LoRa based remote expendable radiosonde network for environmental observations

The aim of the work is to design and develop a remote radiosonde cluster network and receiver station based on LoRa radio communication protocol. The designed remote sensing unit, radiosonde, should be light (less then 20 gr) and expendable as much as possible. The radiosonde tracks variations of physical and chemical quantities in the surrounding environmental ambient. Primary target of this this new kind of radiosonde is to obtain Lagrangian statistics of turbulence fluctuations inside warm clouds, clear-air and cloud-clear-air mixing regions. However, the application of the sensor network is not limited and can be extended to other contexts, such as environmental monitoring over urban and industrial areas. The radiosonde is made of the radioprobe attached to a biodegradable balloon filled with a mixture of helium and air. The system is able to float inside and around clouds for a time span of the order of a few hours and measure fluctuations of air temperature, pressure, humidity position, velocity and acceleration along its own trajectory. In this manner, the system can provide a multipoint endoscopic view of the flow by following the air parcels in passive way

Microphysical time scales and local supersaturation balance at a warm Cloud Top Boundary, ERCOFTAC

Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient. We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodispersed and polydisperse droplets. For the monodisperse population,a clustering of the values of the reaction, phase and evaporation times, that is around 20-30 seconds, is observed in the central area of the mixing layer, just before the location where the maximum value of the supersaturation turbulent flux occurs. This clustering of values is similar for the polydisperse population but also includes the condensation time. The mismatch between the time derivative of the supersaturation and the condensation term in the interfacial mixing layer is correlated with the planar covariance of the horizontal longitudinal velocity derivatives of the carrier air flow and the supersaturation field, thus suggesting that a quasi-linear relationship may exist between these quantities

Turbulent dispersion analysis via distance-neighbor graphs inside a top cloud boundary in temporal decay

We expand on the original studies on atmospheric diffusion shown on a distance neighbour graph, Q, by Lewis F. Richardson (1926), a quantity that effectively defines a distribution of particles over a separation distance, ℓ. Because of its definition we expect Q to evolve according to an equation of type ∂Q/∂t = ∂/∂l (F(l)∂Q∂l). Particular emphasis was put on the search for a correct form of the diffusion function F. Richardson originally proposed an F ∼ l^(4/3) law. His studies have then been revisited by many, among which Obukhov, leading to the so-called Richardson-Obukhov l^2 ∼ t^3 theory, which holds in the homogeneous, isotropic turbulence regime. Our analysis is carried out on direct numerical simulations (DNS) of a time-decaying turbulent shear-free layer which represents a small portion of a top warm cloud boundary, a multiphase simulation where air, water vapor and water drops have been included

Microphysical time scales, supersaturation fluctuations and droplet distance-neighbour statistical analysis at a warm Cloud Top Boundary

Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient. We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodisperse and polydisperse droplet populations. For the monodisperse population, a clustering of the values of the reaction, phase and evaporation times, that is around 20-30 seconds, is observed in the central area of the mixing layer, just before the location where the maximum value of the supersaturation turbulent flux occurs. This clustering of values is similar for the polydisperse population but also includes the condensation time. The mismatch between the time derivative of the supersaturation and the condensation term in the interfacial mixing layer is correlated with the planar covariance of the horizontal longitudinal velocity derivatives of the carrier air flow and the supersaturation field, thus suggesting that a quasi-linear relationship may exist between these quantities

Intermittency acceleration of water droplet population dynamics inside the interfacial layer between cloudy and clear air environments

We use direct numerical simulation to study the temporal evolution of a perturbation localized on the turbulent layer that typically separates a cloud from the surrounding clear air. Across this shearless layer, a turbulent kinetic energy gradient naturally forms. Here, a finite perturbation in the form of a local initial temperature fluctuation is applied to simulate a hydrodynamic instability inside the background turbulent air flow. A numerical initial value problem for two diametrically opposite types of drop population distributions is then solved. Specifically, we consider a mono-disperse population of droplets of 15 $\mu$m of radius and a poly-disperse distribution with radii in the range 0.6 - 30 $\mu$m. For both distributions, it is observed that the evaporation and condensation have a dramatically different weight inside the homogeneous cloudy region and the interfacial anisotropic mixing region. It is observed that the dynamics of drop collisions is highly effected by the turbulence structure of the host region. The two populations show a common aspect during their energy decay transient. That is the increased probability of collisions in the interfacial layer hat houses intense anisotropic velocity fluctuations. This layer, in fact, induces an enhanced differentiation on droplets kinetic energy and sizes. Both polydisperse and monodisperse initial particle distributions contain $10^7$ droplets, matching an initial liquid water content of $0.8 g/m^3$. An estimate of the turbulent collision kernel for geometric collisions used in the population balance equations is given. A preliminary discussion is presented on the structure of the two unsteady non ergodic collision kernels obtained inside the cloud interface region.Comment: Turbulent shearless layer, Cloud-clear air interaction, Inertial particles, Water droplets, DNS, Gravity effects, Collision kerne

Free flying cluster of miniaturized radiosondes for multi-parameter atmospheric fluctuation observations

We present a newly developed methodology to track Lagrangian fluctuations of physical and chemical quantities in the atmosphere. The measurements are carried out by using a freely floating cluster of mini, innovative radiosondes. The radiosonde are light (∼20 gr) and are carried out by biodegradable small balloons. The primary aim of this method is to obtain Lagrangian statistics of the turbulence fluctuations inside warm clouds, their boundaries and the surrounding sub-saturated environmental air. This is important information, difficult to find at the state of the art and very useful for modeling cloud formations which are still a primary source of uncertainty in the numerical simulation of climatic and meteorological information

Small-Scale air turbulence structure, microphysical time scales and local supersaturation balance at a warm Cloud Top Boundary

Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient. We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud-clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodisperse and polydisperse droplets. For the monodisperse population, a clustering of the values of the reaction, phase and evaporation times, that is around 20-30 seconds, is observed in the central area of the mixing layer, just before the location where the maximum value of the supersaturation turbulent flux occurs. This clustering of values is similar for the polydisperse population but also includes the condensation time. The mismatch between the time derivative of the supersaturation and the condensation term in the interfacial mixing layer is correlated with the planar covariance of the horizontal longitudinal velocity derivatives of the carrier air flow and the supersaturation field, thus suggesting that a quasi-linear relationship may exist between these quantities

Microphysical time scales, supersaturation fluctuations and at a warm Cloud Top Boundary in temporal decay

Recent results have shown that there is an acceleration in the spread of the size distribution of droplet populations in the region bordering the cloud and undersaturated ambient1 We have analyzed the supersaturation balance in this region, which is typically a highly intermittent shearless turbulent mixing layer, under a condition where there is no mean updraft. We have investigated the evolution of the cloud - clear air interface and of the droplets therein via direct numerical simulations. We have compared horizontal averages of the phase relaxation, evaporation, reaction and condensation times within the cloud-clear air interface for the size distributions of the initial monodisperse and polydisperse droplet populations

Diffusion of turbulence following both stable and unstable step stratification perturbations

The evolution of a two-phase, air and unsaturated water vapor, time decaying, shearless, turbulent layer has been studied in the presence of both stable and unstable perturbations of the normal temperature lapse rate. The top interface between a warm vapor cloud and clear air in the absence of water droplets was considered as the reference dynamics. Direct, 3D numerical simulations were performed within a 6m x 6m wide and 12m high cloud portion, which was hypothesized to be located close to an interface between the warm cloud and clear air. The Taylor micro-scale Reynolds' number was 250 inside the cloud portion. The squared Froude's number varied over intervals of [0.4; 1038.5] and [-4.2; -20.8]. A sufficiently intense stratification was observed to change the mixing dynamics. The formation of a sub-layer inside the shearless layer was observed. The sub-layer, under a stable thermal stratification condition, behaved like a pit of kinetic energy. On the other hand, it was observed that kinetic energy transient growth took place under unstable conditions, which led to the formation of an energy peak just below the center of the shearless layer. The scaling law of the energy time variation inside the interface region was quantified: this is an algebraic law with an exponent that depends on the perturbation stratification intensity. The presence of an unstable stratification increased the differences in statistical behavior among the longitudinal velocity derivatives, compared with the unstratified case. Since the mixing process is suppressed in stable cases, small-scale anisotropy is also supressed.Comment: Turbulent transport, thermal stratification, stability, initial value problem, passive scala