Noon Local Time Research Articles

In situ evidence of the magnetospheric cusp of Jupiter from Juno spacecraft measurements

The magnetospheric cusp connects the planetary magnetic field to interplanetary space, offering opportunities for charged particles to precipitate to or escape from the planet. Terrestrial cusps are typically found near noon local time, but the characteristics of the Jovian cusp are unknown. Here we show direct evidence of Jovian cusps using datasets from multiple instruments onboard Juno spacecraft. We find that the cusps of Jupiter are in the dusk sector, which is contradicting Earth-based predictions of a near-noon location. Nevertheless, the characteristics of charged particles in the Jovian cusps resemble terrestrial and Saturnian cusps, implying similar cusp microphysics exist across different planets. These results demonstrate that while the basic physical processes may operate similarly to those at Earth, Jupiter’s rapid rotation and its location in the heliosphere can dramatically change the configuration of the cusp. This work provides useful insights into the fundamental consequences of star-planet interactions, highlighting how planetary environments and rotational dynamics influence magnetospheric structures.

Wind-driven emissions of coarse-mode particles in an urban environment

Abstract. Quantifying surface–atmosphere exchange rates of particles is important for understanding the role of suspended particulate matter in radiative transfer, clouds, precipitation, and climate change. Emissions of coarse-mode particles with a diameter greater than 0.5 µm provide giant cloud condensation nuclei and ice nuclei. These emissions are critical for understanding the evolution of cloud microphysical properties yet remain poorly understood. Here we introduce a new method that uses lidar retrievals of the elastic backscatter and Doppler velocity to obtain surface number emissions of particles with a diameter greater than 0.53 µm. The technique is applied to study particle number fluxes over a 2-month period from 1 June to 10 August 2022 during the TRACER campaign at an urban site near Houston, TX, USA. We found that all the observed fluxes were positive (upwards), indicating particle emission from the surface. The fluxes followed a diurnal pattern and peaked near noon local time. Flux intensity varied through the 2 months with multi-day periods of strong fluxes and multi-day periods of weak fluxes. Emission particle number fluxes peaked near ∼ 100 cm−2 s−1. The daily averaged emission fluxes correlated with friction velocity and were anticorrelated with surface relative humidity. The emission flux can be parameterized as F= 3000 u*4, where u* is the friction velocity in m s−1 and the emission flux F is in cm−2 s−1. The u* dependence is consistent with emission from wind-driven erosion. Estimated values for the mass flux are in the lower range of literature values from non-urban sites. These results demonstrate that urban environments may play an important role in supplying coarse-mode particles to the boundary layer. We anticipate that quantification of these emissions will help constrain aerosol–cloud interaction models that use prognostic aerosol schemes.

Study of the Effect of Solar Indices on the Ionosphere Layer of Mars

This paper studies the effect of the solar indices (total sunspot no., solar wind density and coronal mass ejection linear speed) on F2- layer electron density, as well as, the comparison of seasonal variations of electron density of F2- layer, NmF2, for Mars at local noontime and for maximum and minimum solar cycles. Results show that there is an inverse correlation between sunspot number, solar wind density, CME linear speed and ionosphere electron density for Mars, at maximum and minimum solar cycles. This correlation is clear when electron density is at minimum value. The maximum value of NmF2 was in month 4 (Summer), month 21 (Winter) during maximum solar cycle, and month 1 (Spring), month 24 (Spring) during minimum solar cycle. The minimum value of NmF2 was in month 13 (Autumn) during maximum solar cycle, and month 9 (Summer) during minimum solar cycle. NmF2 was approximately constant in months 1- 8 (Spring and Summer) and gradually decreased in months 9- 13 (Summer and Autumn), then, gradually increased in months 14- 18 (Autumn and Winter) during maximum solar cycle (2012, 2013). In other hand, NmF2 was approximately constant in months 1- 5 (Spring and Summer) and gradually decreased in months 6- 9 (Summer), then, gradually increased in months 10- 16 (Autumn and Winter) during minimum solar cycle (2016, 2017).

Measuring and modeling investigation of the net photochemical ozone production rate via an improved dual-channel reaction chamber technique

Abstract. Current process-based research mainly uses box models to evaluate photochemical ozone production and destruction rates, and it is unclear to what extent the photochemical reaction mechanisms are elucidated. Here, we modified and improved a net photochemical ozone production rate (NPOPR, P(O3)net) detection system based on the current dual-channel reaction chamber technique, which makes the instrument applicable to different ambient environments, and its various operating indicators were characterized, i.e., “airtightness”, light transmittance, wall losses of the reaction and reference chambers, conversion rate of O3 to NO2, air residence time, and performance of the reaction and reference chambers. The limits of detection of the NPOPR detection system were determined to be 0.07, 1.4, and 2.3 ppbv h−1 at sampling flow rates of 1.3, 3, and 5 L min−1, respectively. We further applied the NPOPR detection system to field observations at an urban site in the Pearl River Delta (China). During the observation period, the maximum value of P(O3)net was 34.1 ppbv h−1, which was ∼ 0 ppbv h−1 at night within the system detection error and peaked at approximately noon local time. The daytime (from 06:00–18:00 LT) average value of P(O3)net was 12.8 (± 5.5) ppbv h−1. We investigated the detailed photochemical O3 formation mechanism in the reaction and reference chambers of the NPOPR detection system using a zero-dimensional box model. We found that the photochemical reactions in the reaction chamber were very close to those in ambient air, but there was not zero chemistry in the reference chamber because the reaction related to the production and destruction of RO2 (= HO2 + RO2) continued in the reference chamber, which led to a small amount of P(O3)net. Therefore, the P(O3)net measured here can be regarded as the lower limit of the real P(O3)net in the atmosphere; however, the measured P(O3)net was still ∼ 7.5 to 9.3 ppbv h−1 higher than the modeled P(O3)net value depending on different modeling methods, which may be due to the inaccurate estimation of HO2 / RO2 radicals in the modeling study. Short-lived intermediate measurements coupled with direct P(O3)net measurements are needed in the future to better understand O3 photochemistry. Our results show that the NPOPR detection system can achieve high temporal resolution and continuous field observations, which helps us to better understand photochemical O3 formation and provides a key scientific basis for continuous improvement of air quality in China.

Pulse oximetry values from 33,080 participants in the Apple Heart & Movement Study

Wearable devices that include pulse oximetry (SpO2) sensing afford the opportunity to capture oxygen saturation measurements from large cohorts under naturalistic conditions. We report here a cross-sectional analysis of 72 million SpO2 values collected from 33,080 individual participants in the Apple Heart and Movement Study, stratified by age, sex, body mass index (BMI), home altitude, and other demographic variables. Measurements aggregated by hour of day into 24-h SpO2 profiles exhibit similar circadian patterns for all demographic groups, being approximately sinusoidal with nadir near midnight local time, zenith near noon local time, and mean 0.8% lower saturation during overnight hours. Using SpO2 measurements averaged for each subject into mean nocturnal and daytime SpO2 values, we employ multivariate ordinary least squares regression to quantify population-level trends according to demographic factors. For the full cohort, regression coefficients obtained from models fit to daytime SpO2 are in close quantitative agreement with the corresponding values from published reference models for awake arterial oxygen saturation measured under controlled laboratory conditions. Regression models stratified by sex reveal significantly different age- and BMI-dependent SpO2 trends for females compared with males, although constant terms and regression coefficients for altitude do not differ between sexes. Incorporating categorical variables encoding self-reported race/ethnicity into the full-cohort regression models identifies small but statistically significant differences in daytime SpO2 (largest coefficient corresponding to 0.13% lower SpO2, for Hispanic study participants compared to White participants), but no significant differences between groups for nocturnal SpO2. Additional stratified analysis comparing regression models fit independently to subjects in each race/ethnicity group is suggestive of small differences in age- and sex-dependent trends, but indicates no significant difference in constant terms between any race/ethnicity groups for either daytime or nocturnal SpO2. The large diverse study population and study design employing automated background SpO2 measurements spanning the full 24-h circadian cycle enables the establishment of healthy population reference trends outside of clinical settings.

Thermal Removal Method for Chang’e-5 Multispectral Data Using a Heat Conduction Model and Real Terrain

The lunar mineral spectrometer (LMS) onboard the Chang’e-5—China’s lunar exploration mission—collected in-situ multispectral data up to 3 μm over a large area of the lunar surface for the first time. As Chang’e-5 operated near the Moon’s noon local time, the spectral data are influenced by thermal radiation. In particular, the LMS multispectral data are in the form of characteristic spectral bands with discontinuities that make it difficult to directly apply existing empirical models for thermal removal. Here, we present a thermal removal method based on the one-dimensional heat conduction model and real terrain data. A centimeter-scale temperature distribution map of the multispectral measurement region is calculated, which ranged from 330 to 362 K. We calculated the temperatures of four hyperspectral regions using an empirical model, compared them with those of the same region using the proposed method, and obtained a relative error of less than 1%. Afterwards, we removed the effects of thermal radiation in the multispectral data using a thermal removal model with the temperature of the multispectral region. We compared multispectral data after thermal removal using our proposed method with hyperspectral data after thermal removal using an empirical model at similar locations. The results showed good consistency between the data corrected by both methods. This paper proposed method does not depend on the setting of the spectral band, it can provide a reference for thermal removal of Chang’e-5 multispectral data and that of subsequent in-situ non-continuous spectral detection data.

On the impact of meridional wind circulation changes in the electron density distribution over the Indian equatorial and low latitude ionospheric region during a severe geomagnetic storm

Using a suite of instruments, which included a chain of ground-based dual-frequency GPS receivers, and magnetometers, we have studied the importance of thermospheric meridional wind circulation in controlling the distribution of plasma over the Indian low latitude ionospheric regions during the period of a severe geomagnetic storm. The storm on 15 May 2005, which had its onset coinciding with the local noon time sector for the Indian ionospheric zone, was a severe geomagnetic storm with symH ∼ - 305 nT. A steep increase in the Total Electron Content (TEC) of the ionosphere over the entire Indian ionospheric region was observed on May 15. The enhancement in the TEC was well correlated with the increase in ΔH at the dip-equator due to the prompt penetration of the convection electric field associated with the storm. However, contrary to the previous studies on the storm impact over low latitude regions, a clear signature of disturbance dynamo was absent on the day after the storm. Enhancements in the TEC were observed on May 16, a day after the storm, as well, though the ΔH at the dip-equator was quite below the quite-time mean. The TEC remained well above its monthly mean over the entire Indian ionospheric region during the storm recovery period. We suggest that the TEC enhancement on May 16, even though it looked like due to a prompt penetration effect, was directly related to the compositional disturbances as given by the O/N2 ratio. We conclude that the meridional wind circulation plays an important role in the distribution of electron density over the equatorial and low latitudinal region during the period of a geomagnetic storm.

Analysis of Solar Ultraviolet radiation Index over Nigeria, West Africa

UV solar radiation are essential for living here on earth, however, at extreme levels, it becomes harmful to all organism with negative effects on humans due to UV-A and UV-B penetrating the earth’s surface. UV radiation index was analyzed over Nigeria, using ten years daily data extracted from the archive of the Ozone Monitoring Instrument (OMI) on-board the EOS Aura spacecraft at a coordinate of 9.08° N, 9. 67° E. The result showed that solar UV radiation is at its peak at local noon time from January 2010 to December 2019. The peak value was observed in the month of November, December, January, February, and March. Hence, the study revealed that the ultraviolet index over Nigeria's varies from high to extreme (i.e., from the Southern to the Northern regions). In conclusion, our findings will create an awareness on those regions with extreme UV radiation and measures such as using sun glasses, umbrellas and putting on protective clothes against the harmful effect of UV radiation.

Local time dependence of earthquakes occurrence and its possible connection with geomagnetic diurnal variations

ABSTRACT Occurrence of earthquakes is not only controlled by internal processes such as the tectonic processes, but also by external ones as Sun-Earth system processes. The aim of the current study is to examine the distribution of earthquakes occurrence at some active seismic regions in order to determine the dominant period of earthquakes occurrence with respect to local time and its possible connection with geomagnetic diurnal variations. Analyzing long-term datasets from 1986 to 2020 demonstrated that the occurrence of earthquakes at the studied regions is strongly depending on local time where earthquakes tend to occur more often during noon local time. This behavior is in somehow similar to the pattern of geomagnetic diurnal variations. Therefore, the study was extended to investigate the probable correlation between both of them. Diurnal variation of North-South geomagnetic component (X-component) was examined and compared with the local time distribution of earthquakes at each region. Data analysis revealed a significant correlation between the geomagnetic diurnal variations and earthquakes occurrence. Thus, the results support the idea of existence a dominating time interval of earthquakes occurrence and also a relationship between local time dependence of earthquakes and geomagnetic diurnal variations that may help in earthquakes prediction in the future.

UV Index for Public Health Awareness Based on OMI/NASA Satellite Data at King Abdulaziz University, Saudi Arabia

Exposure to ultraviolet radiation (UV) is essential for good health and formation of vitamin D while overexposure poses a risk to public health. Therefore, it is important to provide information to the public about the level of solar UV radiation. The ultraviolet index (UVI) is used to help avoid the negative effects of ultraviolet (UV) radiation on humans and to optimize individual exposure. There is limited ground measurement of solar UV radiation, but satellite Ozone Monitoring Instrument (OMIs) satellite products with a spatial resolution of 1 ° × 1 ° can be used to create UV index climatology at local noon time. In this study, we utilize OMI satellite products collected over the campus of King Abdulaziz University (KAU) (21.5° North and 39.1° East), Jeddah, Saudi Arabia, to estimate changes in exposure to UV over a period of 15 years (2004-2020). The results indicate a significantly increasing trend in UV index over this period. Between 2004 and 2020, daily “extreme” UV ( UVI > 11 , as defined by the World Health Organization (WHO)) occurred on 46.60% of days. The frequency of low UVI ( UVI < 2 ) was only about 0.06%. These results imply dangerous exposure levels to solar UV radiation on the KAU campus and call for safety measures to increase awareness and decrease direct exposure; for example, by implementing the United States Environmental Protection Agency (EPA) general guidelines.

Cloud Detection Over Sunglint Regions With Observations From the Earth Polychromatic Imaging Camera

With the ability to observe the entire sunlit side of the Earth, EPIC data have become an important resource for studying cloud daily variability. Inaccurate cloud masking is a great source of uncertainty. One main region that is prone to error in cloud masking is the sunglint area over ocean surfaces. Cloud detection over these regions is challenging for the EPIC instrument because of its limited spectral channels. Clear sky ocean surface reflectance from visible channels over sunglint is much larger than that over the non-glint areas and can exceed reflectance from thin clouds. This paper presents an improved EPIC ocean cloud masking algorithm (Version 3). Over sunglint regions (glint angle ≤25°), the algorithm utilizes EPIC’s oxygen (O2) A-band ratio (764/780 nm) in addition to the 780 nm reflectance observations in masking tests. Outside the sunglint regions, a dynamic reflectance threshold for the Rayleigh corrected 780 nm reflectance is applied. The thresholds are derived as a function of glint angle. When compared with co-located data from the geosynchronous Earth orbit (GEO) and the low Earth orbit (LEO) observations, the consistency of the new ocean cloud mask algorithm has increased by 4∼10% and 4∼6% in the glint center and granule edges respectively. The false positive rate is reduced by 10∼17%. Overall global ocean cloud detection consistency increases by 2%. This algorithm, along with other improvements to the EPIC cloud masks, has been implemented in the EPIC cloud products Version 3. This algorithm will improve the cloud daily variability analysis by removing the artificial peak at local noon time in the glint center latitudes and reducing biases in the early morning and late afternoon cloud fraction over ocean surfaces.

Spatiotemporal analysis of solar ultraviolet radiation based on Ozone Monitoring Instrument dataset in Iran, 2005–2019

The solar ultraviolet radiation (UVR) at national, provincial and county levels in Iran during 2005–2019 were determined based on Ozone Monitoring Instrument (OMI) dataset. The temporal (annual and monthly) trends and spatial distributions of the UVR in terms of erythemally weighted daily dose (EDD), erythemally weighted irradiance at local solar noon time (EDR), and UV index and the major factors influencing the spatiotemporal trends were analyzed. The population-weighted average values of EDD, EDR, and UV index in Iran were respectively 3631 J/m2, 176.3 mW/m2, 7.1 in 2005 and rose by 0.22% per year to 3744 J/m2, 181.7 mW/m2, and 7.3, respectively in 2019, but the annual trend was not statistically significant. The EDD in Iran during the study period exhibited the highest monthly average value in June (6339 J/m2) and the lowest one in December (1263 J/m2). The solar UVA/UVB ratios at the national level during 2005–2019 were considerably lower in summer. The EDD provincial average values in the study period were in the range of 2717 (Gilan) to 4424 J/m2 (Fars). The spatiotemporal variations of the solar UVR parameters were well described by the linear models as a function of cloud optical thickness (COT), ozone column amount, surface albedo, latitude, and altitude (R2 > 0.961, p value < 0.001) and the temporal changes of the solar UVR parameters were mainly caused by the COT. The results indicated that non-burning exposure to solar UVR in summer can be more efficient for vitamin D synthesis due to higher contribution of UVB in the solar UVR. The spatial distributions and temporal trends should be considered to determine the optimal duration, time and condition of exposure to the solar UVR for the public and occupational training and public health measures.

Ionospheric variability during quiet and disturb geomagnetic conditions for low and high solar activity year

Present Paper describes analysis of GPS-data recorded at low latitude station Hyderabad (Geographic latitude 17 $$^\circ $$ , 25′ N, longitude 78 $$^\circ $$ , 33′ E), India to study the effect of magnetic activity on ionospheric TEC. The total electron content (TEC) data were considered for the ionosphere during five most quiet and most disturbed days for each month of the solar minimum year 2009 and the high solar activity year 2013. The results show that GPS-TEC is found to be more during disturbed days than that during quiet days with a maximum difference during the equinox season. In addition, the difference in TEC during quiet and disturbed days is found to be higher for solar maximum than that for solar minimum year. Moreover the GPS-TEC variations depend on the season with the maximum in equinox season and minimum in summer and winter season. Generally daytime TEC is found to be larger than that in the nighttime which is maximized around the local noontime hour but the peak formation delayed for the solar minimum year. The EIA development process during the solar minimum is quite slow and occurs in late afternoon as compared to that during the high solar activity year. In addition, this delay is larger for summer and winter season than that for equinox months. The formation of post sunset anomaly in the post-sunset sector (1900–2300 LT) is prominent during high solar activity year 2013 whereas same is insignificant for solar minimum year 2009. The post-sunset anomaly could be attributed to pre-reversal enhancement (PRE) of zonal electric field.

Novel estimation of aerosol processes with particle size distribution measurements: a case study with the TOMAS algorithm v1.0.0

Abstract. Atmospheric aerosol microphysical processes are a significant source of uncertainty in predicting climate change. Specifically, aerosol nucleation, emissions, and growth rates, which are simulated in chemical transport models to predict the particle size distribution, are not understood well. However, long-term size distribution measurements made at several ground-based sites across Europe implicitly contain information about the processes that created those size distributions. This work aims to extract that information by developing and applying an inverse technique to constrain aerosol emissions as well as nucleation and growth rates based on hourly size distribution measurements. We developed an inverse method based upon process control theory into an online estimation technique to scale aerosol nucleation, emissions, and growth so that the model–measurement bias in three measured aerosol properties exponentially decays. The properties, which are calculated from the measured and predicted size distributions, used to constrain aerosol nucleation, emission, and growth rates are the number of particles with a diameter between 3 and 6 nm, the number with a diameter greater than 10 nm, and the total dry volume of aerosol (N3–6, N10, Vdry), respectively. In this paper, we focus on developing and applying the estimation methodology in a zero-dimensional “box” model as a proof of concept before applying it to a three-dimensional simulation in subsequent work. The methodology is first tested on a dataset of synthetic and perfect measurements that span diverse environments in which the true particle emissions, growth, and nucleation rates are known. The inverse technique accurately estimates the aerosol microphysical process rates with an average and maximum error of 2 % and 13 %, respectively. Next, we investigate the effect that measurement noise has on the estimated rates. The method is robust to typical instrument noise in the aerosol properties as there is a negligible increase in the bias of the estimated process rates. Finally, the methodology is applied to long-term datasets of in situ size distribution measurements in western Europe from May 2006 through June 2007. At Melpitz, Germany, and Hyytiälä, Finland, the average diurnal profiles of estimated 3 nm particle formation rates are reasonable, having peaks near noon local time with average peak values of 1 and 0.15 cm−3 s−1, respectively. The normalized absolute error in estimated N3–6, N10, and Vdry at three European measurement sites is less than 15 %, showing that the estimation framework developed here has potential to decrease model–measurement bias while constraining uncertain aerosol microphysical processes.

Observations of ionospheric irregularities and its correspondence with sporadic e occurrence over South Korea and Japan

This study analyzed the occurrence of ionospheric irregularities over South Korea and Japan (mid-latitudes) during the years 2010–2015. The irregularities were quantified using the rate of change of total electron content (TEC) index (ROTI), which detects irregularities with scale sizes in the range of 400 m–2.5 km. The ROTI threshold for an ionospheric irregularity to have occurred was set as 0.1 TECU/min. Results showed that ionospheric irregularities mostly occur during night-time and around local noon-time in the seasons of spring and summer. In addition, the percentage of ionospheric irregularities had a high positive correlation with solar flux (F10.7) (r > 0.72). For the first time, we showed good correspondence between ionospheric irregularities measured by the ROTI index and sporadic E (Es). The median ROTI associated with ionospheric irregularities over a South Korea station (DAEJ) and a Japan station (KGNI) were 0.131 and 0.125 TECU/min, respectively. However, in severe cases of ionospheric irregularities, the ROTI values over DAEJ (KGNI) can reach 0.246 (0.217) and 0.314 (0.339) TECU/min during day and night, respectively. These critical ROTI values can be important in interpreting and monitoring ionospheric irregularity occurrence over South Korea and Japan.

Comparisons in the global planetary boundary layer height obtained from COSMIC radio occultation, radiosonde, and reanalysis data 基于无线电掩星数据, 探空资料以及再分析资料估算大气边界层高度的比较

The global planetary boundary layer height (PBLH) estimated from 11 years (2007–17) of Integrated Global Radiosonde Archive (IGRA) data, Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) soundings, and European Center for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-Interim) data, are compared in this study. In general, the spatial distribution of global PBLH derived from ERA-Interim is consistent with the one from IGRA, both at 1200 UTC and 0000 UTC. High PBLH occurs at noon local time, because of strong radiation energy and convective activity. There are larger differences between the results of COSMIC and the other two datasets. PBLHs derived from COSMIC are much higher than those from radiosonde and reanalysis data. However, PBLHs derived from the three datasets all exhibit higher values in the low latitudes and lower ones in the high latitudes. The latitudinal difference between IGRA and COSMIC ranges from −1700 m to −500 m, while it ranges from −500 m to 250 m for IGRA and ERA-Interim. It is found that the differences among the three datasets are larger in winter and smaller in summer for most studied latitudes.摘要用11年的全球无线电掩星数据 (COSMIC) , 无线电探空数据 (IGRA) 以及欧洲中心再分析资料 (ERA-Interim) 对全球大气边界层高度 (PBLH) 进行估算比较. 结果表明: (1) 在1200 UTC和0000 UTC, 由ERA-Interim和IGRA数据估算得到的全球PBLH空间分布较为一致, 相关性较好, 在白天正午时候太阳辐射能力较强, 对流活动频繁, 估算得到的大气边界层高度较高. (2) 由COSMIC掩星数据估算得到的边界层高度比探空数据和再分析数据估算结果整体偏大. (3) COSMIC掩星数据, IGRA 探空数据以及 ERA-Interim 再分析资料估算结果都表明边界层高度在低纬度地区偏大, 高纬度地区偏小. (4) 分析不同数据估算边界层高度纬向季节性差异表明, IGRA探空数据和COSMIC数据间差异为-1700m至-500m, IGRA与ERA-Interim之间的差异为-500m至250m.此外, 对于大多数纬度而言, 三个数据集之间的差异在冬季较大, 在夏季较小.

Sap flow of Amorpha fruticosa: implications of water use strategy in a semiarid system with secondary salinization

A. fruticosa (Amorpha fruticosa L.) is widely used for revegetation in semiarid lands that undergo secondary salinization. Understanding A. fruticosa plants response to soil water and salt stress is essential for water irrigation management and proper revegetation practices. In this study, we measured sap flow, stomatal conductance, meteorological and soil characteristics in an A. fruticosa community that recently experienced secondary salinization in northwestern China. Results of our study showed that daytime and nocturnal sap flows averaged 804.37 g·cm−2·day−1 and 46.06 g·cm−2·day−1, respectively, during the growing season. Within individual days, the highest sap flow appeared around noon local time and followed a similar pattern of photosynthetically active radiation (PAR). Despite the significant effect of meteorological factors on the characteristics of sap flow, our study highlighted that the sap flow of A. fruticosa is strongly regulated by the availability of soil relative extractable water (REW). The daytime sap flow, which is predominant compared to nocturnal sap flow, was strongly affected by PAR, air temperature and vapor-pressure deficit. With water stress in the top 40 cm of the soil (REW0–40 cm < 0.4), daytime sap flow displayed a strong relationship with soil water content (SWC) (positive) and soil electrical conductivity (EC) (negative) in the relatively shallow soil profile (up to 40 cm). For the nocturnal sap flow, our results suggest that in the absence of soil water stress (REW0–40 cm > 0.4), the nocturnal sap flow is mainly used to replenish the stem water content and sustain nocturnal transpiration. Under soil water stress, nocturnal sap flow is mainly used to replenish stem water content. The results of our study indicate that it is necessary to shorten the irrigation cycle during the primary growing period (May–July) of A. fruticosa. Moreover, in the absence of soil water stress (REW0–40 cm > 0.4), A. fruticosa can survive well in an saline environment with soil EC < 5 mS·cm−1.

Assessment of bottomside thickness parameters over magnetic equator and low latitudes during high solar activity of solar cycle 24

Bottomside thickness parameters of eight Digisonde stations over geomagnetic equator and low latitude regions have been investigated and compared with IRI model bottomside parameter during high solar activity (years 2013–2015) of the solar cycle 24. The studied years of each station rely on the GIRO data availability. The proposed B0 (B0_Pro) are computed by using the GIRO ionospheric data and the B0 expression in [16] with an average correction factor of “0.18733”. This average correction factor is derived from an average of 144 values of monthly average correction factors at eleven stations over geomagnetic equator and low latitude regions. The Results show that the seasonal variations of B0_Pro are in good agreements with those of B0_obs evidently as compared to B0_IRI at eight stations for all four seasons. For example, in the southern hemisphere, the absolute percentage distances between B0_Pro and B0_obs range from 13% to 33% with overall averages less than 26% and regional averages of 16.5%, but those between B0_IRI and B0_obs are higher. Moreover, the correlation coefficients between B0_Pro and B0_obs always are larger than 0.87 while excluding a lowest value of “0.7041”, but those between B0_IRI and B0_obs are lower. In the southern hemisphere, two remarkable features can always be reflected by B0_Pro for all studied stations. Meanwhile, in the northern hemisphere, the B0_Pro variations of each dip latitude has unique features at different locations, local times, and seasons. The inter-station differences of B0_Pro can be seen obviously in comparison with B0_IRI and described by the impacts of EEJ strength, vertical plasma drift, and PRE from local noontime to post-sunset periods. The remarkable findings from this present study may enhance the comprehension of bottomside variability and improve the IRI predictability in the future.

GPS derived ionospheric TEC variability with different solar indices over Saudi Arab region

In this paper, we investigate the variation of ionospheric total electron content (TEC) derived from global positioning system (GPS) observations at a low latitude station in Magna (Station code: RASH, Geographic coordinate: 28°17′N, 34°47′E), Saudi Arab. The study includes a linear regression method for validating the relationship between regional TEC and solar indices during the period 2015–2017 representing the descending phase of 24th solar cycle. The results show a relatively better agreement of diurnal variation of TEC with solar extreme ultraviolet (EUV) flux (0.1–50 nm wavelength) as compared to the Sunspot number (SSN) and 10.7 cm radio flux (F10.7). Interestingly, the seasonal variation shows a higher magnitude of TEC during the winter season as compared to the summer and fall equinox seasons, which is reported as the winter anomaly over the low latitude region. The correlation coefficient between VTEC and solar indices is also higher during the winter as compared to summer season. Concerning diurnal variability, the results show a higher correlation coefficient during the local noon time (1200SAST) that gradually descends towards evening time (1800SAST) and after that decays during the night time (2100SAST) to attend the diurnal minima. This manifests the diurnal solar irradiance dependence over the low latitude region. Moreover, the lesser agreement in the linear relationship between the TEC and solar indices during the year 2015 than the year 2017 substantiates the dependence of TEC magnitude and vitiations on solar activity. The outcomes from this strengthens the regional understanding and modeling of ionospheric parameters and would complement towards the global efforts for modeling and mitigating the ionospheric effects on transionospheric communication, timing and navigation services. Above all, the intents of this study are in line with the augmentation of aviation services performances in Saudi Arab that plays a vital role in the international civil aviation and logistic trade due to its central geographic location.

UV Index Forecasting under the Influence of Desert Dust: Evaluation against Surface and Satellite-Retrieved Data

Human exposure to healthy doses of UV radiation is required for vitamin D synthesis, but exposure to excessive UV irradiance leads to several harmful impacts ranging from premature wrinkles to dangerous skin cancer. However, for countries located in the global dust belt, accurate estimation of the UV irradiance is challenging due to a strong impact of desert dust on incoming solar radiation. In this work, a UV Index forecasting capability is presented, specifically developed for dust-rich environments, that combines the use of ground-based measurements of broadband irradiances UVA (320–400 nm) and UVB (280–315 nm), NASA OMI Aura satellite-retrieved data and the meteorology-chemistry mesoscale model WRF-Chem. The forecasting ability of the model is evaluated for clear sky days as well as during the influence of dust storms in Doha, Qatar. The contribution of UV radiation to the total incoming global horizontal irradiance (GHI) ranges between 5% and 7% for UVA and 0.1% and 0.22% for UVB. The UVI forecasting performance of the model is quite encouraging with an absolute average error of less than 6% and a correlation coefficient of 0.93. In agreement with observations, the model predicts that the UV Index at local noontime can drop from 10–11 on clear sky days to approximately 6–7 during typical dusty conditions in the Arabian Peninsula—an effect similar to the presence of extensive cloud cover.