Dayside Diffuse Aurora and the Cold-Plasma Structuring: A Brief Review

Diffuse aurora is generated by the precipitation of hot electrons from the central plasma sheet due to wave-particle interaction. Near magnetic local noon (MLN), the diffuse aurora was often observed in structured forms, such as in stripy or patchy. In the magnetosphere, when the hot electrons meet with a cold plasma structure, the threshold of resonance energy for the electrons in the cold plasma region can be lowered, leading to more electrons being involved in the wave-particle interaction and being scattered into the loss cone. As a result, stronger diffuse aurora can be produced in the correspondent region. Based on this mechanism, the structured dayside diffuse auroras have been suggested to correspond to the cold plasma structures in the dayside outer magnetosphere. This brief review focuses on showing that 1) the stripy diffuse auroras observed near MLN are specifically informative, 2) there are two types of diffuse aurora near MLN, which may correspond to cold plasmas originating from inside and outside the magnetosphere, respectively, and 3) we can study the inside-outside coupling by using the interaction between diffuse and discrete auroras observed near MLN.

Atmospheric Correction of DSCOVR EPIC: Version 2 MAIAC Algorithm

The Earth Polychromatic Imaging Camera (EPIC) onboard the Deep Space Climate Observatory (DSCOVR) provides multispectral images of the sunlit disk of Earth since 2015 from the L1 orbit, approximately 1.5 million km from Earth toward the Sun. The NASA’s Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm has been adapted for DSCOVR/EPIC data providing operational processing since 2018. Here, we describe the latest version 2 (v2) MAIAC EPIC algorithm over land that features improved aerosol retrieval with updated regional aerosol models and new atmospheric correction scheme based on the ancillary bidirectional reflectance distribution function (BRDF) model of the Earth from MAIAC MODIS. The global validation of MAIAC EPIC aerosol optical depth (AOD) with AERONET measurements shows a significant improvement over v1 and the mean bias error MBE = 0.046, RMSE = 0.159, and R = 0.77. Over 66.7% of EPIC AOD retrievals agree with the AERONET AOD to within ± (0.1 + 0.1AOD). We also analyze the role of surface anisotropy, particularly important for the backscattering view geometry of EPIC, on the result of atmospheric correction. The retrieved BRDF-based bidirectional reflectance factors (BRF) are found higher than the Lambertian reflectance by 8–15% at 443 nm and 1–2% at 780 nm for EPIC observations near the local noon. Due to higher uncertainties, the atmospheric correction at UV wavelengths of 340, 388 nm is currently performed using a Lambertian approximation.

Aerosol Optical Depths during Two Harmattan Seasons in Ile-Ife, Nigeria

Aim: To quantify the atmospheric aerosol loading in order to predict the severity and accompanying consequences of aerosols at a tropical location in Ile-Ife, southwest Nigeria. Place and Duration of Study: Department of Physics and Engineering Physics, Obafemi Awolowo University, Ile-Ife, Nigeria, between November 2017 and March 2019. Methodology: Daily measurements of Aerosol Optical Depth (AOD) at about the local noon (12:30 pm–1:30 pm) for two consecutive Harmattan seasons (November 2017–March 2018; and November 2018 – March 2019) were carried out at three different wavelengths, 465 nm, 540 nm and 619 nm using a manually operated hand-held sun photometer (model Calitoo). Results: The mean values of AOD were 0.98, 0.87 and 0.83 in the 465 nm, 540 nm and 619 nm wavelengths respectively for November 2017 – March 2018; and 0.94, 0.83 and 0.78 in the 465 nm, 540 nm and 619 nm wavelengths respectively for November 2018 – March 2019. The values assume high levels of haziness at the study location. Intense Harmattan dust storm was experienced on some typical days with AOD values > 2. The resulting elevated level of atmospheric haziness led to visibility deterioration and visibility values greatly reduced to 1 km on such days. December, January and February months were the peak of the Harmattan. The distribution of the particle size indicated that the dominated aerosol is the coarse mode Harmattan dust during the period of study. Conclusion: The study location experiences a polluted atmosphere during the Harmattan season.

Hagyományos időmérés a modern korban

Az egri Líceum nem csak, mint műemlék fontos épülete a városnak, hanem tudománytörténeti jelentősége is elvitathatatlan. Alapításakor európai szinten is egyedülálló csillagászati felszereltséggel rendelkezett (Monk, 2013). Erre az eszközrendszerre alapozva egy olyan komplex rendszer megvalósítását tűztük ki célul, amely képes detektálni és jelezni a helyi dél időpontját a Líceum építésekor kijelölt meridián vonal felhasználásával a hagyományoknak megfelelően. Tudománytörténeti szempontból érdeklődésre tarthat számot egy ilyen rendszer működése, de fontosnak tartottuk, hogy későbbi feldolgozás érdekében rendelkezzen naplózási funkcióval is. ----- Traditional timing in the modern age ----- The Lyceum in Eger, while being one of the most known Monuments of the city, plays an import- ant role in the history of science. When it was founded, it became one of the best equipped observatories in Europe. Knowing this, our goal is to use its equipment to build a complex system that is able to determine the exact time of the local noon, using the meridian line that was created during the construction of the building. While our primary goal was to research and realize how a system like that could work at its core, a logging feature has also been implemented in the system for later reuse of the data.

Evaluation of Ocean Color Remote Sensing Algorithms for Diffuse Attenuation Coefficients and Optical Depths with Data Collected on BGC-Argo Floats

The vertical distribution of irradiance in the ocean is a key input to quantify processes spanning from radiative warming, photosynthesis to photo-oxidation. Here we use a novel dataset of thousands local-noon downwelling irradiance at 490 nm (Ed(490)) and photosynthetically available radiation (PAR) profiles captured by 103 BGC-Argo floats spanning three years (from October 2012 to January 2016) in the world’s ocean, to evaluate several published algorithms and satellite products related to diffuse attenuation coefficient (Kd). Our results show: (1) MODIS-Aqua Kd(490) products derived from a blue-to-green algorithm and two semi-analytical algorithms show good consistency with the float-observed values, but the Chla-based one has overestimation in oligotrophic waters; (2) The Kd(PAR) model based on the Inherent Optical Properties (IOPs) performs well not only at sea-surface but also at depth, except for the oligotrophic waters where Kd(PAR) is underestimated below two penetration depth (2zpd), due to the model’s assumption of a homogeneous distribution of IOPs in the water column which is not true in most oligotrophic waters with deep chlorophyll-a maxima; (3) In addition, published algorithms for the 1% euphotic-layer depth and the depth of 0.415 mol photons m−2 d−1 isolume are evaluated. Algorithms based on Chla generally work well while IOPs-based ones exhibit an overestimation issue in stratified and oligotrophic waters, due to the underestimation of Kd(PAR) at depth.

High-latitude crochet: solar flare-induced magnetic disturbance independent from low-latitude

Solar flare-induced High latitude (peak at 70–75° geographic latitude) ionospheric current system was studied. Right after the X9.3 flare on 6 September 2017, magnetic stations at 68–77° geographic latitudes (GGlat) near local noon detected northward geomagnetic deviations (ΔB) for more than 3 hours, with peak amplitudes > 200 nT, without any accompanying substorm activities. From its location, this solar flare effect, or crochet, is different from previously studied ones, namely, subsolar crochet (seen at lower latitude), auroral crochet (pre-requires auroral electrojet in sunlight), or cusp crochet (seen only in the cusp). The new crochet is much more intense and longer in duration than the subsolar crochet. The long duration matches with the period of high solar X-ray flux (more than M3-class flare level). Unlike the cusp crochet, interplanetary magnetic field (IMF) BY is not the driver with BY only 0–1 nT out of 3 nT total field. The equivalent ionospheric current flows eastward in a limited latitude range but extended at least 8 hours in local time (LT), forming a zonal current region equatorward of the polar cap on the geomagnetic closed region. EISCAT radar measurements over the same region as the most intense ΔB near local noon show enhancements of electron density (and hence ion-neutral ratio) at these altitudes (~ 100 km) where the background Sq ion convection (> 100 m/s) pre-existed. Therefore, this new zonal current can be related to the Sq convection and the electron density enhancement, e.g., by descending E-region height. However, we have not found why the new crochet is found in a limited latitudinal range, and therefore the mechanism is still unclear compared to the subsolar crochet that is maintained by transient re-distribution of electron density. The signature is sometimes seen in the Auroral Electrojet (AE) index. A quick eye-survey for X-class flares during solar cycle 23 and 24 shows clear AU increases for about half the > X2 flares during non-substorm time, although the latitudinal coverage of the AE stations is not favorable to detect this new crochet. Although some of them could be due to auroral crochet, this new crochet can be rather common feature for X flares.

Upscaling from Instantaneous to Daily Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) for Satellite Products

The fraction of absorbed photosynthetically active radiation (FAPAR) is an essential climate variable (ECV) widely used for various ecological and climate models. However, all the current FAPAR satellite products correspond to instantaneous FAPAR values acquired at the satellite transit time only, which cannot represent the variations in photosynthetic processes over the diurnal period. Most studies have directly used the instantaneous FAPAR as a reasonable approximation of the daily integrated value. However, clearly, FAPAR varies a lot according to the weather conditions and amount of incoming radiation. In this paper, a temporal upscaling method based on the cosine of the solar zenith angle (SZA) at local noon ( c o s ( S Z A n o o n ) ) is proposed for converting instantaneous FAPAR to daily integrated FAPAR. First, the diurnal variations in FAPAR were investigated using PROSAIL (a model of Leaf Optical Properties Spectra (PROSPECT) integrating a canopy radiative transfer model (Scattering from Arbitrarily Inclined Leaves, SAIL)) simulations with different leaf area index (LAI) values corresponding to different latitudes. It was found that the instantaneous black sky FAPAR at 09:30 AM provided a good approximation for the daily integrated black sky FAPAR; this gave the highest correlation (R2 = 0.995) and lowest Root Mean Square Error (RMSE = 0.013) among the instantaneous black sky FAPAR values observed at different times. Secondly, the difference between the instantaneous black sky FAPAR values acquired at different times and the daily integrated black sky FAPAR was analyzed; this could be accurately modelled using the cosine value of solar zenith angle at local noon ( c o s ( S Z A n o o n ) ) for a given vegetation scene. Therefore, a temporal upscaling method for typical satellite products was proposed using a cos(SZA)-based upscaling model. Finally, the proposed cos(SZA)-based upscaling model was validated using both the PROSAIL simulated data and the field measurements. The validated results indicated that the upscaled daily black sky FAPAR was highly consistent with the daily integrated black sky FAPAR, giving very high mean R2 values (0.998, 0.972), low RMSEs (0.007, 0.014), and low rMAEs (0.596%, 1.378%) for the simulations and the field measurements, respectively. Consequently, the cos(SZA)-based method performs well for upscaling the instantaneous black sky FAPAR to its daily value, which is a simple but extremely important approach for satellite remote sensing applications related to FAPAR.

Is there any connection between solar activity and earthquakes?

A possible relationship between solar activity and the seismic activity of the Earth is considered. We analyzed the frequency of occurrence of earthquakes of various magnitudes with the Fourier transform: for M ≥ 7 over the period 1900—2019 and for 2.5 ≤ M ≤ 7 over the period 1973–2019. The average annual, monthly, and daily values of the solar-terrestrial variables, the number of earthquakes with intensities that fall within the specified boundaries are calculated. The epoch overlapping method was used to analyze the possible relationship between the Wolf numbers and the number of earthquakes at the corresponding moment in the cycle. 4 periods of each solar cycle were identified: the phase of ascending, maximum, descending, and minimum. Earthquakes over the entire globe and in the regions of extension and compression of the earth's crust were analyzed for each phase. No statistically significant dependencies between solar-terrestrial variables and earthquake initiation were found for all time intervals and all selected earthquake magnitudes. An interesting fact was established concerning the change in the number of earthquakes at different periods of the day. The number of earthquakes in the nighttime appreciably increases (by ~ 10 %) compared to the daytime. A slight increase in the number of earthquakes after local noon was also detected. We could not confirm the existence of a direct connection between solar activity and the seismic activity of the Earth, but we cannot also claim that such a connection does not exist.

Outgassing-induced acceleration of comet 67P/Churyumov-Gerasimenko

Context. Cometary activity affects the orbital motion and rotation state through sublimation-induced forces. The availability of precise rotation-axis orientation and position data from the Rosetta mission allows us to accurately determine the outgassing of comet Churyumov-Gerasimenko/67P (67P). Aims. We derived the observed non-gravitational acceleration of 67P directly from the trajectory of the Rosetta spacecraft. From the non-gravitational acceleration, we recovered the diurnal outgassing variations and study a possible delay of the sublimation response with respect to the peak of the solar illumination. This allowed us to compare the non-gravitational acceleration of 67P with expectations based on empirical models and common assumptions about the sublimation process. Methods. We used an iterative orbit refinement and Fourier decomposition of the diurnal activity to derive the outgassing-induced non-gravitational acceleration. The uncertainties of the data reduction were established by a sensitivity analysis of an ensemble of best-fit orbits for comet 67P. Results. We find that the Marsden non-gravitational acceleration parameters reproduce part of the non-gravitational acceleration, but need to be augmented by an analysis of the nucleus geometry and surface illumination to draw conclusions about the sublimation process on the surface. The non-gravitational acceleration closely follows the subsolar latitude (seasonal illumination), with a small lag angle with respect to local noon around perihelion. The observed minor changes of the rotation axis do not favor forced precession models for the non-gravitational acceleration. Conclusions. In contrast to the sublimation-induced torques, the non-gravitational acceleration does not place strong constraints on localized active areas on the nucleus. We find a close agreement of the orbit-deduced non-gravitational acceleration and the water production that is independently derived from Rosetta in situ measurements.

Surface erythemal UV irradiance in the continental United States derived from ground-based and OMI observations: quality assessment, trend analysis and sampling issues

Surface full-sky erythemal dose rate (EDR) from the Ozone Monitoring Instrument (OMI) at both satellite overpass time and local noon time is evaluated against ground measurements at 31 sites from the US Department of Agriculture's (USDA) UV-B Monitoring and Research Program (UVMRP) over the period of 2005–2017. We find that both OMI overpass and solar noon time EDR are highly correlated with the measured counterparts (with a linear correlation coefficient of 0.90 and 0.88, respectively). Although the comparison statistics are improved with a longer time window (0.5–1.0 h) for pairing surface and OMI measurements, both OMI overpass and local noon time EDRs have 7 % overestimation that is larger than 6 % uncertainty in the ground measurements and show different levels of dependence on solar zenith angle (SZA) and to lesser extent on cloud optical depth. The ratio of EDR between local noon and OMI overpass time is often (95 % in frequency) larger than 1 with a mean of 1.18 in the OMI product; in contrast, the same ratio from surface observation is normally distributed with 22 % of the times less than 1 and a mean of 1.38. This contrast in part reflects the deficiency in the OMI surface UV algorithm that assumes constant atmospheric conditions between overpass and noon time. The probability density functions (PDFs) for both OMI and ground measurements of noontime EDR are in statistically significant agreement, showing dual peaks at ∼20 and ∼200 mW m−2, respectively; the latter is lower than 220 mW m−2, the value at which the PDF of daily EDR from ground measurements peaks, and this difference indicates that the largest EDR value for a given day may not often occur at local noon. Lastly, statistically significant positive trends of EDR are found in the northeastern US in OMI data, but opposite trends are found within ground-based data (regardless of sampling for either noontime or daily averages). While positive trends are consistently found between OMI and surface data for EDR over the southern Great Plains (Texas and Oklahoma), their values are within the uncertainty of ground measurements. Overall, no scientifically sound trends can be found among OMI data for aerosol total and absorbing optical depth, cloud optical depth and total ozone to explain coherently the surface UV trends revealed either by OMI or ground-based estimates; these data also cannot reconcile trend differences between the two estimates (of EDR from OMI and surface observations). Future geostationary satellites with better spatiotemporal resolution data should help overcome spatiotemporal sampling issues inherent in OMI data products and therefore improve the estimates of surface UV flux and EDR from space.