Investigating the dynamics of thermally driven up-slope flows: analysis of data from measurements in the Inn Valley (Austria) and comparison with a simple model

2021 ◽  
Author(s):  
Mattia Marchio ◽  
Sofia Farina ◽  
Dino Zardi
Keyword(s):  
Surface Temperature ◽  
Prediction Models ◽  
Weather Prediction ◽  
Slope Angle ◽  
Turbulent Fluxes ◽  
Surface Energy Budget ◽  
Valley Wind ◽  
Slope Winds ◽  
Slope Wind ◽  
Slope Flow

<p><span>Diurnal wind systems typically develop in mountainous areas following the daytime heating and nighttime cooling of sloping surfaces. While down-slope winds have been extensively treated in the literature, up-slope winds have received much less attention. In particular, the physical mechanisms associated with the development of these winds, as well as the search for appropriate parameterization of turbulent fluxes of mass, momentum, and heat over slopes in numerical weather prediction models are still open research topics.</span></p><p><span>Here we present some preliminary results from the analysis of turbulence data (sonic wind speed, temperature, humidity, and turbulent fluxes) collected at two slope stations which are part of the i-Box initiative. The i-Box project (Rotach et al. 2017) aims at studying turbulent exchange processes in complex terrain areas. The experimental setup is composed of six stations disseminated in the surroundings of the alpine city of Innsbruck, in the Inn Valley. The two stations adopted for the present study are located at different points on the valley sidewalls, one with a slope angle of 27° (labelled NF27) and one with a slope angle of 10° (NF10). Both stations are located over slopes covered by alpine meadow and at an altitude of about 1000 m MSL (400 m above the valley floor). The station NF27 has two measurement points, 1.5 and 6.8 m AGL, while the station NF10 has one measurement point, at 6.2 m AGL.</span></p><p><span>The analysis shows that criteria proposed in the literature for the selection of valley-wind days may not apply for the identification of slope-wind days. Furthermore, from the analysis of second order moments, scaling relationships are derived for up-slope flow conditions. In addition, measurements representing the evolution of the up-slope flow structure from the early morning to the mid-afternoon are compared with an existing, simplified, analytical model, which provides the evolution of the vertical profiles of temperature and along-slope wind velocity as generated by a sinusoidal forcing representing the daily cycle of surface temperature. An improvement of the existing model, where the surface energy budget is considered as the boundary condition for the surface temperature, is also tested.</span></p>

scholarly journals Evolution of Late Wintertime Thermally Driven Local Flows and Temperature Fields over Far-Western Nepal

2016 ◽  
Vol 21 (1) ◽  
pp. 35-47
Author(s):  
Ram P. Regmi ◽  
Sangeeta Maharjan
Keyword(s):  
Thermal Environment ◽  
Flow Characteristics ◽  
Temperature Fields ◽  
Valley Wind ◽  
Plain Area ◽  
Slope Winds ◽  
Thermally Driven ◽  
Slope Wind ◽  
Wrf Modeling ◽  
Southern Plain

Atmospheric processes over the Himalayan complex terrain are yet to be studied extensively. Only a few significant researches are reported from this region and the Far-Western Region (FWR) of Nepal still remains untouched. Thus, the present study was conceived to understand the meteorological flow characteristics and thermal environment over the region and associated areas during the late wintertime with the application of the state-of-the-art-of Weather Research and Forecasting (WRF) Modeling System. The study revealed that the northern mountainous region developed strong down slope wind during the night and morning times, which sweeps out the southern plain area of Nepal and may reach just beyond the border. The wind over the plain was very shallow whose depth was just about 100 m. The down slope winds over the southern slope of the Daijee and Nandhaur mountain ranges were significantly enhanced by the subsidence of the southerly wind that prevails above 1 km height above the mean sea level. Close to the noon time a very gentle southerly valley wind from the southern plain replaced the nighttime down slope. Very shallow but strong surface inversion builds up over the plain that breaks up in the late morning. The depth of the mixed layer and the valley wind may reach up to 1km in the afternoon. The thermal environment over the FWR of Nepal was fairly hot that may remain around 35°C in the afternoon around the Mahendranagar area whereas the temperature during the nighttime may go as low as 23°C. The study revealed that, contrary to the general perception, temperature over plain areas of Nepal was significantly higher than further southern areas belonging to India. The meteorological flow fields over the FWR of Nepal executed diurnal periodicity with little day-to-day variation during the late wintertime.Journal of Institute of Science and TechnologyVolume 21, Issue 1, August 2016, page: 35-47

scholarly journals Intercomparison of In Situ Sensors for Ground-Based Land Surface Temperature Measurements

Sensors ◽  
2020 ◽  
Vol 20 (18) ◽  
pp. 5268
Author(s):  
Praveena Krishnan ◽  
Tilden P. Meyers ◽  
Simon J. Hook ◽  
Mark Heuer ◽  
David Senn ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Field Experiments ◽  
Prediction Models ◽  
Weather Prediction ◽  
Surface Air Temperature ◽  
Near Surface ◽  
Oak Ridge

Land surface temperature (LST) is a key variable in the determination of land surface energy exchange processes from local to global scales. Accurate ground measurements of LST are necessary for a number of applications including validation of satellite LST products or improvement of both climate and numerical weather prediction models. With the objective of assessing the quality of in situ measurements of LST and to evaluate the quantitative uncertainties in the ground-based LST measurements, intensive field experiments were conducted at NOAA’s Air Resources Laboratory (ARL)’s Atmospheric Turbulence and Diffusion Division (ATDD) in Oak Ridge, Tennessee, USA, from October 2015 to January 2016. The results of the comparison of LSTs retrieved by three narrow angle broadband infrared temperature sensors (IRT), hemispherical longwave radiation (LWR) measurements by pyrgeometers, forward looking infrared camera with direct LSTs by multiple thermocouples (TC), and near surface air temperature (AT) are presented here. The brightness temperature (BT) measurements by the IRTs agreed well with a bias of <0.23 °C, and root mean square error (RMSE) of <0.36 °C. The daytime LST(TC) and LST(IRT) showed better agreement (bias = 0.26 °C and RMSE = 0.67 °C) than with LST(LWR) (bias > 1.1 and RMSE > 1.46 °C). In contrast, the difference between nighttime LSTs by IRTs, TCs, and LWR were <0.47 °C, whereas nighttime AT explained >81% of the variance in LST(IRT) with a bias of 2.64 °C and RMSE of 3.6 °C. To evaluate the annual and seasonal differences in LST(IRT), LST(LWR) and AT, the analysis was extended to four grassland sites in the USA. For the annual dataset of LST, the bias between LST (IRT) and LST (LWR) was <0.7 °C, except at the semiarid grassland (1.5 °C), whereas the absolute bias between AT and LST at the four sites were <2 °C. The monthly difference between LST (IRT) and LST (LWR) (or AT) reached up to 2 °C (5 °C), whereas half-hourly differences between LSTs and AT were several degrees in magnitude depending on the site characteristics, time of the day and the season.

Uncertainty of Tropical Cyclone Wind Radii on Sea Surface Temperature Cooling

2021 ◽  
Author(s):  
Iam-Fei Pun ◽  
John Knaff ◽  
Charles Sampson
Keyword(s):  
Tropical Cyclone ◽  
Surface Temperature ◽  
Sea Surface Temperature ◽  
Prediction Models ◽  
Weather Prediction ◽  
Sea Surface ◽  
Weather Research And Forecasting ◽  
Translation Speed ◽  
Ocean Stratification ◽  
Sst Cooling

&lt;p&gt;The sea surface temperature (SST) beneath a tropical cyclone (TC) is of great importance to its dynamics; therefore, understanding and accurately estimating the magnitude of SST cooling is of vital importance. &amp;#160;Existing studies have explored important influences on SST such as TC translation speed, maximum surface winds, ocean thermal condition and ocean stratification. &amp;#160;But the influence of the TC wind radii (or collectively called the TC size) on SST has been largely overlooked. &amp;#160;In this study we assess the influence of wind radii uncertainty on SST cooling by a total of 15,983 numerical simulations for the western North Pacific during the 2014-2018 seasons. &amp;#160;Results show a 6-20% SST cooling error induced using wind radii from the Joint Typhoon Warning Center official forecast and a 35-40% SST cooling error using wind radii from the operational runs of the Hurricane Weather Research and Forecasting (HWRF) model. &amp;#160;Our results indicate that SST cooling is most sensitive to the radius of 64 kt winds. &amp;#160;The correlation between SST cooling induced by the TC and its size is 0.49, which is highest among all the parameters tested.&amp;#160; This suggests that it is extremely important to get TC size correct in order to predict the SST cooling response, which then impacts TC evolution in numerical weather prediction models.&lt;/p&gt;

scholarly journals Time-dependent solutions for daily-periodic slope flows driven by surface energy budget

2021 ◽  
Author(s):  
Mattia Marchio ◽  
Sofia Farina ◽  
Dino Zardi
Keyword(s):  
Heat Flux ◽  
Surface Energy ◽  
Surface Temperature ◽  
Wind Velocity ◽  
Analytical Model ◽  
Slope Angle ◽  
Time Dependent ◽  
Fourier Series Expansion ◽  
Ambient Atmosphere ◽  
Slope Wind

&lt;p&gt;Diurnal wind systems generated from daytime heating and nighttime cooling of valleys and slopes are a very common feature over mountainous terrains. Despite their frequent occurrence and relevance for a variety of applications, ranging from pollutant transport to convection initiation, slope winds are far from being fully understood and still provide an open research topic.&lt;/p&gt;&lt;p&gt;A well-known steady-state analytical model &lt;span&gt;is the one&lt;/span&gt; developed by Prandtl (1942). Then, a first time-dependent analytical model was proposed by F. Defant (1949) and later extended by Zardi and Serafin (2015). These models provide slope-normal profiles of temperature and along-slope wind velocity as a response to a sinusoidal forcing representing the surface temperature. The resulting profiles exhibit sinusoidal oscillations at every distance from the surface, although with different phase lags under different regimes, determined by different combinations of slope angle and stability of the unperturbed ambient atmosphere. As a consequence, they can not explain the observed differences between daytime upslope and nighttime downslope winds in terms of magnitude and height of the peak of wind velocity, as well as the different timing characterising nighttime, daytime, and the two reversal phases.&lt;/p&gt;&lt;p&gt;In the present work, the solutions derived in Zardi and Serafin (2015) are extended to include a more realistic daily-periodic surface forcing taking into account the daily evolution of the surface temperature computed on the basis of a surface energy &lt;span&gt;budget&lt;/span&gt;. Incoming solar radiation is represented by means of a Fourier series expansion derived from well-established relationships taking into account latitude, day of the year, slope angle, exposition and other astronomical and atmospheric factors. Based on &lt;span&gt;these&lt;/span&gt; expansions, suitable harmonic solutions are derived for the heat flux into the ground and sensible heat flux in the atmosphere, and hence for the daily evolution of slope-normal profiles of along-slope wind velocity and potential temperature.&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;ul&gt;&lt;li&gt;&lt;span&gt;Prandtl L. 1942. F&amp;#252;hrer durch die Str&amp;#246;mungslehre, Chapter 5. Vieweg und Sohn: Braunschweig, Germany. &lt;/span&gt;[English translation: Prandtl L. 1952. Mountain and valley winds in stratified air, in Essentials of Fluid Dynamics: 422&amp;#8211;425. Hafner Publishing Company: New York, NY]&lt;/li&gt; &lt;li&gt;&lt;span&gt;Defant F. 1949. Zur Theorie der Hangwinde, nebst Bemerkungen zur Theorie der Berg- und Talwinde. &lt;/span&gt;Arch. Meteorol. Geophys. Bioklimatol. A 1: 421&amp;#8211;450&lt;/li&gt; &lt;li&gt;Zardi D., Serafin S. 2015. An analytic solution for time&amp;#8208;periodic thermally driven slope flows. Q. J. R. Meteorol. Soc., 141, 1968&amp;#8211;1974, https://doi.org/10.1002/qj.2485&lt;/li&gt; &lt;/ul&gt;

scholarly journals A New Horizontal Length Scale for a Three-Dimensional Turbulence Parameterization in Mesoscale Atmospheric Modeling over Highly Complex Terrain

2019 ◽  
Vol 58 (9) ◽  
pp. 2087-2102 ◽  
Author(s):  
Brigitta Goger ◽  
Mathias W. Rotach ◽  
Alexander Gohm ◽  
Ivana Stiperski ◽  
Oliver Fuhrer ◽  
...  
Keyword(s):  
Complex Terrain ◽  
Prediction Models ◽  
Mesoscale Model ◽  
Weather Prediction ◽  
Atmospheric Modeling ◽  
Length Scale ◽  
Horizontal Shear ◽  
Valley Wind ◽  
Turbulence Parameterization ◽  
Horizontal Length

AbstractThe correct simulation of the atmospheric boundary layer (ABL) in highly complex terrain is a challenge for mesoscale numerical weather prediction models. An improvement in model performance is possible if horizontal contributions to turbulence kinetic energy (TKE) production, such as horizontal shear production, are implemented in the model’s turbulence parameterization. However, 3D turbulence parameterizations often only have a constant horizontal length scale that depends on the horizontal grid spacing. This is unphysical for mesoscale applications, because such parameterizations were initially developed for much smaller model grid spacings (e.g., for large-eddy simulations). In this study, we develop a new physically based horizontal length scale for the high-resolution mesoscale model COSMO. We analyze days dominated by thermally driven circulations (valley wind days) in the Inn Valley, Austria. Results show that the new horizontal length scale improves TKE simulations in the valley, when horizontal shear processes contribute to the overall TKE budget. Vertical profiles of TKE and transects across the valley indicate that the model simulates the ABL in a more realistic way than standard turbulence schemes, because the new scheme is able to account for terrain inhomogeneities. A model validation with 88 stations in Austria for four case study days indicates no change in the mean surface fields of temperature, relative humidity, and wind speed by the new turbulence parameterization.

scholarly journals Assimilation of Satellite-Observed Snow Albedo in a Land Surface Model

2012 ◽  
Vol 13 (3) ◽  
pp. 1119-1130 ◽  
Author(s):  
M. Jahanzeb Malik ◽  
Rogier van der Velde ◽  
Zoltan Vekerdy ◽  
Zhongbo Su
Keyword(s):  
Land Surface ◽  
Snow Depth ◽  
Prediction Models ◽  
Weather Prediction ◽  
Land Surface Model ◽  
Surface Energy Budget ◽  
Shortwave Radiation ◽  
Surface Model ◽  
Snow Albedo ◽  
The Impact

Abstract This study assesses the impact of assimilating satellite-observed snow albedo on the Noah land surface model (LSM)-simulated fluxes and snow properties. A direct insertion technique is developed to assimilate snow albedo into Noah and is applied to three intensive study areas in North Park (Colorado) that are part of the 2002/03 Cold Land Processes Field Experiment (CLPX). The assimilated snow albedo products are 1) the standard Moderate Resolution Imaging Spectrometer (MODIS) product (MOD10A1) and 2) retrievals from MODIS observations with the recently developed Pattern-Based Semiempirical (PASS) approach. The performance of the Noah simulations, with and without assimilation, is evaluated using the in situ measurements of snow albedo, upward shortwave radiation, and snow depth. The results show that simulations with albedo assimilation agree better with the measurements. However, because of the limited impact of snow albedo updates after subsequent snowfall, the mean (or seasonal) error statistics decrease significantly for only two of the three CLPX sites. Though the simulated snow depth and duration for the snow season benefit from the assimilation, the greatest improvements are found in the simulated upward shortwave radiation, with root mean squared errors reduced by about 30%. As such, this study demonstrates that assimilation of satellite-observed snow albedo can improve LSM simulations, which may positively affect the representation of hydrological and surface energy budget processes in runoff and numerical weather prediction models.

Forecasting of Tornadoes and Downbursts

2020 ◽  
Author(s):  
Djordje Romanic
Keyword(s):  
Chaos Theory ◽  
Prediction Models ◽  
Weather Prediction ◽  
Small Scale ◽  
Weather Forecasts ◽  
Wind Speeds ◽  
The Past ◽  
Extreme Wind ◽  
Extreme Wind Speeds ◽  
Numerical Weather Prediction Models

Tornadoes and downbursts cause extreme wind speeds that often present a threat to human safety, structures, and the environment. While the accuracy of weather forecasts has increased manifold over the past several decades, the current numerical weather prediction models are still not capable of explicitly resolving tornadoes and small-scale downbursts in their operational applications. This chapter describes some of the physical (e.g., tornadogenesis and downburst formation), mathematical (e.g., chaos theory), and computational (e.g., grid resolution) challenges that meteorologists currently face in tornado and downburst forecasting.

scholarly journals HGPT2: An ERA5-Based Global Model to Estimate Relative Humidity

2021 ◽  
Vol 13 (11) ◽  
pp. 2179
Author(s):  
Pedro Mateus ◽  
Virgílio B. Mendes ◽  
Sandra M. Plecha
Keyword(s):  
Water Vapor ◽  
Relative Humidity ◽  
Real Time ◽  
Prediction Models ◽  
Weather Prediction ◽  
Precipitable Water ◽  
Precipitable Water Vapor ◽  
Global Navigation Satellite Systems ◽  
International Gnss Service ◽  
Weighted Mean Temperature

The neutral atmospheric delay is one of the major error sources in Space Geodesy techniques such as Global Navigation Satellite Systems (GNSS), and its modeling for high accuracy applications can be challenging. Improving the modeling of the atmospheric delays (hydrostatic and non-hydrostatic) also leads to a more accurate and precise precipitable water vapor estimation (PWV), mostly in real-time applications, where models play an important role, since numerical weather prediction models cannot be used for real-time processing or forecasting. This study developed an improved version of the Hourly Global Pressure and Temperature (HGPT) model, the HGPT2. It is based on 20 years of ERA5 reanalysis data at full spatial (0.25° × 0.25°) and temporal resolution (1-h). Apart from surface air temperature, surface pressure, zenith hydrostatic delay, and weighted mean temperature, the updated model also provides information regarding the relative humidity, zenith non-hydrostatic delay, and precipitable water vapor. The HGPT2 is based on the time-segmentation concept and uses the annual, semi-annual, and quarterly periodicities to calculate the relative humidity anywhere on the Earth’s surface. Data from 282 moisture sensors located close to GNSS stations during 1 year (2020) were used to assess the model coefficients. The HGPT2 meteorological parameters were used to process 35 GNSS sites belonging to the International GNSS Service (IGS) using the GAMIT/GLOBK software package. Results show a decreased root-mean-square error (RMSE) and bias values relative to the most used zenith delay models, with a significant impact on the height component. The HGPT2 was developed to be applied in the most diverse areas that can significantly benefit from an ERA5 full-resolution model.

Sign in / Sign up

Export Citation Format

Share Document