Defense Meteorological Satellite Program Research Articles

Outdoor Light at Night and Diabetes Incidence in the Danish Nurse Cohort Study

Background/Aim: Recent animal studies suggested that light-at-night (LAN) may impair glucose tolerance in rats and disturb glucose homeostasis. We aimed to evaluate the association between exposure to residential outdoor LAN and diabetes incidence in Denmark. Methods: In the nationwide Danish Nurse Cohort consisting of 23,797 nurses, recruited in 1993 or 1999, we identified 1,065 diabetes incident cases through National Diabetes Register up to 2012. The LAN data was estimated using Global Radiance Calibrated products of the Defense Meteorological Satellite Program (DMSP) for 1996, 1999, 2000, 2002, 2004, 2005, and 2010. The full residential address histories were obtained and the LAN exposure was assigned based on the 1996 data for addresses before 1997, and based on the most recent measure for addresses after 1997. Time-varying Cox regression models were used to estimate hazard ratios (HR) (95% confidence intervals (CI)) for the associations of LAN and diabetes incidence, adjusting for individual anthropometric, lifestyle and environmental covariates, such as residential air pollution (PM2.5 and NO2), and night-time road traffic noise determined by validated models. Results: The estimated HR based on a fully adjusted model for incident diabetes with an interquartile range (IQR) (75.6 nW/cm2/sr) increase in cumulative average outdoor LAN was 1.13 (95% CI: 1.05, 1.21). Based on the fully adjusted model of LAN exposure divided into quintiles, where LAN quintile 1 was reference, we found an increase in diabetes incidence at higher LAN levels: LAN quintile 2: HR: 1.04 (95% CI: 0.86-1.27, p = 0.66), LAN quintile 3: HR: 1.04 (95% CI: 0.85-1.26, p = 0.71), LAN quintile 4: HR: 0.99 (0.81-1.20, p = 0.91), and LAN quintile 5: HR: 1.21 (95% CI: 1.0-1.46, p = 0.053). Conclusion: We found suggestive evidence that outdoor LAN exposure may be associated with diabetes incidence, independent of air pollution and road traffic noise.

Identifying and Quantifying Urban Polycentric Development in China From DMSP-OLS Data and Urban Land Data Sets

This study attempted to identify and quantify the morphology of intercity urban polycentric development (UPD) from the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP-OLS) data and urban land (UL) data sets in China at the provincial level. The spatiotemporal change and impact factors of UPD from 2000 to 2012 were also evaluated. The accuracy verification results indicated that the UPD could effectively and accurately identify and evaluate from the DMSP-OLS data and UL data sets in China. China’s urban structure presented a UPD trend from 2000 to 2012 and showed a pattern of high values in the eastern region and low values in the western region. In addition, the gross domestic product was proven to be a significant factor and had an inverted U-shaped impact on the UPD. The study can provide accurate time-series UPD data sets for decision-makers to evaluate the spatiotemporal change and driving mechanism of the intercity urban structure in China at the provincial level.

Spatio-Temporal Variations of CO2 Emission from Energy Consumption in the Yangtze River Delta Region of China and Its Relationship with Nighttime Land Surface Temperature

The rapid development of industrialization and urbanization has resulted in a large amount of carbon dioxide (CO2) emissions, which are closely related to the long-term stability of urban surface temperature and the sustainable development of cities in the future. However, there is still a lack of research on the temporal and spatial changes of CO2 emissions in long-term series and their relationship with land surface temperature. In this study, Defense Meteorological Satellite Program’s Operational Linescan System (DMSP/OLS) data, Suomi National Polar-orbiting Partnership (NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) composite data, energy consumption statistics data and nighttime land surface temperature are selected to realize the spatial informatization of long-term series CO2 emissions in the Yangtze River Delta region, which reveals the spatial and temporal dynamic characteristics of CO2 emissions, spatial autocorrelation distribution patterns and their impacts on nighttime land surface temperature. According to the results, CO2 emissions in the Yangtze River Delta region show an obvious upward trend from 2000 to 2017, with an average annual growth rate of 6.26%, but the growth rate is gradually slowing down. In terms of spatial distribution, the CO2 emissions in that region have significant regional differences. Shanghai, Suzhou and their neighboring cities are the main distribution areas with high CO2 emissions and obvious patch distribution patterns. From the perspective of spatial trend, the areas whose CO2 emissions are of significant growth, relatively significant growth and extremely significant growth account for 8.78%, 4.84% and 0.58%, respectively, with a spatial pattern of increase in the east and no big change in the west. From the perspective of spatial autocorrelation, the global spatial autocorrelation index of CO2 emissions in the Yangtze River Delta region in the past 18 years has been greater than 0.66 (p < 0.01), which displays significant positive spatial autocorrelation characteristics, and the spatial agglomeration degree of CO2 emissions continues to increase from 2000 to 2010. From 2000 to 2017, the nighttime land surface temperature in that region showed a warming trend, and the areas where CO2 emissions are positively correlated with nighttime land surface temperature account for 88.98%. The increased CO2 emissions lead to, to a large extent, the rise of nighttime land surface temperature. The research results have important theoretical and practical significance for the Yangtze River Delta region to formulate a regional emission reduction strategy.

Dual‐Lobe Reconnection and Horse‐Collar Auroras

AbstractWe propose a mechanism for the formation of the horse‐collar auroral configuration during periods of strongly northward interplanetary magnetic field (IMF), invoking the action of dual‐lobe reconnection (DLR). Auroral observations are provided by the Imager for Magnetopause‐to‐Aurora Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP). We also use ionospheric flow measurements from DMSP and polar maps of field‐aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Sunward convection is observed within the dark polar cap, with antisunward flows within the horse‐collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR. We suggest that newly closed flux is transported antisunward and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes. Horse‐collar auroras are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northward IMF. The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low‐latitude boundary layer and cold, dense plasma sheet. We speculate that prolonged DLR could lead to a fully closed magnetosphere, with the formation of horse‐collar auroras being an intermediate step.

Automatic Auroral Boundary Determination Algorithm With Deep Feature and Dual Level Set

AbstractThe morphology of the auroral oval is an important geophysical parameter that helps to further understand the solar wind‐magnetosphere‐ionosphere coupling process. However, it is still a challenging task to automatically obtain auroral poleward and equatorward boundaries completely and accurately. In this paper, a new model based on the deep feature and dual level set method is proposed to extract the auroral oval boundaries in the images acquired by the Ultraviolet Imager (UVI) onboard the Polar spacecraft. With the deep feature extracted by the convolutional neural network (CNN), the corresponding deep feature energy functional is constructed and incorporated into the variational segmentation framework. The dual level set method is implemented to extract the accurate poleward and equatorward boundaries with the gradient descent flow. The experimental results on the test data set demonstrate that this model can extract complete auroral oval contours that are consistent well with annotations and owns higher accuracy compared with the previously proposed methods. Comparison between the extracted auroral boundaries and the precipitating boundaries determined by Defense Meteorological Satellite Program (DMSP) SSJ precipitating particle data validates that the proposed method is trustworthy to capture the global morphology of the auroral ovals.

Westward Plasma Drifts in the Nighttime Equatorial Ionosphere During Severe Magnetic Storms: A New Type of Penetration Electric Fields Caused by Subauroral Polarization Stream

AbstractPenetration electric fields during geomagnetic storms have important effects on the equatorial ionospheric electrodynamics. Previous studies focus on the vertical ion drifts, corresponding to electric fields in the zonal direction, in the equatorial ionosphere. In this study, we analyze the characteristics of the zonal ion drifts in the equatorial region measured by the Defense Meteorological Satellite Program (DMSP) satellites during 10 severe magnetic storms with a minimum Dst < −200 nT in the solar maximum years of 2000–2003. It is found that the net change of the equatorial zonal ion drifts caused by magnetic storms is westward and can reach 200–300 m s−1 in the evening sector and that the westward ion drifts remain in the same direction during both the storm main and recovery phases. The storm‐induced zonal ion drifts are highly correlated with the Dst index, and the correlation coefficient between the average zonal drift and the average Dst value during the 10 storms is 0.89. The magnitude of the storm‐induced westward ion drifts is approximately linearly proportional to the Dst index in the evening sector, and on average, a change of −100 nT in Dst causes a change of −52 m s−1 in the zonal drift. The westward ion drifts caused by magnetic storms become small when Dst recovers to the range of −55 to −123 nT. A new mechanism is proposed to explain the generation of the westward plasma drifts in the nighttime equatorial ionosphere. This new mechanism is that the poleward electric fields associated with the subauroral polarization stream (SAPS) penetrate or extend to low latitudes, producing the westward plasma drifts in the equatorial region. The results of this study provide new insight into equatorial ionospheric electrodynamics during geomagnetic storms.

Modeling the spatiotemporal dynamics of industrial sulfur dioxide emissions in China based on DMSP-OLS nighttime stable light data.

Due to the rapid economic growth and the heavy reliance on fossil fuels, China has become one of the countries with the highest sulfur dioxide (SO2) emissions, which pose a severe challenge to human health and the sustainable development of social economy. In order to cope with the serious problem of SO2 pollution, this study attempts to explore the spatial temporal variations of industrial SO2 emissions in China utilizing the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP-OLS) nighttime stable light (NSL) data. We first explored the relationship between the NSL data and the statistical industrial SO2 emissions at the provincial level, and confirmed that there was a positive correlation between these two datasets. Consequently, 17 linear regression models were established based on the NSL data and the provincial statistical emissions to model the spatial-temporal dynamics of China’s industrial SO2 emissions from 1997 to 2013. Next, the NSL-based estimated results were evaluated utilizing the prefectural statistical industrial SO2 emissions and emission inventory data, respectively. Finally, the distribution of China’s industrial SO2 emissions at 1 km spatial resolution were estimated, and the temporal and spatial dynamics were explored from multiple scales (national scale, regional scale and scale of urban agglomeration). The results show that: (1) The NSL data can be successfully applied to estimate the dynamic changes of China’s industrial SO2 emissions. The coefficient of determination (R2) values of the NSL-based estimation results in most years were greater than 0.6, and the relative error (RE) values were less than 10%, when validated by the prefectural statistical SO2 emissions. Moreover, compared with the inventory emissions, the adjusted coefficient of determination (Adj.R-Square) reached 0.61, with the significance at the 0.001 level. (2) During the observation period, the temporal and spatial dynamics of industrial SO2 emissions varied greatly in different regions. The high growth type was largely distributed in China’s Western region, Central region, and Shandong Peninsula, while the no-obvious-growth type was concentrated in Western region, Beijing-Tianjin-Tangshan and Middle south of Liaoning. The high grade of industrial SO2 emissions was mostly concentrated in China’s Eastern region, Western region, Shanghai-Nanjing-Hangzhou and Shandong Peninsula, while the low grade mainly concentrated in China’s Western region, Middle south of Liaoning and Beijing-Tianjin-Tangshan. These results of our research can not only enhance the understanding of the spatial-temporal dynamics of industrial SO2 emissions in China, but also offer some scientific references for formulating feasible industrial SO2 emission reduction policies.

Multi-Instrumental Observations of Early Morning Equatorial Plasma Depletions During the 2017 Memorial Weekend Storm

We investigate an equatorial plasma depletion (EPD) event in Japan near the early morning sector (04:30–7:30 LT) during the recovery phase of a geomagnetic storm occurred on Memorial weekend (May 28) 2017 by using multi-instrumental measurements, including ground-based Global Navigation Satellite Systems (GNSS) network, ionosonde stations, and space-based Swarm and Defense Meteorological Satellite Program (DMSP) missions. The detailed 2-D evolution of the early morning EPD is well observed using GNSS ROTI maps with high temporal-spatial resolution. Moreover, ROTI data from BeiDou Geostationary Earth Orbit satellites are used to detect the EPD signature for the first time. The dawn EPD signature was also observed at the topside ionosphere by in situ electron density (Ne) measurements and ROTI results by space-borne Swarm Alpha (A), Charlie (C), and DMSP F17 satellites, indicating that the equatorial depletions arose to higher altitudes. We suggest that both the eastward disturbance dynamo electric field and overshielding electric field near the early morning sector created a favorable condition for the growth of the Rayleigh–Taylor (R-T) instability, and thus result in the generation of the dawn EPD.

Spatiotemporal Variations of City-Level Carbon Emissions in China during 2000–2017 Using Nighttime Light Data

China is one of the largest carbon emitting countries in the world. Numerous strategies have been considered by the Chinese government to mitigate carbon emissions in recent years. Accurate and timely estimation of spatiotemporal variations of city-level carbon emissions is of vital importance for planning of low-carbon strategies. For an assessment of the spatiotemporal variations of city-level carbon emissions in China during the periods 2000–2017, we used nighttime light data as a proxy from two sources: Defense Meteorological Satellite Program’s Operational Linescan System (DMSP-OLS) data and the Suomi National Polar-orbiting Partnership satellite’s Visible Infrared Imaging Radiometer Suite (NPP-VIIRS). The results show that cities with low carbon emissions are located in the western and central parts of China. In contrast, cities with high carbon emissions are mainly located in the Beijing-Tianjin-Hebei region (BTH) and Yangtze River Delta (YRD). Half of the cities of China have been making efforts to reduce carbon emissions since 2012, and regional disparities among cities are steadily decreasing. Two clusters of high-emission cities located in the BTH and YRD followed two different paths of carbon emissions owing to the diverse political status and pillar industries. We conclude that carbon emissions in China have undergone a transformation to decline, but a very slow balancing between the spatial pattern of high-emission versus low-emission regions in China can be presumed.

The Low-Latitude Plasma Irregularities after Sunrise from Multiple Observations in Both Hemispheres during the Recovery Phase of a Storm

The daytime plasma density disturbances in the low-latitude ionosphere, referred to as plasma irregularities, mainly occur during the nighttime and are an unusual phenomenon. Based on the observations from multiple low Earth orbiting (LEO) satellites, e.g., the Defense Meteorological Satellite Program (DMSP) F13 and F15, the first Satellite of the Republic of China (ROCSAT-1), the Gravity Recovery and the Climate Experiment (GRACE), and Challenging Mini-satellite Payload (CHAMP) satellites, as well as the ground-based Global Positioning System (GPS) receivers, we report a special event of low-latitude plasma irregularities that were observed after sunrise in the Pacific longitudes on 18 August, 2003, following a moderate geomagnetic storm. Observations from three ground-based GPS stations in both hemispheres showed remarkable total electron content (TEC) disturbances during 20:00 to 21:00 UT (around local sunrise), agreeing well with the in situ plasma density irregularities recorded by the nearby flying LEO satellites. The plasma irregularities observed by these LEO satellites showed quite different depletion intensities at different altitudes. We suggest that the plasma irregularities were freshly generated near sunrise hours due to the disturbance of the dynamo electric field (DDEF), evolving into the post-sunrise and morning sector, but were not the remnant of the plasma irregularities generated during the previous nighttime.

The Seasonal and Longitudinal Variations of Nighttime OI 135.6‐nm Emission at Equatorial Ionization Anomaly Crests Observed by the DMSP/SSUSI

AbstractNighttime atomic oxygen (OI) 135.6‐nm emission observed by the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on board the Defense Meteorological Satellite Program (DMSP) F18 satellite is utilized to investigate the seasonal and longitudinal variations of the equatorial ionization anomaly (EIA) crests at a fixed 20:00 local time (LT) from 1 January 2012 to 31 December 2015. The OI 135.6‐nm emission intensity at the southern and northern EIA crests for each day is considered as a superposition of zonal mean and Zonal Wavenumbers 1–4 components. On the seasonal‐longitudinal variations of the OI 135.6‐nm emission intensity at both EIA crests, the obvious double‐peak structure appears in equinoxes for all 4 years. The longitudinal peaked structures are also prominent in equinoxes, and Peak‐3 structure dominates. The main results are as follows: (1) The zonal mean emission intensity and amplitudes of Wavenumbers 1–4 components at both EIA crests are also evident in equinoxes and have a major semiannual and annual periods, except for amplitude of Wavenumber 4 at the southern EIA crest; the amplitude of Wavenumber 1 component is generally greater than Wavenumbers 2–4; (2) the phases of Wavenumbers 1 and 2 components at both EIA crests have a 1‐year period, and the seasonal variations of the phase of Wavenumber 1 component at both EIA crests are in phase but antiphase in Wavenumber 2; and (3) the phases of Wavenumbers 1 and 2 components between the OI 135.6‐nm emission intensity and the total electron content (TEC) at both EIA crests are almost consistent in April and solstices.

Ionospheric Response to Strong Geomagnetic Storms During 2000–2005: An IMF Clock Angle Perspective

AbstractThis paper presents the equatorial ionospheric response to 11 strong‐to‐severe geomagnetic storms that occurred during the period 2000–2005, the declining phase of the Solar Cycle 23. The analysis has been performed using the global ion density plots of the Defense Meteorological Satellite Program (DMSP). Observations show that for about 91% of the cases, postsunset equatorial irregularities occurred within 3 hr from the time of northward to southward transition of the interplanetary magnetic field (IMF) clock angle, thus bringing out the importance of the role played by IMF By in the process of prompt penetration of electric field (PPEF) in addition to the IMF Bz. This is an improvement from the previously reported (Ray et al., 2015, https://doi.org/10.1002/2014RS005422) 4 hr window of equatorial spread F generation from the southward IMF Bz crossing −10 nT.

Importance of Regional‐Scale Auroral Precipitation and Electrical Field Variability to the Storm‐Time Thermospheric Temperature Enhancement and Inversion Layer (TTEIL) in the Antarctic E Region

AbstractA dramatic thermospheric temperature enhancement and inversion layer (TTEIL) was observed by the Fe Boltzmann lidar at McMurdo, Antarctica during a geomagnetic storm (Chu et al. 2011, https://doi.org/10.1029/2011GL050016). The Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) driven by empirical auroral precipitation and background electric fields cannot adequately reproduce the TTEIL. We incorporate the Defense Meteorological Satellite Program (DMSP)/Special Sensor Ultraviolet Spectrographic Imager (SSUSI) auroral precipitation maps, which capture the regional‐scale features into TIEGCM and add subgrid electric field variability in the regions with strong auroral activity. These modifications enable the simulation of neutral temperatures closer to lidar observations and neutral densities closer to GRACE satellite observations (~475 km). The regional scale auroral precipitation and electric field variabilities are both needed to generate strong Joule heating that peaks around 120 km. The resulting temperature increase leads to the change of pressure gradients, thus inducing a horizontal divergence of air flow and large upward winds that increase with altitude. Associated with the upwelling wind is the adiabatic cooling gradually increasing with altitude and peaking at ~200 km. The intense Joule heating around 120 km and strong cooling above result in differential heating that produces a sharp TTEIL. However, vertical heat advection broadens the TTEIL and raises the temperature peak from ~120 to ~150 km, causing simulations deviating from observations. Strong local Joule heating also excites traveling atmospheric disturbances that carry the TTEIL signatures to other regions. Our study suggests the importance of including fine‐structure auroral precipitation and subgrid electric field variability in the modeling of storm‐time ionosphere‐thermosphere responses.

Does urban spatial structure affect labour income? – research based on 97 cities in China

The purpose of the research is that: In the context of China’s rapid urbanisation in recent 20 years, to discuss about how the spatial structure elements such as the size of city, density, pattern and so on influence the staff’s remuneration. Research method: Using American ‘Defense Meteorological Satellite Program’ night-time light data and Land- Scan population distribution data, three urban distance indicators are calculated to quantify the city geometric shape and urban sprawl indices are measured in order to illustrate the urban spatial structure. China Household Finance Survey (CHFS) data from household surveys are also used to investigate how the city shape affects individual wages with method Instrument Variable (IV). When individual characteristics are controlled, we find that a larger population size and a higher density are conducive to higher labour incomes due to agglomeration advantages, while a ‘worse’ city shape is significantly correlated with lower wages, suggesting that the city shape influences urban agglomeration and the mechanisms through TFP of firms prevails. Further discussion shows that urban density matters less for those working in the secondary sector, while the adverse effect of poor urban geometry can be alleviated in cities with a lower density and in those with a larger extension of highways per capita.

Estimating spatiotemporal dynamics of county-level fossil fuel consumption based on integrated nighttime light data

Rapid urbanization has resulted in increased fossil fuel consumption in China, which is closely related to regional sustainable development and CO2 emissions. This study proposed an improved model to estimate fossil fuel consumption on the county scale in Shandong to understand the dynamics of fossil fuel consumption. This improved model is beneficial for establishing energy-saving and CO2 emission reduction policies for both Shandong and other regions in China. Because of the lack of data on a county scale, this study applied panel data analysis from 1992 to 2017 by integrating the Defense Meteorological Satellite Program’s Operational Linescan System (DMSP-OLS) and NPP-VIIRS (Suomi National Polar-Orbiting Partnership satellite with the Visible Infrared Imaging Radiometer Suit) nighttime light data. Results showed that (1) The new method performed better than previous methods on estimating fossil fuel consumption; (2) Fossil fuel consumption has been rapidly growing in all cities and most districts and counties, mainly concentrated in west and east central Shandong; (3) Regions with high fossil fuel consumption shifted from west central Shandong to east central on the city level, and expanded from the east central to the entire central region on the county level; (4) In regions with a lower level of development, fossil fuel consumption tended to grow faster. These results will improve the understanding of fossil fuel consumption over the long term on county scales, and are beneficial for creating policies on regional energy savings and CO2 emission reduction.

Dynamics of Auroral Precipitation Boundaries Associated With STEVE and SAID

AbstractUsing Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA) satellite observations and ground‐based observations by the THEMIS all‐sky imagers (ASIs) and SuperDARN radars, we determine how the equatorward boundary locations of ring current ions and plasma sheet electrons at pre‐midnight relate to occurrence of strong thermal emission velocity enhancement (STEVE) and intense subauroral ion drifts (SAID) during substorms. We found that the STEVE events are associated with a sharper gradient of electron precipitating flux, lower precipitating ion flux, and a narrower (<1°) latitudinal gap between the equatorward boundaries of trapped ring current ions and precipitating plasma sheet electrons and narrower region‐2 field‐aligned currents (FACs) than for the non‐STEVE events. The narrow gap of the particle boundaries contains intense SAID, higher upflow velocity, lower trough density, and slightly higher electron temperature than those for the non‐STEVE events. The non‐STEVE substorms have much wider gaps between the trapped ions and precipitating electrons, and subauroral polarization streams (SAPS) do not show intense SAID. These results indicate that subauroral flows and downward FACs for the STEVE events can only flow within the latitudinally narrow subauroral low‐conductance region between the ion and electron boundaries, resulting in intense SAID and heating. During the non‐STEVE events, the SAPS flows can flow in the latitudinally wide region without forming intense SAID.

Multiscale Observation of Two Polar Cap Arcs Occurring on Different Magnetic Field Topologies

AbstractThis paper presents observations of polar cap arc substructure down to scale sizes of meters and temporal resolution of milliseconds. Two case studies containing polar cap arcs occurring over Svalbard are investigated. The first occurred on 4 February 2016 and is consistent with formation on closed field lines; the second occurred on 15 December 2015 and is consistent with formation on open field lines. These events were identified using global‐scale images from the Special Sensor Ultra‐violet Spectrographic Imager (SSUSI) instruments on board Defense Meteorological Satellite Program (DMSP) spacecraft. Intervals when the arcs passed through the small‐scale field of view of the Auroral Structure and Kinetics (ASK) instrument, located on Svalbard, were then found using all sky images from a camera also located on Svalbard. These observations give unprecedented insight into small‐scale polar cap arc structure. The energy and flux of the precipitating particles above these arcs are estimated using the ASK observations in conjunction with the Southampton Ionospheric model. These estimates are then compared to in situ DMSP particle measurements, as well as data from ground‐based instrumentation, to infer further information about their formation mechanisms. This paper finds that polar cap arcs formed on different magnetic field topologies exhibit different behavior at small‐scale sizes, consistent with their respective formation mechanisms.

Statistical Analysis of Joule Heating and Thermosphere Response During Geomagnetic Storms of Different Magnitudes

AbstractDuring a geomagnetic storm, the energy deposition from magnetosphere to thermosphere through Joule heating leads to variations in the total mass density of thermosphere. In this study, measurements obtained from the Challenging Minisatellite Payload and Gravity Recovery and Climate Experiment satellites between 2002 and 2008 are used to study the response of thermospheric density during geomagnetic storms of different magnitudes inferred from the Dst index. Based on the height‐integrated Joule heating with data derived from the Defense Meteorological Satellite Program spacecraft, we statistically analyze 265 geomagnetic storm cases to study the characteristics of Joule heating distribution and its influence on thermospheric density. The results show that between thermospheric density and Joule heating during weak and moderate geomagnetic storms, the time lag is only about 0–2 hr, while the same for intense storms is 3–5 hr. This indicates that the time lag is positively correlated with the intensity of geomagnetic storms. Besides, it is found that the peak duration of Joule heating increases for more intense geomagnetic storms.

A Comparative Study of Estimating Auroral Electron Energy from Ground-Based Hyperspectral Imagery and DMSP-SSJ5 Particle Data

Aurora, the spectacular phenomenon commonly occurring in high latitudes, is caused by the precipitation of energetic particles penetrating the Earth’s atmosphere. Being the result of solar-terrestrial interactions, electron precipitation significantly contributes to auroral production. To evaluate its magnitude, a physical quantity describing the characteristics of precipitating auroral electrons—their characteristic energy—is adopted. In this paper, this quantity is derived from joint data observed by the ground-based auroral spectroscopic imager located in Antarctica Zhongshan Station and the particle detectors “Special Sensor J5 (SSJ5)” on the Defense Meteorological Satellite Program (DMSP) satellites. A postprocessing scheme of ground-based spectral data is proposed to infer the characteristic energy that successively uses classical brute-force, recursive brute-force and self-consistent approximation strategies for step-up speed improvement. Then, the inferred characteristic energies are compared to the average energies calibrated from the relevant electron data detected by SSJ5 to confirm whether this inference is valid. Regarding DMSP F18/SSJ5, these two energy estimations about auroral electrons deviate slightly from each other and show a strong linear relationship. It sheds light on further applications of the valuable aurora spectral data.

Identifying and Correcting Signal Shift in DMSP-OLS Data

Defense Meteorological Satellite Program Operational Linescan System (DMSP-OLS) nighttime light data has become a key tool of the environmental and social scientific fields, but suffers from several validity problems. We highlight one such problem—shifts in the digital number position in DMSP-OLS composites in the same satellite. We present techniques for identifying the problem, using moving window raster correlation and visual inspection, and for solving the problem, by assigning control points and manually shifting raster positions. To illustrate the importance of accounting for signal shift, we re-examine a recent analysis of the relationship between public goods provision and patterns of violence in the 2011 Syrian uprising and ensuing civil war. We find the statistical results change considerably when correcting for signal shift. We attribute this change to the systematic undercounting of light intensity in heavily populated areas. We close by identifying the types of research that would most benefit from our correction and suggest future refinements to our technique through automation.