Similarity in Fog and Rainfall Intermittency

Intermittent fog occurrences supply significant amounts of moisture to plants in the form of fog drip onto the soil surface thereby prompting interest in their statistical behavior at multiple timescales. A comparison of rainfall and fog measurements collected at an inland tropical cloud forest in Kenya and a coastal rangeland in Northern California is presented to explore whether fog occurrences have similar intermittency characteristics as rainfall. The results confirm that both rainfall and fog show approximate power law relations for distributions of dry period and event size consistent with predictions from self-organized criticality. Moreover, the spectral exponents of the on-off time series of the fog and rainfall exhibited an approximate f(-0.8) over a broad range of frequencies f, which is remarkably close to scaling exponents across sites experiencing different rainfall generation mechanisms. These results suggest that fog intermittency shares some properties of critical behavior documented in numerous rainfall studies. Plain Language Summary Beyond rainfall, intermittent fog occurrence provides water subsidy that is needed for sustaining transpiration and photosynthesis in forests. To study the connections between fog formation and rainfall, a comparison of rainfall and fog occurrence statistics is carried out at two sites: a Kenyan inland cloud forest and a coastal forest in Northern California. For durations exceeding 1 day, rainfall and fog event sizes and dry periods appear similar. Due to these similarities, intermittency in fog occurrences may abide by general laws describing critical phenomenon.Peer reviewe

A Machine Learning Based Downscaling Approach to Produce High Spatio-Temporal Resolution Land Surface Temperature of the Antarctic Dry Valleys from MODIS Data

To monitor environmental and biological processes, Land Surface Temperature (LST) is a central variable, which is highly variable in space and time. This particularly applies to the Antarctic Dry Valleys, which host an ecosystem highly adapted to the extreme conditions in this cold desert. To predict possible climate induced changes on the Dry Valley ecosystem, high spatial and temporal resolution environmental variables are needed. Thus we enhanced the spatial resolution of the MODIS satellite LST product that is sensed sub-daily at a 1 km spatial resolution to a 30 m spatial resolution. We employed machine learning models that are trained using Landsat 8 thermal infrared data from 2013 to 2019 as a reference to predict LST at 30 m resolution. For the downscaling procedure, terrain derived variables and information on the soil type as well as the solar insolation were used as potential predictors in addition to MODIS LST. The trained model can be applied to all available MODIS scenes from 1999 onward to develop a 30 m resolution LST product of the Antarctic Dry Valleys. A spatio-temporal validation revealed an R2 of 0.78 and a RMSE of 3.32 ∘C. The downscaled LST will provide a valuable surface climate data set for various research applications, such as species distribution modeling, climate model evaluation, and the basis for the development of further relevant environmental information such as the surface moisture distribution

The surface energy balance during foehn events at Joyce Glacier, McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys (MDV) are a polar desert, where glacial melt is the main source of water to streams and the ecosystem. Summer air temperatures are typically close to zero, and therefore foehn events can have a large impact on the meltwater production. A 14-month record of automatic weather station (AWS) data on Joyce Glacier is used to force a 1D surface energy balance model to study the impact of foehn events on the energy balance. AWS data and output of the Antarctic Mesoscale Prediction System (AMPS) on a 1.7 km grid are used to detect foehn events at the AWS site. Foehn events at Joyce Glacier occur under the presence of cyclones over the Ross Sea. The location of Joyce Glacier on the leeward side of the Royal Society Range during these synoptic events causes foehn warming through isentropic drawdown. This mechanism differs from the foehn warming through gap flow that was earlier found for other regions in the MDV and highlights the complex interaction of synoptic flow with local topography of the MDV. Shortwave radiation is the primary control on melt at Joyce Glacier, and melt often occurs with subzero air temperatures. During foehn events, melt rates are enhanced, contributing to 23 % of the total annual melt. Foehn winds cause a switch from a diurnal stability regime in the atmospheric surface layer to a continuous energy input from sensible heat flux throughout the day. The sensible heating during foehn, through an increase in turbulent mixing resulting from gustier and warmer wind conditions, is largely compensated for by extra heat losses through sublimation. Melt rates are enhanced through an additional energy surplus from a reduced albedo during foehn

The health of internally displaced people in Syria: are current systems fit for purpose?

INTRODUCTION: Syria has the largest number of internally displaced people (IDPs) globally with 6.7 million forced from their homes since the uprising erupted in 2011. Most face multiple intersecting vulnerabilities with adverse health impacts. We explore the key health concerns among IDPs, how the various health systems in Syria have responded to the dynamic health needs of IDPs and what modalities have been used by humanitarian actors to address these needs. METHODS: We undertook a scoping review of academic and grey literature for available evidence regarding the health of IDPs in Syria. We then organised an online workshop in November 2021 with around 30 participants who represent local, regional, and international organisations and who have relevant expertise. The discussion focused on how the health systems in Syria's various territories have responded to the health needs of IDPs, what this means to the structure and dynamics of these health systems and their intended outcomes and responsiveness. FINDINGS: These emphasised the weak evidence base around IDP health in Syria, particularly in certain geographical areas. Workshop participants explored the applicability of the term IDP in the Syrian context given the fragmented health system and its impact on IDPs, the importance of considering co-determinants (beyond forced displacement) on the health of IDPs and taking a transectoral, community led approach to identify and respond to needs. CONCLUSION: This manuscript presents some of the current issues with regards to IDP health in Syria, however, there remain numerous unknowns, both for the health of IDP as well as non-IDP populations. We hope that it will be the foundation for further discussions on practical steps relating to research, analysis and interventions which can support health system responses for IDPs in Syria

Interactions between the night time valley-wind system and a developing cold-air pool

This is a pre-copyedited, author-produced PDF of an article accepted for publication in Boundary-Layer Meteorology following peer review. The version of record [Arduini, G., Staquet, C & Chemel, C., ‘Interactions between the night time valley-wind system and a developing cold-air pool’, Boundary-Layer Meteorol (2016) 161:1 (49-72), first published online June 2, 2016, is available at Springer online at doi: 10.1007/s10546-016-0155-8The Weather Research and Forecast (WRF) numerical model is used to characterize the influence of a thermally-driven down-valley flow on a developing cold-air pool in an idealized alpine valley decoupled from the atmosphere above. Results for a three-dimensional (3D) valley, which allows for the formation of a down-valley flow, and for a two-dimensional (2D) valley, where the formation of a down-valley flow is inhibited, are analyzed and compared. A key result is that advection leads to a net cooling in the 2D valley and to a warming in the 3D valley, once the down-valley flow is fully developed. This difference stems from the suppression of the slope-flow induced upward motions over the valley centre in the 3D valley. As a result, the downslope flows develop a cross-valley circulation within the cold-air pool, the growth of the cold-air pool is reduced and the valley atmosphere is generally warmer than in the 2D valley. A quasi-steady state is reached for which the divergence of the down-valley flow along the valley is balanced by the convergence of the downslope flows at the top of the cold-air pool, with no net contribution of subsiding motions far from the slope layer. More precisely, the inflow of air at the top of the cold-air pool is found to be driven by an interplay between the return flow from the plain region and subsidence over the plateaux. Finally, the mechanisms that control the structure of the cold-air pool and its evolution are found to be independent of the valley length as soon as the quasi-steady state is reached and the down-valley flow is fully developed.Peer reviewedFinal Accepted Versio

Numerical simulations of turbulent flow within and in the wake of a small basin

Small terrain features, such as small valleys, basins, sinkholes, low hills, and outcrops, while generally associated with mountainous regions, can also be found over plains. In this study, we present a numerical investigation of the effect of a small terrain feature (a 30mhigh rim) on the mean and turbulent flows inside and downstream of an enclosed basin it surrounds. Results from high-resolution numerical simulations (10m isotropic spatial resolution) indicate that small terrain features in the proximity of larger ones can induce relatively large modifications to the mean and turbulent flows. The 30mhigh rim is found to have an effect on the mean wind speeds at least 600m upstream from the basin. The main effect is a 10% reduction in wind speed up to 120m above ground level due to the upstream blocking effect of the rim. The presence of the rimcan also double the turbulent kinetic energy (TKE) both inside and downstream of the basin compared to an otherwise identical basin without a rim. The slopes of the basin play an important role in first creating and then defining the wake, and in intermittent wind regimes most of the scalar transport from near the slope of the basin happens through slope roll vortices that define the edge of the downstream wake region of the basin. Inside the basin, the rim acts to limit momentum transfer in the lower half of the basin, which suggests a mechanical forcing effect induced by the rim on lower basin environments that could interact with thermal buoyancy effects in heated or cooled basins. Some of the wake features resemble wind-eroded surfaces in the wakes of Martian craters. Results also reveal a critical height level (43m below the rim height) that acts as the most favored location for TKE production and destruction, which could be important for the top-to-bottomturbulence erosion of basin boundary layers. These results stress the importance of resolving small-scale terrain features, as their effects can be nonlocal

Forward-Looking Infrared Cameras for Micrometeorological Applications within Vineyards

We apply the principles of atmospheric surface layer dynamics within a vineyard canopy to demonstrate the use of forward-looking infrared cameras measuring surface brightness temperature (spectrum bandwidth of 7.5 to 14 m) at a relatively high temporal rate of 10 s. The temporal surface brightness signal over a few hours of the stable nighttime boundary layer, intermittently interrupted by periods of turbulent heat flux surges, was shown to be related to the observed meteorological measurements by an in situ eddy-covariance system, and reflected the above-canopy wind variability. The infrared raster images were collected and the resultant self-organized spatial cluster provided the meteorological context when compared to in situ data. The spatial brightness temperature pattern was explained in terms of the presence or absence of nighttime cloud cover and down-welling of long-wave radiation and the canopy turbulent heat flux. Time sequential thermography as demonstrated in this research provides positive evidence behind the application of thermal infrared cameras in the domain of micrometeorology, and to enhance our spatial understanding of turbulent eddy interactions with the surface

Application of UAV techniques to expand beach research possibilities: A case study of coarse clastic beach cusps

Unmanned aerial vehicles (UAVs) have widely been documented as accessible, low cost, high-resolution coastal monitoring platforms. To date, however, UAVs have primarily been employed in coastal research as an alternative to traditional survey methods, such as beach profiling, despite their capabilities far exceeding such uses. In this contribution, we present UAV surveys as a technique to expand upon previous research possibilities through a case study on coarse clastic beach cusps. Currently no consensus exists regarding the primary mechanism responsible for development of these rhythmic features, not least due to the need for more comprehensive and timely observational data. Previous research on beach cusps is limited to repeat monitoring of a small number of cusps, or monitoring large cusp sets at relatively coarse spatial resolution. Here, repeat UAV surveys along a 600 m stretch of composite beach in New Zealand are employed to produce the most comprehensive characterisation of cusp parameters (spacing, amplitude, depth) available to date. Furthermore, the use of UAVs in this mixed sediment environment has made it possible to link cuspate morphology, such as horns and bays, to surface sediment texture. This critical advance provides new opportunities for coupling textural and topographic data in future analyses and modelling approaches. We argue that the enhanced, but still nascent, opportunity to observe morphodynamics using UAV survey methods can be critical to advancing our understanding of complex coastal zone features and changes

Beach cusp morphodynamics on a composite beach observed using UAV structure from motion

Beach cusps are often more prominent on beaches composed of coarse or mixed sediments, as opposed to sand alone. For cusps on mixed sediment beaches, one of the most important morphological characteristics to quantify is the surface sediment texture distribution, differentiating between sand and gravel units on the beachface. Despite this, most research methods to date have been unable to accurately quantify textural zonation, and instead focus on the bed level change as a whole across the beachface. However, new combinations of sensors and technology, such as drone-mounted cameras and Structure from Motion approaches allows for the direct coupling of beach morphological evolution to surface sediment texture. In this contribution we apply image segmentation algorithms to drone imagery in order to classify the extent of surface sand and gravels, and compare this to bed level changes in digital elevation models. The explicit coupling of sediment texture and morphological response shows the beach cusp features to be largely accretionary, with gravel horns initially forming on a sandy beachface. The gravel horns are seen to progressively grow in size, creating well developed beach cusps. As accretion continues, the sandy cusps bays are filled with gravel sediments, resulting in the formation of an alongshore-uniform regular berm feature. This study highlights the utility of drone based sensors to provide a full suite of morphological and textural information about mixed sediment beaches, not achievable with traditional survey methods. Moving forward, this level of information can be used to investigate and understand the relative importance of the two sediment fractions in controlling the form and behaviour of mixed sediment beach cusps

Characteristics of the Springtime Alpine Valley Atmospheric Boundary Layer Using Self-Organized Maps

Vertical profiles of wind velocity and air temperature from a sound detection and ranging (sodar) radio acoustic sounding system (RASS)-derived dataset within an alpine valley of the New Zealand Southern Alps were analyzed. The data covered the month of September 2013, and self-organizing maps (SOM; a dataclustering approach that is based on an unsupervised machine-learning algorithm) are used to detect topological relationships between profiles. The results of the SOM were shown to reflect the physical processes within the valley boundary layer by preserving valley boundary layer dynamics and its response to wind shear. By examining the temporal evolution of ridgetop wind speed and direction and SOM node transitions, the sensitivity of the valley boundary layer to ridgetop weather conditions was highlighted. The approach of using a composite variable (wind speed and potential temperature) with SOM was successful in revealing the coupling of dynamics and atmospheric stability. The results reveal the capabilities of SOM in analyzing large datasets of atmospheric boundary layer measurements and elucidating the connectivity of ridgetop wind speeds and valley boundary layers