scholarly journals Distinguishing Time Scales of Katabatic Flow in Complex Terrain

Atmosphere ◽  
2021 ◽  
Vol 12 (12) ◽  
pp. 1651
Author(s):  
Stephen Drake ◽  
Chad Higgins ◽  
Eric Pardyjak
Keyword(s):  
Cooling Rate ◽  
Complex Terrain ◽  
Atmospheric Modeling ◽  
Lapse Rate ◽  
Small Scale ◽  
Distributed Temperature Sensing ◽  
Local Cooling ◽  
Katabatic Flow ◽  
Drainage Flow ◽  
Spatial And Temporal Scales

To examine spatial and temporal scales of katabatic flow, a distributed temperature sensing (DTS) optical fiber was deployed 2 km down a mild slope irregularly interrupted by small-scale drainage features as part of the Mountain Terrain Atmospheric Modeling and Observation (MATERHORN) experiment conducted at the U.S. Army Dugway Proving Ground, Utah. The fiber was suspended at two heights near the surface, enabling measurement of variations in lapse rate near the surface at meter-scale spatial resolution with 1-min temporal resolution. Experimental results derived from the DTS and tower-mounted instrumentation indicate that airflow through small-scale drainage features regulated the local cooling rate whereas topographic slope and distance along the drainage strongly influenced the larger-scale cooling rate. Empirical results indicate that local cooling rate decays exponentially after local sunset and basin-wide cooling rate decreases linearly with time. The difference in the functional form for cooling rate between local and basin-wide scales suggests that small-scale features have faster timescales that manifests most strongly shortly after local sunset. More generally, partitioning drainage flow by scale provides insight and a methodology for improved understanding of drainage flow in complex terrain.

scholarly journals Assessment of a vertical high-resolution distributed-temperature-sensing system in a shallow thermohaline environment

2011 ◽  
Vol 15 (3) ◽  
pp. 1081-1093 ◽  
Author(s):  
F. Suárez ◽  
J. E. Aravena ◽  
M. B. Hausner ◽  
A. E. Childress ◽  
S. W. Tyler
Keyword(s):  
High Resolution ◽  
Temperature Sensing ◽  
Distributed Temperature Sensing ◽  
Temperature Resolution ◽  
Spatial And Temporal Scales ◽  
Solar Pond ◽  
Salt Gradient ◽  
Time Averages ◽  
Corrosive Environments ◽  
And Storage

Abstract. In shallow thermohaline-driven lakes it is important to measure temperature on fine spatial and temporal scales to detect stratification or different hydrodynamic regimes. Raman spectra distributed temperature sensing (DTS) is an approach available to provide high spatial and temporal temperature resolution. A vertical high-resolution DTS system was constructed to overcome the problems of typical methods used in the past, i.e., without disturbing the water column, and with resistance to corrosive environments. This paper describes a method to quantitatively assess accuracy, precision and other limitations of DTS systems to fully utilize the capacity of this technology, with a focus on vertical high-resolution to measure temperatures in shallow thermohaline environments. It also presents a new method to manually calibrate temperatures along the optical fiber achieving significant improved resolution. The vertical high-resolution DTS system is used to monitor the thermal behavior of a salt-gradient solar pond, which is an engineered shallow thermohaline system that allows collection and storage of solar energy for a long period of time. The vertical high-resolution DTS system monitors the temperature profile each 1.1 cm vertically and in time averages as small as 10 s. Temperature resolution as low as 0.035 °C is obtained when the data are collected at 5-min intervals.

scholarly journals Irradiance Variability Quantification and Small-Scale Averaging in Space and Time: A Short Review

Atmosphere ◽  
2018 ◽  
Vol 9 (7) ◽  
pp. 264 ◽  
Author(s):  
Gerald Lohmann
Keyword(s):  
Short Review ◽  
Power Grids ◽  
Small Scale ◽  
Stable Operation ◽  
Data Sets ◽  
Spatial Smoothing ◽  
Spatial And Temporal Scales ◽  
Output Variability ◽  
Temporal Averaging

The ongoing world-wide increase of installed photovoltaic (PV) power attracts notice to weather-induced PV power output variability. Understanding the underlying spatiotemporal volatility of solar radiation is essential to the successful outlining and stable operation of future power grids. This paper concisely reviews recent advances in the characterization of irradiance variability, with an emphasis on small spatial and temporal scales (respectively less than about 10 km and 1 min), for which comprehensive data sets have recently become available. Special attention is given to studies dealing with the quantification of variability using such unique data, the analysis and modeling of spatial smoothing, and the evaluation of temporal averaging.

Evaluation of Surface Analyses and Forecasts with a Multiscale Ensemble Kalman Filter in Regions of Complex Terrain

2011 ◽  
Vol 139 (6) ◽  
pp. 2008-2024 ◽  
Author(s):  
Brian C. Ancell ◽  
Clifford F. Mass ◽  
Gregory J. Hakim
Keyword(s):  
Kalman Filter ◽  
High Resolution ◽  
Data Assimilation ◽  
Ensemble Kalman Filter ◽  
Complex Terrain ◽  
Error Variance ◽  
Small Scale ◽  
Observation Error ◽  
Grid Spacing ◽  
Background Error

Abstract Previous research suggests that an ensemble Kalman filter (EnKF) data assimilation and modeling system can produce accurate atmospheric analyses and forecasts at 30–50-km grid spacing. This study examines the ability of a mesoscale EnKF system using multiscale (36/12 km) Weather Research and Forecasting (WRF) model simulations to produce high-resolution, accurate, regional surface analyses, and 6-h forecasts. This study takes place over the complex terrain of the Pacific Northwest, where the small-scale features of the near-surface flow field make the region particularly attractive for testing an EnKF and its flow-dependent background error covariances. A variety of EnKF experiments are performed over a 5-week period to test the impact of decreasing the grid spacing from 36 to 12 km and to evaluate new approaches for dealing with representativeness error, lack of surface background variance, and low-level bias. All verification in this study is performed with independent, unassimilated observations. Significant surface analysis and 6-h forecast improvements are found when EnKF grid spacing is reduced from 36 to 12 km. Forecast improvements appear to be a consequence of increased resolution during model integration, whereas analysis improvements also benefit from high-resolution ensemble covariances during data assimilation. On the 12-km domain, additional analysis improvements are found by reducing observation error variance in order to address representativeness error. Removing model surface biases prior to assimilation significantly enhances the analysis. Inflating surface wind and temperature background error variance has large impacts on analyses, but only produces small improvements in analysis RMS errors. Both surface and upper-air 6-h forecasts are nearly unchanged in the 12-km experiments. Last, 12-km WRF EnKF surface analyses and 6-h forecasts are shown to generally outperform those of the Global Forecast System (GFS), North American Model (NAM), and the Rapid Update Cycle (RUC) by about 10%–30%, although these improvements do not extend above the surface. Based on these results, future improvements in multiscale EnKF are suggested.

scholarly journals Investigating patterns and controls of groundwater up-welling in a lowland river by combining Fibre-optic Distributed Temperature Sensing with observations of vertical hydraulic gradients

2012 ◽  
Vol 16 (6) ◽  
pp. 1775-1792 ◽  
Author(s):  
S. Krause ◽  
T. Blume ◽  
N. J. Cassidy
Keyword(s):  
Surface Water ◽  
Water Exchange ◽  
Structural Heterogeneity ◽  
Temperature Sensing ◽  
Small Scale ◽  
Lowland River ◽  
Fibre Optic ◽  
Distributed Temperature Sensing ◽  
Hydraulic Gradients ◽  
Cold Spots

Abstract. This paper investigates the patterns and controls of aquifer–river exchange in a fast-flowing lowland river by the conjunctive use of streambed temperature anomalies identified with Fibre-optic Distributed Temperature Sensing (FO-DTS) and observations of vertical hydraulic gradients (VHG). FO-DTS temperature traces along this lowland river reach reveal discrete patterns with "cold spots" indicating groundwater up-welling. In contrast to previous studies using FO-DTS for investigation of groundwater–surface water exchange, the fibre-optic cable in this study was buried in the streambed sediments, ensuring clear signals despite fast flow and high discharges. During the observed summer baseflow period, streambed temperatures in groundwater up-welling locations were found to be up to 1.5 °C lower than ambient streambed temperatures. Due to the high river flows, the cold spots were sharp and distinctly localized without measurable impact on down-stream surface water temperature. VHG patterns along the stream reach were highly variable in space, revealing strong differences even at small scales. VHG patterns alone are indicators of both, structural heterogeneity of the stream bed as well as of the spatial heterogeneity of the groundwater–surface water exchange fluxes and are thus not conclusive in their interpretation. However, in combination with the high spatial resolution FO-DTS data we were able to separate these two influences and clearly identify locations of enhanced exchange, while also obtaining information on the complex small-scale streambed transmissivity patterns responsible for the very discrete exchange patterns. The validation of the combined VHG and FO-DTS approach provides an effective strategy for analysing drivers and controls of groundwater–surface water exchange, with implications for the quantification of biogeochemical cycling and contaminant transport at aquifer–river interfaces.

scholarly journals Large-Eddy Simulations of Real-World Episodes in Complex Terrain Based on ERA-Reanalysis and Validated by Ground-Based Remote Sensing Data

2019 ◽  
Vol 147 (12) ◽  
pp. 4325-4343 ◽  
Author(s):  
Cornelius Hald ◽  
Matthias Zeeman ◽  
Patrick Laux ◽  
Matthias Mauder ◽  
Harald Kunstmann
Keyword(s):  
Remote Sensing ◽  
Boundary Conditions ◽  
Complex Terrain ◽  
Computing Time ◽  
Remote Sensing Data ◽  
Large Eddy Simulations ◽  
Small Scale ◽  
Sensing Data ◽  
Large Eddy ◽  
Local Weather

Abstract A computationally efficient and inexpensive approach for using the capabilities of large-eddy simulations (LES) to model small-scale local weather phenomena is presented. The setup uses the LES capabilities of the Weather Research and Forecasting Model (WRF-LES) on a single domain that is directly driven by reanalysis data as boundary conditions. The simulated area is an example for complex terrain, and the employed parameterizations are chosen in a way to represent realistic conditions during two 48-h periods while still keeping the required computing time around 105 CPU hours. We show by evaluating turbulence characteristics that the model results conform to results from typical LES. A comparison with ground-based remote sensing data from a triple Doppler-lidar setup, employed during the “ScaleX” campaigns, shows the grade of adherence of the results to the measured local weather conditions. The representation of mesoscale phenomena, including nocturnal low-level jets, strongly depends on the temporal and spatial resolution of the meteorological boundary conditions used to drive the model. Small-scale meteorological features that are induced by the terrain, such as katabatic flows, are present in the simulated output as well as in the measured data. This result shows that the four-dimensional output of WRF-LES simulations for a real area and real episode can be technically realized, allowing a more comprehensive and detailed view of the micrometeorological conditions than can be achieved with measurements alone.

scholarly journals Gravity wave amplitudes and momentum fluxes inferred from OH airglow intensities and meteor radar winds during SpreadFEx

2009 ◽  
Vol 27 (6) ◽  
pp. 2361-2369 ◽  
Author(s):  
F. Vargas ◽  
D. Gobbi ◽  
H. Takahashi ◽  
L. M. Lima
Keyword(s):  
Gravity Waves ◽  
Horizontal Wind ◽  
Small Scale ◽  
Meteor Radar ◽  
Plasma Bubble ◽  
Spatial And Temporal Scales ◽  
Analysis Technique ◽  
Momentum Fluxes ◽  
Different Types ◽  
Wave Directionality

Abstract. We show in this report the momentum flux content input in the mesosphere due to relatively fast and small scale gravity waves (GWs) observed through OH airglow images. The acquisition of OH NIR images was carried out in Brazil at Brasilia (14.8° S, 47.6° W) and Cariri (7.4° S, 36.5° W) from September 2005 to November 2005 during the SpreadFEx Campaign. Horizontal wind information from meteor radar was available in Cariri only. Our findings showed strong wave activity in both sites, mainly in Cariri. High wave directionality was also observed in both sites during SpreadFEx, which have been observed by other investigators using different analysis' techniques and different types of data during the campaign. We discuss also the possibility of plasma bubble seeding by gravity waves presenting spatial and temporal scales estimated with our novel analysis technique during the SpreadFEx campaign.

scholarly journals E-DATA: A Comprehensive Field Campaign to Investigate Evaporation Enhanced by Advection in the Hyper-Arid Altiplano

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 745 ◽  
Author(s):  
Francisco Suárez ◽  
Felipe Lobos ◽  
Alberto de la Fuente ◽  
Jordi Vilà-Guerau de Arellano ◽  
Ana Prieto ◽  
...  
Keyword(s):  
Large Scale ◽  
Spatial Scales ◽  
Open Water ◽  
Water Evaporation ◽  
Distributed Temperature Sensing ◽  
Field Campaign ◽  
Spatial And Temporal Scales ◽  
Airborne Measurements ◽  
Dry Air ◽  
Evaporation Dynamics

In the endorheic basins of the Altiplano, water is crucial for sustaining unique ecological habitats. Here, the wetlands act as highly localized evaporative environments, and little is known about the processes that control evaporation. Understanding evaporation in the Altiplano is challenging because these environments are immersed in a complex topography surrounded by desert and are affected by atmospheric circulations at various spatial scales. Also, these environments may be subject to evaporation enhancement events as the result of dry air advection. To better characterize evaporation processes in the Altiplano, the novel Evaporation caused by Dry Air Transport over the Atacama Desert (E-DATA) field campaign was designed and tested at the Salar del Huasco, Chile. The E-DATA combines surface and airborne measurements to understand the evaporation dynamics over heterogeneous surfaces, with the main emphasis on the open water evaporation. The weather and research forecasting model was used for planning the instruments installation strategy to understand how large-scale air flow affects evaporation. Instrumentation deployed included: meteorological stations, eddy covariance systems, scintillometers, radiosondes and an unmanned aerial vehicle, and fiber-optic distributed temperature sensing. Additional water quality and CO2 fluxes measurements were carried out to identify the link between meteorological conditions and the biochemical dynamics of Salar del Huasco. Our first results show that, in the study site, evaporation is driven by processes occurring at multiple spatial and temporal scales and that, even in the case of available water and energy, evaporation is triggered by mechanical turbulence induced by wind.

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