Sunset Hours Research Articles

A Model for Hourly Solar Radiation Data Generation from Daily Solar Radiation Data Using a Generalized Regression Artificial Neural Network

This paper presents a model for predicting hourly solar radiation data using daily solar radiation averages. The proposed model is a generalized regression artificial neural network. This model has three inputs, namely, mean daily solar radiation, hour angle, and sunset hour angle. The output layer has one node which is mean hourly solar radiation. The training and development of the proposed model are done using MATLAB and 43800 records of hourly global solar radiation. The results show that the proposed model has better prediction accuracy compared to some empirical and statistical models. Two error statistics are used in this research to evaluate the proposed model, namely, mean absolute percentage error and root mean square error. These values for the proposed model are 11.8% and −3.1%, respectively. Finally, the proposed model shows better ability in overcoming the sophistic nature of the solar radiation data.

On the Diurnal Dependence of <i>f<sub>b</sub>E<sub>s</sub></i>-Variations Due to Earthquakes

In the present work, disturbances of the half-transparency frequency fbEs of the ionospheric sporadic E-layer are investigated in connection with earthquakes. The fbEs-frequency is proportional to the square root of the maximum ionisation density of the sporadic E-layer. In this work, it is shown that in 2/3 of the cases, two days before a seismic shock with magnitude M > 5.5 and on the day of the shock, an increase of the fbEs-frequency is obtained at sunset hours at distances from the epicenter R km. In contrast, before sunrise, the fbEs-value decreases. The data analysed are obtained by the three vertical ionospheric sounding stations“Kokubunji”, “Yamagawa”, and “Wakkanai” during some tens of years.

Ionospheric vertical drifts over an Indian low latitude station and its comparison with IRI-2007 vertical drift model

The vertical plasma drift velocity (Vz=dh′Fdt) of the Ionospheric F-Region is calculated using the Ionosonde data over an Indian low latitude station, Waltair (17.7°N, 83.3°E, dip 20°N). The vertical drift velocities thus computed are compared with those of the IRI-2007 vertical drift model during the post sunset hours of the high sunspot period of 2001–2002. The vertical drift values are entirely downward between 2000 and 0700hLT for the IRI-2007 vertical drift model compared to those derived using Ionosonde. The root mean square errors (RMSE) in the vertical drifts during the post sun-set hours computed between the IRI vertical drift model and Ionosonde measured values are found to be 13.54, 21.68 and 22.39m/s for summer, equinox and winter seasons respectively. The average vertical drifts derived using Ionosonde showing pre-reversal enhancements during evening hours (1700–1900hLT) over Waltair are found to be 8, 16 and 12m/s, whereas the IRI-2007 model derived values show 15, 35 and 36m/s during summer, equinox and winter seasons respectively. The correlation analysis of peak drift velocities derived using Ionosonde and those from IRI model with Rz and F10.7 shows more or less similar variation while they are differed in their variation with Ap index. A good correlation is observed between the vertical plasma drift obtained using Ionosonde and Equatorial Electrojet Strength (EEJ) except during winter, while the correlation coefficients computed using IRI model are little higher than those obtained using Ionosonde with maximum values during summer season. The percentage of deviation for IRI-model correlation coefficient and that of Ionosonde-inferred drift for equinoctial and summer months is around 50% and 25% respectively where as it is more than 100% for winter.

Traveling planetary wave ionospheric disturbances and their role in the generation of equatorial spread-F and GPS phase fluctuations during the last extreme low solar activity and comparison with high solar activity

This investigation studies traveling planetary wave ionospheric disturbance (TPWID) type oscillations on the modulation of the F region virtual height rise during the E×B electric field pre-reversal enhancement (PRE), near sunset hours. We also studied their role in the generation of equatorial spread F (ESF) and GPS phase fluctuations during periods of the last extreme low solar activity (LSA) of January 2009 to April 2010 (F10.7¯=73). A comparison is made with periods of high solar activity (HSA) in 2003 and 2004 near equatorial region. The ionospheric irregularities investigated are medium (bottom-side) and large (plasma bubble) scales. Ionospheric F region oscillations with period of days are due to the TPWIDs, which play an important role in producing favorable or unfavorable conditions for equatorial ionospheric irregularities, changing the electron vertical profile and F region height. In this paper, we present simultaneous ionospheric sounding (ionosonde) and GPS vertical total electron content (vTEC) observations carried out near equatorial region (Palmas 10.2°S, 48.2°W) and low latitude region (São José dos Campos 23.2°S, 45.9°W; located under the southern crest of the equatorial ionospheric anomaly), Brazil. Observations show that the occurrence of fresh ESF during LSA and HSA and fresh GPS phase fluctuations at equatorial region follow the trend of day-to-day variations in the F region virtual height, which are due to electric field PRE modulated by TPWID wave like oscillations. During LSA, the altitude of 250km acts as a threshold height for the generation of fresh ionospheric irregularities, whereas during HSA, the threshold height is 300km. The observations also found a strong increase in the generation of fresh ionospheric irregularities from October 2009 to March 2010 during LSA and from September 2003 to March 2004 during the HSA. Furthermore, in LSA, the period of fresh ionospheric irregularities was less than during HSA, though both periods followed a similar seasonal pattern. In the low-latitude, we observed more ESFs than phase fluctuations because ionosonde is more sensitive than GPS. We also observed periods with and without day-to-day oscillations in the F region virtual height. The observations made by GPS stations and ionosondes in the equatorial region, for much of the period analyzed, presented similar results with regard to the generation of equatorial ionospheric irregularities. In the low latitude, some nights of January, February, October, and December 2009 also showed a similarity.

A Comparison of Passive and Active Acoustic Sampling for a Bat Community Impacted by White-Nose Syndrome

Abstract In the summers of 2011 and 2012, we compared passive and active acoustic sampling for bats at 31 sites at Fort Drum Military Installation, New York. We defined active sampling as acoustic sampling that occurred in 30-min intervals between the hours of sunset and 0200 with a user present to manipulate the directionality of the microphone. We defined passive sampling as acoustic sampling that occurred over a 12-h period (1900–0700 hours) without a user present and with the microphone set in a predetermined direction. We detected seven of the nine possible species at Fort Drum, including the federally endangered Indiana bat Myotis sodalis, the proposed-for-listing northern bat M. septentrionalis, the little brown bat M. lucifugus, and the big brown bat Eptesicus fuscus, which are impacted by white-nose syndrome (WNS); and the eastern red bat Lasiurus borealis, the hoary bat L. cinereus, and the silver-haired bat Lasionycteris noctivagans, which are not known to be impacted by WNS. We did not detect two additional WNS-impacted species known to historically occur in the area: the eastern small-footed bat Myotis leibii and the tri-colored bat Perimyotis subflavus. Single-season occupancy models revealed lower detection probabilities of all detected species using active sampling versus passive sampling. Additionally, overall detection probabilities declined in detected WNS-impacted species between years. A paired t-test of simultaneous sampling on 21 occasions revealed that overall recorded foraging activity per hour was greater using active than passive sampling for big brown bats and greater using passive than active sampling for little brown bats. There was no significant difference in recorded activity between methods for other WNS-impacted species, presumably because these species have been so reduced in number that their “apparency” on the landscape is lower. Finally, a cost analysis of standard passive and active sampling protocols revealed that passive sampling is substantially more cost-effective than active sampling per hour of data collection. We recommend passive sampling over active sampling methodologies as they are defined in our study for detection probability and/or occupancy studies focused on declining bat species in areas that have experienced severe WNS-associated impacts.

Trends and variations in the baseline soundscape of America’s first offshore wind farm

With the development of Cape Wind, Nantucket Sound, Massachusetts may become home to America’s first offshore wind farm. The goal of this ongoing project is to establish the baseline (pre-construction) soundscape of anthropogenic and biological activity, including diel and seasonal variability of various sound types, at the construction site and nearby comparison sites. Acoustic recorders have been deployed since April 2012, recording on a 10% duty cycle (sample rate: 80 kHz). Multiple fish sounds have been identified with the predominant signals attributed to cusk eels (Family Ophidiidae). Cusk eel sounds consist of a series of pulses, with energy between 400 and 2500 Hz. They are detectable from April to October, with dense choruses occurring during the summer months. Sound energy levels during these choruses increased near the hours of sunrise and sunset. Vessel traffic also showed diel and seasonal trends, with peaks during the daytime and in the summer. These trends in biological and human activity provide key baseline records for evaluating the possible influence of wind farm construction and operation on a local US soundscape.

X-rays and solar proton event induced changes in the first mode Schumann resonance frequency observed at a low latitude station Agra, India

Effects of two events of X-ray bursts followed by solar proton events (SPEs) occurred on 22 September, 2011 and 06 July, 2012 on the variation of first mode Schumann resonance (SR) frequency monitored at a low latitude station, Agra (Geograph. lat. 27.2°N, long. 78°E) India are examined. The variation of average first mode SR frequency shows a sudden increase in coincidence with the X-ray bursts and a decrease associated with the peak flux of SPE. The increases in the frequency in the two cases are 8.4% and 10.9% and corresponding decreases are 4.3% and 3.3% respectively. The increases in the frequency are interpreted in terms of growth of ionization in the upper part of D-region ionosphere due to X-ray bursts and decreases during SPE are caused by the high ionization in the lower D-region (altitude about 50–60km) in the polar region. The variation of SR frequency is observed to be consistent with other observatories at middle and high latitudes. The effects of X-ray flares on the D-region of the ionosphere at low and equatorial latitudes are also examined by analyzing the amplitude data of VLF transmitter signal (NWC, f=19.8kHz) monitored at Agra. The flare effect observed prior to sun-set hours shows increase of electron density above 60km in the ionosphere.

The role of electric fields in sporadic E layer formation over low latitudes under quiet and magnetic storm conditions

Sporadic E layers are formed dominantly by wind shear mechanism, but their formation and dynamics are driven also by ionospheric electric fields. Investigation of low latitude sporadic E layers under quiet conditions shows that Es layer formation during post sunset hours can be disrupted or enhanced depending upon the vertical structure of the vertical electric field arising from sunset electrodynamic processes. During magnetic storms the formation and disruption of these layers are also strongly controlled by vertical Hall electric field induced by the zonal magnetospheric electric fields that penetrates to equatorial/low latitude ionosphere. Observational results on storm time Es layer responses in the Brazilian and Indian-Asian longitudes are compared. An under-shielding prompt penetration electric field (PPEF) of westward polarity that dominate the night side ionosphere, or an over-shielding electric field also of westward polarity in the evening sector can cause formation of sporadic E layers near 100km, while an eastward polarity electric field, (under-shielding/over-shielding depending upon local time) can lead to disruption of an Es layer in progress. Ionization convergence/divergence leading to the Es layer formation/disruption is driven by a vertical Hall electric field, induced by the primary zonal PPEF, in the presence of storm associated enhanced ratio of field line integrated Hall to Pedersen conductivity (∑H)/(∑P). A downward polarity of the Hall electric field leads to Es layer formation, while an upward polarity causes the Es layer disruption. An enhancement in the ∑H/∑P ratio can result from E layer conductivity enhancement due to energetic particle precipitation peculiar to the longitude of the South Atlantic Magnetic Anomaly (SAMA) and/or from a drastic reduction in integrated Pederson conductivity in the form of reduced foF2 that is observed in all longitudes.

The variability and IRI2007-predictability of hmF2 over South Africa

This paper presents an investigation into the variability and predictability of the maximum height of the ionospheric F2 layer, hmF2 over the South African region. Data from three South African stations, namely Madimbo (22.4°S, 26.5°E, dip angle: −61.47°), Grahamstown (33.3°S, 26.5°E, dip angle: −64.08°) and Louisvale (28.5°S, 21.2°E, dip angle: −65.44°) were used in this study. The results indicate that hmF2 shows a larger variability around midnight than during the daytime for all seasons. Monthly median hmF2 values were used in all cases and were compared with predictions from the IRI-2007 model, using the URSI (Union Radio-Scientifique Internationale) coefficient option. The analysis covers the diurnal and seasonal hourly hmF2 values for the selected months and time sectors e.g. January, July, April and October for 2003 and 2005. The time ranges between (03h00–23h00UT; LT=UT+2h) representing the local sunrise, midday, sunset and midnight hours. The time covers sunrise, midday, sunrise, and midnight hours (03–06h00UT, 07–11h00UT, sunrise 16–18h00UT and 22–23h00UT; LT=UT+2h). The dependence of the results on solar activity levels was also investigated. The IRI-2007 predictions follow fairly well the diurnal and seasonal variation patterns of the observed hmF2 values at all the stations. However, the IRI-2007 model overestimates and underestimates the hmF2 value during different months for all the solar activity periods.

On the nature of low‐latitude Es influencing the genesis of equatorial plasma bubble

The potential influence of the postsunset low‐latitude sporadic E (Es) on the genesis of equatorial plasma bubble (EPB) has been investigated using observations made with the Gadanki radar and two ionosondes, one located at the magnetic equator providing the F layer characteristics and another at magnetically low‐latitude providing the Es parameters. Observations revealed that the occurrence of EPB was associated with either the disruption of Es or presence of nonblanketing‐type Es or intermittently occurring blanketing Es at low‐latitude. In contrast, when blanketing Es occurred for a relatively long duration in the sunset hours, EPB did not occur. Model computation clearly reveals that the growth of the Rayleigh‐Taylor instability depends very much on the thickness, height, and shape of electron density profile of the Es layer. The above findings thus suggest that low‐latitude Es variability plays decisive role on the day‐to‐day variability of EPB through the growth rate of the Rayleigh‐Taylor instability.

Low latitude ionospheric scintillation and zonal irregularity drifts observed with GPS-SCINDA system and closely spaced VHF receivers in Kenya

In this study we have used VHF and GPS-SCINDA receivers located at Nairobi (36.8°E, 1.3°S, dip −24.1°) in Kenya, to investigate the ionospheric scintillation and zonal drift irregularities of a few hundred meter-scale irregularities associated with equatorial plasma density bubbles for the period 2011. From simultaneous observations of amplitude scintillation at VHF and L-band frequencies, it is evident that the scintillation activity is higher during the post sunset hours of the equinoctial months than at the solstice. While it is noted that there is practically no signatures of the L-band scintillation in solstice months (June, July, December, January) and after midnight, VHF scintillation does occur in the solstice months and show post midnight activity through all the seasons. VHF scintillation is characterized by long duration of activity and slow fading that lasts till early morning hours (05:00LT). Equinoctial asymmetry in scintillation occurs with higher occurrence in March–April than in September–October. The occurrence of post midnight VHF scintillation in this region is unusual and suggests some mechanisms for the formation of scintillation structure that might not be clearly understood. Zonal drift velocities of irregularities were measured using cross-correlation analysis with time series of the VHF scintillation structure from two closely spaced antennas. Statistical analyses of the distribution of zonal drift velocities after sunset hours indicate that the range of the velocities is 30–160m/s. This is the first analysis of the zonal plasma drift velocity over this region. Based on these results we suggest that the east–west component of the plasma drift velocity may be related to the evolution of plasma bubble irregularities caused by the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocities and scintillation could be attributed to the asymmetry of neutral winds in the thermosphere that drives the eastward electric fields.

Delayed effects of annular solar eclipse of 15 January 2010 on the tropospheric and lower stratospheric winds along the eclipse path

The annular solar eclipse of 15th January 2010, which was the longest solar eclipse of the millennia, was visible at several parts of South India and China. A host of experiments were carried out at Thumba (8.5° N, 76.9°E) and Gadanki (13.51° N, 79.21° E) in India to study the effect of annular solar eclipse on various atmospheric processes taking place right from surface layer to Ionosphere as the maximum obscuration of the Sun took place during the peak noon hours. Many of the studies reported from these experiments focused on the effect of annular solar eclipse on the geophysical parameters and their variability during the maximum phase of the eclipse. However, there were no efforts to study the delayed effects of the annular solar eclipse on the geophysical parameters. In this regard, the present study discuss the delayed effect (~4hours after the maximum phase of the eclipse) of annular solar eclipse of 15th January 2010 on the troposphere and lower stratosphere winds over the eight geographical locations along the eclipse path [Thumba, Qingdao (36.06° N, 120.33°E), Zhengzhoes (34.71° N, 113.65°E), Enshi (30.28° N, 109.46°E), Chongqing (29.51° N, 106.48°E), Sheyang (33.76° N, 120.25°E), Fuyang (32.86° N, 115.73°E) and Weining (26.86° N, 104.28°E)]. The regular meteorological soundings over these eight locations at 12 UTC are utilized for the present study. The important difference between the observations over Thumba and other latitudes is the local time of occurrence of maximum phase of the eclipse. Over the Thumba the maximum phase of the annular eclipse observed in the mid-day whereas it is observed during the sunset hours over other latitudes. The analysis revealed that significant changes in zonal and meridional winds occurred only over Thumba, but not showed any significant changes over the other latitudes. The results are discussed in the light of present understanding of the eclipse induced atmospheric perturbations.

Comparison of GPS TEC variations with IRI-2007 TEC prediction at equatorial latitudes during a low solar activity (2009–2011) phase over the Kenyan region

This work presents an analysis of the Total Electron Content (TEC) derived from the International GNSS Service (IGS) receivers at Malindi (mal2: 2.9oS, 40.1oE, dip −26.813o), Kasarani (rcmn: 36.89oE, 1.2oS, dip −23.970o), Eldoret (moiu: 35.3oE, 0.3oN, dip −21.037o) and GPS-SCINDA (36.8oE, 1.3oS, dip −24.117o) receiver located in Nairobi for the period 2009–2011. The diurnal, monthly and seasonal variations of the GPS derived TEC (GPS-TEC) and effects of space weather on TEC are compared with TEC from the 2007 International Reference Ionosphere model (IRI-TEC) using the NeQuick option for the topside electron density. The diurnal peaks in GPS-TEC is maximum during equinoctial months (March, April, October) and in December and minimum in June solstice months (May, June, July). The variability in GPS-TEC is minimal in all seasons between 0:00 and 04:00 UT and maximum near noon between 10:00 and 14:00 UT. Significant variability in TEC at post sunset hours after 16:00 UT (19:00 LT) has been noted in all the seasons except in June solstice. The TEC variability of the post sunset hours is associated with the occurrence of the ionization anomaly crest which enhances nighttime TEC over this region. A comparison between the GPS-TEC and IRI-TEC indicates that both the model and observation depicts a similar trend in the monthly and seasonal variations. However seasonal averages show that IRI-TEC values are higher than the GPS-TEC. The IRI-TEC also depicts a double peak in diurnal values unlike the GPS-TEC. This overestimation which is primarily during daytime hours could be due to the model overestimation of the equatorial anomaly effect on levels of ionospheric ionization over the low latitude regions. The IRI-TEC also does not show any response to geomagnetic activity, despite the STORM option being selected in the model; the IRI model generally remains smooth and underestimates TEC during a storm. The GPS-TEC variability indicated by standard deviation seasonal averages has been presented as a basis for extending the IRI-model to accommodate TEC-variability.

Study of disturbance dynamo effects at nighttime equatorial F region in Indian longitude

[1] Post sunset height of F layer may significantly increase or decrease as compared to their monthly quiet time pattern due to superimposed disturbed time electric field associated with either disturbance dynamo (DD) or prompt penetration (PP) or combination of both DD and PP. In this paper, the effects associated with disturbed time eastward electric field causing upward movement of F layer in the post sunset hours are investigated. Ionosonde data recorded at dip equatorial station Trivandrum for the period of 1990–2003 are scaled to obtain the variation of h′F from 17-31LT. Effect of magnetic activity on h′F (ΔH) is obtained by subtracting monthly quiet time average of h′F from disturbed time h′F. The maximum enhancement seen in h′F i.e ΔHmax provides the quantitative estimate of maximum effect of magnetic activity at equatorial F region. Here 97 magnetically disturbed days with ΔHmax ≥ 80 km are studied. Geomagnetic activity index ap is used along with AE and attempt has been made to identify the effects associated with short and long term DD electric field. It is found that the duration of short and long term DD effects seen at equatorial F region decreases with increase in solar flux. However this dependence is not applicable close to early morning hours (≥ 05LT). Time delays required to produce maximum effect at equatorial F region during high solar flux are found to be 16–23 hrs (0.5–4 hrs) for long (short) term DD effects studied here.

Why tropical sorghum sown in winter months has delayed flowering and modified morphogenesis in spite of prevailing short days

Sowing certain late photoperiod-sensitive tropical sorghum varieties under short-day conditions in November–January in the northern hemisphere can result in a pronounced delay in flowering and prostrate, high-tillering forms similar to the rosettes in winter small-grain cereals. The cause of this phenomenon in sorghum has long been questioned and is often attributed to the effects of low night temperatures during this period. Monthly sowings, from December to March, in greenhouse compartments with two contrasting night temperatures and under field conditions with contrasting soil conditions were conducted over two years near Bamako, Mali, with three contrasting sorghum varieties. Dates of panicle initiation, rates of leaf primordia initiation at the stem apex, and rates of leaf appearance were observed. In the greenhouse, colder night temperatures were found to have no effect on prolonging vegetative-phase duration when measured in thermal time and on plant development. Although a prolonged vegetative phase and prostrate forms were observed under field conditions, these were not observed in the greenhouse experiments despite having similar temperature conditions. Although the higher soil fertility of the potting soil increased the development rates slightly, and reduced the vegetative phase relative to natural soil conditions in the field, this difference between greenhouse and field growth remained when a comparison was made between plants grown in pots. Thus, it appears that the greenhouse glass had masked the UV component of sunlight, which would mediate the cue responsible for the delayed flowering and modified morphogenesis. This cue, which has strongly contrasting effects between October and November sowings, could be the daily changes in the sunrise and sunset hour that have negative values from November to July.

Variation of ionospheric slab thickness observations at Chumphon equatorial magnetic location

This study presents the diurnal and seasonal variations of slab thickness at the equatorial magnetic latitudes in Thailand during 2004–2006, corresponding to the declining part of low solar activity. The GPS-derived total electron content (TEC) and the maximum electron density of the F-region (NmF2) are used to compute the slab thickness (τ) at the Chumphon station (10.72°N, 99.37°E), located near the magnetic equator. The results show that large peaks of slab thickness exist during the pre-sunrise hours in all three seasons at Chumphon when compared with other latitudes. The maximum value of slab thickness occurs when the peak electron density in the F2 region is at the lowest level. During daytime, the slab thickness ranges from 200 kilometers to 580 kilometers for all seasons. During nighttime, the maximum value of slab thickness is 1250 kilometers in the summer of 2004. Moreover, the diurnal variation shows two minima that appear around 0900 LT and 1900 LT, during the post-sunrise and sunset hours. The seasonal variations show that the average slab thickness daily value is greater during summer and winter than those during equinox. Our study finds that the slab thickness at Chumphon located near the equatorial latitude is much larger than those found at low, mid, and high latitudes. The difference in slab thickness between the equatorial latitude and other zones is explained by the lack of plasma flow from the plasmasphere to the F2 region at the magnetic equator.

Low-latitude ionospheric-thermospheric response to storm time electrodynamical coupling between high and low latitudes

[1] Using multi-instrumental and multistation data, we present low-latitude ionospheric-thermospheric behavior during the geomagnetic storm of 15 May 2005. The diurnal pattern of total electron content (TEC) at a chain of equatorial to low-latitude stations shows strong positive ionospheric storm on 15 May. Latitudinal variation of TEC shows development of strong equatorial ionization anomaly (EIA) on the same day. Evidence, in terms of equatorial electrojet (EEJ) and magnetogram signatures, is presented for the prompt penetration of interplanetary electric field (IEF) as the cause of the positive ionospheric storm. Consequent to the storm time circulation resulting from the extra energy deposition via Joule heating over high latitudes, compositional changes occur in the global thermosphere. TEC enhancements on 16 May are attributed to enhancement of atomic oxygen at equatorial and low latitudes and the negative ionospheric storm on 17 May observed beyond certain low latitudes is explained in terms of enhancement of molecular species because of the storm time neutral composition changes. Strong ESF plume structures on range time intensity (RTI) map and L-band scintillation and TEC depletions in GPS measurements are observed in the longitude sectors where the local time of sudden storm commencement (SSC) falls after the post sunset hours. The ionospheric zonal electric fields are altered by the combined effects of eastward disturbance dynamo electric fields and direct prompt penetration of eastward electric fields associated with the northward turning of interplanetary magnetic field (IMF) Bz leading to subsequent development of ESF after midnight.

Simple statistical equivalents of Penman–Monteith formula’s parameters in the absence of non-basic climatic factors

The Penman–Monteith (PM) method is the most recommended method for estimating reference evapotranspiration (ETo). The PM equation requires several parameters to be available, either measured or computed. Some of these parameters are conventionally calculated by some slightly sophisticated formulas, especially for handy calculations. This paper aimed to derive some simpler statistical equivalents to these formulas. Simplifications were performed to the formulas of the saturation vapor pressure eo[T], slope of vapor pressure (∆), atmospheric pressure (P), the psychrometric constant (γ), wind speed correction, the long-wave radiation, Rnl; the sunset hour angle, ωs; and the extraterrestrial radiation, Ra. For the first five parameters, the parameter-independent factor was analyzed for its extremes, then fitted by interpolation to a simpler equivalent formula. The last three parameters were fitted to simpler form through data from the FAO-CLIMWAT database. Each of the simplified formulas was compared to the conventional one; some correlation indices were applied to validate the new formulas. The ETo was calculated for all stations in the CLIMWAT database by both simplified and conventional formulas. All the correlation results were excellent, with a minimum correlation coefficient of 0.9966. The simplified formulas were proven to be equivalent in performance, with almost no loss in accuracy but simpler in form and faster in execution in the online database applications.

Feasibility and optical performance of one axis three positions sun-tracking polar-axis aligned CPCs for photovoltaic applications

A new design concept, called one axis three positions sun-tracking polar-axis aligned CPCs (3P-CPCs, in short), was proposed and theoretically studied in this work for photovoltaic applications. The proposed trough-like CPC is oriented in the polar-axis direction, and the aperture is daily adjusted eastward, southward, and westward in the morning, noon and afternoon, respectively, by rotating the CPC trough, to ensure efficient collection of beam radiation nearly all day. To investigate the optical performance of such CPCs, an analytical mathematical procedure is developed to estimate daily and annual solar gain captured by such CPCs based on extraterrestrial radiation and monthly horizontal radiation. Results show that the acceptance half-angle of 3P-CPCs is a unique parameter to determine their optical performance according to extraterrestrial radiation, and the annual solar gain stays constant if the acceptance half-angle, θ a , is less than one third of ω 0,min, the sunset hour angle in the winter solstice, otherwise decreases with the increase of θ a . For 3P-CPCs used in China, the annual solar gain, depending on the climatic conditions in site, decreased with the acceptance half-angle, but such decrease was slow for the case of θ a ⩽ ω 0,min/3, indicating that the acceptance half-angle should be less than one third of ω 0,min for maximizing annual energy collection. Compared to fixed east–west aligned CPCs (EW-CPCs) with a yearly optimal acceptance half-angle, the fixed south-facing polar-axis aligned CPCs (1P-CPCs) with the same acceptance half-angle as the EW-CPCs annually collected about 65–74% of that EW-CPCs did, whereas 3P-CPCs annually collected 1.26–1.45 times of that EW-CPCs collected, indicating that 3P-CPCs were more efficient for concentrating solar radiation onto their coupling solar cells.

Longitudinal development of low‐latitude ionospheric irregularities during the geomagnetic storms of July 2004

During the period 22–28 July 2004, three geomagnetic storms occurred due to a sequence of coronal mass ejections. In this paper we present and discuss the ionospheric observations from a set of in situ satellites and ground‐based GPS total electron content and scintillation receivers, a VHF radar, and two chains of ionosondes (∼300°E and ∼120°E, respectively) that provide the evolutionary characteristics of equatorial and low‐latitude ionospheric irregularities versus longitude during these storm periods. It is found that the irregularities occurred over a wide longitudinal range, extending from around 300°E to 120°E on storm days 25 and 27 July 2004. On 25 July plasma bubbles (PBs) began premidnight in America and postmidnight in Southeast Asia. On 27 July the occurrence of irregularities followed the sunset terminator and was observed sequentially after sunset from American to Southeast Asian longitudes. Past studies have reported that storm‐time low‐latitude ionospheric irregularities are mostly confined to a narrower longitude range, <90°, after sunset hours and are associated with the prompt penetration of eastward electric fields (PPEFs) into low latitudes. In June solstice months the occurrence of range‐type spread F or PBs is very low in Southeast Asian and South American sectors. In contrast, the present results indicate that geomagnetic storms triggered the wide longitudinal development of PBs. In the American sector this was probably due to the effects of PPEFs on both storm days. However, in the Southeast Asian sector the PBs on the 2 days probably arose from disturbance dynamo electric field (DDEF), PPEF, and gravity wave seeding effects. This study further shows that under complex storm conditions, besides the long duration or multiple penetrations, the combined effects of PPEFs and DDEFs could result in a wide longitude extent of ionospheric irregularities at times.