Microphysical process of precipitating hydrometeors from warm-front mid-level stratiform clouds revealed by ground-based lidar observations
<p>Mid-level stratiform precipitations during the passage of warm fronts were detailedly observed on two occasions (light and moderate rain) by a 355 nm polarization lidar and water vapor Raman lidar, both equipped with waterproof transparent roof windows. The hours-long precipitation streaks...
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| Autores principales: | , , , , , |
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| Formato: | article |
| Lenguaje: | EN |
| Publicado: |
Copernicus Publications
2021
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| Materias: | |
| Acceso en línea: | https://doaj.org/article/e1f485a634d64092849c6d9debb028cc |
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| Sumario: | <p>Mid-level stratiform precipitations during the passage of warm fronts were
detailedly observed on two occasions (light and moderate rain) by a 355 nm
polarization lidar and water vapor Raman lidar, both equipped with
waterproof transparent roof windows. The hours-long precipitation streaks
shown in the lidar signal (<span class="inline-formula"><i>X</i></span>) and volume depolarization ratio (<span class="inline-formula"><i>δ</i><sub>v</sub></span>) reveal some ubiquitous features of the microphysical process of
precipitating hydrometeors. We find that for the light-rain case
precipitation that reaches the surface begins as ice-phase-dominant
hydrometeors that fall out of a shallow liquid cloud layer at altitudes above the
0 <span class="inline-formula"><sup>∘</sup></span>C isotherm level, and the depolarization ratio magnitude of
falling hydrometeors increases from the liquid-water values (<span class="inline-formula"><i>δ</i><sub>v</sub><0.09</span>) to the ice/snow values (<span class="inline-formula"><i>δ</i><sub>v</sub>>0.20</span>) during the first 100–200 m of their descent. Subsequently, the
falling hydrometeors yield a dense layer with an ice/snow bright band
occurring above and a liquid-water bright band occurring below (separated by
a lidar dark band) as a result of crossing the 0 <span class="inline-formula"><sup>∘</sup></span>C level. The
ice/snow bright band might be a manifestation of local hydrometeor
accumulation. Most falling raindrops shrink or vanish in the liquid-water
bright band due to evaporation, whereas a few large raindrops fall out of
the layer. We also find that a prominent <span class="inline-formula"><i>δ</i><sub>v</sub></span> peak (0.10–0.40)
always occurs at an altitude of approximately 0.6 km when precipitation
reaches the surface, reflecting the collision–coalescence growth of falling
large raindrops and their subsequent spontaneous breakup. The microphysical
process (at ice-bright-band altitudes and below) of moderate rain resembles
that of the light-rain case, but more large-sized hydrometeors are involved.</p> |
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