The dynamical composition of the Madden-Julian oscillation

2020 ◽  
Author(s):  
José M. Castanheira ◽  
Carlos A. F. Marques
Keyword(s):  
Wave Number ◽  
Convective System ◽  
Diagnostic Study ◽  
Madden Julian Oscillation ◽  
3 Dimensional ◽  
Dynamical Nature ◽  
Zonal Wave Number ◽  
Dynamical Features ◽  
The Waves ◽  
Equatorial Rossby Waves

<p>The Madden-Julian oscillation (MJO) is a major intraseasonal tropical atmospheric mode which modulates the precipitation in the Tropical Indian and Pacific  oceans. It is a large atmospheric convective system, dominated the zonal wave number one scale, that moves eastward from the east coast of Africa to eastern Pacific in a time scale of  30-70 days.</p><p>The MJO can have impact in global weather but is yet poorly simulated in most atmospheric circulation models. Therefore, it is important to understand the convective-dynamical nature of the MJO to understand the reasons for its poor representation in models.</p><p>Here we present a diagnostic study of the MJO by decomposing the circulation associated with a multivariate MJO index onto 3-Dimensional inertio-gravitic and Rossby modes, based on the ERA-I reanalysis. Results show that the main dynamical features of MJO are represented by  a combination of  Kelvin and the first (<em>l<sub>r </sub></em>= 1) equatorial Rossby modes with zonal wavenumbers 1 to 4. The vertical structures of the waves correspond to a first baroclinic mode in the troposphere. Moreover, a space–time spectral analysis confirmed the existence of an eastward moving MJO signal in the equatorial Rossby modes.</p><p>Nonlinear interactions between the westward moving equatorial Rossby waves and eastward moving Kelvin waves may be the cause for the slow eastward progression of the MJO. </p>

scholarly journals Equatorial Waves Including the Madden–Julian Oscillation in TRMM Rainfall and OLR Data

2004 ◽  
Vol 17 (22) ◽  
pp. 4387-4406 ◽  
Author(s):  
Hye-Kyung Cho ◽  
Kenneth P. Bowman ◽  
Gerald R. North
Keyword(s):  
Large Scale ◽  
Longwave Radiation ◽  
Tropical Rainfall Measuring Mission ◽  
Space Time ◽  
Madden Julian Oscillation ◽  
Limited Sampling ◽  
The Tropics ◽  
The Waves ◽  
Section Analysis ◽  
Equatorial Rossby Waves

Abstract Four years of outgoing longwave radiation (OLR) and rainfall data from the Tropical Rainfall Measuring Mission (TRMM) are investigated to find the dominant large-scale wave modes in the Tropics. By using space– time cross-section analysis and spectral analysis, the longitudinal and latitudinal behaviors of the overall waves and the dominant waves are observed. Despite the noisy nature of precipitation data and the limited sampling by the TRMM satellite, pronounced peaks are found for Kelvin waves, n = 1 equatorial Rossby waves (ER), and mixed Rossby–gravity waves (MRG). Madden–Julian oscillation (MJO) and tropical depression (TD)-type disturbances are also detected. The seasonal evolution of these waves is investigated. An appendix includes a study of sampling and aliasing errors due to the peculiar space–time sampling pattern of TRMM. It is shown that the waves detected in this study are not artifacts of these sampling features. The results presented here are compared with previous studies. Consistency with their results gives confidence in the TRMM data for wave studies. The results from this study can be utilized for modeling and testing theories. Also, it may be useful for the future users of the TRMM data to understand the nature of the TRMM satellite sampling.

Contributions of Convectively Coupled Equatorial Rossby Waves and Kelvin Waves to the Real-Time Multivariate MJO Indices

2009 ◽  
Vol 137 (1) ◽  
pp. 469-478 ◽  
Author(s):  
Paul E. Roundy ◽  
Carl J. Schreck ◽  
Matthew A. Janiga
Keyword(s):  
Frequency Domain ◽  
Real Time ◽  
Deep Convection ◽  
Longwave Radiation ◽  
Kelvin Waves ◽  
Wind Data ◽  
Madden Julian Oscillation ◽  
The Real ◽  
The Waves ◽  
Equatorial Rossby Waves

Abstract The real-time multivariate (RMM) Madden–Julian oscillation (MJO) indices have been widely applied to diagnose and track the progression of the MJO. Although it has been well demonstrated that the MJO contributes to the leading signals in these indices, the RMM indices vary erratically from day to day. These variations are associated with noise in the outgoing longwave radiation (OLR) and wind data used to generate the indices. This note demonstrates that some of this “noise” evolves systematically and is associated with other types of propagating modes that project onto the RMM eigenmodes. OLR and zonal wind data are filtered in the wavenumber–frequency domain for the MJO, convectively coupled equatorial Rossby (ER) waves, and convectively coupled Kelvin waves. The filtered data are then projected onto the RMM modes. An example phase space associated with these projections is presented. Linear regression is then applied to isolate the wave signals from random variations in the same bands of the wavenumber–frequency domain, and the regressed data are projected onto the RMM EOFs. Results demonstrate the magnitudes of the contributions of the systematically evolving signals associated with these waves to variations in the RMM principal components, and how these contributions vary with the longitude of the active moist deep convection coupled to the waves.

scholarly journals Investigation of dominant traveling 10-day wave components using long-term MERRA-2 database

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Chunming Huang ◽  
Wei Li ◽  
Shaodong Zhang ◽  
Gang Chen ◽  
Kaiming Huang ◽  
...  
Keyword(s):  
Flow Instability ◽  
Transmission Condition ◽  
Wave Number ◽  
Mean Flow ◽  
Excited Wave ◽  
Propagating Waves ◽  
Zonal Wave Number ◽  
The Mean

AbstractThe eastward- and westward-traveling 10-day waves with zonal wavenumbers up to 6 from surface to the middle mesosphere during the recent 12 years from 2007 to 2018 are deduced from MERRA-2 data. On the basis of climatology study, the westward-propagating wave with zonal wave number 1 (W1) and eastward-propagating waves with zonal wave numbers 1 (E1) and 2 (E2) are identified as the dominant traveling ones. They are all active at mid- and high-latitudes above the troposphere and display notable month-to-month variations. The W1 and E2 waves are strong in the NH from December to March and in the SH from June to October, respectively, while the E1 wave is active in the SH from August to October and also in the NH from December to February. Further case study on E1 and E2 waves shows that their latitude–altitude structures are dependent on the transmission condition of the background atmosphere. The presence of these two waves in the stratosphere and mesosphere might have originated from the downward-propagating wave excited in the mesosphere by the mean flow instability, the upward-propagating wave from the troposphere, and/or in situ excited wave in the stratosphere. The two eastward waves can exert strong zonal forcing on the mean flow in the stratosphere and mesosphere in specific periods. Compared with E2 wave, the dramatic forcing from the E1 waves is located in the poleward regions.

Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

2021 ◽  
Author(s):  
Michal Kozubek ◽  
Peter Krizan
Keyword(s):  
Northern Hemisphere ◽  
Planetary Wave ◽  
Polar Vortex ◽  
Wave Number ◽  
Strong Activity ◽  
Key Characteristics ◽  
Zonal Wave Number ◽  
Show Difference ◽  
Temperature Enhancement ◽  
Stationary Planetary Wave

<p>An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.</p>

Experimental Study and Numerical Analysis of Sihui Metro Depot and the Superstructure

2012 ◽  
Vol 226-228 ◽  
pp. 176-180
Author(s):  
Jing Zhang ◽  
Bin Zhang ◽  
Ying Hua Liu ◽  
Long Qi Wang ◽  
Yu Bin Wu
Keyword(s):  
Time History ◽  
Field Tests ◽  
Element Model ◽  
Test Analysis ◽  
3 Dimensional ◽  
Dimensional Finite Element ◽  
Calculation Results ◽  
History Of ◽  
The Given ◽  
The Waves

Field tests were carried out on Sihui metro depot of Beijing metro line 1 and its superstructure. The acceleration time history of sleepers and floors of the building was obtained, and the waves-propagation laws of building were studied through the tests. Test analysis shows that the structure vibrations show zigzag tendencies ascends with the height of the building. Based on current situation of Sihui metro depot, a metro-soil-building 3-dimensional finite element model is established on ANSYS. By using actual acceleration of sleepers as inputs, the dynamic responds rule of the superstructure is obtained. Compared calculation results with the experimental results, the given numerical model can predict the vibrations of the building induced by moving trains quite well. This method can provide guidance and technical support for future development of superstructure.

scholarly journals Are Sudden Stratospheric Warmings Preceded by Anomalous Tropospheric Wave Activity?

2019 ◽  
Vol 32 (21) ◽  
pp. 7173-7189 ◽  
Author(s):  
Alvaro de la Cámara ◽  
Thomas Birner ◽  
John R. Albers
Keyword(s):  
Climate Model ◽  
State Of The Art ◽  
Source Region ◽  
Lower Troposphere ◽  
Wave Activity ◽  
Mean Flow ◽  
Wave Event ◽  
Dynamical Nature ◽  
The Waves ◽  
Robust Evidence

Abstract A combination of 240 years of output from a state-of-the-art chemistry–climate model and a twentieth-century reanalysis product is used to investigate to what extent sudden stratospheric warmings are preceded by anomalous tropospheric wave activity. To this end we study the fate of lower tropospheric wave events (LTWEs) and their interaction with the stratospheric mean flow. These LTWEs are contrasted with sudden stratospheric deceleration events (SSDs), which are similar to sudden stratospheric warmings but place more emphasis on the explosive dynamical nature of such events. Reanalysis and model output provide very similar statistics: Around one-third of the identified SSDs are preceded by wave events in the lower troposphere, while two-thirds of the SSDs are not preceded by a tropospheric wave event. In addition, only 20% of all anomalous tropospheric wave events are followed by an SSD in the stratosphere. This constitutes statistically robust evidence that the anomalous amplification of wave activity in the stratosphere that drives SSDs is not necessarily due to an anomalous amplification of the waves in the source region (i.e., the lower troposphere). The results suggest that the dynamics in the lowermost stratosphere and the vortex geometry are essential, and should be carefully analyzed in the search for precursors of SSDs.

scholarly journals Investigation of the Occurrence of Nighttime Topside Ionospheric Irregularities in Low-Latitude and Equatorial Regions Using CYGNSS Satellites

Sensors ◽  
2020 ◽  
Vol 20 (3) ◽  
pp. 708 ◽  
Author(s):  
Liang Huang ◽  
Yi Liu ◽  
Qiong Tang ◽  
Guanyi Chen ◽  
Zhuangkai Wang ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Global Analysis ◽  
Satellite System ◽  
Ionospheric Irregularities ◽  
Wave Number ◽  
Significant Finding ◽  
Low Latitude ◽  
Zonal Wave Number ◽  
Global Navigation Satellite ◽  
Maximum Occurrence

By using multi-satellite observations of the L1 signal-to-noise ratio (SNR) from the Cyclone Global Navigation Satellite System (CYGNSS) taken in 2017, we present the occurrence of nighttime topside ionospheric irregularities in low-latitude and equatorial regions. The most significant finding of this study is the existence of longitudinal structures with a wavenumber 4 pattern in the topside irregularities. This suggests that lower atmospheric waves, especially a daytime diurnal eastward-propagating zonal wave number-3 nonmigrating tide (DE3), might play an important role in the generation of topside plasma bubbles during the low solar minimum. Observations of scintillation events indicate that the maximum occurrence of nighttime topside ionospheric irregularities occurs on the magnetic equator during the equinoxes. The current work, which could be regarded as an important update of the previous investigations, would be readily for the further global analysis of the topside ionospheric irregularities.

Longitudinal Waves in a Submerged Cylindrical Rod 1

2010 ◽  
Vol 78 (2) ◽  
Author(s):  
G. Iosilevskii
Keyword(s):  
Boundary Layer ◽  
Wave Number ◽  
Analytical Relation ◽  
Velocity Of Sound ◽  
Longitudinal Displacement ◽  
Wave Propagation Velocity ◽  
Longitudinal Waves ◽  
Short Waves ◽  
The Waves ◽  
Surrounding Fluid

This study is concerned with longitudinal displacement waves propagating in an elastic cylindrical rod submerged in a viscous fluid. Provided that the wave propagation velocity in the rod is small compared with the velocity of sound in the surrounding fluid and the wavelength is large compared with the thickness of the boundary layer around the rod, an analytical relation is obtained between the wave number and the frequency. The presence of the fluid makes the waves disperse—the short waves become faster than the long ones.

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