Supplementary material to "Sensitivity of precipitation formation to secondary ice production in winter orographic mixed-phase clouds"

Abstract. In this paper, we show that in mixed phase clouds, the presence of ice crystals may induce wrong FSSP 100 measurements interpretation especially in terms of particle size and subsequent bulk parameters. The presence of ice crystals is generally revealed by a bimodal feature of the particle size distribution (PSD). The combined measurements of the FSSP-100 and the Polar Nephelometer give a coherent description of the effect of the ice crystals on the FSSP-100 response. The FSSP-100 particle size distributions are characterized by a bimodal shape with a second mode peaked between 25 and 35 μm related to ice crystals. This feature is observed with the FSSP-100 at airspeed up to 200 m s−1 and with the FSSP-300 series. In order to assess the size calibration for clouds of ice crystals the response of the FSSP-100 probe has been numerically simulated using a light scattering model of randomly oriented hexagonal ice particles and assuming both smooth and rough crystal surfaces. The results suggest that the second mode, measured between 25 μm and 35 μm, does not necessarily represent true size responses but corresponds to bigger aspherical ice particles. According to simulation results, the sizing understatement would be neglected in the rough case but would be significant with the smooth case. Qualitatively, the Polar Nephelometer phase function suggests that the rough case is the more suitable to describe real crystals. Quantitatively, however, it is difficult to conclude. A review is made to explore different hypotheses explaining the occurrence of the second mode. However, previous cloud in situ measurements suggest that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is likely to be due to the shattering of large ice crystals on the probe inlet. This finding is supported by the rather good relationship between the concentration of particles larger than 20 μm (hypothesized to be ice shattered-fragments measured by the FSSP) and the concentration of (natural) ice particles (CPI data). In mixed cloud, a simple estimation of the number of ice crystals impacting the FSSP inlet shows that the ice crystal shattering effect is the main factor in observed ice production.

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Comparing model and measured ice crystal concentrations in orographic clouds during the INUPIAQ campaign

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-25647-2015 ◽

2015 ◽

Vol 15 (18) ◽

pp. 25647-25694 ◽

Cited By ~ 3

Author(s):

R. J. Farrington ◽

P. J. Connolly ◽

G. Lloyd ◽

K. N. Bower ◽

M. J. Flynn ◽

...

Keyword(s):

Wrf Model ◽

Surface Flux ◽

Liquid Water Content ◽

Mixed Phase ◽

Field Campaign ◽

Orographic Clouds ◽

Ice Multiplication ◽

Ice Production ◽

Surface Ice ◽

Mixed Phase Clouds

Abstract. This paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in-situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Forecasting model (WRF) simulations over real terrain surrounding Jungfraujoch. During the 2014 winter field campaign, between the 20 January and 28 February, the model simulations regularly underpredicted the observed ice number concentration by 103 L−1. Previous literature has proposed several processes for the high ice number concentrations in orographic clouds, including an increased ice nuclei (IN) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing IN concentrations in the model prevents the simulation of the mixed-phase clouds that were witnessed during the INUPIAQ campaign at Jungfraujoch. Additionally, the inclusion of secondary ice production upwind of Jungfraujoch into the WRF simulations cannot consistently produce enough ice splinters to match the observed concentrations. A surface flux of hoar crystals was included in the WRF model, which simulated ice concentrations comparable to the measured ice number concentrations, without depleting the liquid water content (LWC) simulated in the model. Our simulations therefore suggest that high ice concentrations observed in mixed-phase clouds at Jungfraujoch are caused by a flux of surface hoar crystals into the orographic clouds.

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Impacts of Secondary Ice Production on Arctic Mixed-Phase Clouds based on ARM Observations and CESM2

10.5194/acp-2020-1276 ◽

2020 ◽

Author(s):

Xi Zhao ◽

Xiaohong Liu ◽

Vaughan T. J. Phillips ◽

Sachin Patade

Keyword(s):

Global Climate Model ◽

Single Layer ◽

Ice Nucleation ◽

Number Concentration ◽

Mixed Phase ◽

Department Of Energy ◽

Cloud Base ◽

Ice Crystal ◽

Ice Production ◽

Mixed Phase Clouds

Abstract. For decades, measured ice crystal number concentrations have been found to be orders of magnitude higher than measured ice nucleating particles in moderately cold clouds. This observed discrepancy reveals the existence of secondary ice production (SIP) in addition to the primary ice nucleation. However, the importance of SIP relative to primary ice nucleation remains highly unclear. Furthermore, most weather and climate models do not represent well the SIP processes, leading to large biases in simulated cloud properties. This study demonstrates a first attempt to represent different SIP mechanisms (frozen raindrop shattering, ice-ice collisional break-up, and rime splintering) in a global climate model (GCM). The model is run in the single column mode to facilitate comparisons with the Department of Energy (DOE)'s Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment (M-PACE) observations. We show the SIP importance in the four types of clouds during M-PACE (i.e., multilayer, and single-layer stratus, transition, and front clouds), with the maximum enhancement in ice crystal number concentration by up to 4 orders of magnitude in the moderately-cold clouds. We reveal that SIP is the dominant source of ice crystals near the cloud base for the long-lived Arctic single-layer mixed-phase clouds. The model with SIP improves the occurrence and phase partitioning of the mixed-phase clouds, reverses the vertical distribution pattern of ice number concentration, and provides a better agreement with observations. The findings of this study highlight the importance of considering the SIP in GCMs.

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Supplementary material to "Vertical redistribution of moisture and aerosol in orographic mixed-phase clouds"

10.5194/acp-2019-940-supplement ◽

2020 ◽

Author(s):

Annette K. Miltenberger ◽

Paul R. Field ◽

Adrian H. Hill

Keyword(s):

Mixed Phase ◽

Supplementary Material ◽

Mixed Phase Clouds

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Comparing model and measured ice crystal concentrations in orographic clouds during the INUPIAQ campaign

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-4945-2016 ◽

2016 ◽

Vol 16 (8) ◽

pp. 4945-4966 ◽

Cited By ~ 10

Author(s):

Robert J. Farrington ◽

Paul J. Connolly ◽

Gary Lloyd ◽

Keith N. Bower ◽

Michael J. Flynn ◽

...

Keyword(s):

Wrf Model ◽

Liquid Water Content ◽

Mixed Phase ◽

Ice Crystal ◽

Field Campaign ◽

Orographic Clouds ◽

Ice Multiplication ◽

Ice Production ◽

Surface Ice ◽

Mixed Phase Clouds

Abstract. This paper assesses the reasons for high ice number concentrations observed in orographic clouds by comparing in situ measurements from the Ice NUcleation Process Investigation And Quantification field campaign (INUPIAQ) at Jungfraujoch, Switzerland (3570 m a.s.l.) with the Weather Research and Forecasting model (WRF) simulations over real terrain surrounding Jungfraujoch. During the 2014 winter field campaign, between 20 January and 28 February, the model simulations regularly underpredicted the observed ice number concentration by 103 L−1. Previous literature has proposed several processes for the high ice number concentrations in orographic clouds, including an increased ice nucleating particle (INP) concentration, secondary ice multiplication and the advection of surface ice crystals into orographic clouds. We find that increasing INP concentrations in the model prevents the simulation of the mixed-phase clouds that were witnessed during the INUPIAQ campaign at Jungfraujoch. Additionally, the inclusion of secondary ice production upwind of Jungfraujoch into the WRF simulations cannot consistently produce enough ice splinters to match the observed concentrations. A flux of surface hoar crystals was included in the WRF model, which simulated ice concentrations comparable to the measured ice number concentrations, without depleting the liquid water content (LWC) simulated in the model. Our simulations therefore suggest that high ice concentrations observed in mixed-phase clouds at Jungfraujoch are caused by a flux of surface hoar crystals into the orographic clouds.

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Supplementary material to "Modelling mixed-phase clouds with large-eddy model UCLALES-SALSA"

10.5194/acp-2019-1182-supplement ◽

2020 ◽

Author(s):

Jaakko Ahola ◽

Hannele Korhonen ◽

Juha Tonttila ◽

Sami Romakkaniemi ◽

Harri Kokkola ◽

...

Keyword(s):

Mixed Phase ◽

Large Eddy ◽

Supplementary Material ◽

Mixed Phase Clouds

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