R1 Wave Research Articles

Equatorial Rossby waves on cold surge days and their impact on rainfall

AbstractThis study aims to understand the process that determines the regional rainfall distribution in the equatorial South China Sea (SCS) and its surrounding during the cold surge (CS) days by looking at the different vorticity phases of active equatorial Rossby (R1) waves and the dynamics of the CSs related to the R1 wave. The CS can be thought of as an anticyclonic outflow from midlatitude and behaves like a dispersive group of R1 meridional modes. From the study, it shows the vorticity of the R1 wave arranges itself in such a way that the anticyclonic phase is located to the west and the cyclonic phase is located to the east of the cold CS axis. The CS winds in the equatorial SCS occur early, remain longer, and possess a larger zonal component in the active cyclonic phase compared with the active anticyclonic phase. During the active cyclonic vorticity phase, the rainfall anomalies pattern in the equatorial SCS changes from a “tick‐mark‐like” pattern to a “V‐shape” pattern as a consequence of the westward propagation of the wave. The probability of rainfall increases near the centre of cyclonic vorticity, but for anticyclonic vorticity the probability increases in the southern part of the vorticity centre. There is both increased (decreased) intensity and probability of extreme rainfall events during the active cyclonic (anticyclonic) vorticity phase on CS days. Overall, the rainfall anomalies are largely dominated by changes in the intensity on wet days rather than the number of wet days. These changes indicate the roles of the R1 wave vorticity phase in the rainfall distribution during CS days. The timing of enhancement and suppression of rain will provide additional valuable information to help improve forecast extreme weather events.

Variation on propagation of Rayleigh waves in thermo-poroelastic solids

We analyse the dispersion and attenuation of Rayleigh-wave propagation along on isothermal free surface of a thermo-poroelastic medium. The thermo-poroelastic theory, including the Lord-Shulman (LS) and Green-Lindsay (GL) theories, predicts three compressional waves and one shear wave, which induce two Rayleigh-type surface waves, R1 and R2 modes along the interface by evanescent potential functions specified by vertical imaginary wavenumbers. The GL model can give a stronger P1 and P2 wave thermal attenuation and consequently a stronger velocity dispersion than the LS model. We investigate the influence of frequency and surface boundary condition. The additional thermal diffusion exhibits the inverse dispersion in R1 waves, and makes the pseudo surface-wave transition under the closed (CP) and partial permeable (PP) surface toward high frequencies. Another T wave affects the energy inference along the surface and induce the other R2 waves under the open surface (OP). The thermal dispersion occurs at characteristic frequencies around the thermal relaxation peaks, which induces the high-velocity T wave toward low frequencies when the Maxwell–Vernotte–Cattaneo relaxation time increases. Until the T wave propagates faster than the P2 wave, the Rayleigh equations lose the R2 poles making the prohibition of R2-wave propagation.

Seismic physics-based characterization of permafrost sites using surface waves

Abstract. The adverse effects of climate warming on the built environment in (sub-)arctic regions are unprecedented and accelerating. The planning and design of climate-resilient northern infrastructure, as well as predicting deterioration of permafrost from climate model simulations, require characterizing permafrost sites accurately and efficiently. Here, we propose a novel algorithm for the analysis of surface waves to quantitatively estimate the physical and mechanical properties of a permafrost site. We show the existence of two types of Rayleigh waves (R1 and R2; R1 travels faster than R2). The R2 wave velocity is highly sensitive to the physical properties (e.g., unfrozen water content, ice content, and porosity) of active and frozen permafrost layers, while it is less sensitive to their mechanical properties (e.g., shear modulus and bulk modulus). The R1 wave velocity, on the other hand, depends strongly on the soil type and mechanical properties of permafrost or soil layers. In situ surface wave measurements revealed the experimental dispersion relations of both types of Rayleigh waves from which relevant properties of a permafrost site can be derived by means of our proposed hybrid inverse and multiphase poromechanical approach. Our study demonstrates the potential of surface wave techniques coupled with our proposed data-processing algorithm to characterize a permafrost site more accurately. Our proposed technique can be used in early detection and warning systems to monitor infrastructure impacted by permafrost-related geohazards and to detect the presence of layers vulnerable to permafrost carbon feedback and emission of greenhouse gases into the atmosphere.

COVID-19 can cause blink reflex abnormalities.

Neurological symptoms and complications associated with coronavirus 2019 (COVID-19) are well known. It was aimed to evaluate the brainstem and trigeminal/facial nerves and the pathways between these structures in COVID-19 using the blink reflex test. Thirty patients with post COVID-19 (16 males, 14 females) and 30 healthy individuals (17 males, 13 females) were included in this prospective study. Individuals who previously had a positive nose swap polymerase chain reaction test for severe acute respiratory syndrome coronavirus 2 and whose previously clinical features were compatible with COVID-19 were included in the post COVID-19 patient group. Neurological examination of the participants should be normal. Blink reflex test was performed on all participants. R1, ipsilateral R2 (IR2), and contralateral R2 (CR2) waves obtained from the test were analyzed. The mean ages of healthy individuals and post COVID-19 patients were 34.0±6.4 and 38.4±10.6 years, respectively. Both age and gender were matched between the groups. R1, IR2, and CR2 latencies/amplitudes were not different between the two groups. The side-to-side R1 latency difference was 0.5±0.3 and 1.0±0.8 ms in healthy individuals and post COVID-19 patients, respectively (p=0.011). One healthy individual and 12 patients with post COVID-19 had at least one abnormal blink reflex parameter (p=0.001). This study showed that COVID-19 may cause subclinical abnormalities in the blink reflex, which includes the trigeminal nerve, the seventh nerve, the brainstem, and pathways between these structures.

Conductometric sensing capabilities of Rayleigh modes in ZnO/Si structures

The propagation of the fundamental and higher order Rayleigh modes in c-ZnO/Si(001)< 100 > is theoretically investigated by numerical calculations and 3D finite element model. The dispersion curves of the phase velocity and electroacoustic coupling coefficient K 2 were calculated for the first seven modes, and for two electroacoustic coupling configurations with the interdigital electrodes positioned at the ZnO/Si interface or onto the free surface of the piezoelectric layer. The acoustoelectric response of the Rayleigh modes, i.e. the modes relative frequency and propagation loss shifts induced by the ZnO sheet conductivity changes, was studied aimed at the design of a SAW sensor showing enhanced conductometric sensitivity. The sensitivity of the modes varies with the ZnO layer thickness hZnO and reaches a peak whose magnitude increases from the fundamental Rayleigh wave to the third mode R3, then it decreases with increasing the mode order. The K 2 corresponding to the sensitivity peak is lower than the maximum K 2 value obtainable with the corresponding mode. The Sezawa and R3 waves show the largest sensitivity values among the modes studied. The peak sensitivity of the Sezawa and of the higher order modes occurs at a layer thickness corresponding to the minimum of the derivative of the phase velocity respect to hZnO.

Clinical observation on time-effect of electroacupuncture for idiopathic facial paralysis

To observe the effect of different acupuncture frequency and duration of needle retention on idiopathic facial paralysis, and optimize the acupuncture treatment plan. A total of 140 patients were randomized into a group A (37 cases, 3 cases dropped off), a group B (35 cases, 3 cases dropped off), a group C (34 cases, 1 case dropped off) and a group D (34 cases, 1 case dropped off). Under the same basic treatment, acupuncture intervention time (day 8 of morbidity), acupoint selection [Cuanzhu (BL 2), Yangbai (GB 14), Taiyang (EX-HN 5), Yingxiang (LI 20), Jiache (ST 6), Dicang (ST 4) on the affected side, Chengjiang (CV 24) and Hegu (LI 4) on the unaffected side] and electroacupuncture intervention, different acupuncture interval time and duration of needle retention were applied. In the group A, the treatment was given 20 min once a day, while the group B 30 min once a day, the group C 20 min once every 2 days, the group D 30 min once every 2 days. Totally 20-day treatment were required. The House-Brackmann (H-B) facial nerve function grading system was used to evaluate the improvement of clinical symptom, the situation and latency periods of the R1 wave in blink reflex and facial nerve motor conduction before and after treatment were observed in the 4 groups. After treatment, the cured rates in the 4 groups were 44.1% (15/34), 46.9% (15/32), 57.6% (19/33) and 51.5% (17/33), there was no significant difference among 4 groups (P>0.05). The situation and latency periods of the R1 wave in blink reflex and latency periods and amplitude of facial nerve motor conduction after treatment were improved in the 4 groups (P<0.01, P<0.05), there was no significant difference among 4 groups (P>0.05). Acupuncture 20 min once a day, 30 min once a day, 20 min once every 2 days and 30 min once every 2 days have significant effect on the recovery of idiopathic facial paralysis, and the effect is comparable.

Blink test results in patients with central sleep apnea syndrome

The aim of the study was to evaluate whether there was a problem in the interneuronal junctions of patients with central sleep apnea using the blink reflex test. Twenty-one (21) patients with central type apneas and/or hipopneas and 21 controls were recruited. The blink reflex test was performed and R1, R2 and contralateral R2 (R3) wave values of both groups were recorded in milliseconds (ms). The results of blink test in patients with central sleep apnea were right side R1 = 9.45 ± 4.35 ms, R2 = 33.35 ± 9.97 ms, R3 = 32.15 ± 10.05 ms and left side R1 = 9.90 ± 3.82 ms, R2 = 31.5 ± 10.5 ms, R3 = 29.00 ± 4.77 ms, (p = 0.49, p = 0.69, p = 0.60, respectively), whereas the results of blink test in controls were right side R1 = 9.25 ± 3.50 ms, R2 = 32.75 ± 11.4 ms, R3 = 32.50 ± 13.12 ms and left side R1 = 7.35 ± 2.6 ms, R2 = 27.75 ± 9.75 ms, R3 = 26.65 ± 14.5 ms. (p = 0.015, p = 0.04, p = 0.035, respectively). All left side (R1, R2, R3) blink reflex of the patients with central sleep apnea was statistically significant prolonged than controls. However, there was no statistically significant difference between women with central sleep apnea and controls regarding all right side (R1, R2, R3) blink reflex. There was statistically significant difference in R1, R2 and R3 waves of left sides blink reflex between two groups. The results may be related to central nervous system damage or/and degeneration in the interneuronal junctions of the brain stem in patients with central sleep apnea syndrome.

On spatiotemporal wave–induced radiation distribution in a porous medium under impulsive transverse loadings

Spatiotemporal wave–induced radiation pattern in a semi–infinite fluid filled porous medium to an impulsive transverse loading is investigated under imperfect surface hydraulic contacts. A surface stiffness parameter represents this fluid flow impedance cross the surface. It affects various wave mode radiations dependent on azimuth and depth. In the plane perpendicular (PSV) to the surface, all the wave modes are sensitive to surface stiffness, especially the R1 surface wave. A high surface stiffness can excite the R2 surface wave radiation and the energy redistributions. However, in the plane parallel (SH) to the surface, the SH wave shows no relationship to surface stiffness. Pore pressure polarizes in PSV plane. The R1 wave radiation in pore pressure corresponds to R1P2 transferring on the surface, not in accordance to displacement response. Furthermore, the surface stiffness dominates the fluid diffusivity near surface. For a leakage boundary, a pressure drop by local flow appears. The significant fluid resonance generates under the surface. The redistributed wave radiation in fluid may be a possible risk for near surface medium failure.

Time Parameters of the Blink Reflex in Normal Subjects

Our study was aimed at estimating normal time values for the EMG waves recorded in the blink reflex test. The group examined included 400 healthy subjects (226 women and 174 men, with mean age about 50 years). There was no significant difference between the ages of the male and female subjects. The mean latency of the R1 wave in the response was 10.3 msec, while R2 was obtained after 32.5 msec, on average. The contralateral response component R2c was observed after 34.4 msec, on average. Gender did not influence the results, while age had a significant effect on R1 (P = 0.029) and R2c (P = 0.0003). The older the subject, the longer the latencies of the above waves. The data obtained on a rather large sampling of the tested subjects can be useful as normography for medical and neurophysiological purposes.

Wave fields and spectra of Rayleigh waves in poroelastic media in the exploration seismic frequency band

A better understanding of the influences of different surface fluid drainage conditions on the propagation and attenuation of surface waves as the stipulated frequency is varied is a key issue to apply surface wave method to detect subsurface hydrological properties. Our study develops three-dimensional dynamical Green’s functions in poroelastic media for Rayleigh waves of possible free surface conditions: permeable – “open pore,” impermeable – “closed pore,” and partially permeable boundaries. The full transient response of wave fields and spectra due to a stress impulse wavelet on the surface are investigated in the exploration seismic frequency band for typical surface drainage conditions, viscous coupling–damping, solid frame properties and porous fluid flowing configuration. Our numerical results show that, due to the slow dilatational wave – P2 wave, two types of Rayleigh waves, designated as R1 and R2 waves, exist along the surface. R1 wave possesses high energy as classic Rayleigh waves in pure elastic media for each porous materials. A surface fluid drainage condition is a significant factor to influence dispersion and attenuation, especially attenuation of R1 waves. R2 wave for closed pore and partially permeable surfaces is only observed for a low coupling–damping coefficient. The non-physical wave for partially surface conditions causes the R1 wave radiates into the R2 wave in the negative attenuation frequency range. It makes weaker R1 wave and stronger R2 wave to closed pore surface. Moreover, it is observed that wave fields and spectra of R1 wave are sensitive to frame elastic moduli change for an open pore surface, and to pore fluid flow condition change for closed pore and partially permeable surface.

The Influence of the QBO on the Propagation of Equatorial Waves into the Stratosphere

Abstract The variation of stratospheric equatorial wave characteristics with the phase of the quasi-biennial oscillation (QBO) is investigated using ECMWF Re-Analysis and NOAA outgoing longwave radiation (OLR) data. The impact of the QBO phases on the upward propagation of equatorial waves is found to be consistent and significant. In the easterly phase, there is larger Kelvin wave amplitude but smaller westward-moving mixed Rossby–gravity (WMRG) and n = 1 Rossby (R1) wave amplitude due to reduced propagation from the upper troposphere into the lower stratosphere, compared with the westerly phase. Differences in the wave amplitude exist in a deeper layer in summer than in winter, consistent with the seasonality of ambient zonal winds. There is a strong evidence of Kelvin wave amplitude peaking just below the descending westerly phase, suggesting that Kelvin waves act to bring the westerly phase downward. However, the corresponding evidence for WMRG and R1 waves is less clear. In the lower stratosphere there is zonal variation in equatorial waves. This reflects the zonal asymmetry of wave amplitudes in the upper troposphere, the source for the lower-stratospheric waves. In easterly winters the upper-tropospheric WMRG and R1 waves over the eastern Pacific region appear to be somewhat stronger compared to climatology, perhaps because of the accumulation of waves that are unable to propagate upward into the lower stratosphere. Vertical propagation features of these waves are generally consistent with theory and suggest a mixture of Doppler shifting by ambient flows and filtering. Some lower-stratosphere equatorial waves have a connection with preceding tropical convection, especially for Kelvin and R1 waves in winter.

Influence of fluid saturation on Rayleigh wave propagation

Based on the existing three-phase poroelastic theory, an analytical solution for Rayleigh wave propagation along the traction free, permeable surface of an elastic porous medium, saturated by two immiscible, viscous, compressible fluids, is derived. The analytical expression of the dispersion equation of Rayleigh wave is found to be a cubic polynomial. Through solving the dispersion equation, it is concluded that three different types of Rayleigh wave exist in such medium to be denoted as R1, R2 and R3, respectively. The influences of water saturation on these Rayleigh waves are numerically studied with varying frequencies from 1 Hz to 1 MHz. The results show that water content has significant effects on the velocities and attenuation of the three waves. The amplitudes of the three waves decay in both x - and z - directions, which are parallel to and perpendicular to the propagation direction of the waves, respectively. The R1 wave travels fastest, and the R3 and R2 waves have the second greatest and smallest phase velocities, respectively. The R1 wave is least attenuated, followed by the R2 and R3 waves. The attenuation coefficients of the R2 and R3 waves versus water saturation and excitation frequency have the similar variation trend.

Analysis of dispersion and attenuation of surface waves in poroelastic media in the exploration-seismic frequency band

SUMMARY We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable—‘open pore’, impermeable—‘closed pore’ and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant-Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im(k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays −f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the −f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves.

A mixture theory analysis for the surface-wave propagation in an unsaturated porous medium

The mixture theory is employed to the analysis of surface-wave propagation in a porous medium saturated by two compressible and viscous fluids (liquid and gas). A linear isothermal dynamic model is implemented which takes into account the interaction between the pore fluids and the solid phase of the porous material through viscous dissipation. In such unsaturated cases, the dispersion equations of Rayleigh and Love waves are derived respectively. Two situations for the Love waves are discussed in detail: (a) an elastic layer lying over an unsaturated porous half-space and (b) an unsaturated porous layer lying over an elastic half-space. The wave analysis indicates that, to the three compressional waves discovered in the unsaturated porous medium, there also correspond three Rayleigh wave modes (R1, R2, and R3 waves) propagating along its free surface. The numerical results demonstrate a significant dependence of wave velocities and attenuation coefficients of the Rayleigh and Love waves on the saturation degree, excitation frequency and intrinsic permeability. The cut-off frequency of the high order mode of Love waves is also found to be dependent on the saturation degree.

Equatorial Waves in Opposite QBO Phases

Abstract A methodology for identifying equatorial waves is used to analyze the multilevel 40-yr ECMWF Re-Analysis (ERA-40) data for two different years (1992 and 1993) to investigate the behavior of the equatorial waves under opposite phases of the quasi-biennial oscillation (QBO). A comprehensive view of 3D structures and of zonal and vertical propagation of equatorial Kelvin, westward-moving mixed Rossby–gravity (WMRG), and n = 1 Rossby (R1) waves in different QBO phases is presented. Consistent with expectation based on theory, upward-propagating Kelvin waves occur more frequently during the easterly QBO phase than during the westerly QBO phase. However, the westward-moving WMRG and R1 waves show the opposite behavior. The presence of vertically propagating equatorial waves in the stratosphere also depends on the upper tropospheric winds and tropospheric forcing. Typical propagation parameters such as the zonal wavenumber, zonal phase speed, period, vertical wavelength, and vertical group velocity are found. In general, waves in the lower stratosphere have a smaller zonal wavenumber, shorter period, faster phase speed, and shorter vertical wavelength than those in the upper troposphere. All of the waves in the lower stratosphere show an upward group velocity and downward phase speed. When the phase of the QBO is not favorable for waves to propagate, their phase speed in the lower stratosphere is larger and their period is shorter than in the favorable phase, suggesting Doppler shifting by the ambient flow and a filtering of the slow waves. Tropospheric WMRG and R1 waves in the Western Hemisphere also show upward phase speed and downward group velocity, with an indication of their forcing from middle latitudes. Although the waves observed in the lower stratosphere are dominated by “free” waves, there is evidence of some connection with previous tropical convection in the favorable year for the Kelvin waves in the warm water hemisphere and WMRG and R1 waves in the Western Hemisphere, which is suggestive of the importance of convective forcing for the existence of propagating coupled Kelvin waves and midlatitude forcing for the existence of coupled WMRG and R1 waves.

Effect of Impermeable Boundaries on the Propagation of Rayleigh Waves in an Unsaturated Poroelastic Half-Space

ABSTRACTThis study presents an analytical model for describing propagation of Rayleigh waves along the impermeable surface of an unsaturated poroelastic half-space. This model is based on the existence of the three modes of dilatational waves which employ the poroelastic equations developed for a porous medium containing two immiscible viscous compressible fluids (Lo, Sposito and Majer, [13]). In a two-fluid saturated medium, the three Rayleigh waves induced by the three dilatational waves can be expressed as R1, R2, and R3 waves in descending order of phase speed magnitude. As the excitation frequency and water saturation are given, the dispersion equation of a cubic polynomial can be solved numerically to obtain the phase speeds and attenuation coefficients of the R1, R2, and R3 waves. The numerical results show the phase speed of the R1 wave is frequency independent (non-dispersive). Comparatively, the R1 wave speed is 93 ∼ 95% of the shear wave speed, and 28% to 49% of the first dilatational wave speed for selected frequencies between 50Hz &amp; 200Hz and relative water saturation ranging from 0.01 to 0.99. However, the R2 and R3 waves are dispersive at the frequencies examined. The ratios of R2 and R3 wave phase speeds to the second and third dilatational wave speeds fall between 56% and 90%. The R1 wave attenuates the least while the R3 wave has the highest attenuation coefficient. Furthermore, the phase speed of the R1 wave under an impermeable surface approaches 1.01 ∼ 1.37 times of the R1 wave under a permeable boundary. Impermeability has significant influence on the phase speeds and attenuation coefficients of the R1 and R2 waves at high water saturation due to the existence of confined fluids.

Propagation and attenuation of Rayleigh waves in a semi-infinite unsaturated poroelastic medium

An analytical model for describing the propagation and attenuation of Rayleigh waves along the free surface of an elastic porous medium containing two immiscible, viscous, compressible fluids is developed in the present study based on the poroelastic equations formulated by Lo et al. [Lo WC, Sposito G, Majer E. Wave propagation through elastic porous media containing two immiscible fluids. Water Resour Res 2005;41:W02025]. The dispersion equation obtained is complex-valued due to viscous dissipation resulting from the relative motion of the solid to the pore fluids. As an excitation frequency is stipulated, the dispersion equation that is a cubic polynomial is numerically solved to determine the phase speed and attenuation coefficient of Rayleigh waves in Columbia fine sandy loam permeated by an air–water mixture. Our numerical results show that, corresponding to three dilatational waves, there is also the existence of three different modes of Rayleigh wave in an unsaturated porous medium, which are designated as the R1, R2, and R3 waves in descending order of phase speed, respectively. The phase speed of the R1 wave is non-dispersive (frequency-independent) in the frequency range we examined (10 Hz–10 kHz) and decreases as water saturation increases, whose magnitude ranges from 20% to 49% of that of the first dilatational wave with respect to water content. However, it is revealed numerically that the R2 and R3 waves are functions of excitation frequency. Given the same water saturation and excitation frequency, the phase speeds of the R2 and R3 waves are found to be approximately 90% of those of the second and third dilatational waves, respectively. The R1 wave has the lowest attenuation coefficient whereas the R3 wave attenuates highest.

Convectively Coupled Equatorial Waves. Part I: Horizontal and Vertical Structures

Abstract Multilevel 15-yr ECMWF Re-Analysis (ERA-15) and satellite-observed brightness temperature (Tb) data for the period May–October 1992 are used to examine the horizontal and vertical structures of convectively coupled equatorial waves. Dynamical waves are isolated using a methodology developed previously. Composite structures of convectively coupled equatorial waves are obtained using linear regression/correlation between convection (Tb) and dynamical structures. It is found that the relationship depends on the ambient flow and the nature of the convective coupling, and varies between off-equatorial- and equatorial-centered convection, different hemispheres, and seasons. The Kelvin wave structure in the Western Hemisphere is generally consistent with classic equatorial wave theory and has its convection located in the region of low-level convergence. In the Eastern Hemisphere the Kelvin wave tends to have convection in the region of enhanced lower-tropospheric westerlies and a tilted vertical structure. The Kelvin wave also tends to have a third peak in zonal wind amplitude at 500 hPa and exhibits upward propagation into the lower stratosphere. Lower-tropospheric westward-moving mixed Rossby–gravity (WMRG) and n = 1 Rossby (R1) wave structures and their relationship with convection are consistent with classic equatorial wave theory and the implied lower-tropospheric convergences. In the Eastern Hemisphere the WMRG and R1 waves have first baroclinic mode structures in the vertical. However, in the Western Hemisphere, the R1 wave has a barotropic structure. In the Eastern Hemisphere the R1 wave, like the Kelvin wave, tends to have equatorial convection in the region of enhanced lower-level westerlies, suggesting that enhanced surface energy fluxes associated with these waves may play an important organizing role for equatorial convection in this warm-water hemisphere. In the upper troposphere, eastward-moving Rossby–gravity (EMRG) and n = 1 gravity waves are found in the Eastern Hemisphere, and eastward-moving WMRG and R1 waves are found in the Western Hemisphere, suggestive of Doppler shifting of waves by the ambient flow.

Convectively Coupled Equatorial Waves. Part III: Synthesis Structures and Their Forcing and Evolution

Abstract Building on Parts I and II of this study, the structures of eastward- and westward-moving convectively coupled equatorial waves are examined through synthesis of projections onto standard equatorial wave horizontal structures. The interaction between these equatorial wave components and their evolution are investigated. It is shown that the total eastward-moving fields and their coupling with equatorial convection closely resemble the standard Kelvin wave in the lower troposphere, with intensified convection in phase with anomalous westerlies in the Eastern Hemisphere (EH) and with anomalous convergence in the Western Hemisphere (WH). However, in the upper troposphere, the total fields show a mixture of the Kelvin wave and higher (n = 0 and 1) wave structures, with strong meridional wind and its divergence. The equatorial total fields show what may be described as a modified first internal Kelvin wave vertical structure in the EH, with a tilt in the vertical and a third peak in the midtroposphere. There is evidence that the EH midtropospheric Kelvin wave is closely associated with SH extratropical eastward-moving wave activity, the vertical velocity associated with the wave activity stretching into the equatorial region in the mid–upper troposphere. The midtropospheric zonal wind and geopotential height show a pattern that may be associated with a forced wave. The westward-moving fields associated with off-equatorial convection show very different behaviors between the EH midsummer and the WH transition seasons. In the EH midsummer, the total fields have a baroclinic structure, with the off-equatorial convection in phase with relatively warm air, suggesting convective forcing of the dynamical fields. The total structures exhibit a mixture of the n = 0, 1 components, with the former dominating to the east of convection and the latter to the west of convection. The n = 0 component is found to be closely connected to the lower-level n = 1 Rossby (R1) wave that appears earlier and seems to provide organization for the convection, which in turn forces the n = 0 wave. In the WH transition season the total fields have a barotropic structure and are dominated by the R1 wave. There is evidence that this barotropic R1 wave, as well as the associated tropical convection, is forced by the NH upper-tropospheric extratropical Rossby wave activity. In the EH, westward-moving lower-level wind structures associated with equatorial convection resemble the R1 wave, with equatorial westerlies in phase with the intensified convection. However, westward-moving n = −1 and n = 0 structures are also involved.

Surface-Wave Studies beneath the Pacific Ocean

The fundamental mode Rayleigh, R2, and R3 waves were used to study the phase velocity tomography and surface-wave attenuation variation beneath the Pacific Ocean. The Rayleigh-wave phase velocity estimation for about 4000 propagation paths across the Pacific Ocean were made at time periods of 70, 100, 150, and 230 sec. More than 100 earthquakes, which occurred in the Pacific Ocean and were recorded at about 60 broadband digital seismic networks ascribed to IRIS, OHP, TERRAscope, Pacific 21 (formerly POSEIDON), and the Pacific Northwest Region (UW), are used in this study. The resulting phase velocity maps at varying periods showed a good correlation with known geological and tectonic features of the region. A fast-velocity anomaly is surrounded by a slow-velocity anomaly over the eastern and western parts of the Pacific Ocean, while the central part is associated with a fast-velocity anomaly. Subduction zones and spreading regions are demarcated by slow-velocity anomalies. A slow-velocity anomaly is also clearly visible over the Hawaiian hot spots and the French Polynesia, Micronesia, Japan, and Java–Sumatra trench axis zones. A high-attenuation zone (low Q -value) is visible over the East Pacific rise and Nazca plate and Cocos plate regions of younger lithospheric age, and a low-attenuation anomaly (high Q -value) marks the zones of older lithosphere in the western part of the Pacific Ocean. High-attenuation regions are surrounded by low-attenuation zones in the eastern and western Pacific Ocean. Subduction zones with lower attenuation are flanked by high-attenuation anomalies on both sides, reflecting the plate interaction. The hot spots are associated with a high-attenuation zone of the Pacific Ocean at a depth of 100–300 km.