Using a holographic imager on a tethered balloon system for microphysical observations of boundary layer clouds

Ramelli, Fabiola; Beck, Alexander; Henneberger, Jan; Lohmann, Ulrike

doi:10.5194/amt-13-925-2020

Cited by 43 publications

(55 citation statements)

References 66 publications

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“…An early example of a particle-imaging instrument is the cloud particle imager, which employs a diffraction analysis to image high-altitude cloud ice particles 50 , 51 . Others include the aircraft-mounted HOLODEC instrument for cloud-ice particle imaging 52 , the stationary HOLIMO II instrument 53 and similar HoloBalloon instrument 54 , a submersible DH imager 55 , a DH cloud imager for cable cars called HoloGondel 56 , a stationary pollen imager 57 , and the ICEMET cloud-ice imager 58 . The HAPI instrument described here has features that make it ideally suited for field research in a cost-effective manner in that it need not be carried by commercial aircraft or a research balloon.…”

Section: Introductionmentioning

confidence: 99%

Imaging atmospheric aerosol particles from a UAV with digital holography

Kemppinen

Laning

Mersmann

et al. 2020

Sci Rep

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The lack of quantitative characterization of aerosol particles and their loading in the atmosphere is one of the greatest uncertainties in climate-change science. Improved instrumentation capable of determining the size and shape of aerosol particles is needed in efforts to reduce this uncertainty. We describe a new instrument carried by an unmanned aerial vehicle (UAV) that images free-floating aerosol particles in the atmosphere. Using digital holography, the instrument obtains the images in a non-contact manner, resolving particles larger than ten micrometers in size in a sensing volume of approximately three cubic centimeters. The instrument, called the holographic aerosol particle imager (HAPI), has the unique ability to image multiple particles freely entering its sensing volume from any direction via a single measurement. The construction of HAPI consists of 3D printed polymer structures that enable a sufficiently low size and weight that it may be flown on a commercial-grade UAV. Examples from field trials of HAPI show images of freshly emitted tree pollen and mineral dust.

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Section: Introductionmentioning

confidence: 99%

Imaging atmospheric aerosol particles from a UAV with digital holography

Kemppinen

Laning

Mersmann

et al. 2020

Sci Rep

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“…Another wind‐speed maximum occurs right above the stratus (9 m·s −1 ), which is somewhat underestimated by the model. Although FLS formation is favourable in calm conditions, these high wind speeds at a mature stage are not exceptional: Ramelli et al ., (2020) reported wind speeds around 10 m·s −1 within the cloud layer for a different FLS case over the Swiss Plateau. At midday (Figure 9f), a general increase in wind speeds up to 2,000 m asl is present, which also penetrates the stratus.…”

Section: Resultsmentioning

confidence: 99%

“…Standard radiosonde observations do not include the liquid water content (LWC). LWC could be obtained with measurement devices such as a tethered balloon (Seidel et al ., 2016; Ramelli et al ., 2020), a combination of Light Detection and Ranging (lidar) and microwave radiometer (Navas‐Guzmán et al ., 2014), or a profiling microwave radiometer (Gultepe et al ., 2014).…”

Section: Resultsmentioning

confidence: 99%

Identifying the key challenges for fog and low stratus forecasting in complex terrain

Westerhuis

Fuhrer

Čermák

et al. 2020

Quart J Royal Meteoro Soc

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Forecasting fog and low stratus (FLS) accurately poses a challenge to current numerical weather prediction models, despite many advancements in recent years. We present a novel method to quantify FLS extent bias by comparing forecasts with satellite observations. Evaluating a four‐month period, we show that COSMO‐1, the MeteoSwiss high‐resolution operational model, exhibits a considerable negative FLS bias during wintertime. To study the cause, we conduct a series of sensitivity experiments for a representative case study, where COSMO‐1 dissipated extensive FLS erroneously. Replacing the one‐moment bulk microphysics parameterisation scheme by a two‐moment scheme, as well as increasing the number of vertical levels, did not show any improvements. The FLS dissipation was delayed (but not prevented) by decreasing the lower bound imposed on the turbulent diffusion coefficients from 0.4 to 0.01 m2·s−1, or by reducing horizontal grid spacing from 1.1 km to 550 m. Additionally, simulations at 1.1‐km grid spacing with smoothed orography led to more extensive FLS than the same simulations without smoothed orography. An analysis of the cloud water budget revealed that the model's advection scheme is causing a loss of liquid water content near the cloud top. A simulation with an alternative terrain‐following coordinate system, in which the vertical coordinates are quasihorizontal near the cloud top, reduced the loss of cloud water through advection and improved the evolution of FLS in the case study. In combination, our findings suggest that the advection scheme exhibits numerical diffusion, which promotes spurious mixing in the vertical of cloudy and adjacent cloud‐free grid cells in terrain‐following vertical coordinates; this process can become the root cause for too rapid dissipation of FLS during nighttime in complex terrain.

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“…Moreover, a 14-channel microwave radiometer (HATPRO, Radiometer Physics GmbH, Germany; Rose et al, 2005) provided information about the vertical temperature and humidity profiles as well as the column integrated water vapor content (IWV) and liquid water path (LWP). In situ observations of the low-level microphysical cloud structure were obtained with a tethered balloon system (HoloBalloon; Ramelli et al, 2020). The main component of the measurement platform is the HOLographic cloud Imager for Microscopic Objects (HOLIMO), which can image cloud particles in the size range of 6 µm to 2 mm (Henneberger et al, 2013;Beck et al, 2017;Ramelli et al, 2020).…”

Section: Instrument Setupmentioning

confidence: 99%

“…In situ observations of the low-level microphysical cloud structure were obtained with a tethered balloon system (HoloBalloon; Ramelli et al, 2020). The main component of the measurement platform is the HOLographic cloud Imager for Microscopic Objects (HOLIMO), which can image cloud particles in the size range of 6 µm to 2 mm (Henneberger et al, 2013;Beck et al, 2017;Ramelli et al, 2020). It provides information about the phase-resolved number concentration, water content, size distribution and particle shape.…”

Section: Instrument Setupmentioning

confidence: 99%

Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley

Ramelli¹,

Henneberger²,

David³

et al. 2020

Preprint

Self Cite

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Abstract. Previous studies that investigated orographic precipitation have primarily focused on isolated mountain barriers. Here we investigate the influence of low-level blocking and shear-induced turbulence on the cloud microphysics and precipitation formation in a complex inner-Alpine valley. The analysis focuses on a mid-level cloud in a post-frontal environment, by combining observations from an extensive set of instruments including ground-based remote sensing instrumentation, in situ instrumentation on a tethered balloon system and ground-based precipitation measurements. During this event, the boundary layer was characterized by a blocked low-level flow and a turbulent shear layer, which separated the blocked layer near the surface from the stronger cross-barrier flow aloft. Cloud radar observations indicate changes in the microphysical cloud properties within the turbulent shear layer including enhanced linear depolarization ratio (i.e., change in particle shape) and increased radar reflectivity (i.e., enhanced ice growth). Based on the ice particle habits observed at the surface, we suggest that needle growth and aggregation occurred within the turbulent layer and that collisions of fragile ice crystals (e.g., dendrites, needles) might have contributed to secondary ice production. Additionally, in situ instrumentation on the tethered balloon system observed the presence of a low-level feeder cloud above a small-scale topographic feature, which dissipated when the low-level flow turned from a blocked to an unblocked state. Our observations indicate that the low-level blocking (due to the downstream mountain barrier) caused the low-level flow to ascend the leeward slope of the local topography in the valley, thus producing a low-level feeder cloud. Although the feeder cloud did not enhance precipitation in the present case, we propose that local flow effects such as low-level blocking can induce the formation of feeder clouds in mountain valleys and on the leeward slope of foothills upstream of the main mountain barrier, where they can act to enhance orographic precipitation through the seeder-feeder mechanism.

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Using a holographic imager on a tethered balloon system for microphysical observations of boundary layer clouds

Cited by 43 publications

References 66 publications

Imaging atmospheric aerosol particles from a UAV with digital holography

Imaging atmospheric aerosol particles from a UAV with digital holography

Identifying the key challenges for fog and low stratus forecasting in complex terrain

Influence of low-level blocking and turbulence on the microphysics of a mixed-phase cloud in an inner-Alpine valley

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