Mixed-phase orographic cloud microphysics during StormVEx and IFRACS
<p>Wintertime mixed-phase orographic cloud (MPC) measurements were conducted at the Storm Peak Laboratory (SPL) during the Storm Peak Lab Cloud Property Validation Experiment (StormVEx) and Isotopic Fractionation in Snow (IFRACS) programs in 2011 and 2014, respectively. The data include 92&...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-04-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/19/5387/2019/acp-19-5387-2019.pdf |
| Summary: | <p>Wintertime mixed-phase orographic cloud (MPC) measurements were
conducted at the Storm Peak Laboratory (SPL) during the Storm Peak Lab Cloud
Property Validation Experiment (StormVEx) and Isotopic Fractionation in
Snow (IFRACS) programs in 2011 and 2014, respectively. The data include 92 <span class="inline-formula">h</span>
of simultaneous measurements of supercooled liquid cloud droplet and
ice particle size distributions (PSDs). Average cloud droplet number
concentration (CDNC), droplet size (NMD), and liquid water content (LWC) were
similar in both years, while ice particle concentration (<span class="inline-formula"><i>N</i><sub>i</sub></span>) and ice water
content (IWC) were higher during IFRACS. The consistency of the liquid cloud
suggests that SPL is essentially a cloud chamber that produces a consistent
cloud under moist, westerly flow during the winter. A variable cloud
condensation nuclei (CCN)-related inverse relationship between CDNC and NMD
strengthened when the data were stratified by LWC. Some of this variation is
due to changes in cloud base height below SPL. While there was a weak
inverse correlation between LWC and IWC in the data as a whole, a stronger
relationship was demonstrated for a case study on 9 February 2014 during
IFRACS. A minimum LWC of 0.05 <span class="inline-formula">g m<sup>−3</sup></span> showed that the cloud was not
completely glaciated on this day. Erosion of the droplet distribution at
high IWC was attributed to the Wegener–Bergeron–Findeisen process as the
high IWC was accompanied by a 10-fold increase in <span class="inline-formula"><i>N</i><sub>i</sub></span>. A relationship between
large cloud droplet concentration (25–35 <span class="inline-formula">µm</span>) and small ice particles
(75–200 <span class="inline-formula">µm</span>) under cold (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo><</mo><mo>-</mo><mn mathvariant="normal">8</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="26pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="415b842651695d9b729bd96d87d3f4bb"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5387-2019-ie00001.svg" width="26pt" height="10pt" src="acp-19-5387-2019-ie00001.png"/></svg:svg></span></span> <span class="inline-formula"><sup>∘</sup>C</span>) but not warm
(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>></mo><mo>-</mo><mn mathvariant="normal">8</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="26pt" height="10pt" class="svg-formula" dspmath="mathimg" md5hash="196d1c469658830a85404cbf26c5348b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-19-5387-2019-ie00002.svg" width="26pt" height="10pt" src="acp-19-5387-2019-ie00002.png"/></svg:svg></span></span> <span class="inline-formula"><sup>∘</sup>C</span>) conditions during IFRACS suggests primary
ice particle production by contact or immersion freezing. The effect of
blowing snow was evaluated from the relationship between wind speed and <span class="inline-formula"><i>N</i><sub>i</sub></span>
and by comparing the relative (percent) ice particle PSDs at high and low
wind speeds. These were similar, contrary to expectation for blowing snow.
However, the correlation between wind speed and ice crystal concentration
may support this explanation for high crystal concentrations at the surface.
Secondary processes could have contributed to high crystal concentrations
but there was no direct evidence to support this. Further experimental work
is needed to resolve these issues.</p> |
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| ISSN: | 1680-7316 1680-7324 |