Equatorial Latitudes Research Articles

Linking zonal winds and gravity – II. Explaining the equatorially antisymmetric gravity moments of Jupiter

ABSTRACT The recent gravity field measurements of Jupiter (Juno) and Saturn (Cassini) confirm the existence of deep zonal flows reaching to a depth of 5 per cent and 15 per cent of the respective radius. Relating the zonal wind-induced density perturbations to the gravity moments has become a major tool to characterize the interior dynamics of gas giants. Previous studies differ with respect to the assumptions made on how the wind velocity relates to density anomalies, on the functional form of its decay with depth, and on the continuity of antisymmetric winds across the equatorial plane. For the case of Jupiter, most of the suggested vertical structures exhibit a rather smooth radial decay of the zonal wind, which seems at odds with the observed secular variation of the magnetic field and the prevailing barotropy of the zonal winds. Moreover, the results relied on modifications of the surface zonal flows, an artificial equatorial regularization or ignored the equatorial discontinuity altogether. We favour an alternative structure, where the equatorially antisymmetric zonal wind in an equatorial latitude belt between ±21° remains so shallow that it does not contribute to the gravity signal. The winds at higher latitudes suffice to convincingly explain the measured gravity moments. Our results indicate that the winds are barotropic, i.e. constant along cylinders, in the outer $3000$ km and decay rapidly below. The preferred wind structure is 50 per cent deeper than previously thought, agrees with the measured odd gravity moments, is compliant with the requirement of an adiabatic atmosphere and unbiased by the treatment of the equatorial discontinuity. We discuss possible implications for the interpretation of the secular variation of Jupiter’s magnetic field.

Role of Surface Gravity Waves in Aquaplanet Ocean Climates.

We present a set of idealized numerical experiments of a solstitial aquaplanet ocean and examine the thermodynamic and dynamic implications of surface gravity waves (SGWs) upon its mean state. The aquaplanet's oceanic circulation is dominated by an equatorial zonal jet and four Ekman driven meridional overturning circulation (MOC) cells aligned with the westerly atmospheric jet streams and easterly trade winds in both hemispheres. Including SGW parameterization (representing modulations of air‐sea momentum fluxes, Langmuir circulation, and Stokes‐Coriolis force) increases mixed layer vertical momentum diffusivity by ∼40% and dampens surface momentum fluxes by ∼4%. The correspondingly dampened MOC impacts the oceanic density structure to 1 km depth by lessening the large‐scale advective transports of heat and salt, freshening the equatorial latitudes (where evaporation minus precipitation [E − P] is negative) and increasing salinity in the subtropics (where E − P is positive) by ∼1%. The midlatitude pycnocline in both hemispheres is deepened by the inclusion of SGWs. Including SGWs into the aquaplanet ocean model acts to increase mixed layer depth by ∼10% (up to 20% in the wintertime in midlatitudes), decrease vertical shear in the upper 200 m and alter local midlatitude buoyancy frequency. Generally, the impacts of SGWs upon the aquaplanet ocean are found to be consistent across cooler and warmer climates. We suggest that the implications of these simulations could be relevant to understanding future projections of SGW climate, exoplanetary oceans, and the dynamics of the Southern Ocean mixed layer.

Main Wave Sources of the Longitudinal Structures of Equatorial Electric Field

AbstractThe E‐region equatorial electric field (EEF) modulates distributions in the ionosphere at equatorial and low latitudes via the fountain effect. Using Swarm data during the daytime and geomagnetically quiet periods (Kp ≤ 3), we perform a detailed analysis of the main wave sources of the longitudinal structures of the EEF (LSEEF) in different seasons by fitting the LSEEF with longitudinal wavenumber 1–4 patterns (WN1–WN4), and further matching the dominant tides and stationary planetary waves. The results indicate that: (a) Although the LSEEF exhibit significant seasonal dependence, a prominent one‐peaked structure exists in all seasons (peak: 90°E–120°E; trough: 30°W–70°W). (b) WN1 (WN4) contributes most to the LSEEF over four seasons (spring to autumn) with fractions of 26%–39% (25%–38%). (c) The main wave sources of the LSEEF are DW2 (DE3 and DE2; DE3; DW2 and SW4) in spring (summer; autumn; winter) with each contribution exceeding 15%.

Magnetosphere‐Ionosphere‐Thermosphere (M‐I‐T) Coupling Leading to Equatorial Upward and Westward Drifting Supersonic Plasma Bubble Development and Amplified Subauroral Polarization Streams (SAPS) During the January 21, 2005 Moderate Storm

AbstractBy utilizing multipoint observations, we investigate the January 21, 2005 moderate storm's prompt penetration electric field (PPEF) effects in the American sector, Rayleigh‐Taylor (R‐T) instability driven polarization electric (E) field effects in the African sector, and disturbance dynamo electric field (DDEF) effects in the Northern Hemisphere. We study how these E field effects impacted the equatorial ionization anomaly (EIA) and underlying forward fountain, the midlatitude trough, and the subauroral polarization streams (SAPS). In the daytime sector during the initial phase, the PPEF development was produced by solar wind pressure enhancements. In the dusk sector, the undershielding PEFs triggered R‐T instability mechanisms, which impacted the EIA during a prereversal enhancement (PRE) like scenario and afterwards. These led to the development of supersonic plasma bubbles drifting upward and westward. Supersonic bubbles are characteristics of superstorms, and their detections further verify the January 21, 2005 moderate storm's turbulent and superstorm nature. While the disturbance dynamo‐driven anti‐Sq current system operated, the net subauroral westward currents became enhanced and the net zonal (E‐ and F‐region) drift created a deep O+ trough that deepened the midlatitude trough and led to amplified SAPS flows via positive feedback mechanisms. We conclude that strong magnetosphere‐ionosphere‐thermosphere coupling was present at equatorial latitudes where forward fountain plasma drift‐signatures were seen in the thermospheric neutral wind speed data and where the supersonic bubbles developed, and at subauroral latitudes where the midlatitude trough became deepened during the anti‐Sq current system's operation amplifying the SAPS flows by positive feedback mechanisms.

Global Positioning System Observations of Ionospheric Total Electron Content Variations During the 15th January 2010 and 21st June 2020 Solar Eclipse

AbstractThe dual‐frequency global positioning system (GPS) data acquired from the UNAVCO over different places of Nepal were processed to examine the eclipse‐triggered consequences on total electron content (TEC) in response to the annular solar eclipse of 15th January 2010 and 21st June 2020. These occasions were exceptional since they occurred during solar minimum, additionally as in a magnetically quiet period. The eclipse phase coincided with the peak ionization‐time at the equatorial and low latitude regions. The solar eclipse of 21st June 2020 was an annular solar eclipse with a magnitude of 0.994. Nepal has witnessed a partial eclipse, starting at ∼10:53 NST (05:08 UT), reached the maximum at ∼12:40 NST (6:55 UT), and ended at ∼14:24 NST (8:39 UT) with the total duration of 3 h and 31 min. The annular solar eclipse of 15th January 2010 had the magnitude of 0.919 and Nepal has witnessed a partial eclipse starting at ∼12:24 NST (6:39 UT), reached the maximum at ∼14:10 NST (8:25 UT), and ended at ∼15:40 NST (9:55 UT). The eclipse effect occurs as a trough‐like depression in the curve of TEC at all the GPS stations indicates the effect of sudden attenuation of solar extreme ultra‐violet irradiation on decayed electron content in the ionosphere over the region. Moreover, the extent of the exhaustion in ionospheric TEC was studied by comparing the eclipse day TEC with mean diurnal ionospheric TEC of five quietest days of the month to investigate the eclipse effect on the electron density of the ionosphere over the stations. The study additionally reveals that the measure of the decrease in vertical value of total electron content is proportional to the obscuration of the lunar disc, that is closely associated with the electron production via the photoionization process. Observing the values of TEC during the eclipse day and comparing it with other quiet days, our study showed an apparent variation during the time of the eclipse, which agrees with previous studies on ionospheric responses to the eclipse as well as theoretical assumptions.

GPS TEC variations under quiet and disturbed geomagnetic conditions during the descending phase of 24th solar cycle over the Indian equatorial and low latitude regions

• Quiet time seasonal trend in TEC is not seen during disturbed periods of low solar activity. • TEC difference between disturbed and quiet time periods is higher during the moderate solar activity. • The correlation of day maximum TEC with F 10.7 is found to be reduced during disturbed periods. The present study is focused to understand the geomagnetic storm effects on the short- and long-term variations of ionospheric Total Electron Content (TEC) over the equatorial and low latitude sectors. GPS-TEC observations over a near equatorial station Bangalore and low latitude stations Waltair and Hyderabad during the declining phase of the 24th solar cycle (2015–2019) is analysed. The TEC variations during quiet and disturbed conditions are individually analysed to understand the geomagnetic storm effects on the diurnal, seasonal and solar activity variations. The seasonal variations of disturbed time TEC are following the quiet time trend with equinoctial maximum and summer minimum in the moderate solar activity periods. But, during low solar activity periods, the seasonal dependence of disturbed time TEC is different than that of quiet time. The difference in TEC during disturbed and quiet times is higher during moderate solar activity than that of low solar activity conditions. The TEC difference between disturbed and quiet periods is found to be maximum during summer months of moderate solar activity periods. Further, correlation analysis between F 10.7 cm solar flux and TEC during quiet and disturbed conditions is carried out for three different locations. It is found that the correlation between TEC and F 10.7 cm solar flux is higher during quiet time compared to that during disturbed periods with more correlation at the equator than at low latitudes.

Radial Distributions of Coronal Electron Temperatures: Specificities of the DYN Model

This paper is a follow up of the article where Lemaire and Stegen (2016) introduced their DYN method to calculate coronal temperature profiles from given radial distributions of the coronal and solar wind (SW) electron densities. Several such temperature profiles are calculated and presented corresponding to a set of given empirical density models derived from eclipse observations and in-situ measurements of the electron density and bulk velocity at 1 AU. The DYN temperature profiles obtained for the equatorial and polar regions of the corona challenge the results deduced since 1958 from singular hydrodynamical models of the SW. In these models - where the expansion velocity transits through a singular saddle point - the maximum coronal temperature is predicted to be located at the base of the corona, while in all DYN models the altitude of the maximum temperature is found at significantly higher altitudes in the mid-corona. Furthermore, the maximum of the DYN-estimated temperatures is found at much higher altitudes over the polar regions and coronal holes, than over the equator. However, at low altitudes, in the inner corona, the DYN temperatures are always smaller at high latitudes, than at low equatorial latitudes. This appears well in agreement with existing coronal hole observations. These findings have serious implications on the open questions: what is the actual source of the coronal heating, and where is the maximum energy deposited within the solar corona?

Development and adaptation of relative sunshine hours models for the equatorial latitudes: a case study

This study focuses on the development, adaptation, and validation of relative sunshine hours (RSH) models, which are essential for localizing solar facilities in equatorial latitudes. The RSH models were developed from geographical and climatological variables on a periodic and non-periodic basis using 40-year (1979–2018) RSH data from the National Aeronautics and Space Administration (NASA). The NASA data were filtered and arranged in MS-Excel (V.16) to fit the structure of the developed RSH models and regressed in OriginLab to obtain the coefficients of the models. In the absence of RSH models, the clearness index models have been adapted (transformed) into RSH models. The measured data from the meteorological centers; Lira, Tororo, Kampala, and Mbarara were used in the validation of developed and adapted RSH models. Statistical tools; the root mean square error; RMSE yielded lower and upper limits (0.0635–0.2248), whereas the mean absolute percentage error, MAPE yielded a corresponding value (0.1620–2.5413). These results compare well with the literature results; RMSE (0.033–1.670) and MAPE (0.079–4.316), as the upper limits of the current results lie within the range of the literature results. In addition, the graphical fit of the empirical, developed, and adapted RSH data supports the robustness of the present RSH models. Validated RSH models are recommended for locating solar systems in equatorial latitudes. The oldest and adapted RSH models into equatorial latitudes have failed, so the present work further recommends for the redevelopment of such models with recent data to regenerate their validity.

Conserved fatty acid profiles and lipid metabolic pathways in a tropical reef fish exposed to ocean warming – An adaptation mechanism of tolerant species?

Climate warming is causing rapid spatial expansion of ocean warm pools from equatorial latitudes towards the subtropics. Sedentary coral reef inhabitants in affected areas will thus be trapped in high temperature regimes, which may become the “new normal”. In this study, we used clownfish Amphiprion ocellaris as model organism to study reef fish mechanisms of thermal adaptation and determine how high temperature affects multiple lipid aspects that influence physiology and thermal tolerance. We exposed juvenile fish to two different experimental conditions, implemented over 28 days: average tropical water temperatures (26 °C, control) or average warm pool temperatures (30 °C). We then performed several analyses on fish muscle and liver tissues: i) total lipid content (%), ii) lipid peroxides, iii) fatty acid profiles, iv) lipid metabolic pathways, and v) weight as body condition metric. Results showed that lipid storage capacity in A. ocellaris was not affected by elevated temperature, even in the presence of lipid peroxides in both tissues assessed. Additionally, fatty acid profiles were unresponsive to elevated temperature, and lipid metabolic networks were consequently well conserved. Consistent with these results, we did not observe changes in fish weight at elevated temperature. There were, however, differences in fatty acid profiles between tissue types and over time. Liver showed enhanced α-linolenic and linoleic acid metabolism, which is an important pathway in stress response signaling and modulation on environmental changes. Temporal oscillations in fatty acid profiles are most likely related to intrinsic factors such as growth, which leads to the mobilization of energetic reserves between different tissues throughout time according to organism needs. Based on these results, we propose that the stability of fatty acid profiles and lipid metabolic pathways may be an important thermal adaptation feature of fish exposed to warming environments.

Technology for Placing Cargo into Orbit Based on Magnetic Levitation

The article provides a technology of placing cargo into orbit at middle and equatorial latitudes based on magnetic levitation in the Earth's magnetic field. A method for the implementation of Tsiolkovsky's space elevator using magnetic levitation in the Earth's magnetic field is proposed.

Influence of the QBO on tropical convection and its impact on tropical cyclone activity over the western North Pacific

On the basis of 70 hPa zonal wind (U70)-defined quasi-biennial oscillation (QBO) events, after removing the El Nino–Southern Oscillation (ENSO) signal, the present study investigates the process by which the QBO modulates tropospheric circulation and convection during summer (between July and October), when tropical cyclone (TC) activities enter their peak period. Concurrent with the western phase of the QBO (QBOW), significant tripole pattern modulations over the tropical Indo-Pacific Ocean are regressed onto the residual part of U70 after removing the ENSO signal, with enhanced convection observed over its central branch (0°–10°N, 120°E–180°) and the inactive convection branches located to both sides. A ventilation opening-like effect is exerted on the monsoon trough, which is shifted southward under the QBOW phase. According to the QBO-associated changes in the circulations over the tropical western North Pacific (WNP), equatorial environments (with low-level relative vorticity, high-level divergence, tropospheric vertical wind shear (VWS), and midlevel humidity) tend to be favorable for TC genesis. Consequently, the off-equatorial TC tracks show a significantly decreased occurrence frequency in the northern monsoon trough region. The present study provides a summary sketch showing the QBO-tropospheric circulation modulation process. Considering that the westerly or weak easterly is observed over the upper central Pacific (CP), QBOW phase-associated weak VWS can induce anomalous upward motion at equatorial latitudes, together with the upwelling between the equatorial westerly and off-equatorial easterly, leading to an enlarged convective window over the CP. Affected by the prevailing easterly within the tropics, the actual pumping shifts westward over the tropical WNP.

Sulfuric acid vapor and sulfur dioxide in the atmosphere of Venus as observed by the Venus Express radio science experiment VeRa

The Venus Express radio science experiment VeRa provided more than 900 neutral atmospheric profiles between the years 2006 and 2014. About 800 of these could be used for an analysis of the radio signal absorption at X-Band (wavelength: 3.6 cm), which is mainly caused by sulfuric acid vapor within the Venus atmosphere. The absorptivity profiles were converted into sulfuric acid vapor profiles. The combined measurements from the entire Venus Express mission reveal a distinct latitudinal H2SO4(g) variation. A latitudinal gradient can be observed at the topside of the H2SO4(g) layer, which is located approx. 4 km higher at equatorial latitudes compared to polar latitudes. Regions of enhanced sulfuric acid vapor abundance were found at equatorial and polar latitudes. The highest H2SO4(g) values at equatorial latitudes show mean maximal values of more than 12 ppm at around 47 km altitude. At polar latitudes mean maximal values were found at around 43 km altitude and ranged from 9 to 12 ppm. Both latitudinal regions of increased sulfuric acid vapor abundance are clearly separated by a low abundance region located at mid-latitudes with values of 5 to 7 ppm.A simplified two-dimensional transport model was developed to study the formation processes of sulfuric acid vapor accumulation at equatorial and polar latitudes. It turned out that the H2SO4(g) accumulation observed at high latitudes can be explained by precipitation of H2SO4(l) droplets that evaporate into gaseous sulfuric acid upon entering lower (warmer) altitudes. The influence of wind transport on this formation process was minor. In contrast, the H2SO4(g) accumulation observed at equatorial latitudes could be reproduced in the model by oppositely directed mass transport (upward winds and sedimentation) as well as by simplified evaporation and condensation processes. The low H2SO4(g) abundance observed at mid-latitudes was reproduced by downward winds in the model calculations.The VeRa observations were additionally used to estimate the abundance of SO2 above the cloud bottom. A latitudinal dependence was found with highest values of 90 ± 60 ppm at equatorial latitudes, compared to 150 ± 50 ppm and 160 ± 50 ppm at southern and northern polar latitudes, respectively.Both the equatorial and polar regions displayed show large variability of the H2SO4(g) and SO2 abundances from observation to observation. A weak tidal influence is also visible in the sulfuric acid vapor abundance in the equatorial region. The northern polar H2SO4(g) abundance, as well as the southern and northern SO2 abundances, exhibit distinct long-term variations.

Synoptic timescale linkage between midlatitude winter troughs Sahara temperature patterns and northern Congo rainfall: A building block of regional climate variability

AbstractA coherent synoptic sequence, mostly over North Africa, is identified whereby an upper‐level midlatitude trough (in November–March) excites several days of quasi‐stationary near‐surface warming across the Sahara, leading to rainfall events over northern Congo (NC), and perturbed weather more widely. Ahead of NC rainfall events, composite sequences first identify troughs for several days near Iberia, followed by relatively quick transfer to the Central Mediterranean (CMed). Iberia and CMed daily trough‐strength indices reveal that both lead to warming and NC rainfall. Iberia trough linkages develop through West Africa and take longer to reach NC, while CMed linkages reach NC faster (2–3 days), with impact extent focused mostly south and east of CMed. Building up to the rainfall events, initial warming over the central Sahara migrates southeastward close to NC, ultimately with typical magnitude of about 1–2°C at 10–15°N. Such anomalies are statistically predictive for NC daily rainfall and associated nearby atmospheric features: anomalous low‐level southerly wind and increased moisture; anomalous low‐level westerly wind and vertical easterly shear to 600 hPa; increased mid‐level moisture (600 hPa), which along with low‐level moisture, connects northward into midlatitudes. A secondary route identified by which Iberia troughs can impact NC rainfall is through direct atmospheric teleconnection with precipitation to the west of NC, and subsequent migration of that convection eastward into NC. The eastern side of NC generally shows a small lag on western parts, and links more strongly to CMed troughs. Taken together, the lagged synoptic expression of Iberia and CMed troughs is widespread over several days, including much of North Africa (to equatorial latitudes), southwestern Asia, eastern Africa and the western Indian Ocean. Overall, these results can contribute to situational awareness for weather forecasters across the zones influenced by the troughs, while also providing a framework for climate timescale analyses.

Observations of long period HF Doppler oscillations over the dip equatorial ionosphere in the Indian longitudinal sector

Background/ Objective: The signatures of long period High Frequency Doppler (HFD) oscillations over a dip equatorial station, Trivandrum (8.33◦N, 77◦E, dip 0.4◦N) in the Indian longitudinal sector have been investigated. Methods: High cadence vertical plasma drift measurements obtained using a Multi frequency HF Doppler Radar over Trivandrum along with ground based magnetometer observations over several latitudes/longitudes have been used to address this very aspect. Findings: It has been observed that long period (~15 min.) oscillations of high latitude origin can instantaneously reflect over the equatorial latitudes in the form of coherent HFD oscillations. The study is very important as it provided a unique opportunity not only to understand various characteristics of HFD oscillations, but also expected to have significant implications in the understanding of equatorial ionospheric variability in context of solar wind-magnetosphere-ionosphere coupling. Novelty: In a complementary point of view, the study also highlights the potential of HF Doppler measurements to capture such transient events originating from interplanetary medium with an unprecedented temporal resolution. Keywords: HF Doppler radar; equatorial ionosphere; HF Doppler oscillations

Neoproterozoic evolution of northern Gondwana recorded in detrital zircon grains from the Gheshlagh bauxite deposit, Alborz Mountains, Iran Block

When the Cimmerian Continent separated from Gondwana and drifted northward to equatorial latitudes, sedimentary rocks on the continent underwent intense weathering, resulting in the formation of bauxite deposits. Gheshlagh is one such bauxite deposit, located in the Alborz Mountains in northern Iran. The bauxite deposit at Gheshlagh, 12–18 m in thickness with a strike length > 4 km, is hosted by Permian strata and unconformably overlain by Early Triassic limestone. Detrital zircon grains in the bauxite deposit yielded U-Pb ages ranging from 2.5 Ga to 0.5 Ga, with most ages between ca. 0.9 Ga and 0.5 Ga. The detrital zircon grains with age populations between ca. 0.9 Ga and 0.6 Ga are tabular and rounded with sharp oscillatory zoning, and most likely derived from igneous rocks in the northern part of the Arabian-Nubian Shield. The detrital zircon grains with ages of ~1 Ga are long and rounded in shape with slightly obscure growth zoning and probably originated from metamorphic rocks of the Sinai basement in the northernmost part of the shield. Detrital zircon with ages between 1.8 and 2.5 Ga are smoothly rounded in shape with faint internal zoning, suggesting long transport from a metamorphosed source(s), possibly including the Saharan Metacraton, and/or the Kabul Block. The Gheshlagh deposit contains minor needle-like to prismatic-shaped zircon grains, with U-Pb ages ranging from ca. 571 to 521 Ma, corresponding to the timing of the Cadomian magmatic event in northern Gondwana. The occurrence of such proximal sourced zircons at Gheshlagh supports the notion that northern Gondwana was an active margin in response to southward subduction of Prototethys during late Neoproterozoic to Early Cambrian. Our data also suggest that the Cimmerian Continent was still located on the northern margin of Gondwana during deposition of the bauxite protolith in the Permian.

Conjugate Ionospheric Perturbation During the 2017 Solar Eclipse

AbstractWe report new findings of total electron content (TEC) perturbations in the southern hemisphere at conjugate locations to the northern eclipse on August 21, 2017. We identified a persistent conjugate TEC depletion by 10%–15% during the eclipse time, elongating along magnetic latitudes with at least ∼5° latitudinal width. As the Moon's shadow swept southward, this conjugate depletion moved northward and became most pronounced at lower magnetic latitudes (>−20°N). This depletion was coincident with a weakening of the southern crest of the equatorial ionization anomaly (EIA), while the northern EIA crest stayed almost undisturbed or was slightly enhanced. We suggest these conjugate perturbations were associated with dramatic eclipse initiated plasma pressure reductions in the flux tubes, with a large portion of shorter tubes located at low latitudes underneath the Moon's shadow. These short L‐shell tubes intersect with the F region ionosphere at low and equatorial latitudes. The plasma pressure gradient was markedly skewed northward in the flux tubes at low and equatorial latitudes, as was the neutral pressure. These effects caused a general northward motion tendency for plasma within the flux tubes, and inhibited normal southward diffusion of equatorial fountain plasma into the southern EIA region. We also identified posteclipse ionospheric disturbances likely associated with the global propagation of eclipse‐induced traveling atmospheric disturbances in alignment with the Moon's shadow moving direction.

Seasonal and Spatial Variability of Carbon Monoxide (CO) in the Martian Atmosphere From PFS/MEX Observations

AbstractA subset of more than 100,000 nadir measurements covering more than 7 Martian years (MY 26–MY 33) recorded in the thermal part of the Short Wavelength Channel (SWC) from the Planetary Fourier Spectrometer (PFS) on board Mars Express is exploited to investigate the global distribution and the seasonal cycle of carbon monoxide (CO) on Mars. The retrieval of CO vertical profiles is successfully achieved using a methodology based on the optimal estimation but the low information content is such that we mainly discuss the variability in CO in terms of integrated columns (from the surface to 24 km) or the associated column‐averaged mixing ratio. We find a strong seasonality in CO, especially at mid and high‐latitudes, which confirms earlier work and the current knowledge of the CO2 condensation/sublimation cycles, as implemented for instance in the Global Environmental Multiscale (GEM) general circulation model for Mars, that we use as a basis for comparison. We report a general consistency between model and observation, with a tendency of the latter to provide lower CO volume mixing ratios (VMRs), except at low latitudes. The spatial distribution of the CO column‐averaged VMR is obtained on a seasonal basis and investigated in terms of large‐scale patterns but also local peculiarities. Finally, we show that the retrieved profiles systematically present strong CO vertical gradients close to the surface in mid‐ and equatorial latitudes, likely related to the vertical sensitivity of PFS rather than real near‐surface CO enrichment.

Is Mesospheric Quasi Biennial Oscillation Ephemeral?

AbstractThe time evolution of mesospheric quasi biennial oscillation (MQBO) in the 82–98 km altitude region using long‐term meteor radar observations over low and equatorial latitudes and TIMED Doppler Interferometer (TIDI) observations is discussed for the first time. The wavelet spectra of monthly mean zonal winds over Serpog (6.4°S, 106.7°E; 1993–1998), Koto Tabang (0.2°S, 100.3°E; 2003–2012) and Thumba (8.5°N, 76.9°E; 2006–2015) show the transient nature of the MQBO amplitudes, thus, questioning its perpetuity in the mesosphere‐lower thermosphere (MLT). The time period of the MQBO as well as its amplitude show variability with time. The latitude‐height structures of the MQBO at four time periods (24, 26, 28, and 30 months) are constructed using TIDI measurements, which show diverse latitudinal structure. The significance of the present study lies in bringing out the time evolution of the MQBO and addressing a few outstanding issues on its ephemerality and discrepancies in its amplitudes.

Ionospheric total electron content response to September-2017 geomagnetic storm and December-2019 annular solar eclipse over Sri Lankan region

The geomagnetic storm and solar eclipse are two important transient phenomena that crucially influence the quiet time ionospheric behavior over the low latitudes. The present study investigates the ionospheric total electron content response to the September-2017 geomagnetic storm and December-2019 annular solar eclipse from global navigation satellite system derived total electron content observations over the Sri Lankan equatorial and low latitude region. Four global navigation satellite system stations at Jaffna (1.210 N), Colombo (1.520 S), Kegalle (1.200 S) and Kalutara (1.840 S) within Sri Lanka were used for the study. The results accentuate a noticeable increase/decrease in the ionospheric total electron content during both the events. The results confirm a positive ionospheric storm effect during the solar flare associated severe geomagnetic storm in September 2017 with the total electron content enhancement of about ~11 total electron content units during the main phase of the storm with the highest variation at Kegalle. The abrupt vertical total electron content flipping during the storm are attributed to the prompt penetration electric fields followed by the disturbance dynamo electric fields during the recovery phase. Concerning the annular solar eclipse in December 2019, the four major features such as pre-ascension, major depression, sunset ascension, and secondary depression were perceptible in the total electron content variation at all stations. Moreover, the ionosphere experienced a clear vertical total electron content depletion of about ~4 total electron content units during the maximum phase of the eclipse with a percentual deviation of 23% over Jaffna and 15% over Colombo than the average quiet day values, indicating an interplay between photoionization production and recombination due to temporary solar interruption. The results would strengthen the understanding of ionospheric variability of the southern hemisphere in the Indian longitude sector.

Stability and Evolution of Fallen Particles Around the Surface of Asteroid (101955) Bennu

AbstractIn this study, we study the dynamics of particles around Bennu. The goal is to understand the stability, evolution, and final outcome of the simulated particles around the asteroid. According to the results, the particle sizes can be divided into two main groups depending on their behavior. Particles smaller than a centimeter are quickly removed from the system by solar radiation pressure, while the dynamics of particles larger than a few centimeters is dominated by the gravitational field of Bennu. Because of its shape and spin period, Bennu has eight equilibrium points around it. The structure of the phase space near its equatorial surface is directly connected to these equilibrium points. Therefore, we performed numerical simulations to obtain information about the orbital evolution near the equilibrium points. The results show that most of the particles larger than a few centimeters fall in the equatorial region close to the Kingfisher area or close to the region diametrically opposite to it. In contrast, almost none of these particles fall in the equatorial region close to the Osprey area. In addition, we also performed computational experiments considering a spherical cloud of particles initially orbiting Bennu. Most of the particles in prograde orbits fall on the surface within our integration period, which was limited to 1.14 years. The particles preferentially fall near high‐altitude regions at low equatorial latitudes and close to the north pole. The mid‐latitudes are those more depleted of falls, as in the Nightingale and Sandpiper areas.