11-year Solar Cycle Research Articles

Phase-Locked Impact of the 11-Year Solar Cycle on Tropical Pacific Decadal Variability

Abstract As an important external forcing, the effect of the 11-yr solar cycle on the tropical Pacific decadal variability is an interesting question. Here, we systematically investigate the phase-locking of the atmosphere and ocean covariations to the solar cycle in the tropical Pacific and propose a new mechanism to explain these decadal covariations. In both observation/reanalysis datasets and a solar cycle forced sensitivity experiment (named the SOL experiment), the ocean heat content anomalies (OHCa; 300 m) resemble a La Niña–like pattern in the solar cycle ascending phase, and the Walker circulation shifts westward. In the declining phase, the opposite is true. The accumulative solar irradiation directly contributes to this coherent decadal variability via changing the warm water volume and the solar-related heat is redistributed by the ocean dynamic processes. During the 11-yr solar cycle, the Pacific Walker circulation anomalies maintain the OHCa in the western equatorial Pacific and work as negative feedback for the eastern Pacific to help the OHCa phase transition. In addition, oceanic meridional heat transport via the subtropical cells and the propagation of off-equatorial Rossby waves also provide a lagged negative feedback to the OHCa phase transition according to the 11-yr solar cycle. The decadal coupled responses of the tropical Pacific climate system are 2 years more lag in the SOL experiment than in the observation/reanalysis. Significance Statement Here, we propose a new mechanism that the heating effect of the accumulative solar irradiation during the 11-yr solar cycle can be “integrated” into the tropical Pacific OHC and then provide a bottom-up effect on the atmosphere at decadal time scales. The strongly coupled processes in this region amplify the decadal phase-locking of the covariations to the 11-yr solar cycle. Our study demonstrates the role of the 11-yr solar cycle in the tropical Pacific decadal variability and provides a new explanation for the “bottom-up” mechanism of the solar cycle forcing. Our results update the understanding of the tropical Pacific decadal variability and may help to improve climate predictions at decadal time scales.

Proposed Wave Momentum Source for Generating the 22-Year Solar Cycle

Proposed Wave Momentum Source for Generating the 22-Year Solar Cycle

A New Approach for Low-Latitude Ionospheric Scintillation Prediction

The prediction of ionospheric scintillation is a current research topic. Data-oriented models have been proposed since there is not a mathematical model able to simulate the complex ionospheric mechanisms for the prediction of scintillation. Data-oriented models employ machine learning algorithms that are trained with known, post-mortem data, and then perform predictions from new data. An ensemble method based on sampling boosting applied for a set of decision trees is employed for the prediction of scintillation in a single low-latitude location in Brazil. The prediction was performed considering two classes, occurrence or absence of scintillation. The method uses as input temporal series of the scintillation index S4, the total electron content (TEC), and some geomagnetic and solar indexes for that location. Data encompasses the summer months of the previous solar cycle years (2010-2018), and it was split into mutually-exclusive training and validation/test sets. Prediction performance was promising, showing a potential to be developed for operational use. Data limitations related to time series extension, or also to a balanced distribution of samples/instances covering both classes, since scintillation occurrences are usually scarce, can be further developed as new data are available.

Why Pacific quasi-decadal oscillation has emerged since the mid-20th century

Pacific quasi-decadal oscillation (PQDO) is one component of the multi-time-scale tropical Pacific decadal variability, with a variability center in the equatorial central Pacific (ECP). PQDO has emerged since the 1950s and has a significant impact on decadal climate variability over Asia and North America and Pacific storms. However, why it has intensified since the 1950s remains unknown. Here we test two competing hypotheses, (1) 11-year solar cycle forcing and (2) internal variability arising from El Niño–Southern Oscillation (ENSO) asymmetry, by analyzing simulation results, including one fixed-forcing control (CTRL) experiment and four sensitive experiments with millennial spectral solar irradiance (SSI), obtained from the Community Earth System Model–Last Millennium Ensemble modeling project. The four-member ensemble-averaged SSI experiments suggest that 11-year solar irradiance forcing cannot excite PQDO without stratospheric amplification of solar forcing. By analyzing 144 years of observations and the CTRL experiment, we find that the PQDO is nonstationary, and consecutive La Niña-induced decadal variability can boost PQDO in the ECP. El Niño could induce decadal ENSO signals in the NINO3.4 region but not in PQDO regions. The negative phase of PQDO tends to follow the occurrence of multi-year La Niña. We suggest that the emergence of PQDO since the 1950s is mainly due to the increase in multi-year La Niña events.

Investigating the associations between solar flares and magnetic complexity of active regions

It is generally believed that solar activities are closely linked with magnetic fields on the solar surface. To learn more about how solar flares are produced in relation to solar magnetic configurations, we examined a total of 37,741 soft-X ray solar flare events observed by a series of GOES satellites. The flare and sunspot data catalogued by NOAA were obtained from 1996 July through 2018 December, covering solar cycles 23 and 24. The investigated flares database consists of 38.26% B-, 55.52% C-, 5.78%M- and 0.44% X-class. In accordance with the Hale magnetic complexity categorisation system, a total of 33,562 sunspot groups comprised of 30.65% α -, 57.7% β-, 8.69% βγ, and 2.96% -βγδ-type active regions were counted based on their daily appearances, from the same source and period. The Multi-Taper and cross-correlations analyses were adopted in carrying out the investigation using their daily numbers. Our findings reveal that B-flares are negatively correlated with all the sunspot groups, in contrast to other flare classes that are positively correlated and synchronous. The β-sunspot and C-flares are found to exhibit the typical 11-year solar cycle, including the double-peaks feature during solar maximum. Correspondingly, the measured daily occurrence rates of β-sunspot and C-flares were the highest during the studied two solar cycles. Meanwhile, a total of 22,121 flare events were observed to be occurring concurrently with sunspot groups, out of which 10,019 flare events were found associated with β-sunspot, from which 5,378 happened to be C-class, the highest number obtained, followed by 4,164 with B-class. The X-flares recorded 2 events with α- sunspot group, the least recorded in the studied period. We also confirm that the βγδ-group is more likely to produce any class of flare. However, constrained by their formation rates, resulting in the β-group producing the most flares by number. Periodicities of 9.9, 10.67, and 9.9 years were obtained for α-, β-, and complex (βγ-and-βγδ) respectively while 4.1-6.5, 10.67, 11.2 and 10.64 years were obtained for B-, C-, M-and-X flares.

Cooling and Contraction of the Mesosphere and Lower Thermosphere From 2002 to 2021.

We examine the thermal structure of the mesosphere and lower thermosphere (MLT) using observations from 2002 through 2021 from the SABER instrument on the NASA TIMED satellite. These observations show that the MLT has significantly cooled and contracted between the years 2002 and 2019 (the year of the most recent solar minimum) due to a combination of a decline in the intensity of the 11-year solar cycle and increasing carbon dioxide (CO2.) During this time the thickness of atmosphere between the 1 and 10-4hPa pressure surfaces (approximately 48 and 105km) has contracted by 1,333m, of which 342m is attributed to increasing CO2. All other pressure surfaces in the MLT have similarly contracted. We further postulate that the MLT in the two most recent solar minima (2008-2009 and 2019-2020) was very likely the coldest and thinnest since the beginning of the Industrial Age. The sensitivity of the MLT to a doubling of CO2 is shown to be -7.5K based on observed trends in temperature and growth rates of CO2. Colder temperatures observed at 10-4hPa in 2019 than in the prior solar minimum in 2009 may be due to a decrease of 5% in solar irradiance in the Schumann-Runge band spectral region (175-200nm).

On the time lag between solar wind dynamic parameters and solar activity UV proxies

The solar activity displays variability and periodic behaviours over a wide range of timescales, with the presence of a most prominent cycle with a mean length of 11 years. Such variability is transported within the heliosphere by solar wind, radiation and other processes, affecting the properties of the interplanetary medium. The presence of solar activity–related periodicities is well visible in different solar wind and geomagnetic indices, although their time lags with respect to the solar cycle lead to hysteresis cycles. Here, we investigate the time lag behaviour between a physical proxy of the solar activity, the Ca II K index, and two solar wind parameters (speed and dynamic pressure), studying how their pairwise relative lags vary over almost five solar cycles. We find that the lag between Ca II K index and solar wind speed is not constant over the whole time interval investigated, with values ranging from 6 years to ∼1 year (average 3.2 years). A similar behaviour is found also for the solar wind dynamic pressure. Then, by using a Lomb-Scargle periodogram analysis we obtain a 10.21-year mean periodicity for the speed and 10.30-year for the dynamic pressure. We speculate that the different periodicities of the solar wind parameters with respect to the solar 11-year cycle may be related to the overall observed temporal evolution of the time lags. Finally, by accounting for them, we obtain empirical relations that link the amplitude of the Ca II K index to the two solar wind parameters.

Annual integral solar proton fluences for 1984–2019

Aims. Long-term fluxes or integral fluences of solar energetic particles (SEPs), and their variability within and beyond the 11-year solar cycle, make an important contribution to space physics. However, large uncertainties exist in the evaluation of average SEP fluxes or fluences over the last few decades, as they have been assessed by different methods and from different datasets. Here we revisit the derivation of annual integral SEP fluences from available data based on in situ measurements since 1984. Methods. We reconstructed a full time series of integral SEP fluxes above 10, 30, 60, 100, and 200 MeV for the period from 1984 to 2019 using observations performed by the GOES satellites. Intercalibration of the fluxes was performed via a linear relation between overlapping pairs of observations in order to obtain a uniform dataset. Galactic cosmic ray (GCR) background subtraction and identification of SEP event periods were carefully performed, allowing for a precise calculation of annual SEP fluences. Results. Annual integral fluences of SEPs with energies above 10, 30, 60, 100, and 200 MeV were calculated for the period from 1984 to 2019 (solar cycles 22–24), along with their uncertainties. It is shown that solar cycle 24 was significantly (by a factor of 5–8) weaker in the SEP fluence than the preceding cycles 22 and 23. The cumulative occurrence probability of years with the fluence above a given value is found to be perfectly described by the Weibull distribution. This can be used as a projection for the occurrence of solar extreme eruptive events on the secular timescales.

Regional impact of large-scale climate oscillations on ice out variability in New Brunswick and Maine.

The available ice out (the date of disappearance of ice from a water body) records were analyzed from four relatively closely spaced lakes in southwestern New Brunswick (Harvey, Oromocto, Skiff) and eastern Maine (West Grand Lake), with the longest set of available observations being for Oromocto Lake starting in 1876. Results of a coherence analysis carried out on the ice out data from the four lakes indicates that there is regional coherence and correspondingly, that regional drivers influence ice out. These results also indicate that ice out dates for lakes from the region where records have not been kept can also be interpolated from these results. As the ice out record was coherent, further analysis was done for only Oromocto Lake on the basis of it having the longest ice out record. Cross-wavelet analysis was carried out between the ice out record and a variety of cyclic climate teleconnections and the sunspot record to identify which phenomena best explain the observed ice out trends. The most important observed contributors to ice out were the North Atlantic Oscillation (NAO) and the El Niño Southern Oscillation (ENSO), with observed periodicities at the interannual scale. At the decadal scale the Pacific Decadal Oscillation (PDO) and the 11-year solar cycle were the only patterns observed to significantly contribute to ice out.

Solar variability between 650 CE and 1900 - Novel insights from a global compilation of new and existing high-resolution 14C records

This study investigates solar variability between 650 CE and 1900 based on new and published 14C records with a time resolution of two years or higher. The new high-resolution 14C data presented here are derived from Danish oak and span the period 1058–1250 CE. We determine the durations of past solar minima and periods with moderate solar activity from the solar modulation potential calculated using a carbon-box model with the high-resolution 14C records as input. The observed intervals of solar minima and intermittent periods with moderate activity levels suggest that a Maunder-type minimum occurred in 656–707 CE. We tentatively propose to name this minimum the Horrebow Minimum after Christian Horrebow, an early Danish astronomer who studied the occurrence of sunspots and was the first to propose that they follow a cyclic behaviour. Changes in amplitude and cycle length of the 11-year solar cycle are investigated by bandpass filtering 23 individual 14C records. The filtered 14C data indicate that the length of the 11-year solar cycle may be prolonged before the onset of the Oort, Maunder, and Spörer minima. The amplitude of the 11-year solar cycle associated with solar minima and periods with moderate solar activity between 650 CE and 1900 is estimated to 1.1‰. A two-sample Kolmogorov-Smirnov goodness-of-fit test indicates that there is no significant difference between the amplitude distribution of 11-year solar cycles during solar minima and periods of moderate solar activity. A review of the high-resolution 14C records encompassing the near-Earth supernova events that occurred in 1006 CE, 1054, 1181, 1572, and 1604 suggests that these events were not accompanied by distinct changes in the 14C production rate. Nonetheless, an unusual increase of c. 10‰ in Δ14C between 1048 CE and 1055 is observed and discussed.

Equinoctial asymmetry during solar minima at low to mid latitude

Equinoctial asymmetry (EA) of F2-layer critical frequency (foF2) during minimum years of solar cycle 22–23 (1996) and 23–24 (2008) has been studied for low and mid latitude stations ranges from 20°N - 55° N. Year 2008 provided an opportunity to study this phenomenon in extreme low EUV conditions. Pronounced/reasonable increase in EA strength at low/mid latitudes from 1996 to 2008 indicates role of EUV in EA. In addition to an increase in strength of EA from 1996 to 2008, variation in its strength and sign (positive if Mar Equinox foF2means > Sep Equinox foF2means and vice versa) with latitude and longitude are also observed during both years. Similar to previous studies, EA is observed in daytime during both years. However at low latitude stations, two peaks of foF2 are also observed at night: the first peak in summer and the second peak in the beginning of the September equinox which shows superposition of semi-annual and annual components. Hourly analysis showed asymmetry (Sep Equinox foF2means > Mar Equinox foF2means) from sunset to mid-night at low mid to mid latitude. It appears that the Mid latitude Summer Nighttime Anomaly (MSNA) is extending to September equinox with decreasing magnitudes from Summer to Sep equinox. IRI-16 showed EA during daytime only with over- and under- estimation as compared to observed data. Serious discrepancy between observed and IRI-2016 model values especially during deep minimum suggests modification of model for extreme low EUV condition as well as incorporation of parameters related to global wind pattern in the model.

Solar Cycle 25 Prediction Using Length-to-Amplitude Relations

We propose a simple method for prediction of the 11-year solar cycle maximum that is based on two relations. One of them is well known Waldmeier's rule that binds the amplitude of a cycle and the length of its ascending phase. The second rule relates the length of a given cycle from minimum to minimum and the amplitude of the next one. Using corresponding linear regressions we obtain for the amplitide of cycle 25 in the scale of 13-month smoothed monthly total revised sunspot number ${\rm SN}_{\rm max}(25) = 181\pm46$ and for the moment of the maximum $T_{\rm max}(25) = 2024.2\pm1.0$. Therefore, according to the prediction, cycle 25 will be higher than the previous one (${\rm SN}_{\rm max}(24) = 116$) with probability 0.92.

Unknown effects of daily-scale solar activity on the plant growth: Data from 6-year growth monitoring of Sphagnum riparium.

The influence of solar activity on plant growth has been studied for over 100 years, however, this phenomenon is still poorly understood on a daily scale. The data from extensive monitoring of the growth of peat moss Sphagnum riparium, which we are conducting in the mires of Karelia (Russia), may shed light on this issue. During the 6 years of observation, 161,190 shoots were measured, and 1075 growth rates were obtained. Considering together the growth rates with the sunspot number and involving data on seasonal temperature, we found previously unknown effects of daily-scale solar activity on plant growth. It was found that the sunspot number weakly but significantly inhibits the growth of Sphagnum. The extreme sunspot number in the 4 days before the growth rate values have a stronger influence. The involvement of temperature data showed that inhibition in growth is observed only in the temperature range from 6.7°C to 15.3°C and disappears beyond these limits. In addition, the data obtained showed that the influence of sunspot number on the growth of Sphagnum is progressively increasing along the gradient from the minimum to the maximum of the 11-year solar cycle. The study provides one of the first results on the effect of solar activity on plant growth on a daily scale. The results expand our knowledge of the biological effects of solar activity. Indirectly, they can also be useful to better our understanding of the ozone layer's involvement in this process.

Three decades of remote sensing of NO2 vertical distribution and column content at the A. M. Obukhov Institute of Atmospheric Physics

The paper reviews the results of 30-year spectrometric measurements of vertical distribution and column content of NO2 at the Zvenigorod Scientific Station (ZSS) of the A. M. Obukhov Institute of Atmospheric Physics and presents analysis of NO2 long-term trends and interannual variations. The station is located in the western Moscow region. It is part of the Network for the Detection of Atmospheric Composition Change (NDACC). Measurements are done in the morning and evening twilight by zenith-scattered visible solar radiation. Vertical NO2 profiles are retrieved and column NO2 contents are calculated by profile integration. Long term trends and inter-annual variations of NO2 are analysed by multivariate regression method taking into account autocorrelation of data in a wide range of time scales. Seasonally dependent estimates of NO2 trends and interannual variations due to the quasi-biennial oscillation, El Nino–Southern oscillation, North Atlantic Oscillation, and the 11-year solar cycle are obtained. Most pronounced (in per cent units) trends and circulation and solar cycle effects are peculiar to the winter–spring period of the year. Mutual influence is assessed between the estimates of the trend and the solar cycle effect in stratospheric NO2.

Long short-term memory and gated recurrent neural networks to predict the ionospheric vertical total electron content

This paper provides the application of deep learning models such as Long Short-Term Memory (LSTM) and a recently proposed Gated Recurrent Unit (GRU) in forecasting the ionospheric GPS_VTEC, and compare the performance of the results with that of Multilayer Perceptron (MLP) neural networks, GIM_TEC and the IRI-Plas 2017 models. GPS_VTEC time series data estimated from GPS measurement over low latitude equatorial station MAL2 with (geo.lat -2.70NandLong40.190E) located in Kenya is used in this study. The data span from January 1, 2010 to December 31, 2018 which covers 9 years of solar cycle 24. The data from the year 2010 to 2016 is used for the training, while the year 2017 data is used for validation and finally the data in the year 2018 is used to examine the performance of the models during the testing period. The performance of the models is based on statistical parameters such as root-mean-square error (RMSE) and correlation coefficient (R). The GRU unit shows a correlation coefficient of 0.971 with GPS_VTEC and a prediction error of 2.004 TECU while that of LSTM, MLP, GIM_TEC, and IRI-Plas 2017 models are 0.967, 0.951, 0.832 and 0.774 with a prediction error of 2.055 TECU, 2.336 TECU, 5.913 and 16.183 TECU, respectively. This shows that the predictions of the gated system models are better than the MLP, GIM_TEC and IRI-Plas models. Considering the prediction ability of these models to forecast the GPS-VTEC values under an intense Geomagnetic Storm event, it is observed that the GRU unit can achieve the best prediction accuracy and shows a strong performance for the trend prediction of this event more than the LSTM, MLP, GIM_TEC, and IRI-Plas models. In all, the three deep learning models perform better than the GIM_TEC and the IRI-Plas 2017 model.

Exploring the possible linkage between the precipitation and temperature over Iran and their association with the large-scale circulations: Cumulative spectral power and wavelet coherence approaches

The current study aims at improving our common knowledge of precipitation and surface temperature variabilities in Iran across different time scales (from intra-annual to decadal) by using two methods (the cumulative spectral power and wavelet coherence analyses) and linking the variabilities to several teleconnection indices, namely Mediterranean Oscillation (MO), Quasi-biennial Oscillation (QBO), Southern Oscillation Index (SOI), North Atlantic Oscillation (NAO), and solar activity (~ Sunspot Number (SN)). Furthermore, the interdependence of the spectral components of indices is also explored. We divided the country to eleven climatic zones and performed the analysis for individual zones as well as for the total area by constructing the precipitation and temperature signals for the study period of 1979–2021 based on the gridded data. Based on the wavelet coherence analysis, the surface temperature and precipitation variations are strongly linked together, in particular at annual cycle and the phase status is predominantly anti-phase for all zones as well as for the all temporal scales. In addition, the MO can be regarded as a predictor of the annual variation of both variables over Iran as our results indicate a significant co-variability in the annual band between MO signal and these variables. Furthermore, a similar semi-annual component is detected in both MO and temperature signals with an anti-phase status, but the same component was not found in the precipitation. Other indices have also substantial influences on both temperature and precipitation, mostly at inter-annual and decadal periods. Based on the wavelet coherence and lagged correlation analyses, evidences of common periodicity, namely 11-year solar cycle, between SN and SOI signals is clearly revealed. Moreover, our results show that if the SN signal is considered as the cause and the SOI signal as the effect, the minimum value of the 11-year component of SOI occurs approximately 2.5 to 3 years after the maximum of the same component in the SN signal. By employing the cumulative spectral power analysis, the main quasi-periodic components of the climatic signals, the surface temperature, and precipitation with their power distribution are presented and compared in different frequency bands. The application of both methods on different zones over Iran is also addressed in addition to the whole area. The results show that although some indices have minor impact on the variabilities of the precipitation and temperature for the whole area in some frequency bands, but the large impact is found in a number of individual zones.

Model of galactic cosmic ray spectrum above the Earth’s atmosphere

Abstract Galactic cosmic ray transport in the heliosphere is described by the well-known Parker transport equation. In 1969, Fisk and Axford [1] presented approximate analytical solutions to the cosmic ray transport equation. One of their solutions was later used to construct useful semi-empirical models describing the energy spectra of charged particles during the solar cycle. In this paper, a simplified model of the galactic cosmic ray spectrum is presented. The model can be used to describe the galactic spectra of protons and helium nuclei during the 11-year solar cycle in interplanetary space at about 1 AU.

A comparative study of ionospheric TEC diurnal variations at two stations near cusp latitudes in the Southern Hemisphere

Based on ionospheric total electron content (TEC) data for Zhongshan station (ZHS) and Scott Base station (SBA) in Antarctica, acquired during 2010–2020, high-latitude ionospheric TEC diurnal variations of two near cusp latitude stations were studied. The magnetic latitude and longitude differences between the two stations were approximately 5° and 135°, respectively. It was found that during the 11-year solar activity cycle, the maximum diurnal variation of the ionospheric TEC at ZHS occurred mainly between local noon and magnetic noon. Statistically, the TEC peaks occurred closer to local (magnetic) noon under low (high) solar activity conditions. The maximum diurnal variation of ionospheric TEC at SBA occurred mainly around local noon under low solar activity conditions but before magnetic midnight under high solar activity conditions. The effects of solar radiation, particle precipitation, and polar ionospheric convection pattern on the diurnal variation of TEC were investigated. At both stations, photoionization caused by solar radiation was the main reason for the maximum diurnal variation of ionospheric TEC around local noon. During high solar activity with high concentration plasma in the dayside polar ionosphere, the convection pattern was the dominant influence on the maximum diurnal variation of TEC before magnetic midnight (noon) at SBA (ZHS).

Precipitation and Temperature Trends and Cycles Derived from Historical 1890–2019 Weather Data for the City of Ottawa, Ontario, Canada

Patterns in historical climate data were analyzed for Ottawa, Ontario, Canada, for the interval 1890–2019. Variables analyzed included records of annual, seasonal, and extreme temperature and precipitation, diurnal temperature range, and various environmental responses. Using LOWESS regressions, it was found that annual and seasonal temperatures in Ottawa have generally increased through this interval, precipitation has shifted to a less snowy, rainier regime, and diurnal temperature variation has decreased. Furthermore, the annual growing season has lengthened by 23 days to ~163 days, and the annual number of frost-free days increased by 13 days to ~215 days. Despite these substantial climatic shifts, some variables (e.g., extreme weather events per year) have remained largely stable through the interval. Time-series analyses (including multitaper spectral analysis and continuous and cross wavelet transforms) have revealed the presence of several strong cyclical patterns in the instrumental record attributable to known natural climate phenomena. The strongest such influence on Ottawa’s climate has been the 11-year solar cycle, while the influence of the El Niño-Southern Oscillation, Arctic Oscillation, North Atlantic Oscillation, and Quasi-Biennial Oscillation were also observed and linked with the trends in annual, seasonal, and extreme weather. The results of this study, particularly the observed linkages between temperature and precipitation variables and cyclic climate drivers, will be of considerable use to policymakers for the planning, development, and maintenance of city infrastructure as Ottawa continues to rapidly grow under a warmer, wetter climate regime.

Self-organization of water molecules over 11-year solar cycle

The variations of solar activity and distribution of solar energy due to the rotation of the Earth around its axis and around the Sun exert a strong influence on the self-organization of water molecules. As a result, the rate of hydrolytic processes with the participation of water clusters displays diurnal, very large annual variations, and is also modulated by the 11-year cycles of solar activity. It also depends on the geographic latitude and can be different at the same time in the Northern and Southern Hemispheres. This phenomenon is important for all forms of life on the Earth. It may be well accounted for by the influence of muons which are constantly generated in the upper atmosphere by the solar wind. Muons reach the surface of the Earth and can penetrate to some depth underground. Buildings also absorb muons. For this reason, the rates of hydrolysis outside and inside buildings, as well as underground, can differ significantly from each other.