Decrease In Solar Activity Research Articles

An investigation of ionospheric upper transition height variations at low and equatorial latitudes deduced from combined COSMIC and C/NOFS measurements

In this study we propose the combination of topside in-situ ion density data from the Communication/Navigation Outage Forecast System (C/NOFS) along with the electron density profile measurement from Constellation Observing System for Meteorology, Ionosphere & Climate (COSMIC) satellites Radio Occultation (RO) for studying the spatial and temporal variations of the ionospheric upper transition height (hT) and the oxygen ion (O+) density scale height. The latitudinal, local time and seasonal distributions of upper transition height show more consistency between hT re-calculated by the profile of the O+ using an α-Chapman function with linearly variable scale height and that determined from direct in-situ ion composition measurements, than with constant scale height and only the COSMIC data. The discrepancy in the values of hT between the C/NOFS measurement and that derived by the combination of COSMIC and C/NOFS satellites observations with variable scale height turns larger as the solar activity decreases, which suggests that the photochemistry and the electrodynamics of the equatorial ionosphere during the extreme solar minimum period produce abnormal structures in the vertical plasma distribution. The diurnal variation of scale heights (Hm) exhibits a minimum after sunrise and a maximum around noon near the geomagnetic equator. Further, the values of Hm exhibit a maximum in the summer hemisphere during daytime, whereas in the winter hemisphere the maximum is during night. Those features of Hm consistently indicate the prominent role of the vertical electromagnetic (E×B) drift in the equatorial ionosphere.

Solar pacing of storm surges, coastal flooding and agricultural losses in the Central Mediterranean.

Storm surges, leading to catastrophic coastal flooding, are amongst the most feared natural hazards due to the high population densities and economic importance of littoral areas. Using the Central Mediterranean Sea as a model system, we provide strong evidence for enhanced periods of storminess leading to coastal flooding during the last 4500 years. We show that long-term correlations can be drawn between storminess and solar activity, acting on cycles of around 2200-yr and 230-yr. We also find that phases of increased storms and coastal flooding have impacted upon mid- to late Holocene agricultural activity on the Adriatic coast. Based on the general trend observed during the second half of the 20th century, climate models are predicting a weakening of Mediterranean storminess. By contrast, our new data suggest that a decrease in solar activity will increase and intensify the risk of frequent flooding in coastal areas.

The structure and variability of Mars upper atmosphere as seen in MAVEN/IUVS dayglow observations

AbstractWe report a comprehensive study of Mars dayglow observations focusing on upper atmospheric structure and seasonal variability. We analyzed 744 vertical brightness profiles comprised of ∼109,300 spectra obtained with the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) satellite. The dayglow emission spectra show features similar to previous UV measurements at Mars. We find a significant drop in thermospheric scale height and temperature between LS = 218° and LS = 337–352°, attributed primarily to the decrease in solar activity and increase in heliocentric distance. We report the detection of a second, low‐altitude peak in the emission profile of OI 297.2 nm, confirmation of the prediction that the absorption of solar Lyman alpha emission is an important energy source there. The UV doublet peak intensity is well correlated with simultaneous observations of solar 17–22 nm irradiance at Mars.

Effects of Space Weather on Biomedical Parameters during the Solar Activity Cycles 23-24.

The results of long-term (1998-2012) biomedical monitoring of the biotropic effects of space weather are discussed. A drastic change in statistical distribution parameters in the middle of 2005 was revealed that did not conform to usual sinusoidal distribution of the biomedical data reflecting changes in the number of solar spots over a solar activity cycle. The dynamics of space weather of 2001-2012 is analyzed. The authors hypothesize that the actual change in statistical distributions corresponds to the adaptation reaction of the biosphere to nonstandard geophysical characteristics of the 24th solar activity cycle and the probable long-term decrease in solar activity up to 2067.

The role of the Sun in long‐term change in the F2 peak ionosphere: New insights from EEMD and numerical modeling

AbstractWe applied Ensemble Empirical Mode Decomposition (EEMD) for the first time to ionosonde data to study trends in the critical frequency of the F2 peak, foF2, and its height, hmF2, from 1959 to 2005. EEMD decomposes a time series into several quasi‐cyclical components, called Intrinsic Mode Functions, and a residual, which can be interpreted as a long‐term trend. In contrast to the more commonly used linear regression‐based trend analysis, EEMD makes no assumptions on the functional form of the trend and no separate correction for the influence of solar activity variations is needed. We also adopted a more rigorous significance testing procedure with less restrictive underlying assumptions than the F test, which is normally used as part of a linear regression‐based trend analysis. EEMD analysis shows that trends in hmF2 and foF2 between 1959 and 2005 are mostly highly linear, but the F test tends to overestimate the significance of trends in hmF2 and foF2 in 30% and 25% of cases, respectively. EEMD‐based trends are consistently more negative than linear regression‐based trends, by 30–35% for hmF2 and about 50% for foF2. This may be due to the different treatment of the influence of a long‐term decrease in solar activity from 1959 to 2005. We estimate the effect of this decrease in solar activity with two different data‐based methods as well as using numerical model simulations. While these estimates vary, all three methods demonstrate a larger relative influence of the Sun on trends in foF2 than on trends in hmF2.

Ionospheric foF2 morphology and response of F2 layer height over Jicamarca during different solar epochs and comparison with IRI-2012 model

Diurnal, seasonal and annual foF2 variability and the response of the F2-layer height over Jicamarca (11.9 °S, 76.8 °W, 1 °N dip) during periods of low (LSA), moderate (MSA) and high (HSA) solar activities was investigated. The relative standard deviation (V R ) was used for the analysis. The F2-layer critical frequency pre-noon peak increases by a factor of 2 more than the post-noon peak as the solar activity increases. The variability coefficient (V R ) is lowest during the day (7–16%) for the three solar epochs; increases during nighttime (20–26%, 14–26%, and 10–20%, respectively for the LSA, MSA and HSA years); and attained highest magnitude during sunrise (21–27%, 24–27%, and 19–30%, respectively in similar order). Two major peaks were observed in V R – the pre-sunrise peak, which is higher, and the post-sunset peak. Generally, the variability increases as the solar activity decreases. Annually, V R peaks within 23–24%, 19–24% and 15–24% for the LSA, MSA, and HSA periods, respectively. The ionospheric F2-layer height rises to the higher level with increasing solar activity. The foF2 comparison results revealed that Jicamarca is well represented on the IRI-2012 model, with an improvement on the URSI option. The importance of vertical plasma drift and photochemistry in the F2-layer was emphasized.

Atomic hydrogen in the mesopause region derived from SABER: Algorithm theoretical basis, measurement uncertainty, and results

Atomic hydrogen (H) is a fundamental component in the photochemistry and energy balance of the terrestrial mesopause region (80–100 km). H is generated primarily by photolysis of water vapor and participates in a highly exothermic reaction with ozone. This reaction is a significant source of heat in the mesopause region and also creates highly vibrationally excited hydroxyl (OH) from which the Meinel band radiative emission features originate. Concentrations (cm−3) and volume mixing ratios of H are derived from observations of infrared emission from the OH (υ = 9 + 8, Δυ = 2) vibration-rotation bands near 2.0 µm made by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the NASA Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite. The algorithms for deriving day and night H are described herein. Day and night concentrations exhibit excellent agreement between 87 and 95 km. SABER H results also exhibit good agreement with observations from the Solar Mesosphere Explorer made nearly 30 years ago. An apparent inverse dependence on the solar cycle is observed in the SABER H concentrations, with the H increasing as solar activity decreases. This increase is shown to be primarily due to the temperature dependence of various reaction rate coefficients for H photochemistry. The SABER H data, coupled with SABER atomic oxygen, ozone, and temperature, enable tests of mesospheric photochemistry and energetics in atmospheric models, studies of formation of polar mesospheric clouds, and studies of atmospheric evolution via escape of hydrogen. These data and studies are made possible by the wide range of parameters measured simultaneously by the SABER instrument.

TWO REGIMES IN THE REGULARITY OF SUNSPOT NUMBER

Sunspot numbers WN display quasi-periodical variations that undergo regime changes. These irregularities could indicate a chaotic system and be measured by Lyapunov exponents. We define a functional λ (an index) that is close to the (maximal) Lyapunov exponent for dynamical systems and well defined for series with a random component: this allows one to work with sunspot numbers. We compute λ for the daily WN from 1850 to 2012 within 4 yr sliding windows: λ exhibit sharp maxima at solar minima and secondary maxima at solar maxima. This pattern is reflected in the ratio R of the amplitudes of the main versus secondary peaks. Two regimes have alternated in the past 150 yr, R1 from 1850 to 1915 (large λ and R values) and R2 from 1935 to 2005 (shrinking difference between main and secondary maxima, R values between 1 and 2). We build an autoregressive model consisting of Poisson noise plus an 11 yr cycle and compute its irregularity index. The transition from R1 to R2 can be reproduced by strengthening the autocorrelation a of the model series. The features of the two regimes are stable for model and WN with respect to embedding dimension and delay. Near the time of the last solar minimum (~2008), the irregularity index exhibits a peak similar to the peaks observed before 1915. This might signal a regime change back from R2 to R1 and the onset of a significant decrease of solar activity.

Forcing of stratospheric chemistry and dynamics during the Dalton Minimum

Abstract. The response of atmospheric chemistry and dynamics to volcanic eruptions and to a decrease in solar activity during the Dalton Minimum is investigated with the fully coupled atmosphere–ocean chemistry general circulation model SOCOL-MPIOM (modeling tools for studies of SOlar Climate Ozone Links-Max Planck Institute Ocean Model) covering the time period 1780 to 1840 AD. We carried out several sensitivity ensemble experiments to separate the effects of (i) reduced solar ultra-violet (UV) irradiance, (ii) reduced solar visible and near infrared irradiance, (iii) enhanced galactic cosmic ray intensity as well as less intensive solar energetic proton events and auroral electron precipitation, and (iv) volcanic aerosols. The introduced changes of UV irradiance and volcanic aerosols significantly influence stratospheric dynamics in the early 19th century, whereas changes in the visible part of the spectrum and energetic particles have smaller effects. A reduction of UV irradiance by 15%, which represents the presently discussed highest estimate of UV irradiance change caused by solar activity changes, causes global ozone decrease below the stratopause reaching as much as 8% in the midlatitudes at 5 hPa and a significant stratospheric cooling of up to 2 °C in the mid-stratosphere and to 6 °C in the lower mesosphere. Changes in energetic particle precipitation lead only to minor changes in the yearly averaged temperature fields in the stratosphere. Volcanic aerosols heat the tropical lower stratosphere, allowing more water vapour to enter the tropical stratosphere, which, via HOx reactions, decreases upper stratospheric and mesospheric ozone by roughly 4%. Conversely, heterogeneous chemistry on aerosols reduces stratospheric NOx, leading to a 12% ozone increase in the tropics, whereas a decrease in ozone of up to 5% is found over Antarctica in boreal winter. The linear superposition of the different contributions is not equivalent to the response obtained in a simulation when all forcing factors are applied during the Dalton Minimum (DM) – this effect is especially well visible for NOx/NOy. Thus, this study also shows the non-linear behaviour of the coupled chemistry-climate system. Finally, we conclude that especially UV and volcanic eruptions dominate the changes in the ozone, temperature and dynamics while the NOx field is dominated by the energetic particle precipitation. Visible radiation changes have only very minor effects on both stratospheric dynamics and chemistry.

Solar cycle dependence of the cusp O+access to the near‐Earth magnetotail

Ionospheric origin O+ accelerated in the cusp/cleft region is one source for the O+ observed in the plasma sheet. This O+ is convected over the polar cap, flowing along open field lines to the tail lobes, and finally entering the plasma sheet. In this paper we use Cluster/CODIF data to study how the occurrence of cusp origin O+ in the polar cap and tail lobe changes over the solar cycle. Our study shows that the probability to observe cusp origin O+ decreases steeply during the declining phase of solar cycle 23 and starts to increase again at the start of the solar cycle 24. The decrease is much greater in the tail lobes than in the polar cap. A detailed analysis reveals that the O+ on the dominant transport path moves to higher latitudes in the Northern Hemisphere and more sunward in the Southern Hemisphere during the declining phase of the solar cycle (from the solar maximum to the solar minimum), so that the O+no longer reaches the near‐Earth (<20RE) tail lobes. This change in transport is consistent with a significantly reduced convection velocity and a northward shift of the cusp region as the solar activity decreases, so that the O+ moves much further along the field line before it is convected into the tail. It will therefore enter the plasma sheet much further down the tail.

How Do Coronal Hole Storms Affect the Upper Atmosphere?

The solar cycle, often described as an increase and decrease of solar activity with a period of about 11 years, can strongly affect Earth's thermosphere and ionosphere. Although the longest direct record of solar activity is based on sunspot number, a more quantifiable parameter is solar irradiance at extreme ultraviolet (EUV) wavelengths, which varies by more than a factor of 3 over the sunspot cycle. To first order, upper atmospheric variation is a result of changes in ionizing fluxes at EUV wavelengths. As the solar cycle passes its EUV peak and approaches minimum, the number of solar active regions declines, leading to a reduction and then a near absence of coronal mass ejections (CMEs)—episodic events of high‐energy bursts of solar plasma that cause geomagnetic storms at Earth. During the solar cycle's declining phase, coronal holes begin to occupy lower latitudes on the solar surface and fall in line with the ecliptic plane.

Statistical distribution of GPS amplitude scintillations

This study presents complementary cumulative distribution function (CCDF) as a statistical distribution apparatus for fitting GPS scintillations data. Three years of data at three levels of solar activity, 2002 (high), 2004 (moderate) and 2008 (low) from an equatorial anomaly crest station; Bogota (4.4°N, 74.1°W, dip 16.0°N) [Colombia] in the West Coast of South America were used for the investigation. These data were grouped into daily, monthly and seasonal sets at three levels of solar activity, and tests were introduced on them to reject data from non-ionospheric sources of scintillation, such as multipath. Before fitting each set of data on a CCDF, the data were first visualized with the aid of scatter plots whereby the distributions exhibit non-Gaussian behavior. As a case study, at S4=0.3 threshold, during the year 2002 and 2004, the months of May–July showed probability of occurrence of the order of 0.01 (1% of the observed samples of a given set) for each month, while in 2008, this trend persisted to August (May–August, probability of occurrence of 0.01 or less (1%)). The tails of January and March's distributions were observed to be the heaviest at S4=0.3, although, a relatively heavy tail at this threshold was also observed during the month of November in the year 2004, and during March Equinox and December Solstice in terms of seasons. The heaviness of the tail at this threshold relaxes as solar activity decreases. The calculated probability of occurrences and those derived from the statistical distribution scheme show good consistency. The results presented in this study may be of assistance for future modeling and simulation studies.

Statistics of GPS scintillations over South America at three levels of solar activity

This study characterizes low‐latitude scintillations at L‐band frequency in South America on daily, monthly, and seasonal time scales at three levels of solar activity: high, moderate and low levels. Three years (November 2001–October 2002, 2004 and 2008) of amplitude scintillation data from GPS receivers at three locations: Cuzco (14.0°S, 73.0°W, dip 1.0°S), Iquitos (3.8°S, 73.2°W, dip 7.0°N), and Bogota (4.4°N, 74.1°W, dip 16.0°N) were used for the investigation. These data were grouped into daily, monthly, and seasonal sets. We introduced tests on the data to reject signal fluctuations from non‐ionospheric sources, such as multipath from terrestrial objects. The scintillation events from the data were further classified into three levels: weak (0.3 ≤ S4 < 0.4), moderate (0.4 ≤ S4 < 0.7), and intense (S4 ≥ 0.7) scintillations and their monthly percentage of occurrences and durations were determined. We also used the seasonal averages of daily (1900 LT–2000 LT) TEC values to observe the variability of the equatorial anomaly using a chain of ten GPS receivers that are located at a latitudinal span of 10°N–40°S along the west coast of South America. This study concludes that GPS scintillations in this longitude sector are post‐sunset events and decay before or around local midnight, with intense activity and longer durations in the months of March and January. On seasonal time scales, the highest frequencies and longest durations of events were recorded during March Equinox and December Solstice. The months of May–July (June Solstice) had the least frequencies of occurrence and durations of events. Scintillation activity also increases with solar activity. Finally, scintillations increase in frequencies of occurrence and durations from Cuzco (near the magnetic equator) toward Bogota (near the crest of the equatorial anomaly) during solar maximum. However, a gradual collapse of the anomaly crest, away from Bogota toward Iquitos was observed as solar activity decreases, and as a result, the occurrence frequencies of scintillations at Iquitos increase relative to those at Bogota.

Modeling of the atmospheric response to a strong decrease of the solar activity

AbstractWe estimate the consequences of a potential strong decrease of the solar activity using the model simulations of the future driven by pure anthropogenic forcing as well as its combination with different solar activity related factors: total solar irradiance, spectral solar irradiance, energetic electron precipitation, solar protons and galactic cosmic rays. The comparison of the model simulations shows that introduced strong decrease of solar activity can lead to some delay of the ozone recovery and partially compensate greenhouse warming acting in the direction opposite to anthropogenic effects. The model results also show that all considered solar forcings are important in different atmospheric layers and geographical regions. However, in the global scale the solar irradiance variability can be considered as the most important solar forcing. The obtained results constitute probably the upper limit of the possible solar influence. Development of the better constrained set of future solar forcings is necessary to address the problem of future climate and ozone layer with more confidence.

Decrease of Schumann resonance frequencies and changes in the effective lightning areas toward the solar cycle minimum of 2008–2009

For the period 1988–2002, it has been shown that the SR mode frequencies and Q-factors decrease with the decrease of X-ray radiation toward the solar cycle minimum (Sátori et al., 2005). In the present study, a decrease of frequencies and Q-factors of all first four SR modes from the latest solar cycle maximum to the anomalous minimum of 2008–2009 is found using the data from Modra Observatory. Decreases obtained here for the first two SR modes are evidently greater than those obtained in the study cited above. Moreover, effective thunderstorm areas are calculated from the monthly mean diurnal frequency range of the electric field component. Our study reveals that the difference between the northern and the southern hemisphere summer areas not only declines with the decrease in solar activity but almost vanishes during the deep solar minimum of 2008–2009. Semi-annual variation in the areas dominates in years of the deep solar minimum.

Correlation between the ionospheric WN4 signature and the upper atmospheric DE3 tide

The present work studies the correlation relationship between the longitudinal ionospheric structure of wave number 4 (WN4) and the upper atmospheric tide of nonmigrating tidal mode DE3 (diurnal eastward wave number 3). Global ionospheric maps produced by the Jet Propulsion Laboratory were used to deduce the latitudinal integration of total electron content in the low‐latitude ionosphere, and TIDI/TIMED observations were used to retrieve the atmospheric zonal and meridional winds. By applying Fourier filtering and fitting techniques, the WN4 wave and DE3 tidal components are derived from the ionospheric and upper atmospheric observations, respectively. We found that the observed WN4 wave and DE3 zonal wind components experience very similar annual and interannual variations, but the DE3 meridional wind component behaves in a quite different manner. Both WN4 and DE3 zonal winds are very intense during northern summer and autumn; they also appear in the later spring, but tend to vanish in winter. Their amplitudes increase as the solar activity decreases, and both are stronger in the quasi‐biennial oscillation (QBO) eastward wind phase than in the westward phase. At the same time, the DE3 meridional wind likes to occur only in winter and seems not change with solar activity and QBO phase. We further studied the correlation between the WN4 wave and the two wind components of the DE3 tide. We found that the cross‐correlation coefficient between the WN4 wave and the DE3 zonal wind is much larger, while that between the WN4 wave and the DE3 meridional wind is relatively smaller. Such different correlations are attributed to the different latitudinal symmetry of different DE3 wind components. The DE3 zonal wind is likely in latitudinally symmetric tidal mode; hence, it can efficiently affect the F region ion drifts. In contrast, the meridional wind is mainly in antisymmetric mode and thus seldom affects the ionospheric drifts. The present results support the suggestion that the longitudinal WN4 structure in the ionospheric F region originates from the symmetric modes, mainly the zonal wind component, of the upper atmospheric nonmigrating tidal mode DE3 in the ionospheric E region.

Beryllium-7 atmospheric deposition and sediment inventories in the Neponset River estuary, Massachusetts, USA

Measured monthly atmospheric depositional fluxes of cosmogenically produced 7Be ranged from 1 to 67 mBq/cm 2 in Boston, Massachusetts between September 2000 and August 2007. These fluxes exhibited seasonality and supported a decay-corrected 7Be atmospheric depositional running inventory that ranged from 36 to 144 mBq/cm 2. Annual 7Be deposition exhibited an increasing trend that may reflect a general decrease in solar activity and a general increase in precipitation over the 7-year sampling period. To investigate short-term sediment dynamics and accumulation patterns in the Neponset River estuary, we collected six sediment cores in July 2006 and measured 7Be sediment inventories ranging from 48 to 546 mBq/cm 2 Comparisons of these sediment inventories with the 7Be running inventory from atmospheric deposition (101 mBq/cm 2) at the time of core collection indicated a large degree of spatial heterogeneity in sediment accumulation patterns and its potential use as a tool for assessing the impacts of environmental restoration activities in estuarine environments.

Diurnal and seasonal variations of F2 layer characteristics over Irkutsk during the decrease in solar activity in 2003–2006: Observations and IRI-2001 model predictions

The diurnal and seasonal variations of F2 layer characteristics (critical frequency, peak height and bottomside thickness) over Irkutsk, Russia (52.3 N and 104.3 E) are studied by the method of running medians. The comparison with the IRI-2001 model during the decrease in solar activity in 2003–2006 revealed cases of both close agreement and systematic differences between predictions and observations. The systematic difference is not the only reason for disagreement between IRI and observations; there are also intrayear variations which are not associated with seasonal behavior. The period of observation was too short to make conclusions about solar activity dependence of the noon bottomside thickness and the modification of its diurnal behavior with decreasing solar activity.

Climatology of noctilucent cloud radii and occurrence frequency using SCIAMACHY

We present a climatology of noctilucent cloud (NLC) occurrence rate (northern and southern hemisphere) and particle size (northern hemisphere) based on SCIAMACHY measurements between 2002 and 2007. An interannual analysis of occurrence rates shows no trend in the northern hemisphere despite the decreasing solar activity during that period. The mean NLC particle radius for a Gaussian particle size distribution with σ = 22 nm is 68.0 ± 11.4 nm . There is an increase of the particle size with latitude, with a gradient as large as 2 nm / deg for latitudes larger than 75 ∘ . SCIAMACHY observes an increase of mean NLC particle size during the last 5 years at latitudes higher than 70 ∘ , which might be linked to the decrease in solar activity. The interannual variability of the seasonally averaged particle size is ± 2 nm in a given latitude band. Results concerning the sensitivity of the retrieval to the particle shape and particle size distribution assumed width are also presented.

Early-Holocene climatic oscillations recorded by lake-level fluctuations in west-central Europe and in central Italy

On the basis of lake-level data, the period of the Preboreal oscillation (PBO) at 11 300–11 150 cal yr BP as defined by the GRIP oxygen-isotope record appears to correspond to wetter climatic conditions in west-central Europe and to a marked drying in north-central Italy. Additional short-lived phases of higher lake level have been identified before the PBO at ca 11 450–11 400 and 11 350 cal yr BP in west-central Europe, and at ca 11 500 cal yr BP in Italy. Such multiple climatic oscillations around the PBO have been observed in various records in northwestern Europe. On the basis of various proxies, a map of changes in moisture over western Europe during the PBO indicates a mid-latitude zone between 58 and 43°N characterised by wetter conditions, while a drier climate developed in southern and northern Europe. This wet middle zone shows a larger extension and suggests a more meandering, weaker Atlantic Westerly Jet during the PBO than during the 8.2 kyr event. A comparison of lake-level records in west-central Europe with (1) outbursts from North American and north-European proglacial lakes, and (2) variations in solar activity as reflected by 14C and the 10Be records supports the hypothesis that the PBO was a response to successive meltwater pulses at 11 300, 11 250, 11 200 and 11 170 cal yr BP and to a sudden decrease in solar activity at 11 250 cal yr BP. This study points to the necessity of developing integrated multi-proxy approaches to construct more robust regional event stratigraphies, and of better documenting palaeohydrological changes in the Mediterranean area.