Equatorial Latitudes Research Articles

Can an impulsive variation of the solar wind plasma pressure trigger a plasma bubble? A case study based on CSES, Swarm and THEMIS data

During the August 25, 2018 geomagnetic storm, the new borne CSES-01 satellite and the Swarm A satellite detected a really large equatorial plasma bubble (EPB) in the post-midnight sector over western Africa. We investigated the features of this deep ionospheric plasma depletion using data from the Langmuir probes on-board CSES-01 and Swarm A satellites, and data from the high-precision magnetometer and the electric field detector instruments on-board CSES-01. Using also plasma and magnetic field data from THEMIS-E satellite we found that, during the passage of the magnetic cloud that drove the geomagnetic storm, an impulsive variation lasting about ten minutes characterized the solar wind (SW) pressure. The analysis of the delay time, between the occurrence of such impulsive variation and the detection of the plasma bubble, suggests a possible link between the SW pressure impulsive variation as identified by THEMIS-E and the generation of the EPB as detected by CSES-01 and Swarm A. We put forward the hypothesis that the SW pressure impulsive variation might have triggered an eastward prompt penetrating electric field that propagated from high to equatorial latitudes, overlapping in the nightside region to the zonal westward electric field, causing either a reduction or an inversion, at the base of the EPB triggering.

Asymmetry in the Length Scales of the Solar Supergranulation Network

Abstract Supergranulation is the horizontal velocity pattern on the solar surface with a typical size of 30,000 km and a lifetime of 24 hr. The network structure seen in chromospheric lines, such as Ca ii K 3934 Å, is the manifestation of supergranulation. The network seen in the extreme-ultraviolet lines like He ii 304 Å is the extension of the chromospheric network into the upper solar atmosphere. We have obtained the length scales of the supergranulation network from the autocorrelation function of calcium ii K spectroheliograms from the Kodaikanal archival data. The behavior of the length scales in the horizontal (parallel to the direction of rotation) and vertical (perpendicular to the direction of rotation) have been obtained in different latitudes for a period of about 100 yr. The time-averaged length scales show a nearly symmetric variation in the northern and southern hemispheres. The length scales also show a profound asymmetry in the horizontal and vertical directions, which is dependent on solar latitude. A comparison reveals that both length scales are almost equal near the equatorial latitudes, but the vertical length scales relatively become smaller toward higher latitudes. The asymmetry is independently verified from He ii 304 Å images from the Solar Dynamic Observatory/Atmospheric Imaging Assembly. As the length scales are related to the width of the network, the results point to the asymmetry in the supergranular cell boundary. Supergranulation is one of the basic length scales of solar convection, hence these results can have implications for the convection in Sun-like stars.

Statistical Characteristics and Correlation of Low‐Latitude F Region Bottom‐Type Irregularity Layers and Plasma Plumes Over Sanya

AbstractIonospheric F region bottom‐type irregularity layer has been frequently detected at equatorial latitude and regarded as a possible precursor of equatorial backscatter plumes producing scintillations. In this study, the VHF radar observations of ionospheric F region bottom‐type irregularity layers and plasma plumes over the low‐latitude station Sanya (18.4°N, 109.6°E, dip lat. 12.8°N) during the equinoctial months (March, April, September, and October) of 2011–2018 are analyzed. The results show an equinoctial asymmetry in the occurrence of F region backscatter plumes, wherein the occurrence could be greater in spring or autumn months under different solar activities and background ionospheric conditions (F layer height and density). On the other hand, the bottom‐type irregularity layer occurred almost exclusively in the descending phase of solar cycle (2015–2018). No clear correlation is found between the occurrences of bottom‐type irregularity layer and plasma plume at low latitude. The F layer virtual height (h′F) observations from the Sanya ionosonde show that the average h′F is higher during the months when the plume occurrence is higher, suggesting that the asymmetric plasma vertical drift could play a role in the equinoctial asymmetry of plume occurrence. Larger vertical drift (and higher h′F) could cause higher occurrence of equatorial plasma plumes which extend to low latitudes along magnetic field lines. In contrast, during the days when bottom‐type irregularity layers occur, the h′F is relatively lower. We surmise that only when the background F region is situated at low altitudes (with h′F < ~250 km), the low‐latitude bottom‐type irregularity layer could be generated.

Spatial Variations in Disturbance Ionospheric Currents—Inference From 12 Geomagnetic Storms

AbstractIn this paper, we investigate the latitudinal and longitudinal variations of the disturbance ionospheric current during 12 geomagnetic storms with Dst ranging between −50 and −130 nT. For this purpose, data from 15 geomagnetic stations along three longitudinal sectors at 70°E, 77°E, and 93°E, ranging from middle to equatorial latitudes in both hemispheres are analyzed. Our study reveals the pattern of PP in the different phases of the storm and the competing effects of PP and Ddyn during the recovery phase of the storms. The PP signatures are mainly comparable across longitudes, irrespective of the strength and phase of the storm. The effect of Ddyn shows a seasonal pattern, which is influenced by the strength of the storm. The location of the antifoci during each storm shows latitudinal variability.

Against all odds: a tale of marine range expansion with maintenance of extremely high genetic diversity

The displacement of species from equatorial latitudes to temperate locations following the increase in sea surface temperatures is among the significant reported consequences of climate change. Shifts in the distributional ranges of species result in fish communities tropicalisation, i.e., high latitude colonisations by typically low latitude distribution species. These movements create new interactions between species and new trophic assemblages. The Senegal seabream, Diplodus bellottii, may be used as a model to understand the population genetics of these invasions. In the last decades, this species has undergone an outstanding range expansion from its African area of origin to the Atlantic coast of the Iberian Peninsula, where now occurs abundantly. Mitochondrial and nuclear markers revealed a striking high haplotypic nucleotide and genetic diversity values, along with significant population differentiation throughout the present-day geographical range of the Senegal seabream. These results are not consistent with the central-marginal hypothesis, nor with the expectations of a leptokurtic distribution of individuals, as D. bellottii seems to be able to retain exceptional levels of diversity in marginal and recently colonised areas. We discuss possible causes for hyperdiversity and lack of geographical structure and subsequent implications for fisheries.

Investigation of the Influence of Distant Parameters on Horizontal Component of Ground Magnetic Field.

The influence of distant parameters on the horizontal component of magnetic field was investigated for two years within two locations in Africa. The measure of storm occurrence (Dst-index) was used to select successful storm days. The effect of distant parameters on residual field was investigated using filter analysis. This study was considered on both time domain and frequency domain. The results showed very close correspondence of rapid changes in amplitudes between residual H–component and the selected IMF parameters especially the solar wind velocity, proton density and Bz. The correlation analysis between the distant parameters and residual H–component completely revealed effective dependence of the depression of residual field on the selected parameters. The value of the correlation coefficient (r) with solar wind velocity, proton density and Bz showed significant values of the range of 0.5 and above. This is direct evidence that Solar wind velocity, proton density and Bz are more effective in causing geomagnetic fluctuations at equatorial low latitude stations.

Total electron content at equatorial and low-, middle- and high-latitudes in African longitude sector and its comparison with IRI-2016 and IRI-PLAS 2017 models

Ionosphere plays crucial role in satellite communication as well as the modern space-based positioning, navigation and timing applications. Progressive exploitation of ground and space-based observations across the African region has relatively strengthened the understanding and modeling of spatiotemporal ionospheric variations over the territory. However, it is also equally important to understand the latitudinal behaviour of ionosphere over the African longitude that would reinforce the ionospheric delay error modelling practices for an improved radio communication along the satellite pass. Hence, the aim of this research is to investigate the diurnal, seasonal and latitudinal variations of global positioning system derived total electron content (GPS-TEC) and to assess the performance of the recent version of empirical international reference ionosphere (IRI-2016) and plasmaspheric IRI (IRI-PLAS 2017) models during the ascending phase of solar cycle 24 (2012). The study is also supported by the integrated ionospheric TEC (IONO-TEC) extracted from the Digisonde observations in the vicinity of GPS receiver locations. The 3 GPS stations considered in this study are at a) an equatorial/ low-latitude location Federal University of Technology, Yola (FUTY; 9.35°N, 12.50°E, 4.91°S dip), b) a mid-latitude location Ankara (ANKR; 39.89°N, 32.76°E, 57.62°N dip), and a high-latitude location Tromso (TRO1; 69.66°N, 18.94°E, 78.17°N dip) in the northern hemisphere. Observations show the magnitude of TEC generally decreases with increasing latitude. While the average diurnal maximum of GPS-TEC at equatorial and low-latitude follow an almost equal level of magnitude during March and September equinoxes, the observations at middle and high latitude stations presents the highest magnitudes during the September equinox. Moreover, we noticed obvious higher magnitude of GPS-TEC than IONO-TEC at the three stations suggesting the discrepancies could be corresponding to the topside modeling and plasmaspheric contributions. The other prominent feature is the pattern of diurnal TEC being dome shaped at middle and high latitude locations whereas the equatorial and low latitude location manifested a noon bite-out characteristic in the IONO-TEC, IRI-2016, and IRI-PLAS outcomes. The comparative analysis of IRI-2016 and IRI-PLAS 2017 estimated TEC with the GPS-TEC show a clear overestimation of IRI-PLAS 2017 outcomes irrespective of seasons and latitudinal locations whereas the IRI-2016 outcomes either overestimated or underestimated the GPS-TEC. Hence, this study reveals that IRI-2016 performs better predictions compared to IRI-PLAS 2017 at all the three latitudinal locations. Such a latitudinal comparison across the African-European longitudinal sector may complement towards the efforts for improving the regional as well as global ionospheric model performances.

Skin colour and vitamin D: An update.

Homo sapiens evolved in East Africa and had dark skin, hair, and eyes, in order to protect against deleterious consequences of intensive UV radiation at equatorial latitudes. Intensive skin pigmentation was thought to bear the risk of inefficient vitamin D3 synthesis in the skin. This initiated the hypothesis that within the past 75000years, in which humans migrated to higher latitudes in Asia and Europe, the need for vitamin D3 synthesis served as an evolutionary driver for skin lightening. In this review, we summarize the recent archeogenomic reconstruction of population admixture in Europe and demonstrate that skin lightening happened as late as 5000years ago through immigration of lighter pigmented populations from western Anatolia and the Russian steppe but not primarily via evolutionary pressure for vitamin D3 synthesis. We show that variations in genes encoding for proteins being responsible for the transport, metabolism and signalling of vitamin D provide alternative mechanisms of adaptation to a life in northern latitudes without suffering from consequences of vitamin D deficiency. This includes hypotheses explaining differences in the vitamin D status and response index of European populations.

Ionospheric Plasma Irregularities Based on In Situ Measurements From the Swarm Satellites

AbstractIn this study, we present global climatological distributions of ionospheric plasma irregularities based on measurements by the Swarm satellites. These first global statistics obtained by direct, in situ measurements of plasma variations with Swarm confirm the presence of three main regions of strong ionospheric irregularities: the magnetic equator extending from postsunset to early morning, in the auroral ovals (from dayside cusp to nightside), and inside the polar caps. At equatorial latitudes, ionospheric irregularities form two bands of enhanced plasma fluctuations centered around ±10° magnetic latitude. Due to different plasma processes, ionospheric irregularities at high and low latitudes show different distributions. Though the averaged intensity of plasma irregularities is weaker at equatorial latitudes than at high latitudes, the occurrence rate of significant plasma fluctuations (corresponding to extreme events) is much higher at the equator than that at high latitudes. Equatorial irregularities display clear seasonal and longitudinal variations; that is, they are most prominent over South America during the December solstice and are located over Africa during the June solstice. The magnitude of ionospheric irregularities at all latitudes is strongly controlled by the solar activity. Ionospheric irregularities become significantly weaker after 2016 during the current declining phase of solar activity. The interplanetary magnetic field Bz modulates the occurrence of ionospheric irregularities at both high and low latitudes.

Performance analysis of Neural Networks with IRI-2016 and IRI-2012 models over Indian low-latitude GPS stations

The Global Positioning System (GPS) applications are highly vulnerable to the ionospheric space weather effects. Modelling and forecasting the ionospheric effects such as time delays for GPS signals are important for real time alerts of space weather effects on GPS services. In the present work, the performance of Neural Networks (NN) model is compared with International Reference Ionosphere (IRI) models. The ionospheric Total Electron Content (TEC) observations have been collected during 2015 year, descending phase of 24th solar cycle, over three Indian low latitude GPS stations namely, Bengaluru (Geographic coordinates: 13.02°N and 77.57°E), near to geomagnetic equator, Guntur (Geographic coordinates: 16.37°N and 80.37°E), which is at Equatorial Ionization Anomaly (EIA) and Lucknow (Geographic coordinates: 26.83°N and 80.92°E), which is beyond EIA region. The performance of NN model in predicting the ionospheric TEC values is compared with IRI (IRI-2012 and IRI-2016) models during test period, October–December 2015 over three Indian low latitude regions. It is observed that IRI models (IRI-2012 and IRI-2016) have shown more the temporal differences with GPS-VTEC during sunrise hours compared to sunset hours over three low latitude regions. The performance of IRI-2016 model has apparently better than IRI-2012 model. However, it is observed that IRI-2016 model has large discrepancies over Bengaluru and Guntur station due to high VTEC fluctuations at equatorial and low latitudes. The NN models are well predicted the measured diurnal mean VTEC variations with the less errors, ±5 TECU but the differences of IRI models are ±15 TECU over all the three stations. Later, GPS-data for 10 years, 2009–2018, is collected over Bengaluru station during 24th solar cycle. The performance of NN model is validated during 2016, 2017 and 2018 years over Bengaluru GPS station. The error measurements and experimental results reported that the measured GPS-VTEC values are well predicted by NN model compared to IRI-2016 model over equatorial and low latitude GPS stations.

The youngest Ordovician (latest Katian) coral fauna from eastern Australia, in the uppermost Malachis Hill Formation of central New South Wales

Corals representing the sole occurrence of C/S Fauna IV of the regional biostratigraphic scheme occur in limestone in the uppermost Malachis Hill Formation of the Bowan Park area, central New South Wales. New species described and illustrated from this fauna include the rugosan Bowanophyllum ramosum and tabulate Hemiagetiolites longiseptatus. Also documented are three other distinct species of Hemiagetiolites, H. spinimarginatus (Hall, 1975), H. sp. cf. H. palaeofavositoides (Lin & Chow, 1977) and H. sp., an unnamed species of Paleofavosites, and three heliolitine corals, Heliolites waicunensis Lin & Chow, 1977, Navoites cargoensis (Hill, 1957) and Plasmoporella sp. These descriptions, which complete knowledge of the entire fauna collected over 50 years, enable interesting conclusions to be drawn regarding palaeogeographic affinities of this youngest in situ Ordovician coral fauna known from eastern Australia. Its remarkable similarities to contemporaneous coral faunas from South Tien Shan and the Chu-Ili Terrane indicate strong connections between eastern Australia and the latter two terranes, supporting their positioning in equatorial latitudes of eastern peri-Gondwana. However, it is puzzling that fewer similarities exist between the eastern Australian coral fauna and those from rocks of Katian age in SE China, which may be due to either a slightly younger age of the former fauna or a relatively higher palaeolatitudinal position of South China.Guangxu Wang [gxwang@nigpas.ac.cn], State Key Laboratory of Palaeobiology and Stratigraphy; Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Nanjing Institute of Geology and Palaeontology, Nanjing 210008, China; Ian G. Percival [ian.percival@planning.nsw.gov.au], and Yong Yi Zhen [yong-yi.zhen@planning.nsw.gov.au], Geological Survey of New South Wales, 947–953 Londonderry Road, Londonderry, NSW 2753, Australia.

Quiet-time and storm-time variations of the African equatorial and low latitude ionosphere during 2009–2015

This study investigates the quiet-time and storm-time variations of the African equatorial and low latitude ionosphere during 2009–2015. We obtained TEC observation data from four Global Navigation Satellite System (GNSS) stations over the African equatorial and low latitude, namely: Asab (ASAB, geographic coordinates 13.0°N, 42.65°E; geomagnetic coordinates 4.85°N, 114.34°E), Arba Minch University, (ARMI, 6.03°N, 37.56°E; 3.06°S, 109.29°E), Yamoussoukro (YKRO, 6.87°N, 5.24oW; 2.84°S, 67.41°E) and Mbarara (MBAR, 0.60°S, 30.74°E; 10.27°S, 102.36°E). Seven selected major Geomagnetic Storms (GSs) over solar cycle 24 were investigated and the responses of TEC and Rate of change of TEC Index (ROTI) as proxy for ionospheric irregularities to the storms were also studied. We recorded weaker ionospheric plasma density distributions around the magnetic equator (trough) than at the inner flank of the Equatorial Ionization Anomaly (EIA) crests: A clear evidence of EIA formation. Furthermore, hemispherical asymmetry was observed in the latitudinal distribution of TEC, with consistently higher distribution in the Northern Hemisphere (NH) than Southern Hemisphere (SH). TEC and ionospheric irregularities showed clear dependence on solar activity. Negative responses dominated GSs that occurred at night-time and positive effects for those that occurred during the daytime. The enhancement or inhibition of irregularities during GS is strongly dependent on the time of GS unfolding. As previously established, the daily maximum distribution of TEC at 1400–1600 LT and minimum at 0400–0600 LT were validated by this study, using long time (7 years) data. Seasonally, TEC showed semi-annual pattern of variations, with highest values in equinoxes, and lowest in solstices.

Low-latitude GNSS ionospheric scintillation dependence on magnetic field orientation and impacts on positioning

Ionospheric scintillation often occurs in equatorial and low-latitudes regions between ± 20° geomagnetic latitude and impacts GNSS performance on geodetic applications. In equatorial and low latitude regions, scintillation on the GNSS signal occurs mainly due to small-scale irregularities inside plasma bubbles that are magnetic field-aligned structures. We derived the propagation angle between GNSS ray paths and magnetic field lines to quantify scintillation occurrences of multi-constellation GNSS signals in relation to magnetic field orientation. Precise point positioning (PPP) solutions are obtained to assess the field-aligned scintillation signal impacts on positioning. A case study based on observations in Hong Kong is conducted to characterize a typical low-latitude region near the northern equatorial anomaly crest. Measurements from multiple GNSS constellations, i.e., GPS, GLONASS, Galileo and BDS are used. Results suggest that the GNSS scintillation intensity is enhanced in the local southern sky within the azimuth range of 150°–240° with peak at ~ 180°, where the signal paths closely align with the magnetic field lines. Analysis of the data show that up to five GPS satellites may have their signal paths aligned closely with magnetic field lines simultaneously. This can result in an increase in the kinematic PPP errors from several centimetres to tens of meters. The relationship between the scintillation occurrence and magnetic field orientation could be exploited in the future to mitigate scintillation effects on GNSS applications.

Coronal-jet-producing Minifilament Eruptions as a Possible Source of Parker Solar Probe Switchbacks

Abstract The Parker Solar Probe (PSP) has observed copious rapid magnetic field direction changes in the near-Sun solar wind. These features have been called “switchbacks,” and their origin is a mystery. But their widespread nature suggests that they may be generated by a frequently occurring process in the Sun’s atmosphere. We examine the possibility that the switchbacks originate from coronal jets. Recent work suggests that many coronal jets result when photospheric magnetic flux cancels, and forms a small-scale “minifilament” flux rope that erupts and reconnects with coronal field. We argue that the reconnected erupting-minifilament flux rope can manifest as an outward propagating Alfvénic fluctuation that steepens into an increasingly compact disturbance as it moves through the solar wind. Using previous observed properties of coronal jets that connect to coronagraph-observed white-light jets (a.k.a. “narrow CMEs”), along with typical solar wind speed values, we expect the coronal-jet-produced disturbances to traverse near-perihelion PSP in ≲25 minutes, with a velocity of ∼400 km s−1. To consider further the plausibility of this idea, we show that a previously studied series of equatorial latitude coronal jets, originating from the periphery of an active region, generate white-light jets in the outer corona (seen in STEREO/COR2 coronagraph images; 2.5–15 R ⊙), and into the inner heliosphere (seen in Solar-Terrestrial Relations Observatory (STEREO)/Hi1 heliospheric imager images; 15–84 R ⊙). Thus it is tenable that disturbances put onto open coronal magnetic field lines by coronal-jet-producing erupting-minifilament flux ropes can propagate out to PSP space and appear as switchbacks.

Ice Permafrost ‘‘Oases’’ Close to Martian Equator: Planet Neutron Mapping Based on Data of FREND Instrument Onboard TGO Orbiter of Russian-European ExoMars Mission

We present the first results of Mars neutron sounding by FREND instrument onboard ESA’s Trace Gas Orbiter data analysis. Neutron flux mapping is performed with high spatial resolution, which allows to match epithermal neutron flux variation with relief’s geomorphological structures. Local regions with suppressed neutron flux indicate the presence of considerable amount of hydrogen atoms in the surface material, which is supposedly part of water molecules. Local regions in the equatorial latitudes of the planet with significant decrease of neutron flux are discovered, which points to large mass fraction of water ice in the soil material, ranging from tens to 100 $$\%$$ . Considering high water content, these regions are named ice permafrost ‘‘oases.’’ Estimates of ice mass fraction for 7 such regions are obtained based on neutron measurements analysis and end-to-end numerical modeling of the entire physical process of neutron sounding by FREND on Mars orbit. Possible reasons for formation of such ‘‘oases’’ and their significance for future Mars exploration are discussed.

Ionospheric response to the 26 August 2018 geomagnetic storm using GPS-TEC observations along 80° E and 120° E longitudes in the Asian sector

This study investigates the response of equatorial and low latitude ionosphere during an intense geomagnetic storm of 26 August 2018 (Dst min = −206 nT) using the TEC observations from two chains of GPS stations along 80° E and 120° E longitudes in the Asian sector. These GPS networks include Waltair and four IGS stations (SGOC, IISC, HYDE and LCK4) along 80° E and five IGS stations (SHAO, TCMS, CKSV, PIMO and PGEN) along 120° E longitudes. The [O]/[N2] observations from GUVI have also been used for the present study. Large positive storm effect is observed in the day-time TEC for three consecutive days starting from main phase until the late recovery phases of the storm (26th to 28th August 2018). Significant difference has been observed in TEC response between 80° E and 120° E longitudes particularly during the recovery phase of the storm which is further confirmed by GIM derived TEC. The equatorial ionization anomaly (EIA) exhibit strong enhancement around the anomaly crests during the main phase of the storm. This enhancement in the EIA crest is also evidenced in GIM CODE TEC maps. The positive storm effect during the main and recovery phases is mainly attributed to the eastward prompt penetration electric fields in addition to strongly enhanced ratio of thermosphere neutral composition i.e. [O]/[N2], the results of which are presented in this paper.

Mt. Wendelstein imaging of comet 41P/Tuttle-Giacobini-Kresak during the 2017 perihelion arc

Context.In April 2017 comet 41P/Tuttle-Giacobini-Kresak (41P) passed perihelion close to Earth.Aims.We present observations of the comet and aim to use these to characterize its dust environment in the coma and of physical properties of the nucleus.Methods.41P was imaged in the visible at the Mt. Wendelstein observatory over 45 nights between 2017 March 11 and 2017 July 17. Photometry of the coma provides information on the dust activity of the comet. Nucleus dimensions are determined by comparing radial profiles of observed images with those from models of the brightness distribution in the near-nucleus coma. Coma and tail structures in the images are enhanced using adaptive Laplace filtering and image normalization techniques. The geometry of the coma structures found are compared to results from dust models of the comet in order to obtain information on the nucleus rotation axis and the location of active regions on the nucleus.Results.Analyzing the evolution of the dust activity of the comet versus solar distance gives different results depending on the assumed phase angle corrections for the dust. Contamination from light emissions of the coma gas modified the colors in the coma and the slopes of the radial profiles. The light distribution in the very inner coma indicates some dust fragmentation close to the nucleus. The appearance of a prominent coma fan during the time period from March to May 2017 constrains the rotation axis of the nucleus (52 deg obliquity, 50 deg rotation angle of the perihelion meridian). This fan is produced by an extended region beyond about 50 deg latitude on the nucleus. Two narrow regions at low northern to equatorial latitudes were responsible for the time-variable occurrence of linear dust jets in the coma. An outburst of about 0.6 mag on 2017 May 11 generated various dust structures in the coma. The outburst originated from a region extending over a latitude range from +30 deg to −5 deg and released about 3000 tons of dust into the coma. The brightness of the nucleus indicates an equivalent radius of about 600 m and a minimum axis ratio larger than two.

ОХОЛОДЖЕННЯ НАДДУВНОГО ПОВІТРЯ ГОЛОВНОГО СУДНОВОГО ДВИГУНА ЕЖЕКТОРНОЮ ХОЛОДИЛЬНОЮ МАШИНОЮ В ЕКВАТОРІАЛЬНИХ ШИРОТАХ

The efficiency of cooling the scavenge air of the main low-speed engine of the transport vessel during operation in the equatorial tropical latitudes is analyzed. The peculiarity of the tropical climate is the high relative humidity of the air at the same time its high temperatures and temperatures of seawater. The cooling of the s scavenge air with a refrigerant ejector chiller was investigated by transforming the scavenge air heat into the cold. With this, the potentially possible minimum temperature of the cooled air was determined considering the boiling temperature of the refrigerant and the temperature differences in the heat exchangers of the intermediate water cooling circuit. Refrigerant ejector chiller is used as the most simple and reliable in design. However, the efficiency of converting the heat to cold by ejector chillers is low: their coefficients of performance are approximately 0.3. Circuit-design solution of three-stage cooling system of scavenging air of ship's main engine - in high-temperature (cogeneration) stage using the extracted heat of scavenging air to get cold with ejector chiller and traditional stage for cooling scavenge air by seawater and low-temperature cooling stage by ejector chiller. The effect of deeper cooling of the scavenge air was determined in comparison with the cooling of the scavenge air with seawater, taking into account the changing climatic conditions during the route of the vessel. It is shown that because of the insufficiently high efficiency of transformation of the scavenge air heat by the ejector chiller (low coefficients of performance) the obtained cooling capacity is not sufficient to cool the scavenge air to a potentially possible minimum temperature of 22 °C when operating the ship engine in tropical climates. However, the heat deficit is relatively small and can be covered by the use of additional exhaust gas heat.

ОХОЛОДЖЕННЯ НАДДУВНОГО ПОВІТРЯ ГОЛОВНОГО СУДНОВОГО ДВИГУНА АБСОРБЦІЙНОЮ БРОМИСТОЛІТІЄВОЮ ХОЛОДИЛЬНОЮ МАШИНОЮ В ЕКВАТОРІАЛЬНИХ ШИРОТАХ

The efficiency of cooling the scavenge air of the main low-speed engine of the transport vessel during operation in the equatorial tropical latitudes is analyzed. The peculiarity of the tropical climate is the high relative humidity of the air at the same time its high temperatures and temperatures of seawater. The cooling of the scavenge air with an absorption lithium bromide chiller by transforming the scavenge air heat into the cold was investigated. With this, the potentially possible minimum temperature of the cooled air was determined considering the temperature of the cold water (coolant) from the absorption lithium bromide chiller and the temperature differences in the heat exchangers of the intermediate water circuit of cooling. Absorption lithium bromide chillers are characterized by high efficiency of transformation of waste heat into cold - high coefficients of performance. Circuit-design solution of three-stage cooling system of scavenging air of ship's main engine - in high-temperature (cogeneration) stage using the extracted heat of scavenging air to get cold with absorption chiller and traditional stage for cooling scavenge air by seawater and low-temperature cooling stage by absorption chiller. The effect of deeper cooling of the scavenge air was determined in comparison with the cooling of the scavenge air with seawater, taking into account the changing climatic conditions during the route of the vessel. It is shown that due to the high efficiency of heat transformation in absorption chillers (high coefficients of performance 0.7…0.8), there is a significant amount of excess heat of scavenging air over the heat required to cool it to 22 °C, which reaches almost half of the available scavenge air heat on the Shanghai-Singapore-Shanghai route. This reveals the possibility of additional cooling the inlet of the turbocharger of the engine with the achieving almost double fuel economy due to the cooling of all cycle air of the low-speed engine, including the air at the inlet.

Can Tropical Pacific Winds Enhance the Footprint of the Interdecadal Pacific Oscillation on the Upper-Ocean Heat Content in the South China Sea?

AbstractIn this study, an enhanced footprint of the interdecadal Pacific oscillation (IPO) on the upper-ocean heat content (OHC) in the South China Sea (SCS) since the 1990s is revealed. The negative OHC–IPO correlation is significant (r= −0.71) during 1990–2010 [period 2 (P2)], whereas it is statistically insignificant during 1960–80 [period 1 (P1)]. Analyses show that the scope of the equatorial Pacific wind anomalies is wider during P2 compared with that during P1 due to a larger east–west SST gradient and enhanced tropical warming in the Indian Ocean. When the IPO is negative during P2, a wider scope of the wind stress anomalies associated with the IPO could lead to 1) the southward migration of the North Equatorial Current bifurcation latitude (NECBL) by affecting the wind stress curl over the key region where it is near the climatological NECBL and 2) an increase in the interbasin pressure gradient (sea surface height difference) between the western Pacific and the SCS; these two processes strengthen the Kuroshio and weaken the Luzon Strait transport (LST) or SCS throughflow into the SCS. Also, 3) the equatorial Pacific wind anomalies are wide enough to directly weaken the LST in the SCS through the “island rule.” These three pathways finally change the oceanic gyre in the SCS and increase the OHC. Our results suggest that the scope of the tropical wind stress is the crucial factor when we consider the relationship between the upper ocean thermal conditions in the SCS and the Pacific variability.