Different Phases Of Solar Activity Research Articles

Estimation of Radiation Exposure for Various Flights from Athens International Airport

In recent decades, the exposure of aviation crews and passengers to cosmic radiation has been progressively increasing due to the growing need of flights. Therefore, there is a need for radiation assessment software tools to act as a complement to other radiation protection techniques and countermeasures. In this work, the exposure to cosmic radiation is estimated for flights from Athens International Airport to various international destinations, by performing Monte Carlo simulations with the validated tool DYASTIMA/DYASTIMA-R. The results of the estimated total ambient dose equivalent, as well as the ambient dose equivalent rate for different flights, applying a typical flying level and constant atmospheric conditions, are presented for the first time. This study is carried out for different phases of solar activity for the time period from 1996 to 2019, which includes the two recent Solar Cycles 23 and 24.

Revisiting Ulysses electron data with a triple fit of velocity distributions

Context. Given their uniqueness, the Ulysses data can still provide us with valuable new clues about the properties of plasma populations in the solar wind, and especially about their variations with heliographic coordinates. In the context of kinetic waves and instabilities in the solar wind plasma, the electron temperature anisotropy plays a crucial role. To date, two electron populations (the core and the halo) have been surveyed using anisotropic fitting models, limited in general to the ecliptic observations. Aims. We revisit the electron data reported by the SWOOPS instrument on board the Ulysses spacecraft between 1990 and early 2008. These observations reveal velocity distributions out of thermal equilibrium, with anisotropies (e.g., parallel drifts and/or different temperatures, parallel and perpendicular to the background magnetic field), and quasi-thermal and suprathermal populations with different properties. Methods. We apply a 2D non-linear least squares fitting procedure, using the Levenberg–Marquardt algorithm, to simultaneously fit the velocity electron data (up to a few keV) with a triple model combining three distinct populations: the more central quasi-thermal core, the suprathermal halo, and a second suprathermal population consisting mainly of the electron strahl (or beaming population with a major field-aligned drift). The recently introduced κ-cookbook is used to describe each component with the following anisotropic distribution functions (recipes): Maxwellian distribution, regularized κ-distribution, and generalized κ-distribution. Most relevant are triple combinations selected as best fits (BFs) with minimum relative errors and standard deviations. Results. The number of BFs obtained for each fitting combination is 80.6% of the total number of events (70.7% in the absence of coronal mass ejections). Showing the distribution of the BFs for the entire data set, during the whole interval of time, enables us to identify the most representative fitting combinations associated with either fast or slow winds, and different phases of solar activity. The temperature anisotropy quantified by the best fits is considered a case study of the main parameters characterizing electron populations. By comparison to the core, both suprathermal populations exhibit higher temperature anisotropies, which slightly increase with the energy of electrons. Moreover, these anisotropies manifest different dependences on the solar wind speed and heliographic coordinates, and are highly conditioned by the fitting model. Conclusions. These results demonstrate that the characterization of plasma particles is highly dependent on the fitting models and their combinations, and this method must be considered with caution. However, the multi-distribution function fitting of velocity distributions has a significant potential to advance our understanding of solar wind kinetics and deserves further quantitative analyses.

Energetic Dynamics of the Inner Magnetosphere in Contact with Fast Solar Wind Currents: Case of the Period 1964-2009

The Earth’s magnetosphere is a magnetic shield that protects Earth from high-energy particles and is subject to a series of internal processes caused by jets of the solar wind (SW) that destabilize it. These disturbances affect health as well as technology and become more extreme when SW is more accelerated. Thus, to better understand the impact of high-speed solar wind (HSSW) invasion on the dynamics of the magnetospheric system, a statistical study of HSSW populations was conducted for even (20 and 22) and odd (21 and 23) solar cycles. The regression analysis using the solar-derived fields from all solar cycles, indicates three states of the inner magnetosphere: 1) the 00:00UT-15:00UT period marked by a magnetic reconnection on the day side of the Earth closest to the Sun with the interplanetary magnetic field (IMF) facing South; 2) the 15:00UT-21:00UT period where IMF changes from South to North and remains there until 21:00UT; and 3) the 21:00UT-24:00UT period where there is a reconnection on the night side with stretched field lines. Observations made at different phases of solar activity lead us to suggest that the magnetospheric electric field (EM) and the Bz component of IMF (IMF-Bz) are strongly correlated not only at a particular time scale, but at different time scales. We believe that the daily fluctuations of the electrical and magnetic effects of magnetospheric origin currents play a very important role in the dayside magnetic reconnection rate. Moreover, examination of the cycles with different parities shows important amplitudes of the solar causes for the even cycles compared to the odd solar cycles. Therefore, even solar cycles have a strong influence on our socio-economic system compared to odd cycles.

Transient variations of vertical total electron content at low latitude during the period 2013–2017

Abstract We use GPS networks to measure the vertical Total Electron Content (VTEC) variations at low latitude, in three longitude sectors: America, Europe-Africa and Asia, collected during the period 2013–2017. This period corresponds to the increasing phase of the solar cycle 24 (SC#24) observed around 2013–2014 as well as the decreasing phase around 2014–2017. Our results discussed a morphological analysis of regular variations in ionization during different phases of solar activity: daytime variations, seasonal and semi-annual variations and variations based on the solar cycle 24 in three longitude sectors. In all longitude sectors, the highest VTEC values are displayed during the two months of the spring, located after sunrise and before sunset. The lowest values are found during the summer and winter seasons. We found that the winter anomaly and the presence of equinoxial peaks are the most pronounced effects in VTECs in the increasing and decreasing phase of the SC#24. A strong asymmetry is detected between equinoxial peaks and the location of peaks occurring in March/April and October/November at maximum in the solar flux variations during the increase phase. We show that the daily VTEC maximum values were registered between 14:00 and 16:00 LT and the minimum values between 4:00 and 6:00 LT. Double ionization peak in the morning and evening is observed in VTEC annual variations, due to the proximity of the equatorial fountain stations. From the statistical analysis part, we observed practically the same distribution of the different classes of VTEC (two peaks, bell-shaped and plateau-shaped) variations in the three sectors of longitude. These observations indicate longitudinal variation in the presence of the winter anomaly in the Equatorial Ionized Anomaly (EIA) region. Additionally, we can note a longitudinal variation of the spring-autumn VTEC asymmetry in the EIA region during the five years 2013–2017. We observe also that the occurrence of nocturnal peak recorded around 19 local time (LT) shows the same characteristics as the vertical drift E × B (B: magnetic field is perpendicular to E: electric field.) with respect to solar cycle, season and longitude. Three essential characteristics we noted: 1) the occurrence of the nocturnal peak generally follows the solar cycle. 2) The occurrence of the nocturnal peak is generally stronger at the equinoxes than at the solstices. 3) The occurrence of the nocturnal peak is stronger in the Europe-Africa and America sectors than in the Asia sector. As a result, nocturnal peak occurrence is well related to the PRE at the origin of the GNSS signal scintillations.

Sunspots Influence on Climatic Variability of Karachi and Rohri

The Sun is undoubtedly the most important thrust of the climate system. However, only little is known how variable this force is acting on different time scales ranging from minutes to millennia and how the climate system reacts to changes in this forcing. In the present study possible effect of solar activity on maximum temperature T (max) and minimum temperature T (min), humidity and precipitation have been investigated. The analysis comprises over a period of 2000-2015 that consists of the decreasing phase of solar cycle-23 and the increasing phase of solar cycle-24. To optimize the number of signicant trends, different phases of solar activity have been implemented there to observe the variation in climate of Karachi and Rohri in response of it. These detection and adjustment are carried out using the computer software Statistica and Minitab. Correlation analysis for different seasons of these two regions is performed in this study.
 

Spatial and Temporal Variations of Polar Ionospheric Total Electron Content over Nearly Thirteen Years.

It is of great significance for the global navigation satellite system (GNSS) service to detect the polar ionospheric total electron content (TEC) and its variations, particularly under disturbed ionosphere conditions, including different phases of solar activity, the polar day and night alternation, the Weddell Sea anomaly (WSA) as well as geomagnetic storms. In this paper, four different models are utilized to map the ionospheric TEC over the Arctic and Antarctic for about one solar cycle: the polynomial (POLY) model, the generalized trigonometric series function (GTSF) model, the spherical harmonic (SH) model, and the spherical cap harmonic (SCH) model. Compared to other models, the SCH model has the best performance with ±0.8 TECU of residual mean value and 1.5–3.5 TECU of root mean square error. The spatiotemporal distributions and variations of the polar ionospheric TEC are investigated and compared under different ionosphere conditions in the Arctic and Antarctic. The results show that the solar activity significantly affects the TEC variations. During polar days, the ionospheric TEC is more active than it is during polar nights. In polar days over the Antarctic, the maximum value of TEC always appears at night in the Antarctic Peninsula and Weddell Sea area affected by the WSA. In the same year, the ionospheric TEC of the Antarctic has a larger amplitude of annual variation than that of the TEC in the Arctic. In addition, the evolution of the ionization patch during a geomagnetic storm over the Antarctic can be clearly tracked employing the SCH model, which appears to be adequate for mapping the polar TEC, and provides a sound basis for further automatic identification of ionization patches.

Thermal Properties of Coronal Cavities

We have analyzed 33 cavities observed between 2012 and 2018, from solar activity maximum to minimum. For each cavity we applied a differential emission measure method to obtain both a temperature distribution and a value of the average temperature. We find that cavities are filled with material hotter than the surrounding streamer, with temperatures in the range of 1.67 – 2.15 MK. Differences between temperatures of cavities and surrounding streamers are in the range of 0.11 – 0.32 MK with an average value of 0.21 MK. We found that temperatures of both, cavities and streamers, vary as a function of different phases of solar activity. During solar maximum the structures are slightly hotter than those observed during solar minimum (1.85 – 2.15 MK vs. 1.67 – 1.88 MK for cavities and streamers, respectively).

Study of solar flux dependency of the winter anomaly in GPS TEC

In literature, ionospheric winter anomaly refers to a higher daytime electron density (NmF2) at the F2 peak in winter than in summer that has a well-established mechanism for its formation. A number of researchers have extrapolated the same feature to total electron content (TEC) and have looked for a similar trend in TEC. The present work is a reassessment of the winter anomaly in TEC during different levels of solar flux. For this, we have analyzed TEC data for the period 2005–2012 using dual-frequency GPS receivers at three low-latitude and two mid-latitude stations in the Asian region. This period encompasses the declining and the lowest phase of solar cycle 23, and also the rising phase of solar cycle 24. The results of the study show that if the solar flux in a particular year is higher in winter (December) than in summer (June), only then the winter anomaly in TEC is observed. Thus, our research shows that the winter anomaly is not a consistent feature during all phases of solar activity at the chosen low as well as mid latitudes. If indeed a physical mechanism is responsible for the winter anomaly in TEC, then the anomaly must be observed during different phases of solar activity. To ascertain this, we have also studied the variation of solar-flux-independent TEC determined at a constant level of solar flux. While the semiannual oscillation in solar flux-independent TEC is a consistent feature, the winter anomaly is absent throughout the period 2005–2012. Hence, TEC is not a pertinent parameter to look for the winter anomaly.

Seasonal characteristics of COSMIC measurements over Indian sub-continent during different phases of solar activity

The seasonal characteristics of F2 region is investigated using peak electron density (NmF2) and corresponding altitude (hmF2) measurements obtained by COSMIC observations over Indian sub-continent (Geog. 5–40°N and 60–100°E) for the complete mission during the solar cycle 24 (Apr, 2006–Dec, 2013). A stronger EIA is observed in summer and winter during high solar activity whereas occurs in equinoxes during all levels of solar activity. The noontime winter anomaly in NmF2 is absent/weaker during low (2006–2009)/high (2010–2013) solar activity over equator whereas is stronger in low and moderate solar activity (2006–2007 and 2010–2011) but absent in minimum and maximum (2008–2009 and 2012–2013) solar activity over low-latitude respectively. The higher hmF2 is observed over the equator throughout the day (equator: 230–415km and low-latitude: 220–340km). The observed parameters, NmF2 and hmF2 are compared with the IRI-modeled values using CCIR and URSI options. The comparison exhibits a higher discrepancy in NmF2 in nighttime and morning for equatorial and lower discrepancy for the whole day over the low-latitude whereas smaller (<20%) discrepancy exists in the hmF2 throughout the day using both IRI options. In conclusion, we found CCIR option in more agreement to the observed values for both equatorial and low-latitude regions respectively.

Validation of Earth atmosphere models using solar EUV observations from the CORONAS and PROBA2 satellites in occultation mode

Aims : Knowledge of properties of the Earth’s upper atmosphere is important for predicting the lifetime of low-orbit spacecraft as well as for planning operation of space instruments whose data may be distorted by atmospheric effects. The accuracy of the models commonly used for simulating the structure of the atmosphere is limited by the scarcity of the observations they are based on, so improvement of these models requires validation under different atmospheric conditions. Measurements of the absorption of the solar extreme ultraviolet (EUV) radiation in the upper atmosphere below 500 km by instruments operating on low-Earth orbits (LEO) satellites provide efficient means for such validation as well as for continuous monitoring of the upper atmosphere and for studying its response to the solar and geomagnetic activity. Method : This paper presents results of measurements of the solar EUV radiation in the 17 nm wavelength band made with the SPIRIT and TESIS telescopes on board the CORONAS satellites and the SWAP telescope on board the PROBA2 satellite in the occulted parts of the satellite orbits. The transmittance profiles of the atmosphere at altitudes between 150 and 500 km were derived from different phases of solar activity during solar cycles 23 and 24 in the quiet state of the magnetosphere and during the development of a geomagnetic storm. We developed a mathematical procedure based on the Tikhonov regularization method for solution of ill-posed problems in order to retrieve extinction coefficients from the transmittance profiles. The transmittance profiles derived from the data and the retrieved extinction coefficients are compared with simulations carried out with the NRLMSISE-00 atmosphere model maintained by Naval Research Laboratory (USA) and the DTM-2013 model developed at CNES in the framework of the FP7 project ATMOP. Results : Under quiet and slightly disturbed magnetospheric conditions during high and low solar activity the extinction coefficients calculated by both models agreed with the measurements within the data errors. The NRLMSISE-00 model was not able to predict the enhancement of extinction above 300 km observed after 14 h from the beginning of a geomagnetic storm whereas the DTM-2013 model described this variation with good accuracy.

Variation of monthly mean foF2 and hmF2 over a mid latitude station during the period 1997–2006

Ionosonde data of a mid latitude station Novosibirsk (Geog. Lat. 54.6°N, Geog. Long. 83.2°E) has been analyzed for the years 1997–2006 that covers the major part of solar cycle 23. Our results show the presence of winter anomaly in the daytime F2 layer critical frequency during different phases of solar activity. Results also reveal a semiannual variation of foF2 with two maxima and a minimum that always appears in summer. While the first maximum is in the spring equinox, the second one is found to shift from autumn to winter with the increase of solar activity. The maximum height of F2 layer during the daytime shows variation with the solar activity. It is higher during the higher activity periods and lower during the periods of low activity. Results of ionosonde observations have been compared with those obtained from IRI-2007 model and it is found that model reproduces gross features of foF2 variation. However, the modeled hmF2 variations during equinoxes are significantly different from the ones derived using the ionosonde data. The model also underestimates the hmF2 values.

Similarities and Distinctions in Cosmic-Ray Modulation During Different Phases of Solar and Magnetic Activity Cycles

We study the solar-activity and solar-polarity dependence of galactic cosmic-ray intensity (CRI) on the solar and heliospheric parameters playing a significant role in solar modulation. We utilize the data for cosmic-ray intensity as measured by neutron monitors, solar activity as measured by sunspot number (SSN), interplanetary plasma/field parameters, solar-wind velocity [V] and magnetic field [B], as well as the tilt of the heliospheric current sheet [Λ], and we analyze these data for Solar Cycles 20 – 24 (1965 – 2011). We divide individual solar cycles into four phases, i.e. low, high, increasing, and decreasing solar activity. We perform regression analysis to calculate and compare the CRI-response to changes in different solar/interplanetary parameters during i) different phases of solar activity and ii) similar activity phases but different polarity states. We find that the CRI-response is different during negative (A<0) as compared to positive (A>0) polarity states not only with SSN and Λ but also with B and V. The relative CRI-response to changes in various parameters, in negative (A<0) as compared to positive (A>0) state, is solar-activity dependent; it is ≈ 2 to 3 times higher in low solar activity, ≈ 1.5 to 2 times higher in moderate (increasing/decreasing) activity, and it is nearly equal in high solar-activity conditions. Although our results can be ascribed to the preferential entry of charged particles via the equatorial/polar regions of the heliosphere as predicted by drift models, these results also suggest that we should look for any polarity-dependent response of solar-wind and transport parameters in modulating CRI in the heliosphere.

Study of the solar wind-magnetosphere coupling on different time scales

Solar wind-magnetosphere coupling, its causes and consequences have been studied for the last several decades. However, the assessment of continuously changing behaviour of the sun, plasma and field flows in the interplanetary space and their influence on geomagnetic activity is still a subject of intense research. Search for the best possible coupling function is also important for space weather prediction. We utilise four geomagnetic indices (ap, aa, AE and Dst) as parameters of geomagnetic activity level in the earth's magnetosphere. In addition to these indices, we utilise various solar wind plasma and field parameters for the corresponding periods. We analyse the geomagnetic activity and plasma/field parameters at yearly, half-yearly, 27-day, daily, 3-hourly, and hourly time resolutions. Regression analysis using geomagnetic and solar wind data of different time resolutions, over a continuous long period, and at different phases of solar activity (increasing including maximum/decreasing including minimum) led us to suggest that two parameters BV/1000 (mVm−1) and BV2 (mVs−1) are highly correlated with the all four geomagnetic activity indices not only at any particular time scale but at different time scales. It probably suggests for some role of the fluctuations/variations in interplanetary electric potential, its spacial variation [i.e., interplanetary electric field BV (mVm−1)] and/or time variation [BV2 (mVs−1)], in influencing the reconnection rate.

Electron density distribution and solar plasma correction of radio signals using MGS, MEX, and VEX spacecraft navigation data and its application to planetary ephemerides

The Mars Global Surveyor (MGS), Mars Express (MEX), and Venus Express (VEX) experienced several superior solar conjunctions. These conjunctions cause severe degradations of radio signals when the line of sight between the Earth and the spacecraft passes near to the solar corona region. The primary objective of this work is to deduce a solar corona model from the spacecraft navigation data acquired at the time of solar conjunctions and to estimate its average electron density. The corrected or improved data are then used to fit the dynamical modeling of the planet motions, called planetary ephemerides. We analyzed the radio science raw data of the MGS spacecraft using the orbit determination software GINS. The range bias, obtained from GINS and provided by ESA for MEX and VEX, are then used to derive the electron density profile. These profiles are obtained for different intervals of solar distances: from 12Rs to 215Rs for MGS, 6Rs to 152Rs for MEX, and form 12Rs to 154Rs for VEX. They are acquired for each spacecraft individually, for ingress and egress phases separately and both phases together, for different types of solar winds (fast, slow), and for solar activity phases (minimum, maximum). We compared our results with the previous estimations that were based on in situ measurements, and on solar type III radio and radio science studies made at different phases of solar activity and at different solar wind states. Our results are consistent with estimations obtained by these different methods. Moreover, fitting the planetary ephemerides including complementary data that were corrected for the solar corona perturbations, noticeably improves the extrapolation capability of the planetary ephemerides and the estimation of the asteroids masses.

Formation of coronal mass ejections at different phases of solar activity

This paper investigates the dependence of the observed coronal mass ejections and their parameters on evolutionary changes in the global solar magnetic field at different phases of solar cycles 23–24. Four periods in the evolution of the solar cycle are identified, depending on the dominance ratio of the sectoral and zonal magnetic field structures. The parameters of coronal mass ejections observed during these periods are analyzed. The evolving structure in the global magnetic field is identified, and its influence on coronal mass ejections is examined.

Study of the Diurnal Variation of Cosmic Rays during Different Phases of Solar Activity

The pressure-corrected hourly counting rate data of ground-based super neutron monitor stations, situated in different latitudes, have been employed to study the characteristics of the long-term variation of cosmic-ray diurnal anisotropy for a long (44-year) period (1965 – 2008). Some of these super neutron monitors are situated in low latitudes with high cutoff rigidity. Annual averages of the diurnal amplitudes and phases have been obtained for each station. It is found that the amplitude of the diurnal anisotropy varies with a period of one solar activity cycle (11 years), whereas the diurnal phase varies with a period of 22 years (one solar magnetic cycle). The average diurnal amplitudes and phases have also been calculated by grouping the days on the basis of ascending and descending periods of each solar cycle (Cycles 20, 21, 22, and 23). Systematic and significant differences are observed in the characteristics of the diurnal variation between the descending periods of the odd and even solar cycles. The overall vector averages of the descending periods of the even solar cycles (20 and 22) show significantly smaller diurnal amplitudes compared to the vector averages of the descending periods of the odd solar cycles (21 and 23). In contrast, we find a large diurnal phase shift to earlier hours only during the descending periods of even solar cycles (20 and 22), as compared to almost no shift in the diurnal phase during the descending periods of odd solar cycles. Further, the overall vector average diurnal amplitudes of the ascending period of odd and even solar cycles remain invariant from one ascending period to the other, or even between the even and odd solar cycles. However, we do find a significant diurnal phase shift to earlier hours during the ascending periods of odd solar cycles (21 and 23) in comparison to the diurnal phase in the ascending periods of even solar cycles (20 and 22).

Improvement to the global distribution of coronal plasma and magnetic field on the source surface using expansion factor fs and angular distance θb

In this paper, we have developed an improved model to build a self-consistent global structure on the source surface of 2.5 Rs covering four different phases of solar activity. This model involves the topological effect of the magnetic field expansion factor fs and the minimum angular distance θb(at the photosphere) between an open field foot point and its nearest coronal hole boundary. The purpose of this effect is to separate the open field area and the close field area more effectively. The model uses as input for 136 Carrington Rotations (CRs) covering four different phases of solar activity: (1) an empirical model of the magnetic field topology on the source surface using Line-of-sight (los) photospheric field (Blos) measurements by Wilcox Solar Observatory (WSO); and (2) an empirically derived global coronal density distribution using K coronal polarized brightness (pB) by MKIII in High Altitude Observator (HAO). The solar wind speed on the source surface is specified by the function of both fs and θb, which are obtained by the magnetic field data. Then the coronal mass outputs are analyzed and the self-consistent global distribution on the source surface is numerically studied for the four different phases. Finally, the model estimates the solar wind speed at 1AU as a simple function of the speed on the source surface. Our numerical results indicate reasonable semi-quantitative agreement with observations at different phases of solar activity.

Study of the Diurnal Variation of Cosmic Rays during Different Phases of Solar Activity

Study of the Diurnal Variation of Cosmic Rays during Different Phases of Solar Activity

The statistical and numerical study of the global distribution of coronal plasma and magnetic field near 2.5 Rs over a 10-year period

The basic characteristics of the global distribution for the corona plasma and magnetic field near 2.5 Rs are analyzed with the statistical and numerical methods for 136 Carrington Rotations (CRs) covering four different phases of solar activity. By using the observational data and the velocity distribution model in the corona, the statistical average distribution of the magnetic field, density and the coronal mass outputs are analyzed for the four different phases. Then, a numerical study of the global distribution near 2.5 Rs has been made by solving a self-consistent MHD system. Finally, the solar wind speed at 1 AU is given by mapping the speed at 2.5 Rs to that near 1 AU, and the comparison of the numerical results with the observational measurements and the simulation result of the Wang–Sheeley–Arge (WSA) model are made during more than 5 years. The numerical results indicate that the global distributions on the source surface of 2.5 Rs at different phases of solar activity could be used to predict the change of the solar wind in interplanetary space.

Lifetimes of High-Degree p Modes in the Quiet and Active Sun

We study variations of the lifetimes of high-l solar p modes in the quiet and active Sun with the solar activity cycle. The lifetimes in the degree range l=300 – 600 and ν=2.5 – 4.5 mHz were computed from SOHO/MDI data in an area including active regions and quiet Sun using the time – distance technique. We applied our analysis to the data in four different phases of solar activity: 1996 (at minimum), 1998 (rising phase), 2000 (at maximum), and 2003 (declining phase). The results from the area with active regions show that the lifetime decreases as activity increases. The maximal lifetime variations are between solar minimum in 1996 and maximum in 2000; the relative variation averaged over all l values and frequencies is a decrease of about 13%. The lifetime reductions relative to 1996 are about 7% in 1998 and about 10% in 2003. The lifetime computed in the quiet region still decreases with solar activity, although the decrease is smaller. On average, relative to 1996, the lifetime decrease is about 4% in 1998, 10% in 2000, and 8% in 2003. Thus, measured lifetime increases when regions of high magnetic activity are avoided. Moreover, the lifetime computed in quiet regions also shows variations with the activity cycle.