Vertical Temperature Profiles Research Articles

Meteorological data recommendations for input to dispersion models applied to Jack Rabbit II trials

Abstract The Jack Rabbit II (JR II) chlorine field experiment observations are being used in a multi-dispersion model comparison exercise. So that all models are using consistent meteorological inputs, we analyzed the many early-morning meteorological observations that were taken at Dugway Proving Ground (DPG), Utah, during the nine chlorine release trials during JR II to produce recommendations for surface and vertical profile meteorological variables. The JR II field experiment included a mesonetwork of about 35 surface wind sites, a surface energy balance site, three 32 m towers located 1 km apart, and several vertical sounding instruments. The challenge is to determine a single set of meteorological inputs for the dispersion models. It is assumed that the recommended meteorological conditions represent the flat desert about 100 m upwind of the chlorine release location. Recommendations of surface winds, and momentum and sensible heat fluxes for each early-morning field trial are based on averages of sonic anemometer observations at 2 m on the upwind 32 m tower and at 2.5 m on a nearby “Energy Balance” station, for the half hour period during which the chlorine release took place. These observations were also used to estimate the surface roughness length, zo = 0.5 mm, for the flat desert. Single vertical profiles of wind speed, wind direction, and temperature are specified for each trial for a time close to the chlorine release time, based on medians of observations at five levels on the three 32 m towers, a radiosonde, a minisodar, and two wind profilers (449 MHz and 921 MHz). During the early morning releases, as the sun rose and heated the surface, the boundary layer was transient. The surface boundary layer was stable for releases from about 7:30 to about 8:30 (local time) and was marked by a shallow mixed layer (about 8–16 m) for releases during the next hour. Above the 32 m tower tops, the atmosphere was stable during all release trials up to elevations of a few hundred meters. Large wind direction shears were usually found in this layer, since the near-surface flow was a drainage (katabatic) down-valley flow (from about 165°), while the synoptic flow above 100 m was from the west.

Evaluation of a method to retrieve temperature and wind velocity profiles of the Venusian nightside mesosphere from mid-infrared CO2 absorption line observed by heterodyne spectroscopy

We evaluated a method for retrieving vertical temperature and Doppler wind velocity profiles of the Venusian nightside mesosphere from the CO2 absorption line resolved by mid-infrared heterodyne spectroscopy. The achievable sensitive altitude and retrieval accuracy were derived with multiple model spectra generated from various temperature and wind velocity profiles with several noise levels. The temperature profiles were retrieved at altitudes of 70–100 km with a vertical resolution of 5 km and a retrieval accuracy of ± 15 K. The wind velocity was also retrieved at an altitude of approximately 85 km with a vertical resolution of 10 km and a retrieval accuracy of ± 25–50 m/s. In addition, we studied an event and applied our method to spectra obtained by the HIPWAC instrument attached to the NASA/IRTF 3-m telescope on May 19–22, 2012. Retrieved wind velocities in a latitude of 33° S at 3:00 LT were interpreted as subsolar-to-antisolar (SS-AS) flows at altitudes of 84 ± 6 km and 94 ± 7 km, and they were stronger than expected. This result suggested that the transition between the retrograde superrotational zonal (RSZ) wind and SS-AS flow may occur at altitudes below 90 km which previously was predicted to be the transition region. This work provides a basis for our analysis of further observations obtained by a mid-infrared heterodyne spectrometer MILAHI attached to the Tohoku University 60-cm telescope at Haleakalā, Hawaii.

Electric heating and angular momentum transport in laminar models of protoplanetary discs

ABSTRACT The vertical temperature structure of a protoplanetary disc bears on several processes relevant to planet formation, such as gas and dust grain chemistry, ice lines, and convection. The temperature profile is controlled by irradiation from the central star and by any internal source of heat such as might arise from gas accretion. We investigate the heat and angular momentum transport generated by the resistive dissipation of magnetic fields in laminar discs. We use local 1D simulations to obtain vertical temperature profiles for typical conditions in the inner disc (0.5–4 au). Using simple assumptions for the gas ionization and opacity, the heating and cooling rates are computed self-consistently in the framework of radiative non-ideal magnetohydrodynamics. We characterize steady solutions that are symmetric about the mid-plane and which may be associated with saturated Hall-shear unstable modes. We also examine the dissipation of electric currents driven by global accretion-ejection structures. In both cases we obtain significant heating for a sufficiently high opacity. Strong magnetic fields can induce an order-unity temperature increase in the disc mid-plane, a convectively unstable entropy profile, and a surface emissivity equivalent to a viscous heating of α ∼ 10−2. These results show how magnetic fields may drive efficient accretion and heating in weakly ionized discs where turbulence might be inefficient, at least for a range of radii and ages of the disc.

Environmental Lapse Rate for High‐Resolution Land Surface Downscaling: An Application to ERA5

AbstractIn this study we derive the environmental lapse rate (ELR) from vertical profiles of temperature in the lower troposphere, applying it to downscale air temperature of the new European Centre For Medium‐Range Weather Forecasts (ECMWF) reanalysis ERA5, which replaces ERA‐Interim (ERAI). We focus over the western U.S. region, a data‐rich area with observations of daily maximum and minimum temperature (Global Historical Climatology Network) and snow depth and soil temperature. Observations indicate an ELR of −4.5 K·km−1 in the region, lower than the commonly used −6.5 K·km−1. ERA5 ELR agrees with the observational estimates, with some overestimation in winter and limitations in the diurnal variability. The elevation correction of ERA5 temperature using different ELR showed the benefits of deriving ELR fields from ERA5 vertical profiles, when compared with a constant ELR. Simulations with the ECMWF land surface model, at 9‐km resolution, driven by ERA5 using different ELR corrections showed the added value of the methodology, but the impact of different ELR corrections is limited. However, the validity of the downscaling method in reducing temperature to station altitude suggests that there is sufficient generality for application at kilometer and subkilometer resolutions. By comparing the estimated representativity errors of observations with reanalysis, the improvements from ERAI to ERA5 are mainly visible in the random component of the error. Large systematic biases remain, which require further attention from the modeling and data assimilation, and limit the potential benefits of ELR corrections.

Meroplankton community structure across oceanographic fronts along the South Brazil Shelf

The influence of oceanographic fronts on the abundance and community composition of invertebrate larvae, mostly of benthic species, along nearly 2000 km of the southwestern Atlantic shelf (21–34°S) was investigated. Meroplankton was sampled through vertical hauls at 89 stations, distributed along 14 cross-shelf transects, during late spring 2010 and early summer 2011. Salinity and temperature were registered with a CTD/rosette system, which provided seawater for chlorophyll-a and nutrient concentrations estimations. Vertical profiles of temperature, salinity, chlorophyll-a and nutrients were used as proxies of the fronts. In addition, high-resolution thermosalinograph data were used to detect surface frontal features. Meroplankton abundance peaks were found at several fronts intersected by the ship, including upwelling zones, estuarine and plume fronts, a shelf-break front, and two cyclonic eddies. Furthermore, meroplankton abundance was also relatively higher at small-scale thermal and/or saline surface fronts observed along the shelf. Such increases in meroplankton abundance are likely to be ascribed to high nutrient input and primary production. Distinct taxa of invertebrate larvae occurred at different types of fronts, besides the coastal realm, which was virtually dominated by decapod, cirripede and bivalve larvae. Small-scale shelf fronts presented high abundances of decapod and gastropod larvae, for instance, while larvae of polychaetes were the most frequent in the estuarine front of Patos Lagoon section.

К ВОПРОСУ О ПРОБЛЕМАХ И ЗАДАЧАХ РАЗВИТИЯ ОТЕЧЕСТВЕННЫХ ГИДРОФИЗИЧЕСКИХ ИССЛЕДОВАНИЙ ПРИПОЛЯРНЫХ РЕГИОНОВ МИРОВОГО ОКЕАНА

One of the climatically significant, but the poor studied hydrophysical factor in the polar regions of the world ocean is the subsurface layer of relatively warm seawater of subtropical origin. In the Arctic Ocean, this layer is associated with the waters of the Gulfstream, the highlatitude continuation of which in the form of a spur of the North Atlantic current penetrates into the Arctic basin, where it sinks to the depth of its density and spreads throughout its vast space in the layer of 100–900 m. The existence of a subsurface layer with an anomalous inversion vertical profile of water temperature also occurs in the Southern ocean. The article discusses the problem of monitoring the dynamics of this layer and obtaining data from a field experiment on its interaction with the atmosphere in the context of the to-day climate change of the Arctic and Antarctic. There is a reason to hope that the planned development of modern Russian scientific research in the polar regions of the world ocean will help to solve this important climatic problem. The paper presents some key results of this kind of domestic oceanological studies of the mid-twentieth century, which made a significant contribution to the theory and experiment related to the dynamics of the Southern ocean.

Implementation and Evaluation of an Improved Lake Scheme in Beijing Climate Center Atmosphere‐Vegetation Interaction Model

AbstractTo improve the performance of the second generation of Beijing Climate Center Atmosphere‐Vegetation Interaction Model (BCC_AVIM2.0) with a fine resolution (~45 km) over lake‐rich areas, the default lake scheme in BCC_AVIM2.0 is replaced by the Common Land Surface Model (CoLM)‐Lake scheme with much more realistic treatments of the energy exchanges in the snow‐ice‐water‐sediment system relative to the default lake scheme. Results show that the lake surface temperature (LST) biases produced by BCC_AVIM2.0 with the default lake scheme can be largely reduced by adopting the CoLM‐Lake scheme in winter due to much more realistically simulated vertical water temperature profiles over the Great Lakes region. The spatial distributions and seasonal variations of the LST simulations can also be significantly improved by the CoLM‐Lake scheme within BCC_AVIM2.0. The performances of BCC_AVIM2.0 in simulating the lake ice in winter can be largely improved by replacing the default lake scheme with the CoLM‐Lake scheme. The improvements in the LST simulated by BCC_AVIM2.0 with the CoLM‐Lake scheme further lead to reduced biases in the simulated ground surface temperature. The simulations of air temperature and precipitation in the coupled model are also improved by adopting the CoLM‐Lake scheme over the Great Lakes region, which indicates the improvements in simulating the energy and water exchange between the atmosphere and lakes. This study highlights the importance of a more realistic lake scheme in simulating the ground surface temperature and the energy exchanges between the atmosphere and lakes.

On the impact of atmospheric vs oceanic resolutions on the representation of the sea surface temperature in the South Eastern Tropical Atlantic

Despite the efforts of the modelling community to improve the representation of the sea surface temperature (SST) over the South Eastern Tropical Atlantic, warm biases still persist. In this work we use four different configurations of the fully-coupled AWI Climate Model (AWI-CM) which allow us to gain physics-based insight into the role of the oceanic and atmospheric resolutions of the model in the regional distribution of the SST. Our results show that a sole refinement of the oceanic resolution reduces warm biases further than a single increase of the atmospheric component. An increased oceanic resolution is required (i) to simulate properly the Agulhas Current and its associated rings; (ii) to reinforce the northward-flowing Benguela Current and (iii) to intensify coastal upwelling. The best results are obtained when both resolutions are refined. However, even in that case, warm biases persist, reflecting that some processes and feedbacks are still not optimally resolved. Our results indicate that overheating is not due to insufficient upwelling, but rather due to upwelling of waters which are warmer than observations as a result of an erroneous representation of the vertical distribution of temperature. Errors in the representation of the vertical temperature profile are the consequence of a warm bias in the simulated climate state.

Studying boundary layer methane isotopy and vertical mixing processes at a rewetted peatland site using an unmanned aircraft system

Abstract. The combination of two well-established methods, of quadrocopter-borne air sampling and methane isotopic analyses, is applied to determine the source process of methane at different altitudes and to study mixing processes. A proof-of-concept study was performed to demonstrate the capabilities of quadrocopter air sampling for subsequently analysing the methane isotopic composition δ13C in the laboratory. The advantage of the system compared to classical sampling on the ground and at tall towers is the flexibility concerning sampling location, and in particular the flexible choice of sampling altitude, allowing the study of the layering and mixing of air masses with potentially different spatial origin of air masses and methane. Boundary layer mixing processes and the methane isotopic composition were studied at Polder Zarnekow in Mecklenburg–West Pomerania in the north-east of Germany, which has become a strong source of biogenically produced methane after rewetting the drained and degraded peatland. Methane fluxes are measured continuously at the site. They show high emissions from May to September, and a strong diurnal variability. For two case studies on 23 May and 5 September 2018, vertical profiles of temperature and humidity were recorded up to an altitude of 650 and 1000 m, respectively, during the morning transition. Air samples were taken at different altitudes and analysed in the laboratory for methane isotopic composition. The values showed a different isotopic composition in the vertical distribution during stable conditions in the morning (delta values of −51.5 ‰ below the temperature inversion at an altitude of 150 m on 23 May 2018 and at an altitude of 50 m on 5 September 2018, delta values of −50.1 ‰ above). After the onset of turbulent mixing, the isotopic composition was the same throughout the vertical column with a mean delta value of −49.9 ± 0.45 ‰. The systematically more negative delta values occurred only as long as the nocturnal temperature inversion was present. During the September study, water samples were analysed as well for methane concentration and isotopic composition in order to provide a link between surface and atmosphere. The water samples reveal high variability on horizontal scales of a few tens of metres for this particular case. The airborne sampling system and consecutive analysis chain were shown to provide reliable and reproducible results for two samples obtained simultaneously. The method presents a powerful tool for distinguishing the source process of methane at different altitudes. The isotopic composition showed clearly depleted delta values directly above a biological methane source when vertical mixing was hampered by a temperature inversion, and different delta values above, where the air masses originate from a different footprint area. The vertical distribution of methane isotopic composition can serve as tracer for mixing processes of methane within the atmospheric boundary layer.

On the Analysis of the Performance of WRF and NICAM in a Hyperarid Environment

Abstract The Weather Research and Forecasting (WRF) Model and the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) are forced with the Global Forecast System (GFS) data and run over the United Arab Emirates (UAE) for two 4-day periods: one in the cold season (16–18 December 2017) and another in the warm season (13–15 April 2018). The models’ performance is evaluated against four observational datasets: weather station observations, eddy-covariance flux measurements at Al Ain, microwave radiometer–derived temperature profile, and twice-daily radiosonde measurements at Abu Dhabi. An overestimation of the daily mean air temperature by 1°–3°C is noticed for both models and periods. This warm bias is attributed to the reduced cloud cover and resulting increased surface downward shortwave radiation flux. A comparison with the eddy-covariance data suggested that both models also underestimate the observed albedo. However, when the models predict heavier amounts of precipitation, they tend to be colder than observations, typically by 2°–3°C. NICAM and WRF overpredict the strength of the near-surface wind speed at all weather stations by roughly 1–3 m s−1, which has been attributed to a poor representation of its subgrid-scale fluctuations and surface drag parameterization. WRF tends to be wetter and NICAM drier than the station observations, possibly because of differences in the cloud microphysics schemes. While the performance of both models for the near-surface fields is comparable, NICAM outperforms WRF in the simulation of vertical profiles of temperature, relative humidity, and wind speed, being able to partially correct some of the biases in the GFS data.

Dynamical downscaling of a multimodel ensemble prediction system: Application to tropical cyclones

AbstractThis study attempts dynamical downscaling to improve north Indian ocean (NIO) tropical cyclone prediction from a global multimodel ensemble prediction system using weather research and forecasting (WRF) model. A total of 16 ensembles are used in the WRF simulations, these ensembles are bias‐corrected prior to downscaling for model climatological errors. The ensemble mean constructed from the output of all downscaled ensembles is analyzed for added value to global predictions. This mean is also compared against observation as well as high‐resolution (12 km) deterministic forecast from global forecast system (GFS). Two devastating NIO tropical cyclone cases of year 2017 which were not reliably predicted by global systems have been selected for this study. The results show that downscaled predictions well simulate the intensity and spatial distribution of the rainfall and relative vorticity associated with these cyclonic storms. The wind and temperature vertical profiles during cyclone mature stage are also captured more accurately than raw prediction and high‐resolution global deterministic forecast. The study affirms the adequacy of dynamical downscaling in predicting the cyclonic storms over global real‐time weather forecasting system.

High-Resolution Estimation and Spatial Interpolation of Temperature Structure in the Atmospheric Boundary Layer Using a Small Unmanned Aircraft System

Knowledge of the effects of small-scale fluctuations in temperature on light transmission in the atmosphere is necessary for the calibration of remote sensing instruments as well as for the understanding of turbulent heat transport in the atmospheric boundary layer. Recent developments in small unmanned aircraft systems (sUAS) have allowed for direct, spatial in situ estimation of temperature in the ABL at very high temporal and spatial resolutions. Structure functions are estimated from vertical profiles of temperature collected using an ultrasonic anemometer mounted on an sUAS. Using geostatistical methodologies specifically developed for spatially non-stationary and spatially dependent random variables, we estimate temperature structure from six profiles reaching roughly 500 m in altitude A mean function is specified to account for the variation in temperature with altitude and the structure function is estimated from the residuals. A 2/3 scaling exponent is fitted to the resulting curves commensurate with the inertial subrange of turbulence. The resulting structure functions of residuals are able to resolve the inertial subrange on most profiles at a range of separation distances. We find that geostatistical methods for spatially non-stationary random variables are well suited in certain cases to describing the vertical structure of temperature in the boundary layer.

A multi-technique approach to determine temporal and spatial variability of groundwater-stream water exchange

Characterizing the spatio-temporal distribution of groundwater-surface water exchange fluxes is of paramount importance in understanding catchment behavior. A wide range of field-based techniques are available for such characterization. The objective of this study is to quantify the spatio-temporal distribution of the exchange fluxes along the Cakit stream (Nigde, Turkey) through coupling a set of geophysical techniques and in-stream measurements in a hierarchical manner. First, geological and water quality information were combined at the catchment scale to determine key areas for reach-scale focus. Second, electromagnetic induction (EMI) surveys were conducted along the reach to pinpoint potential groundwater upwelling locations. EMI anomalies guided our focus to a 665 meter-long reach of the stream. Along this selected reach, a fiber-optic distributed temperature sensing (FO-DTS) system was utilized to investigate streambed-temperature profiles at fine spatial and temporal scales. Furthermore, vertical hydraulic gradients and exchange fluxes were investigated using nested piezometers and vertical temperature profiles, respectively, at two potential upwelling locations and a potential downwelling location identified by previous surveys. The results of the study reveal heterogeneity of vertical water-flow components with seasonal variability. The EMI survey was successful in identifying a localized groundwater upwelling location. FO-DTS measurements revealed a warm temperature anomaly during cold air temperature and low streamflow conditions at the same upwelling site. Our point-based methods, namely vertical temperature profiles and vertical hydraulic gradient estimates, however, did not always provide consistent results with each other and with EMI and DTS measurements. This study, therefore, highlights the opportunities and challenges in incorporating multi-scale observations in a hierarchical manner in characterization of the groundwater-surface water exchange processes that are known to be highly heterogeneous in time and space. Overall, a combination of different methods helps to overcome the limitations of each single method and increases confidence in the obtained results.

Reconciling the observed mid-depth exponential ocean stratification with weak interior mixing and Southern Ocean dynamics via boundary-intensified mixing

Munk (Deep Sea Res Oceanogr Abstr 13(4):707–730, 1966) showed that the mid-depth (1–3 km) vertical temperature profile is consistent with a one-dimensional vertical advection–diffusion balance, with a constant upwelling and an interior diapycnal diffusivity of \({\mathcal {O}}(10^{-4})\,\hbox {m}^{2}\,\hbox {s}^{-1}\). However, typical observed diffusivities in the interior are \({\mathcal {O}}(10^{-5})\,\hbox {m}^{2}\,\hbox {s}^{-1}\). Recent work suggested that the mid-depth stratification is set by Southern Ocean (SO) isopycnal slopes, governed by SO wind and eddies, that communicate the surface outcrop positions to the mid-depth ocean. It is shown here, using an idealized ocean general circulation model, that while SO dynamics play an important role by linking the surface water mass transformation by air-sea fluxes with the mid-depth interior stratification, they do not set the observed exponential stratification and that interior mixing must contribute. Strong diapycnal mixing concentrated near the ocean boundaries is shown to be balanced locally by upwelling. A one-dimensional Munk-like balance in these boundary-mixing areas, although with much larger mixing and upwelling, leads to an exponential mid-depth temperature stratification, which spreads via isopycnal advection and mixing to the ocean interior. The exponential profile is robust to vertical variations in the vertical velocity and persists despite the observed weak interior diapycnal mixing. These results may suggest a way to reconcile the observed exponential interior mid-depth temperature stratification, the weak diapycnal diffusivity observed in tracer release experiments, and the role of Southern Ocean dynamics.

Experimental study on confinement velocity in tunnel fires with longitudinal ventilation

A series of experiments were carried out in a model-scale tunnel to investigate the confinement velocity in the tunnel fire with longitudinal ventilation. The significance of longitudinal ventilation to the smoke control in tunnel fire was comprehensively elaborated by both the variation of smoke back-layering length in the upstream and the characteristics of smoke layer in the downstream which was visualized by the laser-sheet and determined objectively by the measured vertical temperature profile. Experimental results show that the smoke back-layering length exhibits a common trend with the increasing longitudinal ventilation velocity, first decreases sharply and then becomes not very sensitive after reaching a turning point. By analyzing the experiment results, it was found that the ratio of confinement velocity, i.e., the velocity corresponding to the turning point to critical velocity was basically identical which could be determined as 0.86. In addition, a quantitative model for directly predicting the confinement velocity was proposed and compared with previous models. The study is expected to provide some references for the application of confinement velocity in actual tunnel fire-fighting.

The Sundowner Winds Experiment (SWEX) Pilot Study: Understanding Downslope Windstorms in the Santa Ynez Mountains, Santa Barbara, California

AbstractSundowner winds are downslope gusty winds often observed on the southern slopes of the Santa Ynez Mountains (SYM) in coastal Santa Barbara (SB), California. They typically peak near sunset and exhibit characteristics of downslope windstorms through the evening. They are SB’s most critical fire weather in all seasons and represent a major hazard for aviation. The Sundowner Winds Experiment Pilot Study was designed to evaluate vertical profiles of winds, temperature, humidity, and stability leeward of the SYM during a Sundowner event. This was accomplished by launching 3-hourly radiosondes during a significant Sundowner event on 28–29 April 2018. This study showed that winds in the lee of the SYM exhibit complex spatial and temporal patterns. Vertical profiles showed a transition from humid onshore winds from morning to midafternoon to very pronounced offshore winds during the evening after sunset. These winds accompanied mountain waves and a northerly nocturnal lee jet with variable temporal behavior. Around sunset, the jet was characterized by strong wind speeds enhanced by mountain-wave breaking. Winds weakened considerably at 2300 PDT 29 April but enhanced dramatically at 0200 PDT 29 April at much lower elevations. These transitions were accompanied by changes in stability profiles and in the Richardson number. A simulation with the Weather Research and Forecasting (WRF) Model at 1-km grid spacing was examined to evaluate the skill of the model in capturing the observed winds and stability profiles and to assess mesoscale processes associated with this event. These results advanced understanding on Sundowner’s spatiotemporal characteristics and driving mechanisms.

Retrieving Volcanic Ash Top Height through Combined Polar Orbit Active and Geostationary Passive Remote Sensing Data

Taking advantage of both the polar orbit active remote sensing data (from the Cloud-Aerosol Lidar with Orthogonal Polarization—CALIOP) and vertical information and the geostationary passive remote sensing measurements (from the Spinning Enhanced Visible and Infrared Imager) with large coverage, a methodology is developed for retrieving the volcanic ash cloud top height (VTH) from combined CALIOP and Spinning Enhanced Visible and Infrared Imager (SEVIRI) data. This methodology is a deep-learning-based algorithm through hybrid use of Stacked Denoising AutoEncoder (SDA), the Genetic Algorithm (GA), and the Least Squares Support Vector Regression (LSSVR). A series of eruptions over Iceland’s Eyjafjallajökull volcano from April to May 2010 and the Puyehue-Cordón Caulle volcanic complex eruptions in Chilean Andes in June 2011 were selected as typical cases for independent validation of the VTH retrievals under various meteorological backgrounds. It is demonstrated that using the hybrid deep learning algorithm, the nonlinear relationship between satellite-based infrared (IR) radiance measurements and the VTH can be well established. The hybrid deep learning algorithm not only performs well under a relatively simple meteorological background but also is robust under more complex meteorological conditions. Adding atmospheric temperature vertical profile as additional information further improves the accuracy of VTH retrievals. The methodology and approaches can be applied to the measurements from the advanced imagers onboard the new generation of international geostationary (GEO) weather satellites for retrieving the VTH science product.

Thermal behavior of window plume generated by fully developed compartment fires in single-skin and double-skin façade scenarios

Glass façade is gaining popularity in modern commercial buildings in recent several decades. The thermal stability of façade structural elements then becomes a great concern in building fire safety. To provide a guidance for glass façade fire protection, an experimental study on the vertical temperature distribution of window plume with apparent external flames was carried out. Experiments were performed by employing reduced-scale compartment façade models with a single wall and with double walls. A propane gas burner, installed at the center of the compartment floor, served as a fire source to simulate quasi-steady state room fires. When apparent external flames exist, the shapes of vertical temperature profile varied with both opening geometry and heat release rate (HRR). Empirical temperature models which considered the effect of volumetric heat release phenomenon was developed by employing mean flame heights as the characteristic length scales. The measured temperature profiles showed a three-phase distribution feature and were well correlated with the dimensionless vertical distance.

Suppression of “Handover” Processes in a Mountain Convective Boundary Layer due to Persistent Wildfire Smoke

Widespread and persistent summer multi-day episodes of dense wildfire smoke affected western Canada in 2017 and 2018. These events often occurred under otherwise clear-sky, anticyclonic weather conditions and can have significant impacts on surface temperatures, air quality, and surface radiation and energy budgets. Based on upward-pointing lidar observations, vertical temperature soundings and numerical mesoscale modelling for a mountain in south-western British Columbia, Canada, we propose a previously undocumented stability-related impact of wildfire smoke layers on mountain meteorology. This positive feedback (that maintains layer structure and extends the lifetime of layers) appears to suppress mountain “handover processes”. Smoke days are characterized by more stable vertical temperature profiles when compared to clear-sky conditions, and are marked by a lack of diurnal variability in boundary-layer structure in lidar backscatter imagery. We expect the processes described to have general application and propose more detailed aerosol modelling to investigate the physical details of the process.

Characterization of Hyporheic Exchange Drivers and Patterns within a Low-Gradient, First-Order, River Confluence during Low and High Flow

Confluences are nodes in riverine networks characterized by complex three-dimensional changes in flow hydrodynamics and riverbed morphology, and are valued for important ecological functions. This physical complexity is often investigated within the water column or riverbed, while few studies have focused on hyporheic fluxes, which is the mixing of surface water and groundwater across the riverbed. This study aims to understand how hyporheic flux across the riverbed is organized by confluence physical drivers. Field investigations were carried out at a low gradient, headwater confluence between Baltimore Brook and Cold Brook in Marcellus, New York, USA. The study measured channel bathymetry, hydraulic permeability, and vertical temperature profiles, as indicators of the hyporheic exchange due to temperature gradients. Confluence geometry, hydrodynamics, and morphodynamics were found to significantly affect hyporheic exchange rate and patterns. Local scale bed morphology, such as the confluence scour hole and minor topographic irregularities, influenced the distribution of bed pressure head and the related patterns of downwelling/upwelling. Furthermore, classical back-to-back bend planform and the related secondary circulation probably affected hyporheic exchange patterns around the confluence shear layer. Finally, even variations in the hydrological conditions played a role on hyporheic fluxes modifying confluence planform, and, in turn, flow circulation patterns.