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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/amt-2020-272
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-272
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  22 Jul 2020

22 Jul 2020

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This preprint is currently under review for the journal AMT.

Linking rain into ice microphysics across the melting layer in stratiform rain: a closure study

Kamil Mróz1, Alessandro Battaglia2,3, Stefan Kneifel4, Leonie von Terzi4, Markus Karrer4, and Davide Ori4 Kamil Mróz et al.
  • 1National Centre for Earth Observation, University of Leicester, Leicester, UK
  • 2University of Leicester, Leicester, UK
  • 3Politecnico of Turin, Turin, Italy
  • 4Institute for Geophysics and Meteorology, University of Cologne, Cologne, Germany

Abstract. This study investigates the link between rain and ice microphysics across the melting layer in stratiform rain systems using measurements from vertically pointing multi-frequency Doppler radars. A novel methodology to examine the variability of the precipitation rate and the mass-weighted melted diameter (Dm)across the melting region is proposed and applied to a 6 h-long case study, observed during the TRIPEx-pol field campaign at the Julich Observatory for Cloud Evolution Core Facility and covering a gamut of ice microphysical processes. The methodology is based on an optimal estimation (OE) retrieval of particle size distributions (PSD) and dynamics (turbulence and vertical motions) from observed multi-frequency radar Doppler spectra applied both above and below the melting layer. The retrieval is first applied in the rain region; based on a one-to-one conversion of raindrops into snowflakes, the retrieved Drop Size Distributions (DSD) are propagated upward to provide a first guess for the snow PSDs. These ice PSDs are then used to constrain the OE snow retrieval where Doppler spectra are simulated based on different snow models, which consistently compute fall-speeds and electromagnetic properties. The results corresponding to the best matching models are then used to compute snow fluxes and Dm, which can be directly compared to the corresponding rain quantities.

For the case study, the total accumulation of rain (2.65 mm) and the melted equivalent accumulation of snow (2.60 mm) show only a 2 % difference. The analysis suggests that the mass flux through the melting zone is well preserved except the periods of intense aggregation and intense riming where the precipitation rates were respectively larger and lower in ice than in the rain below. Moreover, it is shown that, the mean mass weighted diameter of ice is strongly related to the characteristic size of the underlying rain. With a simple scaling, Dmice = 1.21Dmrain, the characteristic size of snow can be predicted with a root-mean-square-error of 0.12 mm. This formula leads to slight underestimation of the ice size during aggregation, potentially due to the breakup of melting snowflakes, and to overestimation during riming where the additional particle growth within the melting layer cannot be unambiguously attributed to one process. The proposed methodology can be applied to long-term observations to advance our knowledge of the processes occurring across the melting region; this can then be used to improve assumptions underpinning space-borne radar precipitation retrievals.

Kamil Mróz et al.

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Kamil Mróz et al.

Kamil Mróz et al.

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Latest update: 27 Oct 2020
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Short summary
The article examines the relationship between the characteristics of rain and the properties of the ice cloud from which the rain originated. Our results confirm widely accepted expectation that the mass flux through the melting zone is well preserved with an exception of extreme aggregation and riming conditions. Moreover, it is shown that the mean (mass weighted) size of particles above and below the melting zone are strongly linked with the former being on average 21 % larger.
The article examines the relationship between the characteristics of rain and the properties of...
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