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Two Types of Ice Clouds (TICs) have been characterized in the Arctic during the polar night and early spring. TIC-1 are composed by non-precipitating small ice crystals of less than 30 µm in diameter. The second type, TIC-2, are characterized by a low concentration of large precipitating ice crystals (>30 µm). Here, we evaluate the Weather Research and Forecasting (WRF) model performance both in space and time after implementing a parameterization based on a stochastic approach dedicated to the simulation of ice clouds in the Arctic. Well documented reference cases provided us in situ data from the spring of 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) campaign over Alaska. Simulations of the microphysical properties of the TIC-2 clouds on 15 and 25 April 2008 (polluted or acidic cases) and TIC-1 clouds on non-polluted cases are compared to DARDAR (raDAR/liDAR) satellite products. Our results show that the stochastic approach based on the classical nucleation theory, with the appropriate contact angle, is better than the original scheme in WRF model to represent TIC-1 and TIC-2 properties (ice crystal concentration and size) in response to the IN acidification.

Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as they relate to climate forcing. The overall goal of NETCARE research has been to use an interdisciplinary approach encompassing extensive field observations and a range of chemical transport, earth system, and biogeochemical models. Several major findings and advances have emerged from NETCARE since its formation in 2013. (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were identified in ocean water (up to 75 nM) and the overlying atmosphere (up to 1 ppbv) in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds, which are widely prevalent, were identified as an important DMS source (with DMS concentrations of up to 6 nM and a potential contribution to atmospheric DMS of 20 % in the study area). (2) Evidence of widespread particle nucleation and growth in the marine boundary layer was found in the CAA in the summertime, with these events observed on 41 % of days in a 2016 cruise. As well, at Alert, Nunavut, particles that are newly formed and grown under conditions of minimal anthropogenic influence during the months of July and August are estimated to contribute 20 % to 80 % of the 30–50 nm particle number density. DMS-oxidation-driven nucleation is facilitated by the presence of atmospheric ammonia arising from seabird-colony emissions, and potentially also from coastal regions, tundra, and biomass burning. Via accumulation of secondary organic aerosol (SOA), a significant fraction of the new particles grow to sizes that are active in cloud droplet formation. Although the gaseous precursors to Arctic marine SOA remain poorly defined, the measured levels of common continental SOA precursors (isoprene

The first airborne measurements of the Far- InfraRed Radiometer (FIRR) were performed in April 2015 during the panarctic NETCARE campaign. Vertical profiles of spectral upwelling radiance in the range 8–50 μm were measured in clear and cloudy conditions from the surface up to 6 km. The clear sky profiles highlight the strong dependence of radiative fluxes to the temperature inversion typical of the Arctic. Measurements acquired for total column water vapour from 1.5 to 10.5mm also underline the sensitivity of the far-infrared greenhouse effect to specific humidity. The cloudy cases show that optically thin ice clouds increase the cooling rate of the atmosphere, making them important pieces of the Arctic energy balance. One such cloud exhibited a very complex spatial structure, characterized by large horizontal heterogeneities at the kilometre scale. This emphasizes the difficulty of obtaining representative cloud observations with airborne measurements but also points out how challenging it is to model polar clouds radiative effects. These radiance measurements were successfully compared to simulations, suggesting that state-of-the-art radiative transfer models are suited to study the cold and dry Arctic atmosphere. Although FIRR in situ performances compare well to its laboratory performances, complementary simulations show that upgrading the FIRR radiometric resolution would greatly increase its sensitivity to atmospheric and cloud properties. Improved instrument temperature stability in flight and expected technological progress should help meet this objective. The campaign overall highlights the potential for airborne far-infrared radiometry and constitutes a relevant reference for future similar studies dedicated to the Arctic and for the development of spaceborne instruments.

A far infrared radiometer (FIRR) dedicated to measuring radiation emitted by clear and cloudy atmospheres was developed in the framework of the Thin Ice Clouds in Far InfraRed Experiment (TICFIRE) technology demonstration satellite project. The FIRR detector is an array of 80 × 60 uncooled microbolometers coated with gold black to enhance the absorptivity and responsivity. A filter wheel is used to select atmospheric radiation in nine spectral bands ranging from 8 to 50 µm. Calibrated radiances are obtained using two well-calibrated blackbodies. Images are acquired at a frame rate of 120 Hz, and temporally averaged to reduce electronic noise. A complete measurement sequence takes about 120 s. With a field of view of 6°, the FIRR is not intended to be an imager. Hence spatial average is computed over 193 illuminated pixels to increase the signal-to-noise ratio and consequently the detector resolution. This results in an improvement by a factor of 5 compared to individual pixel measurements. Another threefold increase in resolution is obtained using 193 non-illuminated pixels to remove correlated electronic noise, leading an overall resolution of approximately 0.015 W m−2 sr−1. Laboratory measurements performed on well-known targets suggest an absolute accuracy close to 0.02 W m−2 sr−1, which ensures atmospheric radiance is retrieved with an accuracy better than 1 %. Preliminary in situ experiments performed from the ground in winter and in summer on clear and cloudy atmospheres are compared to radiative transfer simulations. They point out the FIRR ability to detect clouds and changes in relative humidity of a few percent in various atmospheric conditions, paving the way for the development of new algorithms dedicated to ice cloud characterization and water vapor retrieval.

To explore quantum and classical connection from a new perspective, a Quantum Population Dynamics (QPoD) model based on the logistic relation common to several sciences is investigated from a very broad perspective to explore the numerous links to current physics. From postulates of causality and finiteness a classical quantum entity, a quanta of spacetime, is defined with unitary extension and intensity. Applying the logistic equation to a quantum population of non-local two-state oscillators results in a quantum-classical equation linking wave and particle dynamics with an explicit account of decoherence. Varying over 124 orders of magnitude, the coupling constant acts like a delta Dirac function between regimes. The quantum regime is conform to Schrödinger and Dirac equations according to respective Hamiltonian while the classical mode suppresses the quantum wave function and follows the Hamilton-Jacobi equation. Besides the quantum wave solutions, in the classical range, the general equation admits Fermi-Dirac and Bose-Einstein solutions, relating to thermodynamics. Inertial mass is found in terms of the quantum entropy gradient. The most compact quantum cluster forming a crystal produces a unique flat space filling lattice cells of one simple tetrahedron and one composite truncated tetrahedron corresponding respectively to a fermionic cell and a bosonic cell. From this lattice geometry alone, the mass ratios of all fermions are expressed uniquely in terms of vertices and faces, matching charges properties of three generations and three families. Except for a minor degeneracy correction, the solution is shown to follow the logistic dynamics. The resulting mass equation is a function of dimensionless natural numbers. Many properties of the Standard Model are recovered from geometry at the Planck scale, respecting naturalness, uniqueness and minimality. QPoD may help addressing questions about the nature of spacetime and the physical microstructure of particles. T

The hypothesis according to which higher sulphate concentrations favor ice clouds made of larger ice crystals is tested using data sets from the CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellites. This is a potential consequence of the sulphate-induced freezing inhibition (SIFI) effect, namely, the hypothesis that sulphates contribute to inhibit the onset of ice crystal formation by deactivating ice-forming nuclei during Arctic winter. A simple index based on the backscattering at 532 nm and the color ratio from the CALIPSO lidar measurements is compared against in situ sulphate concentration time series and used as a proxy for this variable. An algorithm using the lidar data and the CloudSat radar microphysical retrievals is also developed for identifying cloud types, focusing on those supposedly favored by the SIFI effect. The analysis includes the effect of the lidar off-nadir angle on the sulphate index and the cloud classification, the validation of the index, as well as the production of circum-Arctic maps of the sulphate index and of the SIFI-favored clouds fraction. The increase of the lidar off-nadir angle is shown to cause an increase in the measured depolarization ratio and hence in the ability to detect ice crystals. The index correlates positively with both sulphates and sea salt concentrations, with a Pearson correlation coefficient (equation image) varying from 0.10 to 0.42 for the different comparisons performed. Ultimate findings are the results of two correlation tests of the SIFI effect, which allow for a new outlook on its possible role in the Arctic troposphere during winter.

Data sets from CloudSat radar reflectivity and CALIPSO lidar backscattering measurements provide a new regard on Arctic and Antarctic winter cloud systems, as well as on the way aerosols determine their formation and evolution. Especially, links between the cloud ice crystal size and the surrounding aerosol field may be further investigated. In this study, the satellite observations are used to heuristically separate polar thin ice clouds into two crystal size categories, and an aerosol index based on the attenuated backscattering and color ratio of the sampled volumes is used for identifying haze in cloud-free regions. Statistics from 386 Arctic satellite overpasses during January 2007 and from 379 overpasses over Antarctica during July 2007 reveal that sectors with the highest proportion of thin ice clouds having large ice crystals at their top are those for which the aerosol index is highest. Moreover, a weak but significant correlation between the cloud top ice effective radius and the above-cloud aerosol index suggests that more polluted clouds tend to have higher ice effective radius, in 10 of the 11 sectors investigated. These results are interpreted in terms of a sulphate-induced freezing inhibition effect.

The Northern Aerosol Regional Climate Model (NARCM) was used to construct a 44-yr climatology of spring Asian dust aerosol emission, column loading, deposition, trans-Pacific transport routes, and budgets during 1960–2003. Comparisons with available ground dust observations and Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) measurements verified that NARCM captured most of the climatological characteristics of the spatial and temporal distributions, as well as the interannual and daily variations of Asian dust aerosol during those 44 yr. Results demonstrated again that the deserts in Mongolia and in western and northern China (mainly the Taklimakan and Badain Juran, respectively) were the major sources of Asian dust aerosol in East Asia. The dust storms in spring occurred most frequently from early April to early May with a daily averaged dust emission (diameter d < 41 μm) of 1.58 Mt in April and 1.36 Mt in May. Asian dust aerosol contributed most of the dust aerosol loading in the troposphere over the midlatitude regions from East Asia to western North America during springtime. Climatologically, dry deposition was a dominant dust removal process near the source areas, while the removal of dust particles by precipitation was the major process over the trans-Pacific transport pathway (where wet deposition exceeded dry deposition up to a factor of 20). The regional transport of Asian dust aerosol over the Asian subcontinent was entrained to an elevation of <3 km. The frontal cyclone in Mongolia and northern China uplifted dust aerosol in the free troposphere for trans-Pacific transport. Trans-Pacific dust transport peaked between 3 and 10 km in the troposphere along a zonal transport axis around 40°N. Based on the 44-yr-averaged dust budgets for the modeling domain from East Asia to western North America, it was estimated that of the average spring dust aerosol (diameter d < 41 μm) emission of ∼120 Mt from Asian source regions, about 51% was redeposited o

From the observations of recent years, there is still not enough evidence to verify the Arctic warming as most global circulation models (GCMs) suggested. This study is dedicated to quantifying the aerosol effect on the Arctic climate change by Northern Aerosol Regional Climate Model (NARCM). The direct and indirect radiative and climate effects of aerosols such as Arctic haze sulfate, black carbon, sea salt, organics, and dust have been evaluated from our NARCM simulations. Within the Arctic Regional Climate Model Intercomparison Project (ARCMIP) our model simulations have been directly compared with the enhanced observation data sets such as the Surface Heat Budget of the Arctic Ocean (SHEBA) and the Atmospheric Radiation Measurement (ARM) in the time period from October 1997 to September 1998. Results show that the climate effects of aerosols strongly depend on the aerosol composition. The surface radiative forcing of pure sulfate aerosols which includes the direct and indirect components reaches up to −7.2 W/m2 in annual mean. The climate responses to radiative forcing of pure sulfate and five kinds of aerosols together are amazingly different. The impacts of aerosols present strong seasonal cycle. In comparison with observations we find the simulation with five kinds of aerosols can better represent the surface temperature from observation. The aerosol radiative and microphysical effects must be taken into account in order to better simulate and predict the change of energy and water cycle occurring in polar climate system.

The Northern Aerosol Regional Climate Model (NARCM) is used to study the visibility and three-dimensional (3-D) evolution of aerosol distributions within the Mexico City basin. NARCM simulates transport, diffusion, deposition, and size distributions of sulphur aerosol particles in the region. The model assumes only simple sulphur oxidation, not taking explicitly into account the urban air chemistry. Rather, it focuses on detailed aerosol microphysics and 3-D optical properties. The simulation performance is compared with upper air and ground-based observations for the following specific days of intensive measurement: 2, 4, and 14 March 1997. Time series at Mexico City airport shows lower values of visibility in the morning due to a shallow mixed layer and higher values in the afternoon following the evolution of the mixed layer depth. Modeled visibility shows large dependence on cardinal direction and size distribution of particles. It is found that better resolution of particle size leads to better representation of coagulation processes and to realistic size distributions which show a characteristic accumulation mode around 0.3 μm. As a result, visibility simulations are closer to those observed at the airport location. Comparing visibility is a stringent test for the model because it requires an accurate representation of 3-D meteorological fields together with a realistic aerosol simulation.