Application of the shipborne remote sensing supersite OCEANET for profiling of Arctic aerosols and clouds during &amp;lt;i&amp;gt;Polarstern&amp;lt;/i&amp;gt; cruise PS106

Griesche, Hannes; Seifert, Patric; Ansmann, Albert; Baars, Holger; Velasco, Carola Barrientos; Bühl, Johannes; Engelmann, Ronny; Radenz, Martin; Yin, Zhenping; Macke, Andreas

doi:10.5194/amt-13-5335-2020

Cited by 34 publications

(38 citation statements)

References 96 publications

(120 reference statements)

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“…PAS-CAL as well as ACLOUD was dedicated to the investigation of processes related to Arctic amplification. During the full period of PS106, continuous remote sensing of aerosols and clouds was performed with the OCEANET-Atmosphere platform aboard Polarstern (Griesche et al, 2020b). The suite of instruments of OCEANET operated during PS106 is listed in Table 1.…”

Section: Instrumentation and Methodologymentioning

confidence: 99%

“…In turn, ground-based profiling studies from the Arctic, which rely on lidar and radar observations, usually provide reasonable data only at heights above 100-150 m above ground, as is the case for the 35 GHz cloud radar (KAZR) of the US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program at the NSA (North Slope of Alaska) site in Utqiaġvik (formerly known as Barrow), USA. Cloud processes that take place at lower heights can thus not thoroughly be characterized (Griesche et al, 2020b).…”

Section: Introductionmentioning

confidence: 99%

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Contrasting ice formation in Arctic clouds: surface-coupled vs. surface-decoupled clouds

et al. 2021

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Abstract. In the Arctic summer of 2017 (1 June to 16 July) measurements with the OCEANET-Atmosphere facility were performed during the Polarstern cruise PS106. OCEANET comprises amongst other instruments the multiwavelength polarization lidar PollyXT_OCEANET and for PS106 was complemented with a vertically pointed 35 GHz cloud radar. In the scope of the presented study, the influence of cloud height and surface coupling on the probability of clouds to contain and form ice is investigated. Polarimetric lidar data were used for the detection of the cloud base and the identification of the thermodynamic phase. Both radar and lidar were used to detect cloud top. Radiosonde data were used to derive the thermodynamic structure of the atmosphere and the clouds. The analyzed data set shows a significant impact of the surface-coupling state on the probability of ice formation. Surface-coupled clouds were identified by a quasi-constant potential temperature profile from the surface up to liquid layer base. Within the same minimum cloud temperature range, ice-containing clouds have been observed more frequently than surface-decoupled clouds by a factor of up to 6 (temperature intervals between −7.5 and −5 ∘C, 164 vs. 27 analyzed intervals of 30 min). The frequency of occurrence of surface-coupled ice-containing clouds was found to be 2–3 times higher (e.g., 82 % vs. 35 % between −7.5 and −5 ∘C). These findings provide evidence that above −10 ∘C heterogeneous ice formation in Arctic mixed-phase clouds occurs by a factor of 2–6 more often when the cloud layer is coupled to the surface. In turn, for minimum cloud temperatures below −15 ∘C, the frequency of ice-containing clouds for coupled and decoupled conditions approached the respective curve for the central European site of Leipzig, Germany (51∘ N, 12∘ E). This corroborates the hypothesis that the free-tropospheric ice nucleating particle (INP) reservoir over the Arctic is controlled by continental aerosol. Two sensitivity studies, also using the cloud radar for detection of ice particles and applying a modified coupling state detection, both confirmed the findings, albeit with a lower magnitude. Possible explanations for the observations are discussed by considering recent in situ measurements of INP in the Arctic, of which much higher concentrations were found in the surface-coupled atmosphere in close vicinity to the ice shore.

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Section: Instrumentation and Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Contrasting ice formation in Arctic clouds: surface-coupled vs. surface-decoupled clouds

et al. 2021

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“…In a laboratory study, Hallett and Mossop (1974) observed that rimesplintering is active at temperatures between −3 and −8 • C when particles grow by riming. Dong and Hallett (1989) showed that at temperatures above −3 • C, droplets spread out on the ice surface and do not build an ice shell, while at temperatures below −8 • C the ice shell of rime might be too strong to break (Griggs and Choularton, 1983). While several observations of secondary ice could be explained by the rime-splintering process (e.g., Ono, 1971Ono, , 1972Harris-Hobbs and Cooper, 1987;Bower et al, 1996), secondary ice was also observed in cases where these requirements were not fulfilled (e.g., , or the SIP by rimesplintering alone was expected to be too slow to explain the observed rapid glaciation (e.g., Hobbs and Rangno, 1990).…”

Section: Secondary-ice Production Mechanismsmentioning

confidence: 99%

Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions

et al. 2021

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Abstract. An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary-ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice-nucleating particle concentration in clouds. The Hallett–Mossop process is active between −3 and −8 ∘C and has been implemented into several models, while all other secondary-ice processes are poorly constrained and lack a well-founded quantification. During 2 h of measurements taken on a mountain slope just above the melting layer at temperatures warmer than −3 ∘C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary-ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at slightly sub-zero temperatures, where primary-ice nucleation is basically absent, and the first ice is initiated by the collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 µm in diameter produces 18 secondary-ice crystals when it fragments upon freezing. The application of the parametrization to our measurements suggests that the actual number of splinters produced by a fragmenting droplet may be up to an order of magnitude higher.

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“…The coefficients are defined as positive, which means that the flux is directed against the mean gradient. Values of K can be derived from parameterizations based on turbulence observations such as proposed by Hanna (1968) or by directly applying Eq. (6) with the measured H , yielding K H .…”

Section: Vertical Profiles Of Turbulent Moisture and Heat Fluxesmentioning

confidence: 99%

Case study of a humidity layer above Arctic stratocumulus and potential turbulent coupling with the cloud top

et al. 2021

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Abstract. Specific humidity inversions (SHIs) above low-level cloud layers have been frequently observed in the Arctic. The formation of these SHIs is usually associated with large-scale advection of humid air masses. However, the potential coupling of SHIs with cloud layers by turbulent processes is not fully understood. In this study, we analyze a 3 d period of a persistent layer of increased specific humidity above a stratocumulus cloud observed during an Arctic field campaign in June 2017. The tethered balloon system BELUGA (Balloon-bornE moduLar Utility for profilinG the lower Atmosphere) recorded vertical profile data of meteorological, turbulence, and radiation parameters in the atmospheric boundary layer. An in-depth discussion of the problems associated with humidity measurements in cloudy environments leads to the conclusion that the observed SHIs do not result from measurement artifacts. We analyze two different scenarios for the SHI in relation to the cloud top capped by a temperature inversion: (i) the SHI coincides with the cloud top, and (ii) the SHI is vertically separated from the lowered cloud top. In the first case, the SHI and the cloud layer are coupled by turbulence that extends over the cloud top and connects the two layers by turbulent mixing. Several profiles reveal downward virtual sensible and latent heat fluxes at the cloud top, indicating entrainment of humid air supplied by the SHI into the cloud layer. For the second case, a downward moisture transport at the base of the SHI and an upward moisture flux at the cloud top is observed. Therefore, the area between the cloud top and SHI is supplied with moisture from both sides. Finally, large-eddy simulations (LESs) complement the observations by modeling a case of the first scenario. The simulations reproduce the observed downward turbulent fluxes of heat and moisture at the cloud top. The LES realizations suggest that in the presence of a SHI, the cloud layer remains thicker and the temperature inversion height is elevated.

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Application of the shipborne remote sensing supersite OCEANET for profiling of Arctic aerosols and clouds during <i>Polarstern</i> cruise PS106

Cited by 34 publications

References 96 publications

Contrasting ice formation in Arctic clouds: surface-coupled vs. surface-decoupled clouds

Contrasting ice formation in Arctic clouds: surface-coupled vs. surface-decoupled clouds

Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions

Case study of a humidity layer above Arctic stratocumulus and potential turbulent coupling with the cloud top

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