equatorial kelvin waves

0000016063 00000 n Flannaghan, T. J., and S. Fueglistaler, 2013: Another reason may be that the two-dimensional wave solutions on the equatorial plane associated with a single or just a few vertical modes in the troposphere were successfully used to account for gross features of large-scale tropical circulation effectively associated with deep convection (e.g., Gill 1980; Zhang and Krishnamurti 1996; Mapes 2000).

The upper-left to lower-right tilt of the temperature anomalies indicates eastward movement which is a sign of an oceanic Kelvin wave. padding: 0; The question is, to what extent is the KW kinetic energy spectrum divergent? To account for uncertainties in the computation of D values due to vertical discretization, we shall refer to their rounded values, although we use the exact values listed above in all computations. An analysis of the vertical structure equation for arbitrary thermal profiles. 2, we ask which VSFs can be expected to represent a baroclinic structure of the mean signal in Fig.

0000001443 00000 n Compared to the previous reanalysis ERA-Interim, the ERA5 has an improved model physics, core dynamics, and data assimilation. In advance, thank you. 10 and 13. The importance of the tropical tropopause layer for equatorial Kelvin wave propagation.

A generalized method of resolving disturbances into progressive and retrogressive waves by space Fourier and time cross-spectral analyses. 2). For example, for k = 1 and k = 2, which are associated with the migrating diurnal and semidiurnal tides, the closest linear theory periods are 40 and 19 h, and 32 and 16 h for D equal to 10 and 7 km, respectively. In other words, the VSFs that are needed to represent the wave signal concentrated in the troposphere have small equivalent depths. The frequency k of a wave component uk(t) is a priori unknown. Both discretizations have top level near 0.4 hPa. The time dependency of wave component (k, m) is described by exp(imkt), where mk is the frequency of linearly propagating wave, derived from the horizontal structure equation as described in section 2d. The barotropic mode is often referred to as m = 0 mode but we see no reason for following that convention for solutions of Eq. SPARC Rep. 10, WCRP-6/2021, 612 pp., https://www.sparc-climate.org/sparc-report-no-10/. The longest period in this time series is about 27 days. As in Fig. Part I: Convective signals, The interaction of waves and convection in the tropics, The eigenfunctions of Laplaces tidal equations over a sphere, Convective inhibition, subgrid-scale triggering energy, and stratiform instability in a toy tropical wave model, Diagnosis of free and convectively coupled equatorial waves, Observed propagation and structure of the 33-h atmospheric Kelvin wave, Generalized Hough modes: The structure of damped global-scale waves propagating on a mean flow with horizontal and vertical shear, Balanced dynamics and convection in the tropical troposphere, Vertically propagating Kelvin waves and tropical tropopause variability, An analysis of the vertical structure equation in sigma coordinates, Spacetime variability of equatorial Kelvin waves and intraseasonal oscillations around the tropical tropopause, Lifetime and longitudinal variability of equatorial Kelvin waves around the tropical tropopause region, The vector harmonic analysis of Laplace tidal equations, Large-scale cloud disturbances associated with equatorial waves. Hendon, H. H., and M. C. Wheeler, 2008: There is a variance gap between JJA and DJF seasons on one side and transitions seasons MAM and SON on the other at planetary scales and equivalent depths greater than about 400 m. The largest KW variance near D 400 m and k = 1 in DJF in Fig. As we demonstrate using reanalysis data up to about 1 hPa, the conditions derived by Cohn and Dee (1989) define typical values of equivalent depths. Submitted by FF on Sat, 04/11/2015 - 02:43. (4). For linear theory periods longer than 2 days and m > 4, the variance spectra are almost indistinguishable (not shown). Streamfunction and velocity potential representation of equatorially trapped waves. Thus we can argue that changes in the distribution of KW variance in the vertical domain through the VSFs (i.e., through 1/D) represent variability in the background flow controlling the KW propagation. 3. opacity: 1; Equatorial Kelvin waves have two phases, which can lead to very different changes in subsurface and sea surface temperature (SSTs) in the eastern tropical Pacific: (A) Downwelling phase: Normally, winds blow from east to west across the tropical Pacific, which piles up warm water in the western Pacific. 0000004147 00000 n ECMWF Newsletter, J. Geophys. Part II: Applications to the atmosphere, Kelvin waves in the nonlinear shallow water equations on the sphere: Nonlinear travelling waves and the corner wave bifurcation, Uniform asymptotics for the linear Kelvin wave in spherical geometry, Convectively coupled equatorial-wave diagnosis using three-dimensional normal modes, An analysis of the vertical structure equation for arbitrary thermal profiles, Stratospheric wave spectra resembling turbulence, Wave fluxes of equatorial Kelvin waves and QBO zonal wind forcing derived from SABER and ECMWF temperature spacetime spectra, Tracking Kelvin waves from the equatorial troposphere into the stratosphere, The importance of the tropical tropopause layer for equatorial Kelvin wave propagation, SPARC Reanalysis Intercomparison Project (S-RIP) final report, Transient response to localized episodic heating in the tropics. width: 100%; 0000010990 00000 n Convectively coupled equatorial waves: A new methodology for identifying wave structures in observational data. (5) and (6) can be associated with the tropical wave circulation. Sci., 57, 34883497, https://doi.org/10.1175/1520-0469(2000)057<3488:OPASOT>2.0.CO;2. Kim, J. E., and M. J. Alexander, 2013: In relation to Fig. However, their temporal variability due to complex spatiotemporal forcings, due to interaction of the waves with cumulus convection and wavewave interactions hampers the identification based on linear propagation properties (phase speeds) as used in WFD. Quart. The link was not copied. 2003, 2007a). Wheeler, M., and G. N. Kiladis, 1999:

A blog about monitoring and forecasting El Nio, La Nia, and their impacts. (6) There does not have to be a rebound upwelling wave. We excluded 10 levels above 0.4 hPa to have the same top boundary for the solution of Eq. Rev., 137, 38583873, https://doi.org/10.1175/2009MWR2816.1; Corrigendum, 138, 24762477, https://doi.org/10.1175/2009MWR3256.1. In section 2 we present the data and the 3D WD method focusing on the solution of the vertical structure equation and the sensitivity of derived equivalent depths to the discretization. #Uz sO{ ",A4:xzBJ!A]G> P ?q7[g LiPlxv{Qcv'5z:Tky1 8T T@J(I$d9uGlmYh6m@qGwoJp8;4;M(M*5;1t)mMmg/nR[gn+vLWnh^L:|YB>UFsw(32qkBT>m(zg9#'PvHlM TAzsNcO/B;kmto40*b[fqT />Q%,Y>/c?L TxGQl)E~/o~8lt{I~G`dN|JE@'fNHHk l7JOwNOyW7n4HUu8;&>l1tI%'.68|*d~MpG8iZh`. You can track ocean data closer to Oregon at this web site: https://www.cpc.ncep.noaa.gov/products/GODAS/, Submitted by michelle.lheureux on Mon, 07/08/2019 - 14:57, In reply to Kelvin Waves effecting Oregon Coastal waters by Jim Leslie, Submitted by Arpit Rathi on Thu, 07/25/2019 - 13:24, Submitted by Ryan on Tue, 09/17/2019 - 05:23, Submitted by Zhiyu Liu on Mon, 09/14/2020 - 05:31, In reply to Downwelling Kelvin wave by Ryan. Your current browser may not support copying via this button. agar, N., J. Tribbia, J. L. Anderson, and K. Raeder, 2009: (2) leads to the daily time series of three-dimensional KWs (, , ) used to compute the KW zonal wind variance in physical space. June 2022 ENSO update: how does your garden grow? Differences to the spherical solutions can be noticed for large D and planetary scales. Sci., 53, 449467, https://doi.org/10.1175/1520-0469(1996)053<0449:LFEWIV>2.0.CO;2. Monthly climatology of the Kelvin wave zonal winds in ERA5 for 19802019 (averaged over 15S15N). Other steps include the removal of variability on time scales longer than the chosen window of 90 days and smoothing of the spectrum in frequency domain. These are blog posts, not official agency communications; if you quote from these posts or from the comments section, you should attribute the quoted material to the blogger or commenter, not to NOAA, CPC, or Climate.gov. Solid lines indicate the KW dispersion curves for the three equivalent depths on the equatorial plane. 7. The paper is organized as follows. Matthews, A., and R. A. Madden, 2000: By filtering to physical space a range of vertical modes and comparing it with the total signal, we can quantify regional and altitude-dependent contributions of various vertical modes to the total KW signal. a. Wavenumber decomposition of the Kelvin wave, d. Vertical eigenfunctions, equivalent depths, and eigenfrequencies, 3. Analysis data are either once (red and magenta) or four times (blue and black curves) per day.

Japan, 60, 156171, https://doi.org/10.2151/jmsj1965.60.1_156. 0000008990 00000 n Their equivalent depths are below 30 m. The first group corresponds to the deep convective heating and the second to the stratiform heating (e.g., Mapes 2000). Soc. For this figure we have set A = 1, a = 2/5, and p = 2/10 with nondimensional time t. (a) As in Fig. Quart. Spacetime spectral analysis and its applications to atmospheric waves. J. Meteor. The longitudinal structure is a superposition of Fourier wave components with different zonal wavenumbers k. Appendix A illustrates the WD for an idealized case of a horizontally propagating signal in a frictionless atmosphere with a background state at rest (implying the horizontally homogeneous temperature). Large-scale cloud disturbances associated with equatorial waves. background: #ddd; The forward projection is applied to daily data at every time step. Submitted by Daniel B. Lluch-Cota on Wed, 06/22/2022 - 17:09, That is a different type of kelvin wave known as a coastal kelvin wave. They behave differently than an equatorial kelvin wave (which balance between the coriolis force in the Northern and Southern Hemisphere), Coastal Kelvin waves balance the Coriolis Force against a Topographic Boundary, Submitted by tom.diliberto on Mon, 06/27/2022 - 09:21, In reply to Coastally trapped Kelvin Wave by Daniel B. Lluch-Cota. One challenge is coupling between the propagation properties of wave signals resulting from WFD at individual vertical levels and associated vertical structures. Sci., 65, 29362948, https://doi.org/10.1175/2008JAS2675.1. https://modes.cen.uni-hamburg.de/download. Mon. According to Eq. Climate, 19, 26652690, https://doi.org/10.1175/JCLI3735.1. Variability is largest in boreal winter, likely due to more equator-centered convection. D1c), the result is similar to that for the full time series, whereas fixing both frequencies and amplitudes (Fig. Equatorial waves in High Resolution Dynamics Limb Sounder (HIRDLS) data. In a frictionless atmosphere with a background state of rest, the wave component uk(t) will propagate at its constant phase speed cFk=F/k, with the subscript F representing the Fourier series expansion in time. 13).

The phase-locking experiment confirms narrowing of the wave variance band on the side of small equivalent depths (Figs. Res., 115, D03103, https://doi.org/10.1029/2009JD012261. The decomposition of data that includes the tidal signals onto free wave solutions from linear theory will thus project such signals to nearby Hough harmonics with different periods. A strong damping acting on divergence starts at 1 hPa (Fujiwara et al. J. Geophys. Figure 8 shows that the modes m = 510 represent most of the KW signal in the troposphere and TTL. Tindall, J. C., J. Thuburn, and E.-J. UCAR/NCAR/CISL/TDD, Low-frequency equatorial waves in vertically sheared zonal flow. The atmospheric Kelvin wave (KW) discussed in this paper is the slowest eastward-propagating eigensolution of the linearized primitive equations (e.g., Kasahara 2020). This is a structure representative of the deep convection and it explains most of the KW signal in the upper troposphere and tropopause layer. 15a. (4) The thermocline is often defined by subsurface temperatures at 20C. J. Roy.

Science, 204, 832835, https://doi.org/10.1126/science.204.4395.832. Meteor. 13 shows that the mean signal (energy spectrum) remains intact as expected. Raymond, D., . Fuchs, S. Gjorgjievska, and S. Sessions, 2015: Terasaki, K., H. Tanaka, and N. agar, 2011: Variations in phases, and to some extent in amplitude, will show up in frequencies different from the analytic linear wave solution due to the time decomposition using Fourier series. No, the tropical wind anomaly often changes on a quicker time scale than the 2-3 months it takes for the Kelvin wave to cross from western to eastern Pacific Ocean. WheelerKiladis frequencywavenumber power spectra of the Kelvin wave zonal wind at = 0.2 in the equatorial belt (15N15S) for 19802019: (a) raw spectrum and (b) raw spectrum divided by background spectrum. The eigenfunctions of Laplaces tidal equations over a sphere. Following initial analysis in 17 period bins, signals are accumulated into four bins that are presented in Fig. J. Meteor. A comparison of (a) the static stability profile 0 = T0/ dT0/d and (b) the equivalent depths D using 43 levels used in the paper (thick gray lines with diamond) and 127 levels from the operational ECMWF model (thin black line with circles). Note however that in the case when Eq. Sci., 44, 499532, https://doi.org/10.1175/1520-0469(1987)044<0499:TRTLEH>2.0.CO;2. (4). Longuet-Higgins, M. S., 1968: Figure A1 (top row) shows the wave for three time steps (t = 0, 1, 2) that can represent consecutive times with available observations or model outputs. Generalized Hough modes: The structure of damped global-scale waves propagating on a mean flow with horizontal and vertical shear. } Section 3 presents KW mean signal and variability for the intramonthly and intraseasonal time scales. 2016; Blaauw and agar 2018) suggests that the KW meridional e-folding scale is up to about 10, similar to that used in two-dimensional WD (Yang et al. Around the 20C layer, ocean temperatures change rapidly (a strong temperature gradient). A smaller magnitude signal can be noticed at D around 75 m. Some spurious signals can still be seen in the westward-propagating sector, and they are due to aliasing, as we do not filter out unresolved frequencies (as is done in Fig.

Going forward, we still need to continue to monitor the Pacific for future downwelling Kelvin waves which may increase the risk of El Nio forming in 2015 (see latest NCEP CFSv2 run). Mean state and variability in wavenumber space, 2) Kinetic energy spectrum of the Kelvin waves, 3) Intramonthly and intraseasonal variability, c. Wavenumber decomposition and linear propagation, 2) Intraseasonal variance and linear theory, 3) Tidal signals in WD and data frequency, 4.

Uniform asymptotics for the linear Kelvin wave in spherical geometry. Thanks for knowledge. (4) has to be solved numerically, which MODES performs by finite differences. J. Roy. margin: 0; 1a are shown in Fig. Rev., 104, 669690, https://doi.org/10.1175/1520-0493(1976)104<0669:NMOUWI>2.0.CO;2. 1a are for average conditions, but differences in 0 among the seasons are relatively small due to global averaging, and cause negligibly small changes in the shapes of VSFs (not shown). Depth-longitude section of the equatorial Pacific upper-ocean (0-300m) temperature anomalies centered on the pentad of 13 January 2015. Any statistical data to show? Has anyone else, out there, experienced such a phenomenon? In the case of constant phase speeds (Fig. Although it is overall smooth, the shape of the distribution is suggestive of a linear wavenumberfrequency dependence (i.e., almost nondispersive waves), in agreement with the analysis of previous section. 2006). Sci., 60, 30093020, https://doi.org/10.1175/1520-0469(2003)060<3009:TIOWAC>2.0.CO;2. -- Thanks for the review and edits from William Kessler, NOAA Pacific Marine Environmental Laboratory (PMEL). (2009) and agar et al. agar, N., M. Blaauw, B. Jesenko, and L. Magnusson, 2016: Diagnosing model performance in the tropics. The third part of this section is the analysis of KW variance in terms of the theoretical KW periods. Normal-mode function representation of global 3D datasets: Open-access software for the atmospheric research community. The phase velocity of the identified wave, p, is not known. Now we modify our 40-yr KW time series in three ways described in section 2d followed by the application of the WK99 WFD to each new time series. However, the effect of the filter on the eastward-propagating signal is unclear in light of the results in the previous section. The spectrum in Fig. Lin, J.-L., and Coauthors, 2006: At each time instant t, WD will lead to a filtered wave, uWD(, t), that will be the same as the observed signal u(, t). The longest linear theory period in our analysis is 50.65 days for D = 8 m and k = 1. Wang, B., and X. Xie, 1996: Convectively coupled equatorial-wave diagnosis using three-dimensional normal modes. Atmos., 7, 4548, https://doi.org/10.2151/sola.2011-012. xlyj1h:q][!]2II`j0k2_:>irbSH;:)] ^.>svfIo Sci., 65, 18171837, https://doi.org/10.1175/2007JAS2466.1. A1. 11b is enhanced variance in periods longer than 3 days in three ranges of the vertical wavenumbers similar to those in Figs. Fujiwara, M., G. L. Manney, L. J. Convectively coupled equatorial waves. The first group are VSFs m = 710 that have a zero crossing in the midtroposphere and an oscillatory structure throughout the stratosphere. 0000011956 00000 n The 3D WD assumes vertical and horizontal time separability of the linearized primitive equations, which leads to two eigenfunction problems: one for the vertical structure and another for the horizontal oscillations. Geosci. The westward-propagating signal is no longer present and there is only little noise left associated with the Fourier series decomposition due to the limited time window. Low-frequency equatorial waves in vertically sheared zonal flow. : The NCAR Command Language (version 6.6.2). We thank Matic avli for the coupler between the SPHEREPACK and MODES, to Kalil Karami for running MODES on ERA5 data and to Sergiy Vasylkevych for the computation of the Hough functions with the realistic background zonal winds. A further illustration of this effect is given in appendix D for a single component of the KW, (k, m) = (1, 7), associated with a large portion of subseasonal variance according to WD. Linear theory provides only a few solutions for the wavenumberfrequency window (k, m) = (14, 14) where the tidal signal can project. (1) At this point, our more inquisitive readers might ask themselves, what happens after this wave hits the coast of South America? Geophys., 47, RG2003. Soc. Applicability of the Fourier series decomposition in time for detangling KW dynamics in the troposphere is questioned by carrying out the WFD of the time series of the KW zonal winds derived by WD. Sci., 64, 34243437, https://doi.org/10.1175/JAS4018.1. 15a. The temporal behavior of the KW zonal winds obtained by wavenumber filtering [Eq.

Quart. Atmos. SIAM J. Stat. The semiannual cycle is dominated by positive perturbations at k = 1 in January and at k = 1, 2 in JuneJuly, and negative perturbations in April and November (not shown). Yang, G.-Y., B. J. Hoskins, and J. Slingo, 2003: Dewan, E., 1979: ECMWF, Reading, United Kingdom, 2633, http://www.ecmwf.int/publications/newsletters. More important for the values of equivalent depths are differences in the discretization, such as the number of levels and their distribution, especially near the model top. This means that the troposphere and stratosphere are considered together (referred to jointly as the tropostratosphere) in terms of vertical structure functions (VSFs) that span the atmosphere from the surface up to the top of the stratosphere. To investigate this, KW energies and variances are organized in 17 bins defined by periods shown in Fig. Quart. A smaller part of the signal is in (k, m) = (1, 1) with a period of 32 h, while a larger part is projected on (k, m) = (1, 2) with a period near 40 h. In contrast, the frequency spectrum from the Fourier decomposition of the energy time series (not shown) has a peak on the diurnal scale as expected. Intramonthly (intraseasonal) KW variance is computed as averaged squared departures of daily zonal winds from monthly (seasonal) means for every month (season) and point (, , ). l!WzEH%Uc*GV@x38 5 with a zero in middle troposphere and a wide variability maximum across the TTL in Fig. This process is entirely external to the ocean ultimately, the ocean will respond to sustained wind forcing. As in Fig. An example in appendix A compares WD and WFD for a simple analytical wave. Japan, 72, 433448, https://doi.org/10.2151/jmsj1965.72.3_433. A substantial part of the signal appears to be associated with KWs with equivalent depths in the range of about 300400 m and periods around 10 days consistent with Figs.

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