A5026562342- Atmospheric aerosols and clouds
- Meteorological Phenomena and Simulations
- Precipitation Measurement and Analysis
- Icing and De-icing Technologies
- Atmospheric chemistry and aerosols
- Cryospheric studies and observations
- Aeolian processes and effects
- nanoparticles nucleation surface interactions
- Crystallization and Solubility Studies
- Arctic and Antarctic ice dynamics
- Soil Moisture and Remote Sensing
- X-ray Diffraction in Crystallography
- Wind and Air Flow Studies
- Particle Dynamics in Fluid Flows
- Atmospheric Ozone and Climate
- Solar Radiation and Photovoltaics
- Winter Sports Injuries and Performance
- Electromagnetic Scattering and Analysis
- Fire effects on ecosystems
- Urban Heat Island Mitigation
- Atmospheric and Environmental Gas Dynamics
- Aerospace and Aviation Technology
- Aerodynamics and Fluid Dynamics Research
- Aerospace Engineering and Energy Systems
- Near-Field Optical Microscopy
University of Reading
2014-2024
National Institute of Meteorology
2013-2024
University of Nottingham
2021
University of Warwick
2004-2006
Systems Dynamics (United States)
1964-1965
Measured ice crystal concentrations in natural clouds at modest supercooling (temperature ~>−10°C) are often orders of magnitude greater than the number concentration primary nucleating particles. Therefore, it has long been proposed that a secondary production process must exist is able to rapidly enhance population following initial nucleation events. Secondary important for prediction and subsequent evolution some types clouds, but physical basis not understood rates well constrained. In...
Abstract Accurate estimates for the fall speed of natural hydrometeors are vital if their evolution in clouds is to be understood quantitatively. In this study, laboratory measurements terminal velocity υt a variety ice particle models settling viscous fluids, along with wind-tunnel and field particles air, have been analyzed compared common methods computing from literature. It observed that while these work well number types, they fail open geometries, specifically those which area ratio...
Abstract A method of estimating dissipation rates from a vertically pointing Doppler lidar with high temporal and spatial resolution has been evaluated by comparison independent measurements derived balloon-borne sonic anemometer. This utilizes the variance mean velocity number sequential samples requires an estimate horizontal wind speed. The noise contribution to can be estimated observed signal-to-noise ratio removed where appropriate. relative size provides measure confidence in...
Abstract The assumed relationship between ice particle mass and size is profoundly important in radar retrievals of clouds, but, for millimeter-wave radars, shape preferred orientation are as well. In this paper the authors first examine consequences fact that widely used “Brown Francis” mass–size has often been applied to maximum dimension observed by aircraft D max rather than mean dimensions two orthogonal directions , which was originally Brown Francis. Analysis images reveals ≃ 1.25...
Abstract. Simultaneous observations of cloud microphysical properties were obtained by in-situ aircraft measurements and ground based Radar/Lidar. Widespread mid-level stratus was present below a temperature inversion (~5 °C magnitude) at 3.6 km altitude. Localised convection (peak updraft 1.5 m s−1) observed 20 west the Radar station. This associated with convergence 2.5 The unable to penetrate capping stratus. vertically thin (~400 m), horizontally extensive (covering 100 s km) persisted...
Abstract This article focuses on the characteristics of persistent thin single‐layer mixed‐phase clouds. We seek to answer two important questions: (i) how does ice continually nucleate and precipitate from these clouds, without available nuclei becoming depleted? (ii) do supercooled liquid droplets persist in spite net flux water vapour growing crystals? These questions are answered quantitatively using situ radar observations a long‐lived cloud layer over Chilbolton Observatory. Doppler...
Using 4 years of radar and lidar observations layer clouds from the Chilbolton Observatory in UK, we show that almost all (95%) ice particles formed at temperatures >-20°C appear to originate supercooled liquid clouds. At colder temperatures, there is a monotonic decline in fraction liquid-topped clouds: 50% -27°C, falling to zero -37°C (where homogeneous freezing water droplets occurs). This strongly suggests that deposition nucleation plays relatively minor role initiation mid-level...
Abstract. In situ high resolution aircraft measurements of cloud microphysical properties were made in coordination with ground based remote sensing observations a line small cumulus clouds, using Radar and Lidar, as part the Aerosol Properties, PRocesses And InfluenceS on Earth's climate (APPRAISE) project. A narrow but extensive (~100 km long) shallow convective clouds over southern UK was studied. Cloud top temperatures observed to be higher than −8 °C, seen consist supercooled droplets...
Abstract In this paper an equation is derived for the mean backscatter cross section of ensemble snowflakes at centimeter and millimeter wavelengths. It uses Rayleigh–Gans approximation, which has previously been found to be applicable these wavelengths due low density snow aggregates. Although internal structure individual snowflake random unpredictable, authors find from simulations aggregation process that their “self-similar” can described by a power law. This enables analytic expression...
Abstract. The accurate representation of ice particles is essential for both remotely sensed estimates clouds and precipitation numerical models the atmosphere. As it typical in radar retrievals to assume that all snow composed aggregate snowflakes, denser rimed mixed-phase cloud which riming occurs may be under-diagnosed therefore difficult evaluate weather climate models. Recent experimental studies have yielded methods using triple-frequency measurements interrogate internal structure...
Abstract The properties of planar ice crystals settling horizontally have been investigated using a vertically pointing Doppler lidar. Strong specular reflections were observed from their oriented basal facets, identified by comparison with second lidar 4 ° zenith. Analysis 17 months continuous high‐resolution observations reveals that these pristine are frequently in falling mid‐level mixed‐phase layer clouds (85% the time for layers at −15 C). Detailed analysis case study indicates...
Abstract A new method of accurately calculating the capacitance realistic ice particles is described: such values are key to accurate estimates deposition and evaporation (sublimation) rates in numerical weather models. The trajectories diffusing water molecules directly sampled, using random “walkers.” By counting how many these intersect surface particle (which may be any shape) escape outside a spherical boundary far from particle, capacitances number model habits have been estimated,...
A simple model of irreversible aggregation under differential sedimentation particles in a fluid is presented. The structure the aggregates produced by this process found to feed back on dynamics such way as stabilise both exponents controlling growth rate, and fractal dimension clusters at readily predictable values. ice crystals form snowflakes considered potential application model.
Abstract Observations have been obtained within an intense (precipitation rates > 50 mm h −1 ) narrow cold‐frontal rainband ( NCFR embedded a broader region of stratiform precipitation. In situ data were from aircraft which flew near steerable dual‐polarisation Doppler radar. The observations to characterise the microphysical properties cold frontal clouds, with emphasis on ice and precipitation formation development. Primary nucleation cloud top (−55°C) appeared be enhanced by convective...
Abstract. Clouds and associated precipitation are the largest source of uncertainty in current weather future climate simulations. Observations microphysical, dynamical radiative processes that act at cloud scales needed to improve our understanding clouds. The rapid expansion ground-based super-sites availability continuous profiling scanning multi-frequency radar observations 35 94 GHz have significantly improved ability probe internal structure clouds high temporal-spatial resolution,...
Abstract. We have identified a region of an ice cloud where sharp transition dual-wavelength ratio occurs at fixed height for longer than 20 min. In this paper we provide evidence that rapid aggregation particles occurred in region, creating large particles. This comes from triple-wavelength Doppler spectrum radar data were fortuitously being collected. Through quantitative comparison the spectra three radars are able to estimate particle size distribution (of larger 0.75 mm) different...
Aggregation of ice crystals is a key process governing precipitation. Individual exhibit considerable diversity shape, and wide range physical processes could influence their aggregation; despite this we show that simple computer model captures features aggregate shape size distribution reported recently from cirrus clouds. The results prompt new way to plot the experimental distributions leading remarkably good dynamical scaling. That scaling independently confirms there single dominant...
Radar reflectivity measurements from three different wavelengths are used to retrieve information about the shape of aggregate snowflakes in deep stratiform ice clouds. Dual-wavelength ratios calculated for models and compared observations at 3, 35, 94 GHz. It is demonstrated that many scattering models, including spherical spheroidal do not adequately describe observed. The consistent with fractal geometries generated by a physically based aggregation model. dimension large aggregates can...
Abstract. The cloud particle concentration, size, and shape data from optical array probes (OAPs) are routinely used to parameterise properties constrain remote sensing retrievals. This paper characterises the response of OAPs using a combination modelling, laboratory, field experiments. Significant uncertainties found exist with such for ice crystal measurements. We describe test two independent methods probe's sample volume that remove most severely mis-sized particles: (1) greyscale image...
Abstract Estimates for the sedimentation rate of realistic ice crystals at sizes smaller than 100 µm are presented. These calculations, which exploit new results capacitance crystals, compared with laboratory studies and found to be in good agreement. The highlight a weakness contemporary particle fall speed parametrizations very small can lead rates being overestimated by factor two. theoretical approach applied here may also useful calculating mobility non‐spherical aerosol particles....
Abstract The radar scattering properties of realistic aggregate snowflakes have been calculated using the Rayleigh–Gans theory. We find that effect snowflake geometry on may be described in terms a single universal function, which depends only overall shape and not or size pristine ice crystals compose flake. This function is well approximated by simple analytic expression at small sizes; for larger we fit curve to our numerical data. then demonstrate how this allows characteristic radius...
Abstract. A method to estimate the size and liquid water content of drizzle drops using lidar measurements at two wavelengths is described. The exploits differential absorption infrared light by 905 nm 1.5 μm, which leads a different backscatter cross section for larger than ≈50 μm. ratio measured from samples below cloud base these (the colour ratio) provides measure median volume drop diameter D0. This strong effect: D0=200 ≈6 dB predicted. Once D0 known, can be used calculate (LWC) other...
"Summer Snowfall Workshop: Scattering Properties of Realistic Frozen Hydrometeors from Simulations and Observations, as well Defining a New Standard for Databases" published on Mar 2018 by American Meteorological Society.
This study considers complex ice particles falling in the atmosphere: predicting drag of such is important for developing climate models parameterizations. A Delayed-Detached Eddy Simulation model developed to predict coefficient snowflakes at Reynolds number between 50 and 2200. We first consider case where orientation particle known a posteriori, evaluate our results against laboratory experiments using 3D-printed same shape, number. Close agreement found cases fall stably, while more...
Abstract The physical and empirical relationships used by microphysics schemes to control the rate at which vapor is transferred ice crystals growing in supercooled clouds are compared with laboratory data evaluate realism of various model formulations. Ice crystal growth rates predicted from capacitance theory measurements three independent studies. When diffusion- limited, consistent measured values within about 20% 14 experiments analyzed, over temperature range −2.5° −22°C. Only two...