Fragmentation in Collisions of Snow with Graupel/Hail: New Formulation from Field Observations

Sammanfattning

Secondary ice production (SIP) has been attributed to the generation of most ice particles observed in precipitating clouds with cloud tops warmer than-36 degrees C, from various aircraft- and ground-based fi eld observations across the globe. One of the known SIP mechanisms is fragmentation during collisions among ice particles. It has been studied with our theoretical formulation, which has been applied in microphysical schemes of atmospheric models in a few studies. These have predicted an extensive impact on cloud glaciation and radiative properties. However, there has been a lack of experimental fi eld studies, especially involving naturally falling snowflakes, to better understand this particular mechanism of SIP. This study reports the fi rst fi eld measurements with modern technology for fragmentation during collisions between naturally falling snowflakes and graupel/hail particles. This was observed with an innovatively designed portable chamber that was deployed outdoors in northern Sweden. Applying the observations from this fi eld-based study, we optimized the existing formulation for predicting numbers of fragments from collisions of snow with graupel/hail. The observations show the average numbers of fragments per collision for dendritic (3-12 mm) and nondendritic (1-3 mm) snow were about 12 and 1, respectively. This represents a boost of predicted fragment numbers relative to our original formulation published in 2017. The updated formulation for breakup in ice-ice collisions can be implemented in the microphysical schemes of atmospheric models.

Nyckelord

Cloud microphysics; Secondary ice production; In situ atmospheric observations; Measurements; Cloud parameterizations; Optimization

Publicerad i

Journal of the Atmospheric Sciences
2024, volym: 81, nummer: 12, sidor: 2149-2164
Utgivare: AMER METEOROLOGICAL SOC

SLU författare

• Smith, Paul

  • Enheten för skoglig fältforskning, Sveriges lantbruksuniversitet
    

UKÄ forskningsämne

Meteorologi och atmosfärsvetenskap

Publikationens identifierare

• DOI: https://doi.org/10.1175/JAS-D-23-0122.1

Permanent länk till denna sida (URI)

https://res.slu.se/id/publ/140007