span class="inline-formula"><i>r</i><sub>e</sub></span> profile, (b) discrepancy in the <span class="inline-formula"><i>β</i></span> and <span class="inline-formula"><i>L</i></span> profiles, or (c) discrepancy in both.</p>https://amt.copernicus.org/articles/18/3819/2025/amt-18-3819-2025.pdf |
| spellingShingle | S. R. Passer M. K. Witte P. Y. Chuang Aircraft evaluation of MODIS cloud drop number concentration retrievals Atmospheric Measurement Techniques |
| title | Aircraft evaluation of MODIS cloud drop number concentration retrievals |
| title_full | Aircraft evaluation of MODIS cloud drop number concentration retrievals |
| title_fullStr | Aircraft evaluation of MODIS cloud drop number concentration retrievals |
| title_full_unstemmed | Aircraft evaluation of MODIS cloud drop number concentration retrievals |
| title_short | Aircraft evaluation of MODIS cloud drop number concentration retrievals |
| title_sort | aircraft evaluation of modis cloud drop number concentration retrievals |
| url | https://amt.copernicus.org/articles/18/3819/2025/amt-18-3819-2025.pdf |
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