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- Author or Editor: Szymon P. Malinowski x
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Abstract
The authors have analyzed the scaling behavior of marine boundary layer (MBL) clouds using high-resolution temperature (T) and liquid water content (LWC) fluctuations from aircraft measurements collected over the Pacific Ocean during the Physics of Stratocumulus Top (POST) research campaign in summer of 2008. As an extension of the past studies for scale-invariant properties of MBL clouds, the authors studied the variability of scaling exponents with height. The results showed that both LWC and T have two distinct scaling regimes: the first one displays scale invariance over a range from about 1–5 m to at least 7 km, and the second one goes from about 0.1–1 to 1–5 m. For the large-scale regime (r > 1–5 m), turbulence in MBL clouds is multifractal, while scale break and scaling exponents vary with height, most significantly in the cloud-top region. For example, LWC spectral exponent β increases from 1.42 at cloud base to 1.58 at cloud top, while scale break decreases from ~5 m at cloud base to 0.8 m at cloud top. The bifractal parameters (H 1, C 1) for LWC increase from (0.14, 0.02) at cloud base to (0.33, 0.1) at cloud top while maintaining a statistically significant linear relationship C 1 ≈ 0.4H 1 − 0.04 in MBL clouds. From near surface to cloud top, (H 1, C 1) for T also increase with height, but above cloud top H 1 increases and C 1 decreases with height. The results suggest the existence of three turbulence regimes: near the surface, in the middle of the boundary layer, and in the cloud-top region, which need to be distinguished.
Abstract
The authors have analyzed the scaling behavior of marine boundary layer (MBL) clouds using high-resolution temperature (T) and liquid water content (LWC) fluctuations from aircraft measurements collected over the Pacific Ocean during the Physics of Stratocumulus Top (POST) research campaign in summer of 2008. As an extension of the past studies for scale-invariant properties of MBL clouds, the authors studied the variability of scaling exponents with height. The results showed that both LWC and T have two distinct scaling regimes: the first one displays scale invariance over a range from about 1–5 m to at least 7 km, and the second one goes from about 0.1–1 to 1–5 m. For the large-scale regime (r > 1–5 m), turbulence in MBL clouds is multifractal, while scale break and scaling exponents vary with height, most significantly in the cloud-top region. For example, LWC spectral exponent β increases from 1.42 at cloud base to 1.58 at cloud top, while scale break decreases from ~5 m at cloud base to 0.8 m at cloud top. The bifractal parameters (H 1, C 1) for LWC increase from (0.14, 0.02) at cloud base to (0.33, 0.1) at cloud top while maintaining a statistically significant linear relationship C 1 ≈ 0.4H 1 − 0.04 in MBL clouds. From near surface to cloud top, (H 1, C 1) for T also increase with height, but above cloud top H 1 increases and C 1 decreases with height. The results suggest the existence of three turbulence regimes: near the surface, in the middle of the boundary layer, and in the cloud-top region, which need to be distinguished.
Abstract
This note presents an analysis of several dozens of direct numerical simulations of the cloud–clear air mixing in a setup of decaying moist turbulence with bin microphysics. The goal is to assess the instantaneous relationship between the homogeneity of mixing and the ratio of the time scales of droplet evaporation and turbulent homogenization. Such a relationship is important for developing improved microphysical parameterizations for large-eddy simulation of clouds. The analysis suggests a robust relationship for the range of time scale ratios between 0.5 and 10. Outside this range, the scatter of numerical data is significant, with smaller and larger time scale ratios corresponding to mixing scenarios that approach the extremely inhomogeneous and homogeneous limits, respectively. This is consistent with the heuristic argument relating the homogeneity of mixing to the time scale ratio.
Abstract
This note presents an analysis of several dozens of direct numerical simulations of the cloud–clear air mixing in a setup of decaying moist turbulence with bin microphysics. The goal is to assess the instantaneous relationship between the homogeneity of mixing and the ratio of the time scales of droplet evaporation and turbulent homogenization. Such a relationship is important for developing improved microphysical parameterizations for large-eddy simulation of clouds. The analysis suggests a robust relationship for the range of time scale ratios between 0.5 and 10. Outside this range, the scatter of numerical data is significant, with smaller and larger time scale ratios corresponding to mixing scenarios that approach the extremely inhomogeneous and homogeneous limits, respectively. This is consistent with the heuristic argument relating the homogeneity of mixing to the time scale ratio.
Abstract
A new version of an ultrafast aircraft resistance thermometer (UFT-F) with a time constant of the order 10−4 s,for use in both cloudy and cloudless air, is described. It evolved from an earlier version (UFT-S). Its sensing element is similar to that in UFT-S and consists of a 5-mm-long and 2.5-μm-thick platinum-coated tungsten wire, located on a rotatable vane behind a thin vertical rod that protects the sensor against direct impact of cloud droplets and other objects. Such construction introduces much smaller thermal disturbances than do more massive housings of other types of immersion thermometers and permits taking full advantage of low thermal inertia of the sensing wire. However, aerodynamic disturbances created by vortex shedding from the protective rod induce adiabatic fluctuations of temperature, which appear on the temperature records as “noise.” In the case of the UFT-S the level of this noise has become intolerable at airspeeds of about 40 m s−1, limiting applicability of this instrument to slow aircraft or gliders. For UFT-F the shape of the protective rod has been redesigned and endowed with a special system of reducing aerodynamic disturbances behind it, which made it usable at airspeeds up to 100 m s−1 in cloudless air or warm clouds. For use in supercooled clouds, a special variety of UFT-F (denoted here UFT-D) has been designed. As in its predecessor, its sensing element is a 5-mm-long, 2.5-μm-thick, platinum-coated tungsten resistive wire protected against impact of cloud droplets by an airfoil-shaped rod, but all its icing-sensitive parts are electrically heated to prevent buildup of ice. This modification required a total change of mechanical structure of the instrument. Tests during the Third Canadian Freezing Drizzle Experiment showed that UFT-D can perform fairly well in water clouds supercooled down to at least −8°C and that its heating system introduces no intolerable disturbances into the record. Use of UFT-D in ice or mixed clouds is limited by the fact that the protective rod is not effective enough against ice crystals bigger than about 200 μm, which can quickly destroy the delicate sensing element.
The paper gives details of construction as well as results of wind tunnel and in-flight tests of these instruments.
Abstract
A new version of an ultrafast aircraft resistance thermometer (UFT-F) with a time constant of the order 10−4 s,for use in both cloudy and cloudless air, is described. It evolved from an earlier version (UFT-S). Its sensing element is similar to that in UFT-S and consists of a 5-mm-long and 2.5-μm-thick platinum-coated tungsten wire, located on a rotatable vane behind a thin vertical rod that protects the sensor against direct impact of cloud droplets and other objects. Such construction introduces much smaller thermal disturbances than do more massive housings of other types of immersion thermometers and permits taking full advantage of low thermal inertia of the sensing wire. However, aerodynamic disturbances created by vortex shedding from the protective rod induce adiabatic fluctuations of temperature, which appear on the temperature records as “noise.” In the case of the UFT-S the level of this noise has become intolerable at airspeeds of about 40 m s−1, limiting applicability of this instrument to slow aircraft or gliders. For UFT-F the shape of the protective rod has been redesigned and endowed with a special system of reducing aerodynamic disturbances behind it, which made it usable at airspeeds up to 100 m s−1 in cloudless air or warm clouds. For use in supercooled clouds, a special variety of UFT-F (denoted here UFT-D) has been designed. As in its predecessor, its sensing element is a 5-mm-long, 2.5-μm-thick, platinum-coated tungsten resistive wire protected against impact of cloud droplets by an airfoil-shaped rod, but all its icing-sensitive parts are electrically heated to prevent buildup of ice. This modification required a total change of mechanical structure of the instrument. Tests during the Third Canadian Freezing Drizzle Experiment showed that UFT-D can perform fairly well in water clouds supercooled down to at least −8°C and that its heating system introduces no intolerable disturbances into the record. Use of UFT-D in ice or mixed clouds is limited by the fact that the protective rod is not effective enough against ice crystals bigger than about 200 μm, which can quickly destroy the delicate sensing element.
The paper gives details of construction as well as results of wind tunnel and in-flight tests of these instruments.
Abstract
We report on the Azores Stratocumulus Measurements of Radiation, Turbulence and Aerosols (ACORES) campaign, which took place around Graciosa and Pico Islands/Azores in July 2017. The main objective was to investigate the vertical distribution of aerosol particles, stratocumulus microphysical and radiative properties, and turbulence parameters in the eastern North Atlantic. The vertical exchange of mass, momentum, and energy between the free troposphere (FT) and the cloudy marine boundary layer (MBL) was explored over a range of scales from submeters to kilometers. To cover these spatial scales with appropriate measurements, helicopter-borne observations with unprecedented high resolution were realized using the Airborne Cloud Turbulence Observation System (ACTOS) and Spectral Modular Airborne Radiation Measurement System–Helicopter-Borne Observations (SMART-HELIOS) instrumental payloads. The helicopter-borne observations were combined with ground-based aerosol measurements collected at two continuously running field stations on Pico Mountain (2,225 m above sea level, in the FT), and at the Atmospheric Radiation Measurement (ARM) station on Graciosa (at sea level). First findings from the ACORES observations we are discussing in the paper are as follows: (i) we have observed a high variability of the turbulent cloud-top structure on horizontal scales below 100 m with local temperature gradients of up to 4 K over less than 1 m vertical distance, (ii) we have collected strictly collocated radiation measurements supporting the relevance of small-scale processes by revealing significant inhomogeneities in cloud-top brightness temperature to scales well below 100 m, and (iii) we have concluded that aerosol properties are completely different in the MBL and FT with often-complex stratification and frequently observed burst-like new particle formation.
Abstract
We report on the Azores Stratocumulus Measurements of Radiation, Turbulence and Aerosols (ACORES) campaign, which took place around Graciosa and Pico Islands/Azores in July 2017. The main objective was to investigate the vertical distribution of aerosol particles, stratocumulus microphysical and radiative properties, and turbulence parameters in the eastern North Atlantic. The vertical exchange of mass, momentum, and energy between the free troposphere (FT) and the cloudy marine boundary layer (MBL) was explored over a range of scales from submeters to kilometers. To cover these spatial scales with appropriate measurements, helicopter-borne observations with unprecedented high resolution were realized using the Airborne Cloud Turbulence Observation System (ACTOS) and Spectral Modular Airborne Radiation Measurement System–Helicopter-Borne Observations (SMART-HELIOS) instrumental payloads. The helicopter-borne observations were combined with ground-based aerosol measurements collected at two continuously running field stations on Pico Mountain (2,225 m above sea level, in the FT), and at the Atmospheric Radiation Measurement (ARM) station on Graciosa (at sea level). First findings from the ACORES observations we are discussing in the paper are as follows: (i) we have observed a high variability of the turbulent cloud-top structure on horizontal scales below 100 m with local temperature gradients of up to 4 K over less than 1 m vertical distance, (ii) we have collected strictly collocated radiation measurements supporting the relevance of small-scale processes by revealing significant inhomogeneities in cloud-top brightness temperature to scales well below 100 m, and (iii) we have concluded that aerosol properties are completely different in the MBL and FT with often-complex stratification and frequently observed burst-like new particle formation.
The second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field study is described. The field program consisted of nine flights in marine stratocumulus west-southwest of San Diego, California. The objective of the program was to better understand the physics a n d dynamics of marine stratocumulus. Toward this end special flight strategies, including predominantly nocturnal flights, were employed to optimize estimates of entrainment velocities at cloud-top, large-scale divergence within the boundary layer, drizzle processes in the cloud, cloud microstructure, and aerosol–cloud interactions. Cloud conditions during DYCOMS-II were excellent with almost every flight having uniformly overcast clouds topping a well-mixed boundary layer. Although the emphasis of the manuscript is on the goals and methodologies of DYCOMS-II, some preliminary findings are also presented—the most significant being that the cloud layers appear to entrain less and drizzle more than previous theoretical work led investigators to expect.
The second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) field study is described. The field program consisted of nine flights in marine stratocumulus west-southwest of San Diego, California. The objective of the program was to better understand the physics a n d dynamics of marine stratocumulus. Toward this end special flight strategies, including predominantly nocturnal flights, were employed to optimize estimates of entrainment velocities at cloud-top, large-scale divergence within the boundary layer, drizzle processes in the cloud, cloud microstructure, and aerosol–cloud interactions. Cloud conditions during DYCOMS-II were excellent with almost every flight having uniformly overcast clouds topping a well-mixed boundary layer. Although the emphasis of the manuscript is on the goals and methodologies of DYCOMS-II, some preliminary findings are also presented—the most significant being that the cloud layers appear to entrain less and drizzle more than previous theoretical work led investigators to expect.
