scholarly journals Linking rain into ice microphysics across the melting layer in stratiform rain: a closure study

2020 ◽  
Author(s):  
Kamil Mróz ◽  
Alessandro Battaglia ◽  
Stefan Kneifel ◽  
Leonie von Terzi ◽  
Markus Karrer ◽  
...  
Keyword(s):  
Particle Growth ◽  
Melting Zone ◽  
Characteristic Size ◽  
Electromagnetic Properties ◽  
Size Distributions ◽  
Melting Layer ◽  
Stratiform Rain ◽  
Melting Region ◽  
Ice Microphysics

Abstract. This study investigates the link between rain and ice microphysics across the melting layer in stratiform rain systems using measurements from vertically pointing multi-frequency Doppler radars. A novel methodology to examine the variability of the precipitation rate and the mass-weighted melted diameter (Dm)across the melting region is proposed and applied to a 6 h-long case study, observed during the TRIPEx-pol field campaign at the Julich Observatory for Cloud Evolution Core Facility and covering a gamut of ice microphysical processes. The methodology is based on an optimal estimation (OE) retrieval of particle size distributions (PSD) and dynamics (turbulence and vertical motions) from observed multi-frequency radar Doppler spectra applied both above and below the melting layer. The retrieval is first applied in the rain region; based on a one-to-one conversion of raindrops into snowflakes, the retrieved Drop Size Distributions (DSD) are propagated upward to provide a first guess for the snow PSDs. These ice PSDs are then used to constrain the OE snow retrieval where Doppler spectra are simulated based on different snow models, which consistently compute fall-speeds and electromagnetic properties. The results corresponding to the best matching models are then used to compute snow fluxes and Dm, which can be directly compared to the corresponding rain quantities. For the case study, the total accumulation of rain (2.65 mm) and the melted equivalent accumulation of snow (2.60 mm) show only a 2 % difference. The analysis suggests that the mass flux through the melting zone is well preserved except the periods of intense aggregation and intense riming where the precipitation rates were respectively larger and lower in ice than in the rain below. Moreover, it is shown that, the mean mass weighted diameter of ice is strongly related to the characteristic size of the underlying rain. With a simple scaling, Dmice = 1.21Dmrain, the characteristic size of snow can be predicted with a root-mean-square-error of 0.12 mm. This formula leads to slight underestimation of the ice size during aggregation, potentially due to the breakup of melting snowflakes, and to overestimation during riming where the additional particle growth within the melting layer cannot be unambiguously attributed to one process. The proposed methodology can be applied to long-term observations to advance our knowledge of the processes occurring across the melting region; this can then be used to improve assumptions underpinning space-borne radar precipitation retrievals.

scholarly journals Linking rain into ice microphysics across the melting layer in stratiform rain: a closure study

2021 ◽  
Vol 14 (1) ◽  
pp. 511-529
Author(s):  
Kamil Mróz ◽  
Alessandro Battaglia ◽  
Stefan Kneifel ◽  
Leonie von Terzi ◽  
Markus Karrer ◽  
...  
Keyword(s):  
Mass Flux ◽  
Optimal Estimation ◽  
Melting Zone ◽  
Electromagnetic Properties ◽  
Size Distributions ◽  
Melting Layer ◽  
Stratiform Rain ◽  
Melting Region ◽  
Ice Microphysics

Abstract. This study investigates the link between rain and ice microphysics across the melting layer in stratiform rain systems using measurements from vertically pointing multi-frequency Doppler radars. A novel methodology to examine the variability of the precipitation rate and the mass-weighted melted diameter (Dm) across the melting region is proposed and applied to a 6 h long case study, observed during the TRIPEx-pol field campaign at the Jülich Observatory for Cloud Evolution Core Facility and covering a gamut of ice microphysical processes. The methodology is based on an optimal estimation (OE) retrieval of particle size distributions (PSDs) and dynamics (turbulence and vertical motions) from observed multi-frequency radar Doppler spectra applied both above and below the melting layer. First, the retrieval is applied in the rain region; based on a one-to-one conversion of raindrops into snowflakes, the retrieved drop size distributions (DSDs) are propagated upward to provide the mass-flux-preserving PSDs of snow. These ice PSDs are used to simulate radar reflectivities above the melting layer for different snow models and they are evaluated for a consistency with the actual radar measurements. Second, the OE snow retrieval where Doppler spectra are simulated based on different snow models, which consistently compute fall speeds and electromagnetic properties, is performed. The results corresponding to the best-matching models are then used to estimate snow fluxes and Dm, which are directly compared to the corresponding rain quantities. For the case study, the total accumulation of rain (2.30 mm) and the melted equivalent accumulation of snow (1.93 mm) show a 19 % difference. The analysis suggests that the mass flux through the melting zone is well preserved except the periods of intense riming where the precipitation rates were higher in rain than in the ice above. This is potentially due to additional condensation within the melting zone in correspondence to high relative humidity and collision and coalescence with the cloud droplets whose occurrence is ubiquitous with riming. It is shown that the mean mass-weighted diameter of ice is strongly related to the characteristic size of the underlying rain except the period of extreme aggregation where breakup of melting snowflakes significantly reduces Dm. The proposed methodology can be applied to long-term observations to advance our knowledge of the processes occurring across the melting region; this can then be used to improve assumptions underpinning spaceborne radar precipitation retrievals.

scholarly journals A 3D study on the amplification of regional haze and particle growth by local emissions

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Wei Du ◽  
Lubna Dada ◽  
Jian Zhao ◽  
Xueshun Chen ◽  
Kaspar R. Daellenbach ◽  
...  
Keyword(s):  
Atmospheric Stability ◽  
Ground Level ◽  
Particle Growth ◽  
Chemical Compositions ◽  
Size Distributions ◽  
Aerosol Composition ◽  
Regional Haze ◽  
Haze Formation ◽  
Beijing China

AbstractThe role of new particle formation (NPF) events and their contribution to haze formation through subsequent growth in polluted megacities is still controversial. To improve the understanding of the sources, meteorological conditions, and chemistry behind air pollution, we performed simultaneous measurements of aerosol composition and particle number size distributions at ground level and at 260 m in central Beijing, China, during a total of 4 months in 2015–2017. Our measurements show a pronounced decoupling of gas-to-particle conversion between the two heights, leading to different haze processes in terms of particle size distributions and chemical compositions. The development of haze was initiated by the growth of freshly formed particles at both heights, whereas the more severe haze at ground level was connected directly to local primary particles and gaseous precursors leading to higher particle growth rates. The particle growth creates a feedback loop, in which a further development of haze increases the atmospheric stability, which in turn strengthens the persisting apparent decoupling between the two heights and increases the severity of haze at ground level. Moreover, we complemented our field observations with model analyses, which suggest that the growth of NPF-originated particles accounted up to ∼60% of the accumulation mode particles in the Beijing–Tianjin–Hebei area during haze conditions. The results suggest that a reduction in anthropogenic gaseous precursors, suppressing particle growth, is a critical step for alleviating haze although the number concentration of freshly formed particles (3–40 nm) via NPF does not reduce after emission controls.

scholarly journals Size distributions of elemental carbon in the atmosphere of a coastal urban area in South China: characteristics, evolution processes, and implications for the mixing state

2008 ◽  
Vol 8 (19) ◽  
pp. 5843-5853 ◽  
Author(s):  
X.-F. Huang ◽  
J. Z. Yu
Keyword(s):  
Urban Area ◽  
Elemental Carbon ◽  
Southern China ◽  
Global Climate ◽  
Particle Growth ◽  
Size Distributions ◽  
Hygroscopic Growth ◽  
Mixing State ◽  
Cloud Processing ◽  
Fine Mode

Abstract. Elemental carbon (EC), as one of the primary light-absorbing components in the atmosphere, has a significant impact on both regional and global climate. The environmental impacts of EC are strongly dependent on its particle size. Little is known about the size distribution characteristics of EC particles in China's ambient environments. We report size distributions of EC particles in the urban area of Shenzhen in Southern China. In our samples, EC was consistently found in two modes, a fine mode and a coarse mode. The majority of EC mass (~80%) in this coastal metropolitan city resided in particles smaller than 3.2 μm in diameter. The fine mode peaked at around either 0.42 μm or 0.75 μm. While the mode at 0.42 μm could be ascribed to fresh vehicular emissions in the region, the mode at 0.75 μm was likely a result of particle growth from smaller EC particles. We theoretically investigated the particle growth processes that caused the EC particles to grow from 0.42 μm to 0.75 µm in the atmosphere. Our calculations indicate that the EC peak at 0.75 μm was not produced through either coagulation or H2SO4 condensation; both processes are too slow to lead to significant EC growth. Hygroscopic growth was also determined to be insignificant. Instead, addition of sulfate through in-cloud processing was found to cause significant growth of the EC particles and to explain the EC peak at 0.75 μm. We also estimated the mixing state of EC from the EC size distributions. In the droplet size, at least 45–60% of the EC mass in the summer samples and 68% of the EC mass in the winter samples was internally mixed with sulfate as a result of in-cloud processing. This information on EC should be considered in models of the optical properties of aerosols in this region. Our results also suggest that the in-cloud processing of primary EC particles could increase the light absorbing capacities through mixing EC with sulfate.

scholarly journals Aged boreal biomass burning aerosol size distributions from BORTAS 2011

2014 ◽  
Vol 14 (17) ◽  
pp. 24349-24385 ◽  
Author(s):  
K. M. Sakamoto ◽  
J. D. Allan ◽  
H. Coe ◽  
J. W. Taylor ◽  
T. J. Duck ◽  
...  
Keyword(s):  
Size Distribution ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Climate Model ◽  
Sampling Period ◽  
Characteristic Size ◽  
Entrainment Rate ◽  
Size Distributions ◽  
Eastern Canada ◽  
Median Diameter

Abstract. Biomass-burning aerosols contribute to aerosol radiative forcing on the climate system. The magnitude of this effect is partially determined by aerosol size distributions, which are functions of source fire characteristics (e.g. fuel type, MCE) and in-plume microphysical processing. The uncertainties in biomass-burning emission number size-distributions in climate model inventories lead to uncertainties in the CCN concentrations and forcing estimates derived from these models. The BORTAS-B measurement campaign was designed to sample boreal biomass-burning outflow over Eastern Canada in the summer of 2011. Using these BORTAS-B data, we implement plume criteria to isolate the characteristic size-distribution of aged biomass-burning emissions (aged ∼1–2 days) from boreal wildfires in Northwestern Ontario. The composite median size-distribution yields a single dominant accumulation mode with Dpm = 230 nm (number-median diameter), σ = 1.7, which are comparable to literature values of other aged plumes of a similar type. The organic aerosol enhancement ratios (ΔOA / ΔCO) along the path of Flight b622 show values of 0.05–0.18 μg m−3 ppbv−1 with no significant trend with distance from the source. This lack of enhancement ratio increase/decrease with distance suggests no detectable net OA production/evaporation within the aged plume over the sampling period. A Lagrangian microphysical model was used to determine an estimate of the freshly emitted size distribution corresponding to the BORTAS-B aged size-distributions. The model was restricted to coagulation and dilution processes based on the insignificant net OA production/evaporation derived from the ΔOA / ΔCO enhancement ratios. We estimate that the fresh-plume median diameter was in the range of 59–94 nm with modal widths in the range of 1.7–2.8 (the ranges are due to uncertainty in the entrainment rate). Thus, the size of the freshly emitted particles is relatively unconstrained due to the uncertainties in the plume dilution rates.

scholarly journals Arctic marine secondary organic aerosol contributes significantly to summertime particle size distributions in the Canadian Arctic Archipelago

2019 ◽  
Vol 19 (5) ◽  
pp. 2787-2812 ◽  
Author(s):  
Betty Croft ◽  
Randall V. Martin ◽  
W. Richard Leaitch ◽  
Julia Burkart ◽  
Rachel Y.-W. Chang ◽  
...  
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Secondary Organic Aerosol ◽  
Canadian Arctic ◽  
Particle Growth ◽  
Organic Aerosol ◽  
The Arctic ◽  
Canadian Arctic Archipelago ◽  
Size Distributions ◽  
Fractional Error

Abstract. Summertime Arctic aerosol size distributions are strongly controlled by natural regional emissions. Within this context, we use a chemical transport model with size-resolved aerosol microphysics (GEOS-Chem-TOMAS) to interpret measurements of aerosol size distributions from the Canadian Arctic Archipelago during the summer of 2016, as part of the “NETwork on Climate and Aerosols: Addressing key uncertainties in Remote Canadian Environments” (NETCARE) project. Our simulations suggest that condensation of secondary organic aerosol (SOA) from precursor vapors emitted in the Arctic and near Arctic marine (ice-free seawater) regions plays a key role in particle growth events that shape the aerosol size distributions observed at Alert (82.5∘ N, 62.3∘ W), Eureka (80.1∘ N, 86.4∘ W), and along a NETCARE ship track within the Archipelago. We refer to this SOA as Arctic marine SOA (AMSOA) to reflect the Arctic marine-based and likely biogenic sources for the precursors of the condensing organic vapors. AMSOA from a simulated flux (500 µgm-2day-1, north of 50∘ N) of precursor vapors (with an assumed yield of unity) reduces the summertime particle size distribution model–observation mean fractional error 2- to 4-fold, relative to a simulation without this AMSOA. Particle growth due to the condensable organic vapor flux contributes strongly (30 %–50 %) to the simulated summertime-mean number of particles with diameters larger than 20 nm in the study region. This growth couples with ternary particle nucleation (sulfuric acid, ammonia, and water vapor) and biogenic sulfate condensation to account for more than 90 % of this simulated particle number, which represents a strong biogenic influence. The simulated fit to summertime size-distribution observations is further improved at Eureka and for the ship track by scaling up the nucleation rate by a factor of 100 to account for other particle precursors such as gas-phase iodine and/or amines and/or fragmenting primary particles that could be missing from our simulations. Additionally, the fits to the observed size distributions and total aerosol number concentrations for particles larger than 4 nm improve with the assumption that the AMSOA contains semi-volatile species: the model–observation mean fractional error is reduced 2- to 3-fold for the Alert and ship track size distributions. AMSOA accounts for about half of the simulated particle surface area and volume distributions in the summertime Canadian Arctic Archipelago, with climate-relevant simulated summertime pan-Arctic-mean top-of-the-atmosphere aerosol direct (−0.04 W m−2) and cloud-albedo indirect (−0.4 W m−2) radiative effects, which due to uncertainties are viewed as an order of magnitude estimate. Future work should focus on further understanding summertime Arctic sources of AMSOA.

scholarly journals Quantifying multiple electromagnetic properties in EMI surveys: A case study of hydromorphic soils in a volcanic context – The Lac du Puy (France)

Geoderma ◽  
2020 ◽  
Vol 361 ◽  
pp. 114084 ◽  
Author(s):  
François-Xavier Simon ◽  
Mathias Pareilh-Peyrou ◽  
Solène Buvat ◽  
Alfredo Mayoral ◽  
Philippe Labazuy ◽  
...  
Keyword(s):  
Electromagnetic Properties ◽  
Hydromorphic Soils

Activity size distributions of radioactive airborne particles in an arid environment: a case study of Kuwait

2020 ◽  
Vol 27 (26) ◽  
pp. 33032-33041
Author(s):  
Anfal Ismaeel ◽  
Abdulaziz Aba ◽  
Hanadi Al-Shammari ◽  
Aishah Al-Boloushi ◽  
Omar Al-Boloushi ◽  
...  
Keyword(s):  
Arid Environment ◽  
Airborne Particles ◽  
Size Distributions

scholarly journals Characteristic scales of earthquake rupture from numerical models

2003 ◽  
Vol 10 (6) ◽  
pp. 573-584 ◽  
Author(s):  
M. H. Heimpel
Keyword(s):  
Numerical Models ◽  
Three Dimensional ◽  
Characteristic Size ◽  
Strength Distribution ◽  
Earthquake Rupture ◽  
Size Distributions ◽  
Seismogenic Fault ◽  
Smooth Model ◽  
Heterogeneous Models ◽  
Asperity Model

Abstract. Numerical models of earthquake rupture are used to investigate characteristic length scales and size distributions of repeated earthquakes on vertical, planar fault segments. The models are based on exact solutions of static three-dimensional (3-D) elasticity. Dynamical rupture is approximated by allowing the static stress field to expand from slip motions at a single velocity. To show how the vertical fault width affects earthquake size distributions for a broad range of fault behaviors, two different fault strength models are used; a smooth model and a heterogeneous asperity model. The smooth model is a simplified version of the Dieterich-Ruina rate and state dependent friction law. The heterogeneous asperity model uses a slip-dependent random powerlaw strength distribution. It is shown that the characteristic scale of fault segmentation is proportional to the vertical width of a seismogenic fault. This conclusion holds for both the smooth and the heterogeneous models. For the smooth models characteristic quake distributions result, with populations of large events that are obviously distinct from smaller events. The distributions of large events have well-defined mean lengths and moments. The heterogeneous models result in Gutenberg-Richter (GR) powerlaw distributions of event sizes up to a characteristic quake size. Quakes larger than the characteristic size fall off the GR distribution such that the powerlaw would greatly overestimate the probability of occurrence of the larger events.

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