Long-period Fluctuations Research Articles

Optimization of seismic insulation parameters of frame buildings using adaptive methods

Objective. The purpose of the work is to calculate frame buildings with flexible connections and with flexible and switch-off connections, to make recommendations for the use of seismic insulation methods depending on the characteristics of seismic events. Method. Development of an algorithm for calculating frame buildings of a frame structural system with seismic protection in buildings with flexible connections and with flexible and switchable connections Result. A method for calculating frame buildings of a frame structural system with seismic insulation in the form of flexible connections and flexible and switchable connections has been developed. A computer calculation program for seismically insulated and nonseismically insulated frame buildings in the Delphi 5.0 programming environment in the Object Pascal language using the Runge-Kutta numerical method of the 4th order for solving differential equations has been compiled Conclusion. It is determined that the construction of frame buildings with the seismic insulation methods considered in this paper, namely with flexible connections and with flexible connections and disconnecting connections, is not impractical for territories where long-period fluctuations are possible, due to the fact that excessively high deformations occur.

Additive singular spectral model of a dendrochronological signal

Relevance. Allocation of structural components in a dendrochronological signal of annual rings of coniferous trees expands the possibilities of the bioindication method and allows obtaining information about changes in environmental conditions in the past for extended territories. Aim. Creation of an additive singular spectral model based on the frequency trigonometric components of the dendrochronological signal; reconstruction of changes in the total ozone content in the atmosphere in the past, affecting the level of ultraviolet radiation in the B range radiation. Objects. Time series of total ozone content in the atmosphere (data from 1932), width and density of annual rings (data from 1686–2004) on the example of the territory near the observatory in Arosa, Switzerland, time series of stable oxygen isotopes δ18Oc, France. Methods. Time series analysis (decomposition of a time series, identification of model parameters, prediction of a time series), statistical analysis (F-criterion, χ2 – Pearson criterion), experimental measurements of the percentage components of the wood of annual rings, correlation analysis, spectral singular analysis. Results. Decomposition of the dendrochronological signal of individual chronologies into trigonometric components in the Caterpillar program. Correlation analysis of the sensitivity of trees to atmospheric effects. Reconstruction of the ozone level in the stratosphere using the first trigonometric component of the dendrochronological signal. In cellulose, the first low-frequency component of the signal and the structural component of wood, a reliable response of trees to long-period fluctuations in the total ozone content is recorded. This allows assessment of the impact of the stress factor on conditions of exploitation of forest resources. The use of data on the width of the annual rings allows you to expand the territorial boundaries of the method.

Comparative Dynamics Analysis of Simple Mathematical Models of the Plankton Communities Considering Various Types of Response Function

The paper proposes a two-component discrete-time model of the plankton community, taking into account features of the development and interaction of phytoplankton and zooplankton. To describe the interaction between these species and to compare the system dynamics, we use the following set of response functions: type II and III Holling function and the Arditi–Ginzburg response function, each of which describes trophic interactions between phytoplankton and zooplankton. An analytical and numerical study of the model proposed is made. The analysis shows that the variation of trophic functions does not change the dynamic behavior of the model fundamentally. The stability loss of nontrivial fixed point corresponding to the coexistence of phytoplankton and zooplankton can occur through a cascade of period-doubling bifurcations and according to the Neimark–Saker scenario, which allows us to observe the appearance of long-period oscillations representing the alternation of peaks and reduction in the number of species as a result of the predator-prey interaction. As well, the model has multistability areas, where a variation in initial conditions with the unchanged values of all model parameters can result in a shift of the current dynamic mode. Each of the models is shown to demonstrate conditional coexistence when a variation of the current community structure can lead to the extinction of the entire community or its part. Considering the characteristics of the species composition, the model with the type II Holling function seems a more suitable for describing the dynamics of the plankton community. Such a system is consistent with the idea that phytoplankton is a fast variable and predator dynamics is slow; thus, long-period fluctuations occur at high phytoplankton growth rates and low zooplankton ones. The model with the Arditi–Ginzburg functional response demonstrates quasi-periodic fluctuations in a narrow parametric aria with a high predator growth rate and low prey growth rate. The quasi-periodic dynamics regions in the model with the Holling type III functional response correspond to the conception of fast and slow variables, however in this case, the stability of the system increases, and the Neimark-Sacker bifurcation occurs even at a higher growth rate of zooplankton.

Numerical Simulation of Non-Isothermal Mixing Flow Characteristics with ELES Method

Thermal fatigue caused by turbulent thermal mixing in tee pipes is always one of the failure factors of industrial pipes. At present, computational fluid dynamics (CFD) is still the main research method to study the thermal fatigue mechanism. Due to the limitations of the large eddy simulation (LES) model and the classical Reynolds Averaged Navier–Stokes (RANS) model in simulating thermal mixing, an advanced Embedded LES (ELES) model was developed. By comparing the model with data in the open literature, the validity of the ELES model to iso-thermal mixing was evaluated and proven. After that, the flow characteristics of the backflow upstream with different momentum ratios (MR) were studied using the ELES method, as well as the temperature characteristics near the wall where the backflow appears. It was found that the characteristics of the backflow and the temperature distribution upstream in the tee were different with different MR values and some regions under specified MR values are found to be more prone to thermal fatigue at the intersection of the tee upstream. Moreover, the frequency analysis at specified points near the wall under three different MR values was estimated to evaluate thermal fatigue and the results showed that long-period fluctuations of lower frequencies than 6 Hz upstream were observed. This work helps form a comprehensive understanding of the backflow in thermal mixing and the relationship between fatigue and backflow in the tee.

Formulating Wave Overtopping at Vertical and Sloping Structures with Shallow Foreshores Using Deep-Water Wave Characteristics

The state-of-The-Art formulas for mean wave overtopping (q) assessment typically require wave conditions at the toe of the structure as input. However, for structures built either on land or in very shallow water, obtaining accurate estimates of wave height and period at the structure toe often proves difficult and requires the use of either physical modeling or high-resolution numerical wave models. Here, we follow Goda's method to establish an accurate prediction methodology for both vertical and sloping structures based entirely on deep-water characteristics-where the influence of the foreshore is captured by directly incorporating the foreshore slope and the relative water depth at the structure toe (htoe/Hm0,deep). Findings show that q decreases exponentially with htoe/Hm0,deep due to the decrease of the incident wave energy; however, the rate of reduction in q decreases for structures built on land or in extremely shallow water (htoe/Hm0,deep ≤ 0.1) due to the increased influence of wave-induced setup and infragravity waves-which act as long-period fluctuations in mean water level-generated by nonlinear wave transformation over the foreshore.

The properties of vertical electric field during haze event in Xi'an, China

This paper analyses the characteristics of vertical electric field (Ez) fluctuations and their correlation with other quantities during haze event in Xi'an, China. Our results indicate that in regard to long-period fluctuations (period > 30 min), when the RH (relative humidity) change rate is positive at the development stage of haze event, secondary chemical reactions increase the PM10 (particulate matter 10 μm or smaller in diameter) concentration. When the charge properties of particles are different, three types of spatial electric field changes occur. When the RH change rate is negative, if both the PM10 concentration and absolute value of Ez decrease, this suggests that the haze event has entered the dissipation stage. If the PM10 concentration and Ez do not change notably over time, this indicates that no secondary chemical reactions occur, and no new particles are produced. Regarding short-period fluctuations, Ez fluctuations with a period longer than 100 s notably contribute to the overall Ez fluctuations, and the Ez fluctuations exhibit a good correlation with the RH and PM10 concentration. In addition, Ez fluctuations with a period shorter than 30 s yield an important contribution to the overall Ez fluctuations, but the correlation between Ez fluctuations and the RH and PM10 concentration is poor, which indicates that Ez fluctuations with a period shorter than 30 s are not caused by RH variation. These results are of great significance to the identification of pollutant gases during haze periods and the prevention and control of haze events.

Evaluation on the performance fluctuation after water ingestion for a turbofan engine compressor during flight descent

Turbofan engine compressor is most severely threatened by the entry of liquid water during flight descent. This study aims to deeply understand the fluctuations of compressor performance parameters caused by water ingestion through frequency spectrum analysis. The water content and droplet diameter distribution are determined based on the real heavy rain environment. Results reveal that most of the droplets actually entering the core compressor have a particle size of less than 100 μm. In addition, the formation and motion of water film plays a critical role in affecting the fluctuation characteristics. Water ingestion deteriorates the compression performance and aggravates the unsteady fluctuations of the fan. However, the performance of the core compressor is less affected by water ingestion, but their fluctuations are still exacerbated. For some important parameters, such as inlet mass flow rate, total pressure ratio, total temperature ratio, compression work and efficiency, their main frequency of fluctuation are switched from the original blade passing frequency to the rotor passing frequency, and their amplitudes are correspondingly amplified to varying degrees. These phenomena can be observed in both the fluctuations of the fan and core compressor. Moreover, the operating point of them will be in the long-period and large-amplitude fluctuations, which leads them experiences the non-optimal state for a long time and threatens their operating stability.

Coupling of the Surface and Near-Bottom Currents in the Gulf of Mexico.

Coupling between the surface and near‐bottom currents in the Gulf of Mexico (GoM) has been reported in many case studies. However, geographical variations of this coupling need more examination. In this study, surface geostrophic currents derived from satellite‐observed sea surface height and subsurface currents from a collection of deep ocean moorings are used to examine the surface and bottom coupling in different parts of the GoM. The short‐period (30–90 days) fluctuations generated by the Loop Current (LC) and the LC eddies (LCEs) have a more vertically coherent structure and stronger deep ocean expressions than the long‐period fluctuations (>90 days). In addition, the strength of the coupling is modulated by the long‐period variations of the LC and LCE sheddings. Moreover, the surface and bottom coupling varies geographically. In the LC region, the surface fluctuations along the eastern side of the LC are important in causing the bottom current fluctuations through baroclinic instability under the LC and through traveling topographic Rossby waves (TRWs) north of the LC. In the central deep GoM, the bottom currents are affected by the upper fluctuations of the northern LC through both local baroclinic instability and remote TRW propagation. In the northwestern GoM, the bottom current fluctuations are largely related to the remote surface variability from the west side of the LC by TRWs propagating northwestward. This study will help us better understand mechanisms of the bottom current fluctuations that are important for the dispersal of deep ocean materials and properties.

Reconstructing seafloor age distributions in lost ocean basins

Reconstructions of past seafloor age make it possible to quantify how plate tectonic forces, surface heat flow, ocean basin volume and global sea level have varied through geological time. However, past ocean basins that have now been subducted cannot be uniquely reconstructed, and a significant challenge is how to explore a wide range of possible reconstructions. Here, we investigate possible distributions of seafloor ages from the late Paleozoic to present using published full-plate reconstructions and a new, efficient seafloor age reconstruction workflow, all developed using the open-source software GPlates. We test alternative reconstruction models and examine the influence of assumed spreading rates within the Panthalassa Ocean on the reconstructed history of mean seafloor age, oceanic heat flow, and the contribution of ocean basin volume to global sea level. The reconstructions suggest variations in mean seafloor age of ~15 Myr during the late Paleozoic, similar to the amplitude of variations previously proposed for the Cretaceous to present. Our reconstructed oceanic age-area distributions are broadly compatible with a scenario in which the long-period fluctuations in global sea level since the late Paleozoic are largely driven by changes in mean seafloor age. Previous suggestions of a constant rate of seafloor production through time can be modelled using our workflow, but require that oceanic plates in the Paleozoic move slower than continents based on current reconstructions of continental motion, which is difficult to reconcile with geodynamic studies.

Multiscale Fluctuation Dynamics of Polymer Gels

Using a single experimental approach, namely dynamic light scattering in polyacrylamide and fibrin gels, the fluctuation dynamics of polymer gels was studied for the first time in parallel at two scales. One scale is congruent with gel network macrostructure, and another is microscopic at this level. Long-period fluctuations of the network structure with characteristic times in the range ~10–70 min have been detected, during which the microdynamics of network fibers remains practically unchanged in the range 0.1–106 μs. The limits of applicability of the “frozen” inhomogeneities approximation widely used in studying gels microdynamics have been established. The approach developed forms a basis for extending the range of investigations of polymer gel dynamics.

Long-period changes of the air temperature in Tatarstan and their forecast till the end of the 21st century

Long-term changes in air temperature on the territory of the Republic of Tatarstan in the 20th–21st centuries are considered. The periods of unambiguous changes in the surface air temperature are determined. It is established that the average winter temperature from the 1970s to 2017, increased in the Kazan region by more than 3 °C and the average summer temperature increased by about 2 °C over the same period. The contribution of global scale processes to the variability of the temperature of the Kazan region is shown: it was 37 % in winter, 23 % in summer. The correlation analysis of the anomalies of average annual air temperature in Kazan and the series of air temperature anomalies in each node over the continents, as well as the ocean surface temperature in each coordinate node on Earth for 1880 –2017, was performed. Long-distance communications were detected in the temperature field between Kazan and remote regions of the Earth. It is noted that long-period climate fluctuations in Kazan occur synchronously with fluctuations in the high latitudes of Asia and North America, with fluctuations in ocean surface temperature in the Arctic ocean, with fluctuations in air temperature in the Far East, and with fluctuations in ocean surface temperature in the Southern hemisphere in the Indian and Pacific oceans, as well as air temperature in southern Australia. It is suggested that there is a global mechanism that regulates long-term climate fluctuations throughout the Earth in the considered interval of 200 years of observations. According to the CMIP5 project, climatic scenarios were built for Kazan until the end of the 21st century.

Role of hydrometeorological factors and solar activity in interannual variability of ice extent in the East Siberian Sea

Interannual changes of the summer ice coverage were investigated, and the role of hydrometeorological factors and solar activity in long-period fluctuations of the ice area in the East Siberian Sea was determined. Multivariate statistical analysis of time series of the ice cover, hydrometeorological elements, and the solar activity (SA), was performed for the period from 1950 to 2012 with regard for the cross-correlations of the analyzed variables that made possible to develop the equations of interannual fluctuations of the ice coverage in the East Siberian Sea in August and September. The equations include the following variables: air temperature in June–August of the current year TVI‑VIII; the atmospheric circulation presented by indices of Arctic oscillation (Arctic Oscillation, AO), Arctic dipole (Arctic Dipole, AD), Pacific North American oscillation (Pacific North American Oscillation, PNA); average annual runoff of river waters into the Laptev and East Siberian seas (RivLES) with a time shift of one and two years; average annual index of the North Atlantic thermal state (AMO) with a time lag of eight years; solar activity SA, presented by the average annual Wolf number with advancing of one year. Diagnostic calculations of the ice area by the obtained equations using the actual values of the indices did show a good agreement between the actual and calculated values in August and September from 1950 to 2012. These equations were used to calculate contribution of each factor to the general dispersion of fluctuations of the ice coverage. The most important factors influencing the ice cover of the Sea in August and September are: the air temperature; the atmospheric circulation, presented by the Arctic Oscillation at the end of winter; and Atlantic waters which are characterized by AMO with a time lag of eight years. The role of other factors, i.e. summer atmospheric circulation, river runoff into the above seas, and 11-year cycle of solar activity were found to be equal to only 5–10% for each. Basing on these estimates, it has been concluded that the obtained statistical equations may be used as the diagnostic models of interannual changes in the ice coverage.

CLIMATE AND ITS DYNAMICS IN THE PLEISTOCENE-HOLOCENE AS A BASIS FOR THE OCCURRENCE OF DIFFERENT RISKS UNDER THE DEVELOPMENT OF CRYOLITHOZONE

Abstract: Earth’s climate global changes are considered as the main conditions for the risk occurrence under the Arctic region development, where is cryolithozone. Study is conducted for the North of Russia. Main factors of climate change, causes of Cenozoic cooling, conditions for permafrost and glacier forming are considered. Climate oscillatory nature throughout the Earth’s history as the main climate property is analyzed. Cryolithozone development in the Pleistocene and Holocene, together with mainly negative cryogenic processes, follows climate variations. Current climatic epoch is a stage in this oscillatory course. Due to disagreements over the modern warming causes (natural course or anthropogenic influence), climate variations in the 20th century are studied. The reasons for the relationship between atmospheric temperature and CO2 concentration (modern warming main factor according to opinion of anthropogenic influence supporters) are considered. It is concluded that both long-period past fluctuations and short-period modern fluctuations are determined by natural factors caused by common sources of energy: solar radiation and heat flux from Earth’s interior. On the basis of the revealed patterns, ideas on future climate development trends are expressed, which must be taken into account when organizing long-term structures in cryolithozone. It is assumed that the Earth’s global climate will develop in the direction of prolonged cooling. Against this background, oscillations of different periods and different amplitudes will remain, the extremes of which will have ever lower temperatures. In the near future some warming can be expected as a continuation of the warming period that has replaced the Little Ice Age.

FEATURES OF SEA LEVEL OSCILLATIONS IN INLAND BASINS OF THE ATLANTIC OCEAN

Problem Statement and Purpose. The determination of the impact of planetary regularities not only to the entire dynamic system of the World Ocean but also on its separate regions stimulates the development of mechanisms for rational nature management in the coastal zone for various space-time scales. The aim of the work is to compare the long-term characteristics and trends of sea level variability in the inner basins of the Atlantic Ocean, to establish their seasonal features.Data & Methods. Level measurements at gauging stations of the Baltic, Black and Azov Seas which are given in the public sources were used for this research. Most of these stations have the data series in the Baltic reference system for the same time period: from 1875 to 2006 for the mean annual level and from 1977 to 2006 for the average monthly values. The correlation analysis was used to determine statistical connections, the spectral analysis was used for finding the dominant oscillations.Results. The positive trends (from 0,7 to 2,9 mm year-1) in the dynamics of the average annual sea level (1875-2006) at the eastern coast of the Baltic and the northern coast of the Azov-Black Sea basin were established for the whole period. Long-period fluctuations of the level within each sea are well correlated (0,84-0,94) and there is practically no connection between the basins. The seasonal variation in the seas being compared has an anti-phase character (correlation coefficient from -0,64 to -0,87). Sea-level fluctuations have the value from one to tens of years, with the most significant quasi-two-year and 3-5-year periods.

Instability of secular variations in the horizontal components of the geomagnetic field: quasi-periodic fluctuations and jerks

Two types of fluctuations, with a short period (SPFs, 3 ± 0.15 years) and with a long period (LPFs, 10-70 years), have previously been found in the secular variation rate (SVR) of the horizontal component H, the vertical component Z, and the inclination I of the geomagnetic field (GMF). The fluctuations of SVR for the horizontal components of the GMF (X, Y, and D) and the periods and amplitudes of their SPFs are estimated in this study. The SVR fluctuations for Y and D are synchronous and have identical phases, and the SVR fluctuations for X are opposite to them in phase, except the areas near the magnetic poles. The SPF periods for X, Y, and D are almost the same (2.80 ± 0.14 years). Jerks in the SVR of Y, especially significant in Europe in 1969 and 1978, were studied. It is shown that jerks are a component of long-period fluctuations in the SVR of Y; they appear at the coincidence of extrema of the same sign in LPFs and SPFs. Jerks need not be considered a special phenomenon because they can be presented as the sum of quasi-periodic LPFs and SPFs.

Sea level anomaly in the North Atlantic and seas around Europe: Long-term variability and response to North Atlantic teleconnection patterns

Sea level anomaly (SLA), provided globally by satellite altimetry, is considered a valuable proxy for detecting long-term changes of the global ocean, as well as short-term and annual variations. In this manuscript, monthly sea level anomaly grids for the period 1993–2013 are used to characterise the North Atlantic Ocean variability at inter-annual timescales and its response to the North Atlantic main patterns of atmospheric circulation variability (North Atlantic Oscillation, Eastern Atlantic, Eastern Atlantic/Western Russia, Scandinavian and Polar/Eurasia) and main driven factors as sea level pressure, sea surface temperature and wind fields. SLA variability and long-term trends are analysed for the North Atlantic Ocean and several sub-regions (North, Baltic and Mediterranean and Black seas, Bay of Biscay extended to the west coast of the Iberian Peninsula, and the northern North Atlantic Ocean), depicting the SLA fluctuations at basin and sub-basin scales, aiming at representing the regions of maximum sea level variability. A significant correlation between SLA and the different phases of the teleconnection patterns due to the generated winds, sea level pressure and sea surface temperature anomalies, with a strong variability on temporal and spatial scales, has been identified. Long-term analysis reveals the existence of non-stationary inter-annual SLA fluctuations in terms of the temporal scale. Spectral density analysis has shown the existence of long-period signals in the SLA inter-annual component, with periods of ~10, 5, 4 and 2years, depending on the analysed sub-region. Also, a non-uniform increase in sea level since 1993 is identified for all sub-regions, with trend values between 2.05mm/year, for the Bay of Biscay region, and 3.98mm/year for the Baltic Sea (no GIA correction considered). The obtained results demonstrated a strong link between the atmospheric patterns and SLA, as well as strong long-period fluctuations of this variable in spatial and temporal scales.

Registration of weak ULF/ELF oscillations of the surface electric field strength

Measurements of the atmospheric electric field strength made by an electrostatic fluxmeter with a unique threshold sensitivity for such devices (6 × 10–2–10–3 V m–1 Hz–1/2 in the 10–3–25 Hz frequency range) and wide dynamic (120 dB) and spectral (0–25 Hz) ranges, are presented. The device parameters make it possible to observe the electric component of global electromagnetic Schumann resonances and long-period fluctuations in the atmospheric electric field strength.

SANDY COASTS OF INTERIOR SEAS UNDER LEVEL RISE: ASSESSMENT OF FUTURE DEVELOPMENT

Modern coastal zone is an open morpholithodynamics system characterized by a set of constant and variable parameters. Estimations of these parameters allows to assess the future development of the whole system. Constant parameters are geological and geomorphologic composition of the coast and its wind-wave mode. Variables are long-period fluctuations of water level due to eustatic variations, tectonic and glacio-isostatic movements. Prediction of the evolution of the coastal zone includes the assessment of the trends of the variable parameters of the morpholithodynamics system. In this study, the above problem is analyzed on the examples of south-eastern coast of the Baltic Sea and the Russian sector of the Caspian sea. The possible rise of the Baltic Sea level by 1.0–1.5 m by the end of the XXI century will result in the further destruction of sea coasts, flooding, waterlogging and salinization of coastal areas, which will lead to negative consequences for industrial, municipal and agricultural infrastructures. In the case of the Caspian Sea, the majority of its coasts regardless of the underwater slope has transformed into lagoons due to the sea level rise in recent decades. Coastal erosion will start only when the sea level reaches the 1929 yr stage from which the sea level drop started in the mid XX century. At this stage, a noticeable change of surface slope occurs. At the majority of Caspian coasts activation of coastal erosion will occur when the sea level rise above – 26 m a.s.l.

Будова дерново-літогенного ґрунту на червоно-бурій глині в екологічному аспекті

The dynamics of spatial heterogeneity of the sod-lithogenic soil on red-clay burіh clays has been studied in the environmental aspect in terms of hardness. The ecomorphic analysis of vegetation of the section was carried ont. The ordination of data of soil hardness has been realized by the non-metric multidimensional scaling. The three-dimensional variant of multidimensional scaling was applied. The relationship of varying the hardness of the soil and environmental factors has been determined using phytoindicative scales. Using the technique of spatial data analysis (PCNM) the elements of spatial autocorrelation data of soil hardness and defined processes underlying its formation have been highlighted. It was established that statistically significant phytoindicative scales describe from 7 to 49% of the variability of the multidimensional measurements. Temperature value of soil and cryoregime have a value for the formation of the first coordinate axis. The axis marks the conditions distinguishing soil hardness in layers of 10–35 cm from those located above and below of the selected block. The second coordination axis reflects the opposite phenomenon in soil structure above and below the level of 20 cm and describes the representation of gigromorphes in plant community. The highest values in the formation of the third coordination axis have light scales and ombroregime. Measurement selects the contrast on the basis of hardness at the level 10–35 cm from the surrounding soil layers. During fractionation of variations hardness of the studied soil site it was established that environmental factors determine 56 % of the total variability of the results. PCNM-variables describe 7 % of the variation of indicators of soil hardness and spatial patterns deterministic environment – 10 % of feature variability. Herewith the most important environmental factors for describing of large-scale spatial component of variation of soil hardness are the content of carbonate salts, digestible forms of nitrogen, thermo- and ombroregime, salt regime and continentality climate. The components of the spatial variability of the hardness of a long-period fluctuations are associated with the distribution of plant gigromorphes. Spatial variability of detailed scale components is dependent on soil aeration and ombroregime. High-frequency periodic oscillations of hardness are related to such factors as aeration of the soil, ombroclimate and also distribution structure of trophomorphes, gigromorphes and heliomorphes.

The rhythm of fountains: the length and time scales of rise height fluctuations at low and high Froude numbers

AbstractThe magnitude and frequency of vertical fluctuations of the top of an axisymmetric miscible Boussinesq fountain forms the focus of this work. We present measurements of these quantities for saline-aqueous fountains in uniform quiescent surroundings. Our results span source Froude numbers $0. 3\leq {\mathrm{Fr} }_{0} \leq 40$ and, thereby, encompass very weak, weak, intermediate and forced classes of fountain. We identify distinct scalings, based on known quantities at the fountain source, for the frequency of fountain height fluctuations which collapse our data within bands of ${\mathrm{Fr} }_{0} $. Notably, our scalings reveal that the (dimensionless) frequency takes a constant value within each band. These results highlight characteristic time scales for the fluctuations which we decompose into a single, physically apparent, length scale and velocity scale within each band. Moreover, within one particular band, spanning source Froude numbers towards the lower end of the full range considered, we identify unexpectedly long-period fluctuations indicating a near balance of inertia and (opposing) buoyancy at the source. Our analysis identifies four distinct classes of fluctuation behaviour (four bands of ${\mathrm{Fr} }_{0} $) and this classification matches well with existing classifications of fountains based on rise heights. As such, we show that an analysis of the behaviour of the fountain top alone, rather than the entire fountain, provides an alternative approach to classifying fountains. The similarity of classifications based on the two different methods confirms that the boundaries between classes mark tangible changes in the physics of fountains. For high ${\mathrm{Fr} }_{0} $ we show that the dominant fluctuations occur at the scale of the largest eddies which can be contained within the fountain near its top. Extending this, we develop a Strouhal number, ${\mathrm{Str} }_{top} $, based on experimental measures of the fountain top, defined such that ${\mathrm{Str} }_{top} = 1$ would suggest the dominant fluctuations are caused by a continual cycle of eddies forming and collapsing at this largest physical scale. For high-${\mathrm{Fr} }_{0} $ fountains we find ${\mathrm{Str} }_{top} \approx 0. 9$.