Sunrise Sunset Research Articles

Continuous Leaf Area Index (LAI) Observation in Forests: Validation, Application, and Improvement of LAI-NOS

The leaf area index (LAI) is one of the core parameters reflecting the growth status of vegetation. The continuous long-term observation of the LAI is key when assessing the dynamic changes in the energy exchange of ecosystems and the vegetation’s response indicators to climate change. The errors brought about by non-standard operations in manual LAI measurements hinder the further research utilization of this parameter. The long-term automatic LAI observation network is helpful in reducing errors from manual measurements. To further test the applicability of automatic LAI observation instruments in forest environments, this study carried out comparative validation research of the LAI-NOS (LAI automatic network observation system) at the Wanglang Mountain Ecological Remote Sensing Comprehensive Observation Station, China, comparing it with the results measured by the LAI-2200 Plant Canopy Analyzer (LI-COR, Lincoln, NE, USA), the LAI-probe handheld instrument, and a fisheye lens digital camera (DHP method). Instead of using the original “smoothest window” method, a new method, the “sunrise–sunset” method, is used to extract daily LAI-NOS LAI, and the corresponding confidence level is used to filter the data. The results of the data analysis indicate the following: LAI-NOS has a high data stability. The automatically acquired daily data between two consecutive days has a small deviation and significant correlations. Single-angle/multi-angle LAI measurement results of the LAI-NOS have good correlations with the LAI-2200 (R2 = 0.512/R2 = 0.652), the LAI-probe (R2 = 0.692/R2 = 0.619), and the DHP method (R2 = 0.501/R2 = 0.394). The daily LAI obtained from the improved method, when compared to the original method, both show the same vegetation growth trend. However, the improved method has a smaller dispersion. This study confirms the stability and accuracy of automatic observation instruments in mountainous forests, demonstrating the distinct advantages of automatic measurement instruments in the long-term ground observation of LAIs.

Long-Term Solar Power Time-Series Data Generation Method Based on Generative Adversarial Networks and Sunrise–Sunset Time Correction

Constructing long-term solar power time-series data is a challenging task for power system planners. This paper proposes a novel approach to generate long-term solar power time-series data through leveraging Time-series Generative Adversarial Networks (TimeGANs) in conjunction with adjustments based on sunrise–sunset times. A TimeGAN model including three key components, an autoencoder network, an adversarial network, and a supervised network, is proposed for data generation. In order to effectively capture autocorrelation and enhance the fidelity of the generated data, a Recurrent Neural Network (RNN) is proposed to construct each component of TimeGAN. The sunrise and sunset time calculated based on astronomical theory is proposed for adjusting the start and end time of solar power time-series, which are generated by the TimeGAN model. This case study, using real datasets of solar power stations at two different geographic locations, indicates that the proposed method is superior to previous methods in terms of four aspects: annual power generation, probability distribution, fluctuation, and periodicity features. A comparison of production cost simulation results between using the solar power data generated via the proposed method and using the actual data affirms the feasibility of the proposed method.

Arecibo measurements of D-region electron densities during sunset and sunrise: implications for atmospheric composition

Abstract. Earth's lower ionosphere is the region where terrestrial weather and space weather come together. Here, between 60 and 100 km altitude, solar radiation governs the diurnal cycle of the ionized species. This altitude range is also the place where nanometre-sized dust particles, recondensed from ablated meteoric material, exist and interact with free electrons and ions of the ionosphere. This study reports electron density measurements from the Arecibo incoherent-scatter radar being performed during sunset and sunrise conditions. An asymmetry of the electron density is observed, with higher electron density during sunset than during sunrise. This asymmetry extends from solar zenith angles (SZAs) of 80 to 100∘. This D-region asymmetry can be observed between 95 and 75 km altitude. The electron density observations are compared to the one-dimensional Sodankylä Ion and Neutral Chemistry (SIC) model and a variant of the Whole Atmosphere Community Climate Model incorporating a subset SIC's ion chemistry (WACCM-D). Both models also show a D-region sunrise–sunset asymmetry. However, WACCM-D compares slightly better to the observations than SIC, especially during sunset, when the electron density gradually fades away. An investigation of the electron density continuity equation reveals a higher electron–ion recombination rate than the fading ionization rate during sunset. The recombination reactions are not fast enough to closely match the fading ionization rate during sunset, resulting in excess electron density. At lower altitudes electron attachment to neutrals and their detachment from negative ions play a significant role in the asymmetry as well. A comparison of a specific SIC version incorporating meteoric smoke particles (MSPs) to the observations revealed no sudden changes in electron density as predicted by the model. However, the expected electron density jump (drop) during sunrise (sunset) occurs at 100∘ SZA when the radar signal is close to the noise floor, making a clear falsification of MSPs' influence on the D region impossible.

Understanding how diel and seasonal rhythms affect the movements of a small non‐migratory bird

AbstractDiel and seasonal rhythms affect an animal's environment and life history. Understanding how these rhythms influence movement increases our knowledge on how animals adjust to changing resources, environmental conditions, and risk to their survival. To better understand how diel and seasonal rhythms affect animals, we evaluated movements of Northern Bobwhite (Colinus virginianus, hereafter bobwhite). Because bobwhite are a small non‐migratory species that must cope with daily and seasonal changes in their environment year‐around, they are a model species to study how diel and seasonal rhythms influence animal movement of a non‐migratory species. GPS data from transmitters attached to bobwhite at four wildlife management sites across Oklahoma were collected during 2019–2021. We parsed the diel data as daytime (7:00 AM–7:00 PM Central Daylight Savings Time [CDT]) and nighttime (7:00 PM–7:00 AM CDT), and diurnal (sunrise–sunset) and nocturnal (sunset–sunrise), as well as by astronomical season. We calculated three movement metrics: net displacement (Euclidean distance from the starting fix to the ending fix of a path, which encompasses consecutive relocations in a time series of geographic fixes); cumulative distance (sum of all Euclidean distances between each consecutive fix along the path); and hourly movement. We modeled the data using a generalized linear mixed modeling approach. Across season, model predictions showed that net displacement was highest during spring, and daytime cumulative distance slowly increased as the year progressed. Bobwhite had two movement peaks during the diurnal period, one during 9:00 AM–10:00 AM and the other during 5:00 PM–8:00 PM depending on the season. Despite being diurnal, bobwhite occasionally made nocturnal movements, likely in response to a disturbance by a predator, inclement weather, or energetic demands. Movement peaks during the diurnal period may reflect changes in behavior in response to energy requirements, predator risk, and changes in air temperature. Life history events likely cause seasonal differences in movement. This study furthers our understanding of how animals move daily and seasonally, suggesting the importance of analyzing movement across the entire year because animals move differently across the day and year.

ELIFAN, an algorithm for the estimation of cloud cover from sky imagers

Abstract. In the context of a network of sky cameras installed on atmospheric multi-instrumented sites, we present an algorithm named ELIFAN, which aims to estimate the cloud cover amount from full-sky visible daytime images with a common principle and procedure. ELIFAN was initially developed for a self-made full-sky image system presented in this article and adapted to a set of other systems in the network. It is based on red-to-blue ratio thresholding for the distinction of cloudy and cloud-free pixels of the image and on the use of a cloud-free sky library, without taking account of aerosol loading. Both an absolute (without the use of a cloud-free reference image) and a differential (based on a cloud-free reference image) red-to-blue ratio thresholding are used. An evaluation of the algorithm based on a 1-year-long series of images shows that the proposed algorithm is very convincing for most of the images, with about 97 % of relevance in the process, outside the sunrise and sunset transitions. During those latter periods, however, ELIFAN has large difficulties in appropriately processing the image due to a large difference in color composition and potential confusion between cloud-free and cloudy sky at that time. This issue also impacts the library of cloud-free images. Beside this, the library also reveals some limitations during daytime, with the possible presence of very small and/or thin clouds. However, the latter have only a small impact on the cloud cover estimate. The two thresholding methodologies, the absolute and the differential red-to-blue ratio thresholding processes, agree very well, with departure usually below 8 % except in sunrise–sunset periods and in some specific conditions. The use of the cloud-free image library gives generally better results than the absolute process. It particularly better detects thin cirrus clouds. But the absolute thresholding process turns out to be better sometimes, for example in some cases in which the sun is hidden by a cloud.

Performance of Landscape Roses Grown with Minimal Input in the North-central, Central, and South-central United States

Landscape roses (Rosa sp.) are popular flowering shrubs. Consumers are less willing or able to maintain landscape beds than in years past and require plants that are not only attractive, but well-adapted to regional climatic conditions, soil types, and disease and pest pressures. Marketing and distribution of rose cultivars occurs on a national level; therefore, it is difficult for U.S. consumers in the U.S. Department of Agriculture (USDA) Plant Hardiness Zones 3 to 5 to identify well-adapted, cold-hardy cultivars. Identifying suitable cultivars that have strong genetic resistance to pests and disease and that will tolerate temperature extremes without winter protection in the USDA Plant Hardiness Zones 3 to 5 is of tremendous value to consumers and retailers in northern states. Twenty landscape rose cultivars, primarily developed in north-central North America, were evaluated at five locations in the United States (three in the north-central United States, one in the central United States, and one in the south-central United States) using the low-input, multiyear Earth-Kind® methodology. Six roses had ≥75% plant survival at the end of the study and were in the top 50% of performers for overall mean horticultural rating at each of the three north-central U.S. sites: ‘Lena’, ‘Frontenac’, ‘Ole’, ‘Polar Joy’, ‘Sunrise Sunset’, and ‘Sven’. Five of these six roses met the same criteria at the central United States (exception ‘Lena’) and the south-central United States (exception ‘Polar Joy’) sites. Cultivar, rating time, and their interaction were highly significant, and block effects were not significant for horticultural rating for all single-site analyses of variance. Significant positive correlations were found between sites for flower number, flower diameter, and overall horticultural rating. Significant negative correlations were found between flower number and diameter within each site and also between black spot (Diplocarpon rosae) lesion size from a previous study and overall horticultural rating for three of the five sites. Cane survival ratings were not significantly correlated with overall horticultural rating, suggesting some cultivars can experience severe winter cane dieback, yet recover and perform well. Data from this study benefit multiple stakeholders, including nurseries, landscapers, and consumers, with evidence-based regional cultivar recommendations and breeders desiring to identify regionally adapted parents.

A kinetic Monte Carlo simulation of film growth by physical vapor deposition on rotating substrates

Abstract Film growth by physical vapor deposition on rotating substrates is modeled via a kinetic Monte Carlo algorithm on a two-dimensional hexagonal lattice. The motivation is to provide insight on the evolution of porosity during the deposition of thermal barrier coatings (TBCs). The model is implemented on an atomic scale that incorporates the effect of surface diffusion as well as the interplay between surface topography and the changing vapor incidence angle. It is shown that substrate rotation generates voids with a periodicity dependent on the amount of material deposited per revolution. The onset of pore formation and morphology of the pores are linked to the presence of shadowing features on the surface, either in the form of stochastic or crystallographic peaks and valleys evolving during columnar growth, or pre-existing roughness typical of polycrystalline oxide substrates. In addition, various forms of anisotropy develop in the microstructure as a result of the “sunrise–sunset” pattern of vapor incidence characteristic of TBC deposition on, for example, turbine airfoils. Comparison with observations on actual TBCs reveals that the simulations, in spite of their simplicity, capture several key microstructural features characteristic of these complex films.

Microstructure and texture of EB-PVD TBCs grown under different rotation modes

The role of vapor incidence pattern (VIP) on the microstructure and texture of thermal barrier coatings (TBCs) produced by electron-beam physical vapor deposition (EB-PVD) is examined. Two distinct VIPs are induced by proper design of the substrate rotation mode. One is the sunrise–sunset pattern typical of conventional deposition on the curved face of a rotating cylinder (mode A), and the other is a conical pattern resulting when deposition is done on the cylinder base at an offset distance from the plume axis (mode P). These geometries afford fundamental insight on the processes of microstructure and texture evolution and also have practical implications to the variability of properties that may be expected between the body and platform regions of a turbine airfoil. Comparable deposition rates and thickness uniformity can be achieved by proper selection of the experimental geometry. Both coatings exhibit the typical 〈100〉 texture normal to the substrate, but mode A also yields a preferred in-plane orientation which is absent in mode P. The ensuing differences in column packing and tip shadowing yield lower densities and larger pipe-like inter-columnar voids in mode P. The absence of an in-plane evolutionary selection mechanism in the latter also leads to narrower columns than in mode A.

Surface Temperature Related Variations in Tropical Cirrus Cloud as Measured by SAGE II

Data from the Stratospheric Aerosol and Gas Experiment II (SAGE II) solar occultation satellite instrument have been used to study the properties of tropical cloud over the altitude range 10.5–18.5 km. By virtue of its limb viewing measurement geometry, SAGE II has good vertical resolution and sensitivity to subvisual cloud not detectable by most other satellite instruments. The geographical distribution and temporal variation of the cloud occurrence have been examined over all longitudes on timescales from less than 1 day to that of the El Niño-Southern Oscillation (ENSO) cycle. Significant variations in cloud occurrence are found on each of these scales and have been compared with the underlying surface temperature changes. Maximum cloud occurs over the warm pool region of the Pacific Ocean, with secondary maxima over the South American and Central African landmasses, where the percentage of cloud occurrence in the upper troposphere can exceed 75%. Cloud occurrence at all altitudes within the Tropics, over both land and ocean, increases with the underlying surface temperature at a rate of approximately 13%°C−1. Extrapolated threshold temperatures for the formation of cloud are about 5°C lower than those found from nadir viewing observations. This difference is believed to be a consequence of the averaging process and the inclusion of outliers in the dataset. ENSO cycle changes in cloud occurrence are observed, not only over the Tropics but also over the subtropics, indicating a difference in the meridional Hadley circulation between ENSO warm and cold years. Sunrise–sunset cloud differences indicate that large-scale variations, whose form resembles that of the Hadley and Walker circulations, are present, with a timescale of 1 day or less. The global distribution of upper-tropospheric ice and its positive correlation with surface temperature on all timescales are generally consistent with the behavior of lightning and the global electrical circuit.

Tropical behavior of mesospheric ozone as observed by SMM

The seasonal behavior of low latitude mesospheric ozone, as observed by the SMM satellite solar occultation experiment, is detailed for the 1985–1989 period. Annual as well as semi-annual waves are observed in the 50–70 km altitude region. In the latitude range of ±30 the ozone phase and amplitude are functions of temperature and seasonal changes in solar flux. Temperature is the controlling factor for the equatorial region and seasonal changes in solar flux become more dominant at latitudes outside the equatorial zone (greater than ±15). There is a hemispheric asymmetry in the ozone annual wave in the 20 30 region, with northern hemispheric ozone having a larger amplitude than southern hemispheric ozone. In this region temperature is nearly in phase with ozone in both hemispheres and is reduced in amplitude in the northern hemisphere. The equatorial region is characterized by a strong semi-annual wave in addition to the annual variation, and temperature is nearly out of phase with ozone. At all latitudes there is a larger ozone concentration at sunrise than at sunset. The sunrise sunset difference increases with increasing altitude

The Night Sky in January

THE moon is full on January 2d. 15h. 42m. U.T. and new on January 16d. 21h. 32m. Lunar conjunctions with the planets occur on the following dates: Mercury on January 18d. 5h., Mercury 4°S.; Venus on January 18d. 13h., Venus 2° N.; Mars on January 24d. 8h., Mars 5° N.; Saturn on January 25d. 17h., Saturn 3° N.; Jupiter on January 27d. 10h., Jupiter 5° KT. On January 2 id. Ih. Mercury is in. conjunction with Venus, Mercury being 6.2° S. Mars, Jupiter and Saturn are well placed for observation during the night, and Saturn's ring system is well presented for observation. Venus can be seen in the evening hours in the west and does not set until 19h. in the middle of the month. The earth makes its closest approach to the sun on January 2. The Quadrantid meteor shower is active on the first few days of January: the radiant is at R.A. 5h. 24m., Dec. 51° N., but this shower is not usually very conspicuous. On January 26d. 22h. 17m. there will be an occultation of y Tauri, mag. 3-9. During the month the interval from sunsetto sunrise in the latitude of London shortens by 1h. 12m.