Annual Oscillation Research Articles

Analysis and prediction of polar motion using MSSA method

Polar motion is the movement of the Earth's rotational axis relative to its crust, reflecting the influence of the material exchange and mass redistribution of each layer of the Earth on the Earth's rotation axis. To better analyze the temporally varying characteristics of polar motion, multi-channel singular spectrum analysis (MSSA) was used to analyze the EOP 14 C04 series released by the International Earth Rotation and Reference System Service (IERS) from 1962 to 2020, and the amplitude of the Chandler wobbles were found to fluctuate between 20 and 200 mas and decrease significantly over the last 20 years. The amplitude of annual oscillation fluctuated between 60 and 120 mas, and the long-term trend was 3.72 mas/year, moving towards N56.79 °W. To improve prediction of polar motion, the MSSA method combining linear model and autoregressive moving average model was used to predict polar motion with ahead 1 year, repeatedly. Comparing to predictions of IERS Bulletin A, the results show that the proposed method can effectively predict polar motion, and the improvement rates of polar motion prediction for 365 days into the future were approximately 50% on average.

Relating 27-Day Averages of Solar, Interplanetary Medium Parameters, and Geomagnetic Activity Proxies in Solar Cycle 24

Correlations between solar, interplanetary-medium parameters, and geomagnetic-activity proxies in 27-day averages (a Bartels rotation) were analyzed for the 2009 – 2016 time interval. In this analysis, two new proxies were considered: i) \(B_{zs}\) GSM (Geocentric Solar Magnetic), calculated as the daily percentage of the IMF southward component along the GSM \(z\)-axis and then averaged every 27 days; ii) four magnetospheric indices (T-indices), calculated from the local north–south (\(x\)) contributions of the magnetosphere’s cross-tail (TAIL), the symmetric ring current (SRC), the partial ring current (PRC), and the Birkeland current (FAC), derived from the Tsyganenko and Sitnov (J. Geophys. Res. 110, A03208, 2005: TS05) semi-empirical magnetospheric model. Our results suggest that, among the parameters tested in this study, solar facular areas, interplanetary magnetic-field intensity and new proxies derived from the TS05 model could be taken into account in an empirical model, with a 27-day resolution, to explain geomagnetic activity felt on the Earth’s surface in terms of solar-surface features and the IMF condition. We further retrieve a clear annual oscillation in series of 27-day-mean values of toward/away asymmetries of geomagnetic-activity indices, which can be interpreted in the light of the Russell–McPherron hypothesis for the semiannual variation of geomagnetic activity.

On the shoulders of Laplace

In 1799, Laplace derived the system of differential equations (now called Liouville-Euler) that fully describes the motions of the rotation axis of any celestial body. Laplace showed that only the gravitational forces and kinetic moments from other celestial bodies influence the rotation of any one of them. The equations involve three Euler angles that specify the motions of a body's rotation axis; they can be reduced to a system of two equations for the inclination and time derivative of the declination of the rotation axis. Laplace showed the existence of a forced annual oscillation and the so-called free Chandler wobble. Most current theories retain only two Euler angles and invoke an elastic Earth to match observations. We analyze the much longer time series of polar motion (coordinates m1 and m2 of the rotation pole at the Earth's surface) now available, in order to further explore phenomena that Laplace could not investigate, given the dearth of data in his time. We use singular spectral analysis (SSA) to extract components of the time series. The first three components (trend or Markowitz drift, forced annual oscillation and free Chandler oscillation) account for 73% of the variance of polar motion. Under the current theory, their modulation is thought to be a response to reorganization of oceanic and atmospheric masses. However, the periods of the first six SSA components of polar motion have been encountered in previous studies of sunspots and in the ephemerids of Jovian planets. We also analyze the derivatives of the envelopes of the three SSA components of polar motion. Again, most of these components have periods and modulations that correspond to the ephemeris (periods and combinations of commensurable periods) of Jovian planets. Examples include 171.5 yr (the Jose cycle linked to Neptune), 90 yr (the Gleissberg cycle linked to Uranus), 40 yr (a commensurable period linked to the Jovian planets), 22 yr, 11 yr (Jupiter, Sun), 60 yr, 30 yr (Saturn). Fig. 3 can be considered as the central result of the paper. It shows that the sum of forces of the four Jovian planets matches in a striking way the polar motion reconstructed with SSA components (the Markowitz trend removed). All our results argue that significant parts of Earth's polar motion are a consequence (rather than a cause) of the evolution of planetary ephemerids. The Sun's activity and many geophysical indices show the same signatures, including many climate indices. Two different mechanisms (causal chains) are likely at work: a direct one from the Jovian Planets to Earth, another from planetary motions to the solar dynamo; variations in solar activity would in turn influence meteorological and climatic phenomena. Given the remarkable coincidence between the quasi-periods of many of these phenomena, it is reasonable to assume that both causal chains are simultaneously at work. In that sense, it is not surprising to find the signatures of the Schwabe, Hale and Gleissberg cycles in many terrestrial phenomena, reflecting the characteristic periods of the combined motions of the Jovian planets.

Climatology of Interhemispheric Mesopause Temperatures Using the High‐Latitude and Middle‐Latitude Meteor Radars

AbstractWe present the climatology of mesopause temperatures using high‐latitude and middle‐latitude meteor radars. The daily mesopause temperatures are estimated using ambipolar diffusion coefficient data from the meteor radars at Davis Station (68.6°S, 77.9°E), in Antarctica, Svalbard (78.3°N, 16°E), Tromsø (69.6°N, 19.2°E) in the Arctic, and Mohe (53.5°N, 122.3°E) and Beijing (40.3°N, 116.2°E) in the northern middle latitudes. The seasonal variations in the meteor radar‐derived temperatures are in good agreement with the temperatures from the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the TIMED satellite. Interhemispheric observations indicate that the mesopause temperatures over the southern and northern polar regions show a clear seasonal asymmetry. The seasonal variations in the Davis Station meteor radar temperatures in the southern polar mesopause are dominated by an annual oscillation (AO) with a relatively weak semiannual oscillation (SAO), which show a clear minimum during summer and a maximum during winter. The mesopause temperatures in the northern high and middle latitudes observed by the Svalbard, Tromsø, Mohe, and Beijing meteor radars mainly show an AO, with a maximum during winter and a minimum during summer. The AO in the northern polar regions is stronger than that in the southern polar regions, while the SAO in the southern polar regions is relatively strong compared to that in the northern polar regions.

Evaluation of hydrological and cryospheric angular momentum estimates based on GRACE, GRACE-FO and SLR data for their contributions to polar motion excitation

In geodesy, a key application of data from the Gravity Recovery and Climate Experiment (GRACE), GRACE Follow-On (GRACE-FO), and Satellite Laser Ranging (SLR) is an interpretation of changes in polar motion excitation due to variations in the Earth’s surficial fluids, especially in the continental water, snow, and ice. Such impacts are usually examined by computing hydrological and cryospheric polar motion excitation (hydrological and cryospheric angular momentum, HAM/CAM). Three types of GRACE and GRACE-FO data can be used to determine HAM/CAM, namely degree-2 order-1 spherical harmonic coefficients of geopotential, gridded terrestrial water storage anomalies computed from spherical harmonic coefficients, and terrestrial water storage anomalies obtained from mascon solutions. This study compares HAM/CAM computed from these three kinds of gravimetric data. A comparison of GRACE-based excitation series with HAM/CAM obtained from SLR is also provided. A validation of different HAM/CAM estimates is conducted here using the so-called geodetic residual time series (GAO), which describes the hydrological and cryospheric signal in the observed polar motion excitation. Our analysis of GRACE mission data indicates that the use of mascon solutions provides higher consistency between HAM/CAM and GAO than the use of other datasets, especially in the seasonal spectral band. These conclusions are confirmed by the results obtained for data from first 2 years of GRACE-FO. Overall, after 2 years from the start of GRACE-FO, the high consistency between HAM/CAM and GAO that was achieved during the best GRACE period has not yet been repeated. However, it should be remembered that with the systematic appearance of subsequent GRACE-FO observations, this quality can be expected to increase. SLR data can be used for determination of HAM/CAM to fill the one-year-long data gap between the end of GRACE and the start of the GRACE-FO mission. In addition, SLR series could be particularly useful in determination of HAM/CAM in the non-seasonal spectral band. Despite its low seasonal amplitudes, SLR-based HAM/CAM provides high phase consistency with GAO for annual and semiannual oscillation.

Long-period meteor radar temperature variations over Collm (51°N, 13°E) and Kazan (56°N, 49°E)

We have estimated temperatures from meteor radar measurements using the gradient method and the full width at half maximum method over Kazan (56°N 49°E) and Collm (51°N, 13°E). The time series cover the period 2016–2019. The temperature gradient model is constructed from SABER temperature observations. We demonstrate that annual mean, amplitudes and phases of the annual and semiannual oscillations of the radar temperatures are close to those of the MLS and SABER temperatures. The annual mean temperatures over Kazan and Collm differ non-significantly. The seasonal variability of the radar temperature is mostly due to the annual cycle which tends to grow with latitude. The gradient method produces temperatures which agree with the SABER temperatures better than with the MLS ones. The harmonics of the annual oscillations from periods of 73 days up to periods of about 40 days are the most significant day-to-day temperature oscillations and have zonal wavenumber zero. Their periods and phases are in good correspondence with those of the MLS and SABER ones. We also show some results which demonstrate that at 56°N the FWHM method is not as robust as the gradient method.

Observations of a quasi-90-day oscillation in the MLT winds and tides over an equatorial station using meteor radar winds

An evident signature of a least studied quasi-90-day oscillation is found in the winds and tides in the MLT from an equatorial station, São João do Cariri (7.4°S, 36.5°W). The oscillation is found to appear mainly in certain intervals with small but appreciable seasonal (fourth harmonic of annual oscillation) contribution. The maximum amplitude of the oscillation is found to be around 10 m/s in the zonal wind. The enhancement peak of the oscillation exhibits downward movement indicating a plausible role of upward moving waves/tides in carrying its imprint from below to the MLT. Similar oscillation feature in the tropospheric zonal wind and ozone may imply its lower atmospheric origin as a component of the intraseasonal oscillation (ISO) that moves upward by modulating the tides. Subsequently, the propagating tides (mainly semidiurnal) are enhanced by the ozone in the stratosphere through absorption of solar UV radiation and finally manifest the oscillation in the MLT. Consistency of the present findings with the past investigations are observed in some aspects of the oscillation, whereas existing mismatches in others are believed to be due to geophysical variability depending on space and time among various locations on the globe.

Analysis of temperature and humidity in Oman using singular spectrum analysis

The purpose of this paper is to study hourly time series of temperature and humidity from six meteorological stations in Oman from 2009 to 2018. Since our data contains missing values due to device failures, we have compared several methods of imputation and found that regression with lagging is most reasonable. To extract the annual oscillations and daily periodicities from hourly time series we apply Singular Spectrum Analysis. By applying the Mann–Kendall test, Spearman’s rho test and the ITM test to the annual oscillations and daily periodicities monotonic trends in temperature and humidity over the ten year period have not been confirmed.

Synchronized interdecadal variations behind regime shifts in the Pacific Decadal Oscillation

Interdecadal climate variability over the North Pacific is investigated using a reconstructed 298-year-long annual Pacific Decadal Oscillation Index during 1700–1997. Here, we show that its interdecadal component can be decomposed into the bi-decadal (~ 20 years), the tri-decadal (~ 30 years), and the multi-decadal variations (~ 60 years) through bandpass filtering. The phase reversals of the bi-decadal and the tri-decadal variations were synchronized throughout the data, while the synchronization of the bi-decadal and the multi-decadal variations was maintained during 1780–1880 and 1920–1997. Monte Carlo simulation reveals that this synchronous temporal structure is statistically significant and could not occur from random processes. We further demonstrate that these three phase-locked variations play an important role in the regime shifts in the North Pacific, both during the data period (1700–1997) and thereafter. The bi-decadal variation, which is self-sustained through the North Pacific mid-latitude air–sea interaction, is also found to be possibly linked to the lunar nodal cycle. Moreover, the tri-decadal and the multi-decadal variations, whose periods are approximately 1.5 and 3 times longer than that of the bi-decadal variation, may be linked to the bi-decadal variation through nonlinear process. This simple relationship could largely contribute to understanding and predicting the interdecadal climate variability.

Seasonal Variation of Vertical Heat and Energy Fluxes due to Dissipating Gravity Waves in the Mesopause Region Over the Andes

AbstractVertical energy transports due to dissipating gravity waves in the mesopause region (85–100 km) are analyzed using over 400 h of observational data obtained from a narrow‐band sodium wind‐temperature lidar located at Andes Lidar Observatory (ALO), Cerro Pachón (30.25°S, 70.73°W), Chile. Sensible heat flux is directly estimated using measured temperature and vertical wind; energy flux is estimated from the vertical wavenumber and frequency spectra of temperature perturbations; and enthalpy flux is derived based on its relationship with sensible heat and energy fluxes. Sensible heat flux is mostly downward throughout the region. Enthalpy flux exhibits an annual oscillation with maximum downward transport in July above 90 km. The dominant feature of energy flux is the exponential decrease from 10−2 to 10−4 W m−2 with the altitude increases from 85 to 100 km and is larger during austral winter. The annual mean thermal diffusivity inferred from enthalpy flux decreases from 303 m2 s−1 at 85 km to minimum 221 m2 s−1 at 90 km then increases to 350 m2 s−1 at 99 km. Results also show that shorter period gravity waves tend to dissipate at higher altitudes and generate more heat transport. The averaged vertical group velocities for high, medium, and low frequency waves are 4.15 m s−1, 1.15 m s−1, and 0.70 m s−1, respectively. Gravity wave heat transport brings significant cooling in the mesopause region at an average cooling rate of 6.7 ± 1.1 K per day.

Variations of Thermospheric Winds Observed by a Fabry–Perot Interferometer at Mohe, China

AbstractA Fabry–Perot interferometer (FPI) system was deployed to observe the thermospheric winds at Mohe (53.5°N, 122.3°E), the northernmost observatory of space environment in the mainland of China, in July 2019. Thermospheric winds variations revealed from the 1 year FPI observations are as follows: (1) For the diurnal variation, southward meridional winds prevail at night and peak after midnight with amplitudes from 70 to 110 m/s; meridional winds are northward (∼40 m/s) at dusk and dawn in winter. For the zonal winds, eastward winds prevail only at dusk in summer, while it can sustain after midnight in winter. The maximum amplitudes of eastward winds are 50–130 m/s. Westward winds are strongest at dawn, with amplitudes of 75–120 m/s. (2) For the seasonal variation, both the meridional and zonal winds are dominated by annual oscillations. The semi‐annual oscillations can be observed at midnight. (3) The eastward (southward) winds become strong (weak) at midnight in January and December. An empirical model of thermospheric winds was established based on Mohe FPI observations and compared with HWM14. The variation trends of thermosphere winds described by HWM14 is basically consistent with the observations at Mohe. Moreover, Mohe FPI observations were compared with those by Kelan (38.7°N, 111.6°E) FPI. Variations of thermospheric winds showed some discrepancies between these two locations. The southward winds were significantly stronger at Mohe than at Kelan after midnight; and the semi‐annual and tri‐annual oscillations in the midnight zonal winds are observed at Mohe but not significant at Kelan.

GOCO06s – a satellite-only global gravity field model

Abstract. GOCO06s is the latest satellite-only global gravity field model computed by the GOCO (Gravity Observation Combination) project. It is based on over a billion observations acquired over 15 years from 19 satellites with different complementary observation principles. This combination of different measurement techniques is key in providing consistently high accuracy and best possible spatial resolution of the Earth's gravity field. The motivation for the new release was the availability of reprocessed observation data for the Gravity Recovery and Climate Experiment (GRACE) and Gravity field and steady-state Ocean Circulation Explorer (GOCE), updated background models, and substantial improvements in the processing chains of the individual contributions. Due to the long observation period, the model consists not only of a static gravity field, but comprises additionally modeled temporal variations. These are represented by time-variable spherical harmonic coefficients, using a deterministic model for a regularized trend and annual oscillation. The main focus within the GOCO combination process is on the proper handling of the stochastic behavior of the input data. Appropriate noise modeling for the observations used results in realistic accuracy information for the derived gravity field solution. This accuracy information, represented by the full variance–covariance matrix, is extremely useful for further combination with, for example, terrestrial gravity data and is published together with the solution. The primary model data consisting of potential coefficients representing Earth's static gravity field, together with secular and annual variations, are available on the International Centre for Global Earth Models (http://icgem.gfz-potsdam.de/, last access: 11 June 2020). This data set is identified with the following DOI: https://doi.org/10.5880/ICGEM.2019.002 (Kvas et al., 2019b). Supplementary material consisting of the full variance–covariance matrix of the static potential coefficients and estimated co-seismic mass changes is available at https://ifg.tugraz.at/GOCO (last access: 11 June 2020).

Analysis of the correlation between horizontal wind and 11-year solar activity over Langfang, China

In this study, long term observations of medium frequency (MF) radar at Langfang site (39.4°N, 116.7°E) from 2009 to 2020 have been used to analyze the dependence of the 11-year solar cycle on horizontal winds in the local mesosphere and lower thermosphere (MLT). The results show that the zonal wind is positively correlated with solar activity during spring at 80–84 km, and during summer at 80–82 km; the meridional wind is positively correlated with solar activity during spring at 84–88 km and during summer at 84–90 km. In contrast, the results show no correlation between the horizontal wind and solar activity in autumn and winter. We attempt to explain the correlations in terms of the changes in stratospheric temperature and the net flux of gravity waves during solar activities. In addition, annual and semiannual oscillations of the zonal/meridional wind were found by using the least squares fitting method on daily horizontal winds, which show negative correlations with solar activity at heights of 80–90 km.

Enhanced saturation of liquid-saturated porous medium with atmosphere gases due to surface temperature oscillations

We study the non-isothermal diffusion transport of a poorly soluble substance in a porous liquid-saturated medium being in contact with the reservoir of this substance. The surface temperature of a half-space porous medium oscillates in time, which creates a decaying temperature wave propagating deep into sediments. Since the solubility exponentially strongly depends on temperature, a decaying running solubility wave forms in the porous medium. In such a system, the zones of saturated solution and non-dissolved phase coexist with the zones of undersaturated solution. The effect is considered for the case of annual oscillation of the surface temperature of water-saturated ground being in contact with atmosphere. We reveal the phenomenon of formation of a near-surface bubbly horizon due to the temperature oscillation for one- and two-component solutes. In the case of a two-component solute, the solubility depends on the composition of the nondissolved phase, which necessitates the construction of a corresponding mathematical model of dissolution of multicomponent mixtures. We develop an analytical theory of the phenomenon of formation of the bubbly horizon. In both analytical theory and numerical simulations, the temperature dependence of the molecular diffusion coefficient is taken into account. In the presence of a propagating temperature wave, the nonlinear interaction between this dependence and the temperature dependence of the solubility creates an additional nonzero contribution to the mean-over-period mass flux. For multicomponent solutions, we report the formation of a diffusive boundary layer, which is not possible for single-component solutions. We construct an analytical theory for this boundary layer and derive effective boundary conditions for the problem of the diffusive transport beyond this layer. Theoretical results are in fair agreement with the results of numerical simulation.

Seasonal Variations of High-Frequency Gravity Wave Momentum Fluxes and Their Forcing toward Zonal Winds in the Mesosphere and Lower Thermosphere over Langfang, China (39.4° N, 116.7° E)

Meteor radar data collected over Langfang, China (39.4° N, 116.7° E) were used to estimate the momentum flux of short-period (less than 2 h) gravity waves (GWs) in the mesosphere and lower thermosphere (MLT), using the Hocking (2005) analysis technique. Seasonal variations in GW momentum flux exhibited annual oscillation (AO), semiannual oscillation (SAO), and quasi-4-month oscillation. Quantitative estimations of GW forcing toward the mean zonal flow were provided using the determined GW momentum flux. The mean flow acceleration estimated from the divergence of this flux was compared with the observed acceleration of zonal winds displaying SAO and quasi-4-month oscillations. These comparisons were used to analyze the contribution of zonal momentum fluxes of SAO and quasi-4-month oscillations to zonal winds. The estimated acceleration from high-frequency GWs was in the same direction as the observed acceleration of zonal winds for quasi-4-month oscillation winds, with GWs contributing more than 69%. The estimated acceleration due to Coriolis forces to the zonal wind was studied; the findings were opposite to the estimated acceleration of high-frequency GWs for quasi-4-month oscillation winds. The significance of this study lies in estimating and quantifying the contribution of the GW momentum fluxes to zonal winds with quasi-4-month periods over mid-latitude regions for the first time.

Characteristics of the upper troposphere wind field according to the satellite measurements and their connection with climatic parameters

The results of the study of the spatio-temporal variability of the main characteristics of jet streams and turbulence zones in the upper troposphere of the Northern Hemisphere according to measurements from European geostationary meteorological satellites for the period 2007 - 2018 are presented. Their relationship with the essential parameters of the Earth’s climate system — the temperature of the troposphere, the area of sea ice, and also large-scale atmospheric phenomena is considered. It has been shown that over the past 12 years there has been a significant increase in the area of regions occupied by relatively weak and moderate turbulence and a slight decrease in areas with strong and very strong turbulence. Based on the cross-wavelet analysis in the time-frequency space, the relationships between the variations in the areas of the turbulent regions and the majority of the characteristics of jet streams are revealed. A close relationship has been established between the characteristics of jet streams and the areas of turbulent zones with the temperature of the upper troposphere. In this case, the effect of temperature on the area of turbulent zones manifests itself indirectly through the characteristics of jet streams. A significant association of variations in the average area of the jet stream and the latitudinal position of its center with the area of sea ice are noted. According to spectral and wavelet analysis of the characteristics of jet streams, along with annual and quasi-biennial oscillations, short-period oscillations are observed with periods in the range of 10-40 days, which can be interpreted as a manifestation of Rossby waves..

Multi-scale Characteristics of Precipitation and Its Relationship with ENSO and AO

Wang, J.J.; Shi, B.; Pan, X.Y., and Liu, L.F., 2020. Multi-scale characteristics of precipitation and its relationship with ENSO and AO. In: Guido Aldana, P.A. and Kantamaneni, K. (eds.), Advances in Water Resources, Coastal Management, and Marine Science Technology. Journal of Coastal Research, Special Issue No. 104, pp. 23–28. Coconut Creek (Florida), ISSN 0749-0208.This study aims to reveal the multi-scale characteristics of precipitation and its response relationship with El Nino Southern Oscillation (ENSO) and Arctic Oscillation (AO) in Shandong province of China. Historical total monthly precipitation data of 21 meteorological stations in the research region from 1961 to 2017 were preprocessed firstly by wavelet power spectrum for analyzing the intensity of oscillations in different time-frequency scales. The results of wavelet power spectrum reveal that the 12-month periodicity was significant of precipitation. Then, the ensemble empirical mode decomposition (EEMD) was used to analyse the periodicity of precipitation, the precipitation time series was decomposed into 8 IMFs (Intrinsic Mode Function, IMF) and 1 residual, the significance test of IMFs shows that the annual periodicity oscillation is stronger than the interdecadal periodicity. The results reveal that the period of IMF2 was 12-month through the fast Fourier transform analysis, and the periodicity passed the significance test of 99%. Finally, the cross wavelet analysis and wavelet coherence were used to analyse the resonance periodicity and coherence of precipitation with ENSO and AO in different time-frequency scales. The results show that ENSO and precipitation were mainly in negative phase, and the resonance periodicity of 12-month and 32-64 months were strong. Simultaneously, the phase relationship between AO and precipitation is complicated, the resonance periodicity of 12 months was strong too. This research preliminarily explores of the multi-scale characteristics of precipitation in Shandong province of China, which can provide some references for precipitation prediction and water resources utilization in this region.

Dynamic behavior and economic analysis of sustainable building integrating cob and phase change materials

The will of reducing energetic and environmental impact of building sector has led to a renewed interest in earth construction. For its low environmental impact compared to conventional construction materials, cob construction could help achieve the previous mentioned will and also value local materials. In this work, new thermal insulation and structure made from cob were developed and thermo-physically characterized. The impacts of these new materials equipped in a residential house on heating loads and the indoor comfort are analyzed by means of dynamic simulation using TRNSYS software considering a Typical Meteorological Year (TMY) of eight French cities referring to the representative zones of the RT2012. Thermal performance of the cob house assessed by comparison to a conventional case of the house built with conventional construction materials. A PCM layer is integrated into the external wall (0.24 W/mK) of the Cob house. The major finding of this work is that the investigated cob house integrated PCM layer allows reducing the annual temperature oscillation and the heating loads compared to the conventional case. Moreover, a Life Cycle Cost (LCC) analysis is performed with the local market cost in order to investigate the competitiveness of the cob house enhanced PCM compared to the conventional case.

Oscillations in Neutral Winds Observed by GOCE

AbstractThis study explores intra‐annual oscillations (IAOs) in upper thermospheric winds using GOCE cross‐track wind measurements between 70°S and 70°N. Due to the Sun‐synchronous dawn‐dusk orbit of GOCE, the cross‐contamination between seasonality and local time variations in winds is minimal, which makes it a unique space‐based data set to extract IAOs and study their latitudinal variation. Our analysis reveals that the annual (AO), semiannual (SAO), and terannual (TAO) oscillations are robust features in thermospheric winds. The AO is strongest at middle latitudes; SAO and TAO amplitudes increase with increasing latitude. The latitudinally averaged amplitudes of the AO, SAO, and TAO for dusk/dawn are 30.0/35.0, 8.5/11.3, and 6.0/6.6 m/s, respectively. The phase of AO reverses around the equator. SAO and TAO phases vary with latitude but do not reverse like the AO. For both the SAO and TAO, the average phase at dusk and dawn differs by ∼30 days.

Increase in sea level variability with ocean warming associated with the nonlinear thermal expansion of seawater

Sea level variability increasingly contributes to coastal flooding and erosion as global sea levels rise, partly due to the thermal expansion of seawater, which accelerates with increasing temperature. Climate model simulations with increasing greenhouse gas emissions suggest that future sea level variability, such as the annual and interannual oscillations that alter local astronomical tidal cycles and contribute to coastal impacts, will also increase in many regions. Here, we present an analysis of the CMIP5 climate model projections of future sea level to show that there is a tendency for a near-global increase in sea level variability with continued warming that is robust across models, regardless of whether ocean temperature variability increases. Specifically, for an upper-ocean warming by 2 °C, which is likely to be reached by the end of this century, sea level variability increases by 4 to 10% globally on seasonal-to-interannual timescales because of the nonlinear thermal expansion of seawater. As the oceans continue to warm, future ocean temperature oscillations will cause increasingly larger buoyancy-related sea level fluctuations that may alter coastal risks.