Monday, 28 August 2023
Boundary Waters (Hyatt Regency Minneapolis)
Secondary ice production (SIP) has an essential role in cloud and precipitation microphysics, most notably within mixed-phase environments, the modelling of which is a key challenge in atmospheric and climate sciences. In recent years, substantial insights were gained into SIP by combining experimental, modeling, and observational approaches. Remote sensing instruments, and among them meteorological radars, offer a unique possibility to study clouds and precipitation in extended areas over long time periods, and are highly valuable to understand the spatio-temporal structure of microphysical processes. Multi-modal Doppler spectra measured by vertically-pointing radars reveal the coexistence, within a radar resolution volume, of hydrometeor populations with distinct properties; as such, they can provide decisive insights into precipitation microphysics.
This contribution leverages polarimetric radar Doppler spectra as a tool to study the microphysical processes that took place during a snowfall event on 27 January 2021, during the ICE GENESIS campaign, in the Swiss Jura Mountains. A multi-layered cloud system was present, with ice particles sedimenting through a supercooled liquid water (SLW) layer in an orographic seeder-feeder configuration. Multimodal features are persistently identified in the Doppler spectra, for several hours, and extending over several kilometers above the ground. To investigate the microphysical mechanisms behind these signatures, we build on an existing Doppler peak detection algorithm, and implement a peak labeling procedure to identify the particle types that may be present within a radar resolution volume. This makes use of the radar moments and polarimetric in variables (slanted linear depolarization ratio, SLDR) associated with each mode in the Doppler spectrum. This approach reveals that different types of hydrometeors are responsible for the multimodal spectra at different time frames of the event, which in turn points to the occurrence of distinct microphysical mechanisms.
Taking the analysis a step further, we focus on three 30-minute phases of the case study. The detailed information contained in the Doppler spectra is combined with dual-frequency radar measurements, which are used to detect W-band attenuation, pointing to the presence of liquid cloud layers. The radar data are complemented with aircraft in-situ images, and simulated profiles of atmospheric variables. In this way, we can narrow down the possible processes that may be responsible for the observed signatures. Depending on the availability of SLW and the droplet sizes, on the temperature range, and on the interactions between the liquid and ice particles, various SIP processes are identified as plausible, with distinct fingerprints in the radar Doppler spectra. A simple modeling approach proposed in previous work suggests that the ice crystal number concentrations exceeds the typical concentrations of ice nucleating particles – in this geographical region and temperature range – by one to four orders of magnitude, which supports the hypothesis that SIP is occurring in the different phases of the event.
While a robust proof of the occurrence of SIP through a given mechanism cannot be easily established, the multi-sensor data provide various independent elements, each supporting the proposed interpretations. This study highlights the relevance of combining multi-frequency radar measurements and dual-polarization Doppler spectra, combined with in situ observations, for the identification and study of complex microphysical processes in mixed-phase environments, and provides insights into SIP processes that may occur under seeder-feeder configurations.
This contribution leverages polarimetric radar Doppler spectra as a tool to study the microphysical processes that took place during a snowfall event on 27 January 2021, during the ICE GENESIS campaign, in the Swiss Jura Mountains. A multi-layered cloud system was present, with ice particles sedimenting through a supercooled liquid water (SLW) layer in an orographic seeder-feeder configuration. Multimodal features are persistently identified in the Doppler spectra, for several hours, and extending over several kilometers above the ground. To investigate the microphysical mechanisms behind these signatures, we build on an existing Doppler peak detection algorithm, and implement a peak labeling procedure to identify the particle types that may be present within a radar resolution volume. This makes use of the radar moments and polarimetric in variables (slanted linear depolarization ratio, SLDR) associated with each mode in the Doppler spectrum. This approach reveals that different types of hydrometeors are responsible for the multimodal spectra at different time frames of the event, which in turn points to the occurrence of distinct microphysical mechanisms.
Taking the analysis a step further, we focus on three 30-minute phases of the case study. The detailed information contained in the Doppler spectra is combined with dual-frequency radar measurements, which are used to detect W-band attenuation, pointing to the presence of liquid cloud layers. The radar data are complemented with aircraft in-situ images, and simulated profiles of atmospheric variables. In this way, we can narrow down the possible processes that may be responsible for the observed signatures. Depending on the availability of SLW and the droplet sizes, on the temperature range, and on the interactions between the liquid and ice particles, various SIP processes are identified as plausible, with distinct fingerprints in the radar Doppler spectra. A simple modeling approach proposed in previous work suggests that the ice crystal number concentrations exceeds the typical concentrations of ice nucleating particles – in this geographical region and temperature range – by one to four orders of magnitude, which supports the hypothesis that SIP is occurring in the different phases of the event.
While a robust proof of the occurrence of SIP through a given mechanism cannot be easily established, the multi-sensor data provide various independent elements, each supporting the proposed interpretations. This study highlights the relevance of combining multi-frequency radar measurements and dual-polarization Doppler spectra, combined with in situ observations, for the identification and study of complex microphysical processes in mixed-phase environments, and provides insights into SIP processes that may occur under seeder-feeder configurations.
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