Synoptic Maps Research Articles

Aggregation Characteristics of the Sun’s Large-Scale Magnetic Field Associated with a Global Magnetic Anomaly in the Last Extended Solar Cycle

The solar cycle represents the Sun’s periodically changing magnetic state, which is potentially subject to global magnetic anomalies emerging on it. What the characteristics are of the Sun’s large-scale magnetic field playing roles in these anomalies is a key to clarifying how the Sun deviates from its normal magnetic state. This article reports aggregation characteristics of the large-scale magnetic field associated with a global magnetic anomaly that emerged when the Sun went through one of the longest solar cycles in two hundred years. The characteristics were identified by extracting cluster feature values of solar surface magnetic fields via a population ecological method from synoptic maps, obtained by the longest homogeneous series of magnetic field observations for the past several decades. We found that the anomaly was due to the uneven clustering of positive and negative surface magnetic fields that occurred during the solar minimum leading to the last extended solar cycle. Our findings may provide new insight into magnetic field characteristics peculiar to a solar minimum with an extended cycle length.

A Uniform Series of Low-Latitude Coronal Holes in 1973\u20132018

Coronal holes (CHs) are regions in the solar corona characterized by plasma density lower than in the surrounding quiet Sun. Therefore they appear dark in images of the solar atmosphere made, e.g., in extreme ultraviolet (EUV). Identifying CHs on solar images is difficult since CH boundaries are not sharp, but typically obscured by magnetic structures of surrounding active regions. Moreover, the areas, shapes, and intensities of CHs appear differently in different wavelengths. Coronal holes have been identified both visually by experienced observers and, more recently, by automated detection methods using different techniques. In this article, we apply a recent, robust CH identification algorithm to a new set of homogenized EUV synoptic maps based on four EUV lines measured by the Solar and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope (SOHO/EIT) in 1996–2018 and the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) in 2010–2018 and create corresponding CH synoptic maps. We also use CHs of the hand-drawn McIntosh archive (McA) from 1973–2009 to extend the CH database to earlier times. We discuss the success of the four EUV lines to find CHs at high or low latitudes, and confirm that the combined EIT 195 Å/AIA 193 Å series applies best for both polar and low-latitude CH detection. While the polar CH detection suffers from the vantage-point limitation, the low-latitude CH areas extracted from this line correlate with the McA CH data very well. Using the simultaneous measurements between EIT and McA and EIT and AIA, we scale the different data series to the same level and form the longest uniform series of low-latitude CHs in 1973–2018. We find that, while the solar cycle maxima of low-latitude CHs in the descending phase of Solar Cycles 21–23 attain roughly similar values, the corresponding maximum during Solar Cycle 24 is reduced by a factor of two. This suggests that magnetic flux emergence is crucial for the formation of low-latitude CHs.

Observing and modelling the young solar analogue EK Draconis: starspot distribution, elemental abundances, and evolutionary status

ABSTRACT Observations and modelling of stars with near-solar masses in their early phases of evolution are critical for a better understanding of how dynamos of solar-type stars evolve. We examine the chemical composition and the spot distribution of the pre-main-sequence solar analogue EK Dra. Using spectra from the HERMES Spectrograph (La Palma), we obtain the abundances of 23 elements with respect to the solar ones, which lead to a [Fe/H] = 0.03, with significant overabundance of Li and Ba. The s-process elements Sr, Y, and Ce are marginally overabundant, while Co, Ni, Cu, Zn are marginally deficient compared to solar abundances. The overabundance of Ba is most likely due to the assumption of depth-independent microturbulent velocity. Li abundance is consistent with the age and the other abundances may indicate distinct initial conditions of the pre-stellar nebula. We estimate a mass of 1.04 M⊙ and an age of $27^{+11}_{-8}$ Myr using various spectroscopic and photometric indicators. We study the surface distribution of dark spots, using 17 spectra collected during 15 nights using the CAFE Spectrograph (Calar Alto). We also conduct flux emergence and transport (FEAT) simulations for EK Dra’s parameters and produce 15-d-averaged synoptic maps of the likely starspot distributions. Using Doppler imaging, we reconstruct the surface brightness distributions for the observed spectra and FEAT simulations, which show overall agreement for polar and mid-latitude spots, while in the simulations there is a lack of low-latitude spots compared to the observed image. We find indications that cross-equatorial extensions of mid-latitude spots can be artefacts of the less visible southern-hemisphere activity.

Spatial–temporal evolution of photospheric weak-field shifts in solar cycles 21–24

Context. Weak magnetic field elements make a dominant contribution to the total magnetic field on the solar surface. Even so, little is known of their long-term occurrence. Aims. We study the long-term spatial–temporal evolution of the weak-field shift and skewness of the distribution of photospheric magnetic field values during solar cycles 21−24 in order to clarify the role and relation of the weak field values to the overall magnetic field evolution. Methods. We used Wilcox Solar Observatory (WSO) and the Synoptic Optical Long-term Investigations of the Sun Vector SpectroMagnetograph synoptic maps to calculate weak-field shifts for each latitude bin of each synoptic map, and thereby constructed a time–latitude butterfly diagram for shifts. We also calculated butterfly diagrams for skewness for all field values and for weak field values only. Results. The weak-field shifts and (full-field) skewness depict a similar spatial–temporal solar cycle evolution to that of the large-scale surface magnetic field. The field distribution has a systematic non-zero weak-field shift and a large skewness already at (and after) the emergence of the active region, even at the highest resolution. We find evidence for coalescence of opposite-polarity fields during the surge evolution. This is clearly more effective at the supergranulation scale. However, a similar dependence of magnetic field coalescence on spatial resolution was not found in the unipolar regions around the poles. Conclusions. Our results give evidence for the preference of even the weakest field elements toward the prevailing magnetic polarity since the emergence of an active region, and for a systematic coalescence of stronger magnetic fields of opposite polarities to produce weak fields during surge evolution and at the poles. We also find that the supergranulation process is reduced or turned off in the unipolar regions around the poles. These observations improve the understanding not only of the development of the weakest magnetic field elements, but also of the dynamics of magnetic fields at large, and even of processes below the solar surface.

МЕТЕОРОЛОГИЧЕСКИЕ УCЛОВИЯ ВОЗНИКНОВEНИЯ ШТОРМОВОГО ВEТРA И ПЫЛЬНОЙ БУРИ В AТЫРAУCКОЙ ОБЛACТИ В ЯНВAРE 2021 Г.

The article discusses the atmospheric processes that caused the occurrence of storm wind and a dust storm in the Atyrau region on January 14, 2021. We provide synoptic maps and satellite images, actual and forecast data, analyze in detail the synoptic situation that led to the occurrence of the dangerous phenomena, as well as the general characteristics of the formation of dust storms in the western part of Kazakhstan. In the winter period, the north-eastern part of the Caspian Sea and the entire Atyrau region are under the influence of the western ridge of the Asian (Siberian) high pressure area. The center of high pressure in the winter is located over the central part of Mongolia, in the summer - over the European territory of Russia, therefore winds with a northerly component are a frequent phenomenon in the Atyrau region. We have established that the occurrence and development of dust storms were conditioned by a complex of meteorological factors, including a strong gale wind (more than 15 m/s), shallow freezing of the soil, desiccation and dispersion of the upper layer of the soil, absence of snow cover and ice crusts, weak vegetation cover, and presence of vast open spaces. The total material damage from the observed complex of dangerous phenomena in the territory of the Atyrau region amounted to 14.5 million tenge (34 thousand dollars).

Differential Rotation of the Chromosphere in the He I Absorption Line

Abstract Differential rotation is the basis of the solar dynamo theory. Synoptic maps of He I intensity from Carrington rotations 2032–2135 are utilized to investigate the differential rotation of the solar chromosphere in the He I absorption line. The chromosphere is surprisingly found to rotate faster than the photosphere below it. The anomalous heating of the chromosphere and corona has been a big problem in modern astronomy. It is speculated that the small-scale magnetic elements with magnetic flux in the range of (2.9–32.0) × 1018 Mx, which are anchored in the leptocline, heat the quiet chromosphere to present the anomalous temperature increase, causing it to rotate at the same rate as the leptocline. The differential of rotation rate in the chromosphere is found to be strengthened by strong magnetic fields, but in stark contrast, at the photosphere strong magnetic fields repress the differential of rotation rate. A plausible explanation is given for these findings.

Machine-learning Approach to Identification of Coronal Holes in Solar Disk Images and Synoptic Maps

Abstract Identification of solar coronal holes (CHs) provides information both for operational space weather forecasting and long-term investigation of solar activity. Source data for the first problem are typically from the most recent solar disk observations, while for the second problem it is convenient to consider solar synoptic maps. Motivated by the idea that the concept of CHs should be similar for both cases we investigate universal models that can learn CH segmentation in disk images and reproduce the same segmentation in synoptic maps. We demonstrate that convolutional neural networks trained on daily disk images provide an accurate CH segmentation in synoptic maps and their pole-centric projections. Using this approach we construct a catalog of synoptic maps for the period of 2010–20 based on SDO/AIA observations in the 193 Å wavelength. The obtained CH synoptic maps are compared with magnetic synoptic maps in the time-latitude and time-longitude diagrams. The initial results demonstrate that while in some cases the CHs are associated with magnetic flux-transport events there are other mechanisms contributing to the CH formation and evolution. To stimulate further investigations the catalog of synoptic maps is published in open access.

Analysis of aerosol optical depth over Bahrain and Eastern Province of Saudi Arabia based on MERRA-2 model

Spatial and temporal variability of aerosol optical depth (AOD) together with aerosol-type specification were analyzed over Eastern Province of Kingdom of Saudi Arabia (KSA) and Bahrain from 2008 to 2019. To investigate study region with more details, the Eastern Province of Saudi Arabia and Bahrain was divided into three and four zones, respectively. This work utilized comprehensive satellite-based air quality data using NASA’s Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) model. The retrieved total AOD data exhibited relatively lower average values in the Bahraini zones in comparison with the Eastern KSA during the study period. The monthly total AOD values in Bahraini zones were in the range of 0.20 and 0.87, while they were in the range of 0.23 and 0.91 in KSA zones. The AOD values were positively correlated with ambient air temperature (r = 0.43), while they were negatively correlated with relative humidity (r = 0.59) in Bahrain. Seasonal wind rose diagrams for Bahrain and monthly synoptic maps of (20–40°N, 40–60°E) West Asia region demonstrates that dominant wind direction is from NNW to Bahrain. The data assimilation algorithms in MERRA-2 showed that the major aerosol species that contributed to total AOD were as follows: mineral dust (68–74%), sulfate (17–20%), organic carbon (4–5%), sea salt (3–5%) and black carbon (2%). Monthly, seasonal and annual variations of speciated AOD values assisted in understanding aerosols loading over study area.

Identifying solar-like magnetic cycles with Zeeman-Doppler-Imaging

ABSTRACT We are reaching the point where spectropolarimetric surveys have run for long enough to reveal solar-like magnetic activity cycles. In this paper, we investigate what would be the best strategy to identify solar-like magnetic cycles and ask which large-scale magnetic field parameters best follow a solar-type magnetic cycle and are observable with the Zeeman-Doppler-Imaging (ZDI) technique. We approach these questions using the 3D non-potential flux transport simulations of Yeates & Mackay (2012) modelling the solar vector magnetic field over 15 yr (centred on solar cycle 23). The flux emergence profile was extracted from solar synoptic maps and used as input for a photospheric flux transport model in combination with a non-potential coronal evolution model. We synthesize spectropolarimetric data from the simulated maps and reconstruct them using ZDI. The ZDI observed solar cycle is set into the context of other cool star observations and we present observable trends of the magnetic field topology with time, sunspot number, and S-index. We find that the axisymmetric energy fraction is the best parameter of the ZDI detectable large-scale field to trace solar-like cycles. Neither the surface averaged large-scale field or the total magnetic energy is appropriate. ZDI seems also to be able to recover the increase of the toroidal energy with S-index. We see further that ZDI might unveil hints of the dynamo modes that are operating and of the global properties of the small-scale flux emergence like active latitudes.

Uncertainty Estimates of Solar Wind Prediction Using HMI Photospheric Vector and Spatial Standard Deviation Synoptic Maps

Current solar wind prediction is based on the Wang & Sheeley empirical relationship between the solar wind speed observed at 1 AU and the rate of magnetic flux tube expansion (FTE) between the photosphere and the inner corona, where FTE is computed by coronal models that take the photospheric flux density synoptic maps as their inner boundary conditions to extrapolate the photospheric magnetic fields to deduce the coronal and the heliospheric magnetic field configuration. Since these synoptic maps are among the most widely-used of all solar magnetic data products, the uncertainties in the model predictions that are caused by the uncertainties in the synoptic maps are worthy of study. However, such an estimate related to synoptic map construction was not available until Bertello et al. (Solar Physics, 289, 2014) obtained the spatial standard deviation synoptic maps; 98 Monte-Carlo realizations of the spatial standard deviation maps for each photospheric synoptic maps. In this paper, we present an estimate of uncertainties in the solar wind speed predicted at 1 AU by the CSSS model due to the uncertainties in the photospheric synoptic maps. We also present a comparison of the coronal hole locations predicted by the models with the STEREO/SECCHI EUV synoptic maps. In order to quantify the extent of the uncertainties involved, we compared the predicted speeds with the OMNI solar wind data during the same period (taking the solar wind transit time into account) and obtained the root mean square error between them. To illustrate the significance of the uncertainty estimate in the solar wind prediction, we carried out the analysis for three Carrington rotations, CR 2102, CR 2137 and CR 2160 at different phases of the solar cycle. The uncertainty estimate is critical information necessary for the current and future efforts of improving the solar wind prediction accuracies.

Seiсhes Excited by the Atmospheric Disturbances within the Range of the Meteotsunami Periods nearby the Southern Part of the Sakhalin Island

Purpose. The aim of the paper is to study four synoptic situations, in which the seiches energy increase was observed in the coastal zone of the southern part of the Sakhalin Island, and to consider their possible meteorological origin. Methods and Results. Records of the waves obtained in the Institute of Marine Geology and Geophysics in 2008 using both the instruments installed in eight points in the coastal zone of the southern part of the Sakhalin Island, and the synoptic maps provided by the Sakhalin Hydrometeorological Service Department, were used. For all the observation points, four synoptic situations characterized by increase of the seiches energy within the meteotsunami existence range were considered. It is shown that the amplitudes of the main part of the observed waves exceed the criterion equal to 4 xrms. Therefore the events under consideration can be related to meteotsunami; at that, their energy is distributed almost all over the whole range of tsunami waves. When meteotsunami is absent, energy of the sea level oscillations in the range 4–120 min is reduced by an order. Since fluctuations are observed in the coastal zone possessing the resonant properties, arrival of meteotsunamis to these areas eventually results in exciting the seiches which are recorded. It is shown that in the coastal zone, cold fronts generate meteotsunamis, which, in their turn, give rise to seiches. Conclusions. The conditions for generating sea waves by the atmospheric disturbances within the range of the tsunami periods 2–120 minutes are described. It is found that movement of an extended cold front in the east-south direction leads to generation of the large-amplitude seiches in the region of the southern part of the Sakhalin Island, just where all the settlements are located. At a synoptic situation when two cold fronts are moving over the island, generation of high-amplitude seiches is possible in the places, near which a cold front is passing.

Seyshi, vyzyvayemyye atmosfernymi vozmushcheniyami v diapazone periodov meteotsunami, u poberezh'ya yuzhnoy poloviny ostrova Sakhalin

Purpose. The aim of the paper is to study four synoptic situations, in which the seiches energy in-crease was observed in the coastal zone of the southern part of the Sakhalin Island, and to consider their possible meteorological origin. Methods and Results. Records of the waves obtained in the Institute of Marine Geology and Geophys-ics in 2008 using both the instruments installed in eight points in the coastal zone of the southern part of the Sakhalin Island, and the synoptic maps provided by the Sakhalin Hydrometeorological Service Department, were used. For all the observation points, four synoptic situations characterized by in-crease of the seiches energy within the meteotsunami existence range were considered. It is shown that the amplitudes of the main part of the observed waves exceed the criterion equal to 4 xrms. There-fore the events under consideration can be related to meteotsunami; at that, their energy is distributed almost all over the whole range of tsunami waves. When meteotsunami is absent, energy of the sea level oscillations in the range 4–120 min is reduced by an order. Since fluctuations are observed in the coastal zone possessing the resonant properties, arrival of meteotsunamis to these areas eventually results in exciting the seiches which are recorded. It is shown that in the coastal zone, cold fronts generate meteotsunamis, which, in their turn, give rise to seiches. Conclusions. The conditions for generating sea waves by the atmospheric disturbances within the range of the tsunami periods 2–120 minutes are described. It is found that movement of an extended cold front in the east-south direction leads to generation of the large-amplitude seiches in the region of the southern part of the Sakhalin Island, just where all the settlements are located. At a synoptic situation when two cold fronts are moving over the island, generation of high-amplitude seiches is possible in the places, near which a cold front is passing.

A Comprehensive Lagrangian Transport Study in A Long-Narrow Bay, Xiangshan Bay, China

Study on the transport and mixing in coastal waters is of great concern to the ocean resources exploitation and ecological system protection. Lagrangian methods are direct and effective of researching mass transport. Two Lagrangian tools were adopted and combined to describe water transport in a long-narrow bay, Xiangshan Bay, China. Based on the fields of tidal velocity simulated from the 3-D hydrodynamic model, Lagrangian Coherent Structures (LCSs) and synoptic Lagrangian maps (SLMs) were calculated in the study area. Through comparison of the results, the features and relation of the two tools were discussed. The results show that the LCSs act as the separatrix of the water regions with different transport characteristics and can identify the water areas with different transport time scales. The comprehensive application of the Lagrangian tools is helpful to obtain more insight into the water transport process.

The Deflection of Coronal Mass Ejections by the Ambient Coronal Magnetic Field Configuration

AbstractSolar coronal mass ejections (CMEs) are sometimes deflected during their propagation. This deflection may be the consequence of an interaction between the CME and the ambient coronal field, for example, a coronal hole, or the solar wind. The coronal magnetic field configuration is computed from daily synoptic maps of magnetic field from SOHO/MDI and SDO/HMI using a Potential Field Source Surface model. We analyze 30 halo‐CMEs whose deflection angle exceeds 90° by comparing the ambient magnetic field configuration and the measurement position angles of the CMEs. We find that the deflection of 87% of the CMEs (26 of 30) is consistent with the ambient magnetic field configuration, agreeing with previous studies. Of these 26, 69% are deflected toward the heliospheric current sheet, the boundary between the magnetic field polarities, and 31% toward a pseudo‐streamer, the boundary between same‐polarity magnetic field regions. This implies that the ambient coronal magnetic field configuration plays an important role in the deflection of CMEs and that the current sheet configuration is more important than a pseudo‐streamer. Of the 26 CMEs, the average and standard deviation of the minimum values of the deflection angle in three dimensions relative to an initially radial trajectory are 28° and 14°, respectively.

MASONRY IN PARALLEL. A KNOWLEDGE BASED STRATEGY POST CENTRAL ITALY EARTHQUAKE 2016

Abstract. This research aims to propose a classification of masonry typologies in Central Italy after the earthquakes that in 2016 involved about 120 municipalities. This territory, since several decades, presents high fragility features due to the depopulation process that increase the vulnerability and risk degree. This condition affects even the maintenance practices of traditional buildings by the inhabitants and the extraordinary post-traumatic situation acts as an accelerating factor of the abandonment. In this article we will explain deeply the first part of the research, focusing in particular on methods and tools that were defined and used to carry out this study. The research highlights the need of a specific comparative tool for masonry facades classification. This was elaborated through the comparison of existed bibliography as the EMS-98, the Aedes schedules and the local classification by Umbria Region and the De Meo book. The result then is the production of another synoptic map that would simplifies the correlation between different approaches to classification and the censed facades. Moreover, it was elaborated a second synoptic map moving from the analyses of many survey forms already discuss in literature. The result of this comparison is a new survey form to carry out the field research on vernacular masonry buildings. This new form focuses on the characteristics of the buildings that the research aims to study in Central Italy. The two tools that are illustrate in the following paper were applied on one hundred survey of masonry buildings carried out during August 2018. The last part of this paper proposes a statistical analysis of the results of the field research.

Ka-Band Doppler Scatterometry over a Loop Current Eddy

Doppler scatterometry is a promising new technique for the simultaneous measurement of ocean surface currents and winds. These measurements have been recommended by the recent US NRC Decadal Review for NASA as being priority variables for the coming decade of Earth observations. In addition, currents and winds are useful for many applications, including assessing the operating conditions for oil platforms or tracking the dispersal of plastic or oil by surface currents and winds. While promising, Doppler scatterometry is relatively new and understanding the measurement characteristics is an important area of research. To this end, Chevron sponsored the deployment of DopplerScatt, a NASA/JPL Ka-band Doppler scatterometer, over instrumented sites located at the edge of a Gulf of Mexico Loop Current Eddy (LCE). In addition to in situ measurements, coincident synoptic maps of surface currents were collected by the Areté ROCIS instrument, an optical current measurement system. Here we report on the results of this experiment for both surface currents and winds. Surface current comparisons show that the Ka-band Current Geophysical Model Function (CGMF) needs to include wind drift currents, which could not be estimated with prior data sets. Once the CGMF is updated, ROCIS and DopplerScatt show good agreement for surface current speeds, but, at times, direction differences on the order of 10° can occur. Remote sensing optical and radar data agree better among themselves than with ADCP currents measured at 5 m depth, showing that remote sensing is sensitive to the the currents in top 1 m of the ocean. The LCE data provided a unique opportunity to study the effects of surface currents and stability conditions on scatterometer winds. We show that, like Ku-band, Ka-band estimates of winds are related to neutral winds (and wind stress) and are referenced relative to the moving frame provided by the current. This is useful for the study of air-sea interactions, but must be accounted for when using scatterometer winds for weather prediction.

Pseudoprospective Evaluation of UCERF3-ETAS Forecasts during the 2019 Ridgecrest Sequence

ABSTRACTThe 2019 Ridgecrest sequence provides the first opportunity to evaluate Uniform California Earthquake Rupture Forecast v.3 with epidemic-type aftershock sequences (UCERF3-ETAS) in a pseudoprospective sense. For comparison, we include a version of the model without explicit faults more closely mimicking traditional ETAS models (UCERF3-NoFaults). We evaluate the forecasts with new metrics developed within the Collaboratory for the Study of Earthquake Predictability (CSEP). The metrics consider synthetic catalogs simulated by the models rather than synoptic probability maps, thereby relaxing the Poisson assumption of previous CSEP tests. Our approach compares statistics from the synthetic catalogs directly against observations, providing a flexible approach that can account for dependencies and uncertainties encoded in the models. We find that, to the first order, both UCERF3-ETAS and UCERF3-NoFaults approximately capture the spatiotemporal evolution of the Ridgecrest sequence, adding to the growing body of evidence that ETAS models can be informative forecasting tools. However, we also find that both models mildly overpredict the seismicity rate, on average, aggregated over the evaluation period. More severe testing indicates the overpredictions occur too often for observations to be statistically indistinguishable from the model. Magnitude tests indicate that the models do not include enough variability in forecasted magnitude-number distributions to match the data. Spatial tests highlight discrepancies between the forecasts and observations, but the greatest differences between the two models appear when aftershocks occur on modeled UCERF3-ETAS faults. Therefore, any predictability associated with embedding earthquake triggering on the (modeled) fault network may only crystalize during the presumably rare sequences with aftershocks on these faults. Accounting for uncertainty in the model parameters could improve test results during future experiments.

Analysis of the He i chromosphere in relation to the magnetic field activity over solar cycle time periods

ABSTRACT Solar synoptic maps of both He i 10 830 Å intensity and the magnetic field, which are observed by the Vacuum Telescope at National Solar Observatory/Kitt Peak from 2005 July to 2013 March are utilized to study relationship of He i intensity of the weakly magnetized chromosphere with the respective magnetic field strength. Strong absorption in He i intensity presents the butterfly-pattern latitude migration zone as active regions do, indicating that strong magnetic field corresponds to high-temperature structures of the active chromosphere. For He i intensity and magnetic field strength, their distribution at the time-latitude coordinate and their time series at each of the 180 measurement latitude are found to be significantly negatively correlated with each other in most cases. When a solar hemisphere is divided into three latitude bands: low, middle, and high latitude bands, and even after large magnetic field values not taken into account, they are still negatively correlated in most cases, and further when large magnetic field values are subtracted He i intensity varies more sensitively with magnetic field strength than the corresponding cases when large magnetic field values are not subtracted. He i intensity in the quiet chromosphere thus mainly presents a negative correlation with the magnetic field, and the heating of the quiet chromosphere is inferred to be caused mainly by small-scale magnetic elements.

Bay of Bengal Sea surface salinity variability using a decade of improved SMOS re-processing

Monsoon rain and rivers bring large freshwater input to the Northern Bay of Bengal (BoB), yielding low Sea Surface Salinity (SSS) after the monsoon. The resulting sharp upper-ocean salinity stratification is thought to influence tropical cyclones intensity and biological productivity by inhibiting vertical mixing. Despite recent progresses, the density of in situ data is far from sufficient to monitor the BoB SSS variability, even at the seasonal timescale. The advent of satellite remotely-sensed SSS (SMOS, Aquarius, SMAP) offers a unique opportunity to provide synoptic maps of the BoB SSS every ~8 days. Previous SMOS SSS retrievals did not perform well in the BoB. Here, we show that improved systematic error corrections and quality control procedures yield a much better performance of the new “debiased v4” CATDS level-3 SSS from SMOS (~0.8 correlation, 0.04 bias and 0.64 root-mean-square difference to more than 28,000 collocated in situ data points over 2010–2019). The SMOS product now performs equivalently to Aquarius, and is slightly inferior to SMAP over the BoB. In particular, SMAP and SMOS are able to capture salinity variations close to the east coast of India (r > 0.8 within 75–150 km of the coast). They thus capture the seasonal freshening there, associated with equatorward advection of the Northern BoB low-salinity water by the East Indian Coastal Current (EICC) after the summer monsoon. The 10-year long SMOS record further allows to describe the BoB interannual SSS variability, which is strongest in boreal fall in relation with the Indian Ocean Dipole (IOD). Positive IOD events induce a weakening of the southward export of freshwater by the EICC, and hence negative SSS anomalies in the Northern BoB and positive ones along the East Indian coast. This confirms results from earlier studies based on modelling, sparse in situ data, or shorter satellite records, but this time from a 10-year long SSS record. Overall, our study indicates that the new SMOS retrieval can be confidently used to monitor the BoB SSS and to study its mechanisms. We end by a brief description of the BoB SSS anomalies associated with the extreme 2019 IOD event and highlight the very good performance over the BoB of a new multi-satellite product developed by the European Space Agency merging SMOS, Aquarius and SMAP data.

70 Years of Chromospheric Solar Activity and Dynamics

Abstract From 1915 to 1985 the monitoring program of the Mount Wilson Observatory, one of the Observatories of the Carnegie Institution of Washington, has taken over 35,000 daily images (spectroheliograms) of the Sun in the chromospheric resonance line of Ca ii K. This important database constitutes a unique resource for a variety of retrospective analyses of the state of solar magnetism on multidecadal timescales. These observations may also hold the key for untangling some of the mysteries behind the solar dynamo, which in turn could result in a better predictive capability for current dynamo models. We describe here a procedure to calibrate and rescale these images so that homogeneous Carrington synoptic maps can be derived for the whole period covered by these observations. Temporal variations in full-disk chromospheric activity clearly show the signature of the 11 yr solar cycle, but no evidence is found for a statistically significant north/south hemispheric asymmetry. Using a feature-tracking technique we were also able to obtain the average solar rotation profile. We find no indication of any detectable periodicity in the temporal behavior of the orthogonalized rotation rate coefficients, suggesting the global chromospheric dynamics has not changed during the 70 years investigated in this work. We found also no significant evidence in our analysis for a hemispheric asymmetry in rotation rates.