Persistence of orographic mixed‐phase clouds

Lohmann, Ulrike; Henneberger, Jan; Henneberg, Olga; Fugal, Jacob P.; Bühl, Johannes; Kanji, Zamin A.

doi:10.1002/2016gl071036

Cited by 48 publications

(61 citation statements)

References 30 publications

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“…Our 50 % frozen cloud fractions fall within the range reported from airborne, ground based, and satellite measurements as summarized in McCoy et al (2016) (Figure 13). Furthermore, these results are 30 remarkably consistent with the typically observed transition zones between supercooled liquid and ice clouds in models and observations (Costa et al, 2017;Henneberg et al, 2017;Lohmann et al, 2016;McCoy et al, 2016b;Pithan et al, 2014). Indeed, global circulation models partition liquid and ice in a given atmospheric volume as a monotonic function of temperature, but precipitation and freezing and melting cycles affect the liquid water to ice ratio, thereby modifying the cloud phase transition in often 35 poorly constrained ways (Cesana et al, 2015;McCoy et al, 2015).…”

Section: Inp Concentration Parameterizationsupporting

confidence: 75%

Ice nucleating particles measured in Swiss alpine snow samples are spatially, temporarily and chemically heterogeneous

Brennan

David

Borduas-Dedekind

2019

Preprint

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Ice nucleating particles (INPs) produce ice from supercooled water droplets through heterogeneous 10 freezing in the atmosphere. Since the concentration of ice crystals affects the radiative properties of clouds as well as precipitation, constraining the liquid water to ice ratio could help reduce aerosol-cloud interaction uncertainties. INPs have been collected at the Jungfraujoch research station (at 3500 m a.s.l.) in central Switzerland; yet spatially diverse data on INP occurrence in the Swiss Alps are scarce and remain uncharacterized. We address this scarcity through our Swiss Alpine snow sample study which 15 took place during the winter of 2018. We collected a total of 88 fallen snow samples across the Alps at different locations, altitudes, terrains, times since last snowfall and depths. The INP concentrations were measured using the homebuilt DRoplet Ice Nuclei Counter Zurich (DRINCZ) and were then compared to spatial, meteorological and physiochemical parameters. We also extend an alternative way of displaying frozen fraction (FF) versus temperature data through visualizing freezing temperatures as a 20boxplot to field collected samples. This plotting method displays the freezing temperature in one dimension, instead of the former two dimensions of FF vs temperature, allowing a condensed display of freezing temperature measurements. In the collected snow samples, large variability in INP occurrence was found, even for samples collected 10 m apart on a plain and 1 m apart in depth. Furthermore, undiluted samples had INP concentrations ranging between 1 and 100 INP ml -1 of snow water over a 25 temperature range of −5 to −19 C. From this field-collected data set, we parameterize the INP concentrations per milliliter of meltwater as a function of temperature with the following equation * ( ) = − . − . , comparing well with previously reported precipitation data presented in Petters and Wright, 2015. 30 When assuming a cloud water content of 0.4 g m -3 and a critical INP concentration for glaciation of 10 m -3 , the majority of the snow precipitated from clouds with glaciation temperatures between −5 and −20 °C. Based on the observed variability in INP concentrations, we conclude that studies conducted at the high-altitude research station Jungfraujoch are representative for INP measurements in the Swiss Alps. Furthermore, the INP concentration precipitation estimates allow us to extrapolate the 35 concentrations to a cloud frozen fraction. Indeed, this approach for estimating the liquid water to ice ratio in mixed phase clouds compares well with aircraft measurements, ground-based lidar and satellite retrievals of cloud frozen fractions. In all, the generated parameterization for INP concentrations in meltwater could help estimate cloud glaciation temperatures.

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Section: Inp Concentration Parameterizationsupporting

confidence: 75%

Ice nucleating particles measured in Swiss alpine snow samples are spatially, temporarily and chemically heterogeneous

Brennan

David

Borduas-Dedekind

2019

Preprint

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“…Clouds can either consist purely of ice crystals or water droplets or they can be mixed phase. Even though mixed-phase clouds (MPCs) are thermodynamically unstable, they occur worldwide, mainly in areas of deep convection (Rosenfeld & Woodley, 2000), mountainous terrain (Lohmann et al, 2016), or the polar latitudes (Morrison et al, 2011;Shupe et al, 2006). While former analyses of cloud organization have been limited to warm clouds in the lower latitudes, there is visual evidence from satellite data that high-latitude MPCs may also organize into different morphological regimes, even far away from large-scale synoptic features ( Figure 1).…”

Section: 1029/2019gl084959mentioning

confidence: 99%

“…Organized cloud structures have been frequently observed in the subtropical trade wind region (Bretherton & Blossey, 2017;Wood & Hartmann, 2006). Even though mixed-phase clouds (MPCs) are thermodynamically unstable, they occur worldwide, mainly in areas of deep convection (Rosenfeld & Woodley, 2000), mountainous terrain (Lohmann et al, 2016), or the polar latitudes (Morrison et al, 2011;Shupe et al, 2006). Cloud types span a multitude of thermodynamic states.…”

Section: Introductionmentioning

confidence: 99%

Cloud Ice Processes Enhance Spatial Scales of Organization in Arctic Stratocumulus

Eirund

Lohmann

Possner

2019

Geophysical Research Letters

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Stratocumulus clouds around the globe tend to organize into cellular patterns, a phenomenon that has been primarily studied for the subtropical trade wind region. However, stratocumulus are also prevalent in high latitudes, where they often occur as mixed-phase clouds. Yet little research has been conducted regarding mechanisms of cloud organization in the mixed-phase regime. In cloud-resolving model simulations we investigate the processes driving organization in open-cell mixed-phase stratocumuli. Similar to warm-phase clouds, mixed-phase clouds develop a subcloud circulation of evaporated/sublimated precipitation, cold pool formation, and consecutive updrafts driving new convective cells. For a larger ice to liquid water ratio, we find locally stronger precipitation and larger cloud cells. Hence, a higher concentration of ice nucleating particles can induce a breakup of the stratocumulus organization, with implications for the radiative balance at the surface. A decrease in cloud condensation nuclei concentration is also found to intensify precipitation and impact cloud organization.Plain Language Summary Low-lying clouds have been found to organize into honeycomb-like spatial patterns. This has been primarily studied for liquid clouds in the subtropical regions but has remained unexplored in the high latitudes. Previous studies focusing on precipitating open-cell clouds have found that below cloud base a continuous cycle of evaporation and subsequent latent cooling, sinking, and lateral spreading of the air mass can be observed. Colliding air masses push the air upward which leads to localized updrafts and new cloud formation. In this study, we explore the organization of open-cell polar clouds, which consist of both liquid cloud droplets and ice crystals (so-called mixed-phase clouds).We show that open-cell mixed-phase clouds also form honeycomb-like spatial patterns following the same mechanism as liquid clouds. However, the spatial extent of cloud patterns changes with the amount of cloud ice. Clouds that contain ice produce precipitation earlier and more intensively. As a result, the cooling below cloud base is strengthened and the cloud cells grow larger. This has implications for the radiative balance at the surface. The stronger growth of ice-containing clouds leads to a breakup of the organized structures, which increases the amount of outgoing radiation.

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“…This allows simultaneous growth of supercooled liquid droplets and ice crystals [57]. However, as the ICNC exceeds the concentration of INP by orders of magnitude, no influence of anthropogenic aerosols on the persistence of MPCs could be deduced.…”

Section: Aerosol Effects On Orographic Mpcsmentioning

confidence: 99%

“…Stratiform MPCs are prevalent in the Arctic [67,89] and in orographic terrain [28,50,57]. In situ observations and surface remote sensing suggest that clouds in the mixedphase temperature range in mid-latitudes tend to consist almost entirely of ice or of liquid water [10,11,48].…”

Section: Aerosol Effects On Stratiform and Shallow Convective Mpcsmentioning

confidence: 99%

Anthropogenic Aerosol Influences on Mixed-Phase Clouds

Lohmann

2017

Curr Clim Change Rep

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Aerosol effects on mixed-phase clouds (MPCs) are more complex than in warm clouds because aerosol particles can act both as cloud condensation nuclei and as ice nucleating particles and more microphysical pathways exist. Stratiform MPCs are most prevalent in the Arctic where cloud top cooling enables heterogeneous ice formation and in orographic terrain where large updrafts prevail. Recently, aerosol effects on stratiform MPCs have also been considered in global climate models. The estimated effective aerosol radiative forcing due to aerosol-cloud and aerosol-radiation interactions (ERFaci+ari) at the top-ofthe-atmosphere (TOA) in stratiform warm and MPCs, which is an update of the estimate given in the fifth assessment report (AR5) of the Intergovernmental Panel of Climate Change, is −1.2 W m −2 with a 5-95 % range between −0.8 and −2.0 W m −2 . Since AR5, only one new estimate of ERFaci+ari including aerosol effects on both stratiform and convective clouds of −1.4 W m −2 has been published. In all cases, ERFaci+ari is dominated by changes in the shortwave TOA radiation with changes in the longwave TOA radiation amounting to 0.15 W m −2 .

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Persistence of orographic mixed‐phase clouds

Cited by 48 publications

References 30 publications

Ice nucleating particles measured in Swiss alpine snow samples are spatially, temporarily and chemically heterogeneous

Ice nucleating particles measured in Swiss alpine snow samples are spatially, temporarily and chemically heterogeneous

Cloud Ice Processes Enhance Spatial Scales of Organization in Arctic Stratocumulus

Anthropogenic Aerosol Influences on Mixed-Phase Clouds

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