Modelling plant transpiration and leaf climate using CFD

Research into vertical farms or plant factories is steadily increasing over the years, as the demand for sustainable food production and a shift to more environmental friendly food production is occurring. Modelling plant climate in these confined spaces is therefore essential to guarantee optimal growing conditions. Modelling of plant climate has already been done in greenhouses, but at length scales much bigger than individual leaves. In this study, one single plant will be modelled, using computational fluid dynamics and by incorporating additional source terms in the relevant transport equations. Plants are modelled using the big leaf approach, where a plant is modelled as one artificial leaf. Water vapour flux in plants is controlled by two resistances in series, the aerodynamic resistance, which is a function of the boundary layer around the leaves and the stomatal resistance, which is the resistance against water vapour transport in leaves. Two different plants are studied, impatiens pot plant and basil plants. Values of stomatal resistance for these crops are obtained from literature or were measured. Evapotranspiration was compared with the Penman-Monteith equation.

Atmospheric Rivers: An overlooked threat to the marginal snowpack of the Australian Alps

Atmospheric Rivers (ARs) are tropospheric corridors that provide ~90% of poleward water vapour transport. They are predicted to increase in frequency and intensity if global warming continues unabated. Here we present a case study of the first direct observations of the impact of AR rain-on-snow (RoS) events on the marginal snowpack of the Australian Alps. Reanalysis data show ARs embedded within strong northwesterly airflow extended over 4000 km from the eastern Indian Ocean to southeast Australia, where orographic processes enhanced RoS. We quantify for the first-time radiation and turbulent energy flux exchanges using eddy covariance and, the contribution of rain heat flux to the snowpack during the AR RoS events. The hydrological response of an above snowline catchment that includes Australia’s highest peak during the events was rapid, with discharge increasing by nearly two orders of magnitude above historical mean winter discharge. This reflects the isothermal properties of the marginal Australian snowpack, where small increases in energy from RoS can trigger rapid snowmelt leading to flash flooding. Discharge decreased quickly following the passage of the ARs and onset of cold air advection. Based on climate projections of ≈ +2.5 °C warming in the Australian Alps by mid-century combined with an already historically, close-to-ripe snowpack, we postulate that AR induced RoS events will accelerate the loss of snow cover.

Upstream of hydroclimate extremes : maxima of moisture transport

<p>The prevailing westerly winds provide Europe with an average flow of moisture from the North Atlantic. We document the climatological transport of water vapour across Europe's western border, from the south of the Iberic Peninsula to Northern Scandinavia. Four state-of-the-art reanalyses (NCEP CFSR, JRA 55, MERRA 2 and ERA 5) are confronted to satellite observations (QUIKSCAT and ASCAT) and to radiosoundings (IGRA) from six coastal sites.  Over the datasets' common time range (2000-2011), the agreement is generally good in terms of yearly and monthly fluxes. The satellite products have generally lower values than the rest of the ensemble. Some disparities appear on the vertical. A longer time range (1980-2020) excludes satellite data but allows to detect local increases in moisture transport in the later years.</p><p>Beyond the climatological picture, day to day moisture fluxes present significant fluctuations, both in the dry and wet directions. The variability is consistent between reanalyses and radiosondes but slightly weaker in the satellite data. The fluxes on pressure levels are strongly correlated to their vertically integrated counterpart. We take advantage of the vertical coherence to stratify humidity and wind profiles according to quantiles of integrated moisture transport. The respective role of humidity and wind changes becomes apparent. Wind speed and direction determines the moisture transport more than the humidity field on a short term basis. On the scale of decades, there was no discernable change of circulation. It was moistening that drove the increase in water vapour transport. The effect was disproportionate for higher quantiles as a consequence of the non-linear Clausius-Clapeyron equation.</p>

A study on comfort properties of oak Tasar silk waste and acrylic blended fabrics

Oak Tasar is wild silk with natural golden brown colour and unique texture available in Himalayan region of India. A lot of fibre waste is generated during hand spinning of oak Tasar silk yarn which can be utilized by blending it with compatible fibre to incorporate the properties of both fibres in the yarn. The present study aimed to develop Oak Tasar silk waste and acrylic blended fabrics and study their comfort properties. The oak Tasar silk and acrylic blended plain weave and twill weave fabrics were prepared with five different blend ratios viz. 100:0, 60:40, 50:50, 40:60 and 0:100. The prepared fabrics were studied for comfort properties like thermal insulation (clo, TIV %), Q-max (warm/cool feeling), air permeability, water vapour transport rate and were statistically analysed. Results revealed that thermal insulation and clo value were found to be increased with increasing acrylic content in the fabric whereas Q- max, air permeability, water vapour permeability values were reduced with the addition of oak Tasar silk fiber in the blend. The 50:50 blended plain weave fabric among the blended fabrics had the highest clo value, i.e. 0.52 and 50:50 blended twill weave fabric had highest Q max value i.e. 0.109W/cm2. It was found from the study that the developed fabrics are comfortable and can be used for light winters.

On the performance of the snow model Crocus driven by in situ and reanalysis data at Villum Research Station in northeast Greenland

Reliable and detailed snow data are limited in the Arctic. We aim at overcoming this issue by addressing two questions: (1) Can the reanalysis ERA5 replace limited in situ measurements in high latitudes to drive snow models? (2) Can the Alpine model Crocus simulate reliably Arctic snow depth and stratigraphy? We compare atmospheric in situ measurements and ERA5 reanalysis and evaluate simulated and measured snow depth, density and specific surface area (SSA) in northeast Greenland (October 2014–October 2018). To account for differences between Alpine and Arctic region, we introduce a new parametrisation for the density of new snow.Our results show a good agreement between in situ and ERA5 atmospheric variables except for precipitation, wind speed and direction. ERA5’s resolution is too coarse to resolve the topography in the study area adequately, leading presumably to the detected biases. Nevertheless, measured snow depth agrees better with ERA5 forced simulations than forced with in situ measurements.Crocus can simulate satisfactory the evolution of snow depth, but simulations of SSA and density profiles for both forcings are biased compared to field measurements. Adjusting the new snow density parametrisation leads to improvements in the simulated snow stratigraphy. In conclusion, ERA5 can be used instead of in situ measurements to force snow models but the use of Crocus in the Arctic is affected by limitations likely due to the missing vertical water vapour transport and snow redistribution during strong winds. These limitations strongly affect the accuracy of the vertical profiles of physical snow properties.

High-Latitude Atmospheric River Cross-Sections over the North Atlantic: Assessing Optimized Airborne Sounding Strategies

<p>Regarding arctic amplification, meridional transports of moisture and heat from subpolar regions represent a crucial phenomenon. Among such intrusions, Atmospheric Rivers (ARs) are characterized by narrow and transient moisture flows, which are responsible for up to 90% of vertical integrated water vapour transport (IVT) into the Arctic. Moreover, they are relevant for meridional air mass transformations and precipitation events. To identify local sources and sinks of moisture associated with such AR pathways, the accurate determination of total IVT along the AR cross-sections is indispensable. However, since ARs primarily occur over ocean basins, e.g. the North Atlantic, there is a lack of measurements inside ARs. Spaceborne sensors struggle to profile the interior of AR cores, leading to a blind zone where the majority of water vapour is located.</p><p>Conversely, airborne released dropsondes currently provide the most detailed insights on ARs. The frequency of dropsonde releases is, however, technically limited, so that uncertainties in the calculated total IVT of the AR transect may be significant. In particular, when the IVT within the AR core has high lateral variability, unresolved AR-IVT characteristics can constrain the moisture budget analysis. During the North Atlantic Waveguide and Downstream Impact Experiment (NAWDEX), conducted in autumn 2016, the High Altitude and LOng- Range research aircraft (HALO) performed several flight segments along high-latitude AR cross-sections. From these North Atlantic ARs associated with strong meridional water vapour transport, we exemplarily present high-resolution measurements and sounding profiles in the interior of AR cross-sections. We focus on a polar case (research flight RF10, 13<sup>th</sup> October 2016) and include simulations from the cloud-resolving model ICON-2km, to investigate the lateral AR-IVT variability.  </p><p>Comparing dropsonde IVT values with the simulations from ICON-2km, the model shows a valid representation of the AR. Therefore, we use the high-resolution simulations to generate additional synthetic observations. They allow us to identify major sources of error for observational representation of IVT variability in AR cross-sections. Analysing the vertical profile of water vapour transport, we find that specific humidity and wind speed contribute to lateral IVT variability at different heights. With regard to the total cross-section IVT, we derive across-track sounding resolutions required for typical arctic AR-IVT characteristics. The considered AR shows the presence of a low-level jet, a pre-cold-frontal strong wind corridor below 1000 m, resulting from the temperature gradient across the cold front. Since maximum values and increasing lateral variability of IVT appear close to this low-level jet, our results emphasize the need of high-resolution, i.e frequent sonde releases, around the low-level jet to calculate the cross-section total IVT. Our findings aim at optimizing observational airborne strategies for future campaigns, e.g. HALO-AC³ in 2022, in order to lower the uncertainties of IVT in high-latitude and arctic ARs.</p>

Barrier Properties of Footwear Packages against Water Vapour Transport and Thermal Resistance

In this paper the authors focused on the analysis of relations between the material (such as knitted fabrics with a two and three dimensional structure) configurations and hygienic parameters of packages. In order to measure hygienic properties, the water vapour permeability and absorption were both used with the thermal resistance capacity. The connector role in the packages measured was played by air (in the case of two – layered package), polyurethane foam and three – dimensional knitted fabric with similar characteristics to polyurethane foam in respect of the mass per square metre and thickness. On the basis of the results obtained, a statistical model of the barrier was created and the changes in water vapour transport process described.

A critique on ‘A Boltzmann transformation method for investigation of water vapour transport in building materials’

In 2011, this journal published the paper ‘A Boltzmann transformation method for investigation of water vapour transport in building materials’, proposing a dynamic measurement of building materials’ vapour permeability via the Boltzmann-Matano method. This critique points out that this publication is flawed, since it proposes an invalid approach and presents erroneous results. The analysis first shows that the presented vapour permeability values cannot be reproduced and instead far lower vapour transport properties are obtained. These corrected outcomes are however also much below the dry-cup reference values, and it is established that these deviations stem from the invalidity of the proposed approach, due to disregarding the material’s hygroscopicity. Given its erroneous results and invalid approach, it is finally recommended to have the paper officially retracted by the journal.