Land surface temperature variability across India: a remote sensing satellite perspective

Land surface temperature (LST) plays a key role in the surface energy budget computation and land surface process studies. The Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard the Aqua and Terra satellites provide comprehensive global LST estimates at a fine spatial resolution. The MODIS products were recently upgraded to Collection 6, and shown to be more accurate than its predecessor Collection 5 products. In this study, LST and its variability have been examined across India from Collection 6 of the Aqua MODIS data at 0.05° spatial resolution for the period of 2003 to 2017. All-India mean LST characteristics show distinctive features as compared to the well-documented mean characteristics of near-surface air temperature. All land cover types except permanent snow & ice, and cold desert areas exhibit bimodal peaks in seasonal variations of daytime LST. The daytime LST over the coldest and high-altitude regions of northern India shows anomalous positive linear relationship with NDVI at a monthly scale. However, monthly domain-mean daytime LST of cropland regions is largely negatively correlated with NDVI as compared to other land cover types. Results reveal that about 17% of the Indian landmass received its hottest LST during 2010 followed by 2016. Linear trend analysis for the 15-year period of mean annual LST shows a decrease in diurnal temperature range over most parts of the country due to rather rapid increase in nighttime LST than daytime LST, similar as changes in near-surface air temperature across the country

CFD-DEM Investigation on van der Waals Force in Gas-Solid Bubbling Fluidized Beds

Effect of interparticle force on the hydrodynamics of gas-solid fluidized beds was investigated using the combined method of computational fluid dynamics and discrete element method (CFD-DEM). The cohesive force between particles was considered to follow the van der Waals equation form. The model was validated by experimental results from literature in terms of bed voidage distribution and Eulerian solid velocity field. The results revealed that the incorporated model can satisfactorily predict the hydrodynamics of the fluidized bed in the presence of interparticle forces. Effect of interparticle force on the bubble rise characteristics, such as bubble stability, bubble diameter and bubble velocity, was investigated. It was shown that the emulsion voidage increases with increasing the interparticle force in the bed and it can hold more gas inside its structure. In addition, by increasing the interparticle force, size of bubbles and rise velocity of bubbles increase while the average velocity of particles decreases

Experimental Investigation of Hydraulic Parameters of Flow in Sluice Gates with Different Openings

Here, the contraction coefficient, discharge coefficient, hydraulic jump length, and relative energy dissipation in which the gate acts as a supercritical flow generator were investigated at different openings. The maximum value of the contraction coefficient is related to the gate with the lowest amount of opening. The amount of gate opening is inversely related to the discharge coefficient. At a certain discharge, increasing opening leads to a decrease in relative energy dissipation. Moreover, with increasing Froude number, relative energy dissipation increases. Here, the amplitude of the Froude number changed from 2.2 to 14.2, which has a direct effect on the hydraulic jump length, and with increasing opening, the Froude number and jump length decreased. The amount of opening is inversely related to the upstream water depth and the hydrodynamic force applied to the gate. Regression nonlinear polynomial relationships were presented to predict relative energy dissipation and discharge coefficient with appropriate statistical indicators of root mean square error and Kling Gupta. For the discharge coefficient, mdecreasedore than 78% of the data have an error of less than ±1.5%. In addition, for energy dissipation relative to the upstream and downstream, more than 88% of the data have a relative error of less than ±5 and ±1%, respectively

Experimental Investigation of Hydraulic Jump Parameters in Sill Application Mode with Various Synthesis

Here, the effect of sill application on hydraulic jump parameters has been investigated. The model of sills is made of polyethylene in various dimensions. The sills were investigated in different positions relative to the gate in single, double, and triple arrangements. In a certain opening, the sill leads to more energy dissipation. By increasing the ratio of initial depth to sequent depth, the ∆EAB/yA decreases. It occurs due to the convergence of initial and sequent depths. In the under gate suppressed sill state, the ∆EAB/EA is 11.05% more than the upstream tangential position, while it's 14.56% for downstream specific energy. The results showed that the energy dissipation decreases with increasing the opening by at most 34.88%. In the same opening of no-sill and with sill cases, the use of suppressed sill leads to a decrease in the sequent depth compared to the no-sill one. The application of the sill causes an increase in the initial depth and accordingly the initial specific energy decreases; therefore, the sill leads to the reduction of the specific energy in the flow conjugate depths. The regression nonlinear polynomial equations were proposed to estimate the relative energy dissipation. Statistical indicators Relative Error (RE), Root Mean Square Error (RMSE), and Kling Gupta Efficiency (KGE) have been used to check the accuracy of presented equations. The mean RE% and RMSE for presented equation of ∆EAB/EA are 0.78%, and 0.004, respectively. These values are 0.87%, and 0.009 for ∆EAB/EB, respectively. The KGE is in very good range for equations

Sill role effect on the flow characteristics (Experimental and Regression Model analytical)

This study investigates the effects of gate openings and different sill widths on the sluice gate’s energy dissipation and discharge coefficient (Cd). The physical model of the sills includes rectangular sills of different dimensions. The results show that the gate opening size is inversely related to the Cd for a gate without a sill. In addition, increasing the gate opening size for a given discharge decreases the relative energy dissipation, and increasing the Froude number increases the relative energy dissipation. The results also show that the Cd and relative energy dissipation decrease when the width of the sill is decreased, thus increasing the total area of the flux flowing through the sluice gate and vice versa. According to the experimental results, the relative energy dissipation and the Cd of the sluice gate are larger for all sill widths than without the sill. Finally, non-linear polynomial relationships are presented based on dimensionless parameters for predicting the relative energy dissipation and outflow coefficient

Observed Differences between Near-Surface Air and Skin Temperatures Using Satellite and Ground-based Data

Accurate estimates of long-term land surface temperature (Ts) and near-surface air temperature (Ta) at finer spatio-temporal resolutions are crucial for surface energy budget studies, for environmental applications, for land surface model data assimilation, and for climate change assessment and its associated impacts. The Atmospheric Infrared Sounder (AIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) sensors onboard the Aqua satellite provide a unique opportunity to estimate both temperatures twice daily at the global scale. In this study, differences between Ta and Ts were assessed locally over regions of North America from 2009 to 2013 using ground-based observations covering a wide range of geographical, topographical, and land cover types. The differences between Ta and Ts during non-precipitating conditions are generally 2–3 times larger than precipitating conditions. However, these differences show noticeable diurnal and seasonal variations. The differences between Ta and Ts were also investigated at the global scale using the AIRS estimates under clear-sky conditions for the period 2003–2015. The tropical regions showed about 5–20 °C warmer Ts than Ta during the day-time, whereas opposite characteristics (about 2–5 °C cooler Ts than Ta) are found over most parts of the globe during the night-time. Additionally, Ts estimates from the AIRS and the MODIS sensors were inter-compared. Although large-scale features of Ts were essentially similar for both sensors, considerable differences in magnitudes were observed (\u3e6 °C over mountainous regions). Finally, Ta and Ts estimates from the AIRS and MODIS sensors were validated against ground-based observations for the period of 2009–2013. The error characteristics notably varied with ground stations and no clear evidence of their dependency on land cover types or elevation was detected. However, the MODIS-derived Ts estimates generally showed larger biases and higher errors compared to the AIRS-derived estimates. The biases and errors increased steadily when the spatial resolution of the MODIS estimates changed from finer to coarser. These results suggest that representativeness error should be properly accounted for when validating satellite-based temperature estimates with point observations

Numerical Investigation on Effective Parameters on Hydraulic Flows in a Sluice Gate with Sill on Free-Flow Condition

The presence of a sill under the sluice gate is one of the solutions to control the flow rate. This study was conducted to numerically investigate the discharge coefficient (Cd) of sluice gates with different heights and widths of sills in free flow conditions. The simulations were performed using FLOW-3D software. Results show that Cd increases as the gate opening decreases. Also, results showed that reducing the gate opening from 5 cm to 2 cm increases the Cd in the gate with sill by 9% compared to the non-sill gate. Discharge coefficients with 1 cm and 4 cm sills, compared to the non-sill condition were estimated at 1.5% and 18%, respectively. Examination of sill width changes showed that decreasing the width reduces the discharge coefficient by reducing the amount of velocity and flow pressure along the sill sides. The effects of three parameters of the gate opening, sill height, and sill width were compared. The results showed that increasing the sill width compared to the two mentioned parameters has the maximum increase in the Cd