low latitudes
Recently Published Documents


TOTAL DOCUMENTS

1120
(FIVE YEARS 256)

H-INDEX

55
(FIVE YEARS 7)

2022 ◽  
Author(s):  
kadri kurt

Abstract In this paper, (pure, slow, and fast) Alfvèn waves for the accepted conditions in Northern-hemisphere at E-region of ionospheric plasma were calculated with low latitudes by using Eq. (20,25-26) and the real geometry of Earth’s magnetic field, at hours 12.00 LT for the 1990 year which sunspot is maximum. One of the most important results of this study is to show analytically that the “MHD modes= (pure, slow and fast) Alfvèn waves” depend not only on the angle between the wave propagation vector (k) and the magnetic field (B) but also on the declination (D=It is the angle value between the direction of the sun's rays and the equatorial plane) and magnetic dip angle (I=It is the angle between real north and magnetic north). From the results obtained, the behavior of the magnitudes of the squares of the phase velocities of all MHD modes is consistent with the behavior of the distribution of electron density with low geographic latitude, even if the magnetic field vector is both perpendicular and parallel to the propagation vector of the wave. In parallel, the phase velocities of the waves are greater in summer than in winter. It has been determined that the propagation velocities of the fast and slow MHD mode in the magnetic equatorial trough region at (q = I) are very small, the energy is almost non-existent, but if q = 90 + I, the energy increases with latitude and is approximately maximum at the low latitude limit. It can be said that the minimum points are between 0-10 oN latitudes where the wave energies are the smallest, and the maximum points are between 20-30 oN latitudes the wave energies are the biggest.


GPS Solutions ◽  
2022 ◽  
Vol 26 (1) ◽  
Author(s):  
V. K. D. Srinivasu ◽  
Nirvikar Dashora ◽  
D. S. V. V. D. Prasad ◽  
K. Niranjan

Atmosphere ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 69
Author(s):  
Oswald Didier Franck Grodji ◽  
Vafi Doumbia ◽  
Paul Obiakara Amaechi ◽  
Christine Amory-Mazaudier ◽  
Kouassi N’guessan ◽  
...  

In this paper, we investigated the impact of solar flares on the horizontal (H), eastward (Y) and vertical (Z) components of the geomagnetic field during solar cycles 23 and 24 (SC23/24) using data of magnetometer measurements on the sunlit side of the Earth. We examined the relation between sunspot number and solar flare occurrence of various classes during both cycles. During SC23/24, we obtained correlation coefficient of 0.93/0.97, 0.96/0.96 and 0.60/0.56 for C-class, M-class and X-class flare, respectively. The three components of the geomagnetic field reached a peak a few minutes after the solar flare occurrence. Generally, the magnetic crochet of the H component was negative between the mid-latitudes and Low-latitudes in both hemispheres and positive at low latitudes. By contrast, the analysis of the latitudinal variation of the Y and Z components showed that unlike the H component, their patterns of variations were not coherent in latitude. The peak amplitude of solar flare effect (sfe) on the various geomagnetic components depended on many factors including the local time at the observing station, the solar zenith angle, the position of the station with respect to the magnetic equator, the position of solar flare on the sun and the intensity of the flare. Thus, these peaks were stronger for the stations around the magnetic equator and very low when the geomagnetic field components were close to their nighttime values. Both cycles presented similar monthly variations with the highest sfe value (ΔHsfe = 48.82 nT for cycle 23 and ΔHsfe = 24.68 nT for cycle 24) registered in September and lowest in June for cycle 23 (ΔHsfe = 8.69 nT) and July for cycle 24 (ΔHsfe = 10.69 nT). Furthermore, the sfe was generally higher in cycle 23 than in cycle 24.


2021 ◽  
Author(s):  
Fashae Joshua Fashae ◽  
Olawale Segun Bolaji ◽  
A. Babatunde Rabiu
Keyword(s):  

2021 ◽  
Vol 14 (1) ◽  
pp. 33
Author(s):  
Shaopeng Li ◽  
Bo Jiang ◽  
Jianghai Peng ◽  
Hui Liang ◽  
Jiakun Han ◽  
...  

The surface all-wave net radiation (Rn) plays an important role in the energy and water cycles, and most studies of Rn estimations have been conducted using satellite data. As one of the most commonly used satellite data sets, Moderate Resolution Imaging Spectroradiometer (MODIS) data have not been widely used for radiation calculations at mid-low latitudes because of its very low revisit frequency. To improve the daily Rn estimation at mid-low latitudes with MODIS data, four models, including three models built with random forest (RF) and different temporal expansion models and one model built with the look-up-table (LUT) method, are used based on comprehensive in situ radiation measurements collected from 340 globally distributed sites, MODIS top-of-atmosphere (TOA) data, and the fifth generation of European Centre for Medium-Range Weather Forecasts Reanalysis 5 (ERA5) data from 2000 to 2017. After validation against the in situ measurements, it was found that the RF model based on the constraint of the daily Rn from ERA5 (an RF-based model with ERA5) performed the best among the four proposed models, with an overall validated root-mean-square error (RMSE) of 21.83 Wm−2, R2 of 0.89, and a bias of 0.2 Wm−2. It also had the best accuracy compared to four existing products (Global LAnd Surface Satellite Data (GLASS), Clouds and the Earth’s Radiant Energy System Edition 4A (CERES4A), ERA5, and FLUXCOM_RS) across various land cover types and different elevation zones. Further analyses illustrated the effectiveness of the model by introducing the daily Rn from ERA5 into a “black box” RF-based model for Rn estimation at the daily scale, which is used as a physical constraint when the available satellite observations are too limited to provide sufficient information (i.e., when the overpass time is less than twice per day) or the sky is overcast. Overall, the newly-proposed RF-based model with ERA5 in this study shows satisfactory performance and has strong potential to be used for long-term accurate daily Rn global mapping at finer spatial resolutions (e.g., 1 km) at mid-low latitudes.


MAUSAM ◽  
2021 ◽  
Vol 64 (4) ◽  
pp. 605-612
Author(s):  
NANDITAD GANGULY

{kksHkeaMy esa vkst+ksu dh ek=k dks izHkkfor djus okys egRoiw.kZ dkjd vkst+ksu dk lerkieaMy {kksHkeaMy esa ijLij fofue; ¼STE½ dk gksuk gSA ;g loZekU; ckr gS fd fuEu v{kka’kksa ij lerkieaMy {kksHkeaMy fofue; ¼STE½ vis{kkd`r vlkekU; gksrk gSA blfy, bl 'kks/k i= esa vkstksu lkSans] mixzg ,oa ijkcSaxuh izdk’kfed vkst+ksu fo’ys"kd vkadM+ksa dk mi;ksx djrs gq, Hkkjr ds fuEu v{kka’k ij fLFkr Å".k dfVca/kh; vkst+ksu ds lerkieaMy {kksHkeaMy fofue; ¼STE½ dh ?kVuk dk xgjkbZ ls v/;;u fd;k x;k gSA Stratosphere Troposphere Exchange (STE) of ozone is an important factor influencing the budget of ozone in the troposphere. It is well established that STE is relatively uncommon at low latitudes. Therefore a case study of deep STE event of ozone at a low latitude tropical coastal site of India is presented in the paper using ozonesonde, satellite and UV photometric ozone analyzer data.


2021 ◽  
Vol 4 ◽  
Author(s):  
Yaru Zhang ◽  
Yongshuo Fu ◽  
Xiaojun Geng ◽  
Shouzhi Chen ◽  
Yahui Guo ◽  
...  

Leaf-out phenology plays a key role in ecosystem structure and functioning. Phenological changes have often been linked to climatic factors and have received considerable attention, with most studies focusing on trends of leaf-out phenology. Leaf-out variation (LOV), which reflects the stability of phenological responses, may also be affected by climate change, yet this has received less scientific attention. In this study, we examined spring LOV in response to climate change in China during the period 1963–2008 using in situ records of 15 species at 25 phenological observation sites across several climate zones and explored spatiotemporal changes of LOV and the underlying mechanisms. We observed a significant decrease of LOV toward higher latitudes (−0.2 ± 0.1 days⋅°N–1;P < 0.001) across all species. Temporally, we found that the LOV was significantly increased from the period 1963–1986 (6.9 ± 2.8 days) to the period 1987–2008 (7.9 ± 3.7 days, P < 0.05). Furthermore, the LOV changes between 1987–2008 and 1963–1986 were significantly smaller at high latitudes (average decrease of 1.0 day) than at low latitudes (average increase of 1.5 days). The spatial pattern of LOV is likely due to both increased heat requirements and greater temperature sensitivity at low latitudes compared with high latitudes. The temporal pattern of LOV is likely related to increased heat requirements for leaf-out during 1987–2008 when the average air temperature was higher. Our analysis indicated that the phenology response to climate change is reflected not only in the temporal trends for long time series but also in the variation of phenological dates. Results from this study improve our understanding of phenological responses to climate change and could be applied in the assessment of regional phenology changes to evaluate better the impacts of climate change on ecosystem structure and function.


2021 ◽  
Vol 8 ◽  
Author(s):  
Alessandro Marrone ◽  
Daniele La Russa ◽  
Elvira Brunelli ◽  
Gianfranco Santovito ◽  
Mauro Francesco La Russa ◽  
...  

Antarctica represents a unique natural laboratory for ecotoxicological studies as it is characterized by low internal pollutants emissions but high external contamination levels. Indeed, warm temperatures promote pollutant evaporation (low latitudes), while cool temperatures (high latitudes) promote its deposition from the atmosphere on land/water. Metals are the most important pollutants in ecosystems and represent a serious and global threat to aquatic and terrestrial organisms. Since 2000, the risks posed by metals have led many States to ratify protocols aimed at reducing their emissions. Endemic Antarctic organisms represent excellent bioindicators in order to evaluate the efficacy of global measures adopted to mitigate pollutants release into the environment. In this study (supported by PNRA18-00133), we estimated the metals contamination levels and the metallothionein-1 expression in liver samples of two Antarctic fish species, the icefish Chionodraco hamatus and the red-blooded Trematomus bernacchii, collected in the same area during 2002 and 2014. The chosen area is located in the Ross Sea, a unique area as it is also isolated from the rest of the Southern Ocean. The analysis of contamination trends throughout this period showed, in both species, a significant increase over time of metals bioaccumulation and metallothionein-1 expression. In addition, our result clearly indicated that the detoxifying ability of the two organisms analyzed greatly differs, probably due to haemoglobin presence/absence. Our work represents an important early step to obtain valuable information in conservation strategies for both Antarctic and non-Antarctic ecosystems.


Space Weather ◽  
2021 ◽  
Author(s):  
Qiong Tang ◽  
Chen Zhou ◽  
Huixin Liu ◽  
Yi Liu ◽  
Jiaqi Zhao ◽  
...  

Sign in / Sign up

Export Citation Format

Share Document