Global Responses of Gravity Waves and Zonal Mean Winds to the Madden‐Julian Oscillation and the Latitudinal Dependence of Their Relations using MERRA‐2

Abstract Four Tropical Rainfall Measuring Mission (TRMM) datasets of latent heating were diagnosed for signals in the Madden–Julian oscillation (MJO). In all four datasets, vertical structures of latent heating are dominated by two components—one deep with its peak above the melting level and one shallow with its peak below. Profiles of the two components are nearly ubiquitous in longitude, allowing a separation of the vertical and zonal/temporal variations when the latitudinal dependence is not considered. All four datasets exhibit robust MJO spectral signals in the deep component as eastward propagating spectral peaks centered at a period of 50 days and zonal wavenumber 1, well distinguished from lower- and higher-frequency power and much stronger than the corresponding westward power. The shallow component shows similar but slightly less robust MJO spectral peaks. MJO signals were further extracted from a combination of bandpass (30–90 day) filtered deep and shallow components. Largest amplitudes of both deep and shallow components of the MJO are confined to the Indian and western Pacific Oceans. There is a local minimum in the deep components over the Maritime Continent. The shallow components of the MJO differ substantially among the four TRMM datasets in their detailed zonal distributions in the Eastern Hemisphere. In composites of the heating evolution through the life cycle of the MJO, the shallow components lead the deep ones in some datasets and at certain longitudes. In many respects, the four TRMM datasets agree well in their deep components, but not in their shallow components and in the phase relations between the deep and shallow components. These results indicate that caution must be exercised in applications of these latent heating data.

Download Full-text

A Reduced-Order Representation of the Madden–Julian Oscillation Based on Reanalyzed Normal Mode Coherences

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-18-0197.1 ◽

2019 ◽

Vol 76 (8) ◽

pp. 2463-2480 ◽

Cited By ~ 3

Author(s):

Vassili Kitsios ◽

Terence J. O’Kane ◽

Nedjeljka Žagar

Keyword(s):

Normal Mode ◽

Gravity Waves ◽

Rossby Waves ◽

Spatial Scales ◽

Longwave Radiation ◽

Kelvin Waves ◽

Madden Julian Oscillation ◽

Kelvin Wave ◽

Zonal Wavenumber ◽

Vertical Scales

Abstract The Madden–Julian oscillation (MJO) is presented as a series of interacting Rossby and inertial gravity waves of varying vertical scales and meridional extents. These components are isolated by decomposing reanalysis fields into a set of normal mode functions (NMF), which are orthogonal eigenvectors of the linearized primitive equations on a sphere. The NMFs that demonstrate spatial properties compatible with the MJO are inertial gravity waves of zonal wavenumber k = 1 and the lowest meridional index n = 0, and Rossby waves with (k, n) = (1, 1). For these horizontal scales, there are multiple small vertical-scale baroclinic modes that have temporal properties indicative of the MJO. On the basis of one such eastward-propagating inertial gravity wave (i.e., a Kelvin wave), composite averages of the Japanese 55-year Reanalysis demonstrate an eastward propagation of the velocity potential, and oscillation of outgoing longwave radiation and precipitation fields over the Maritime Continent, with an MJO-appropriate temporal period. A cross-spectral analysis indicates that only the MJO time scale is coherent between this Kelvin wave and the more energetic modes. Four mode clusters are identified: Kelvin waves of correct phase period and direction, Rossby waves of correct phase period, energetic Kelvin waves of larger vertical scales and meridional extents extending into the extratropics, and energetic Rossby waves of spatial scales similar to that of the energetic Kelvin waves. We propose that within this normal mode framework, nonlinear interactions between the aforementioned mode groups are required to produce an energetic MJO propagating eastward with an intraseasonal phase period. By virtue of the selected mode groups, this theory encompasses both multiscale and tropical–extratropical interactions.

Download Full-text

Dynamical Roles of Mixed Rossby–Gravity Waves in Driving Convective Initiation and Propagation of the Madden–Julian Oscillation: General Views

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0050.1 ◽

2020 ◽

Vol 77 (12) ◽

pp. 4211-4231

Author(s):

Daisuke Takasuka ◽

Masaki Satoh

Keyword(s):

Gravity Waves ◽

Longwave Radiation ◽

Boreal Winter ◽

Madden Julian Oscillation ◽

Atmospheric Variability ◽

Convective Initiation ◽

Low Level ◽

Initiation And Propagation ◽

The Indian Ocean

AbstractMotivated by the previous case study, this work shows that dynamical variations of mixed Rossby–gravity waves with tropical depression–type circulations (MRGTDs) are possible drivers of convective initiation and propagation of the Madden–Julian oscillation (MJO) by performing statistical analysis. MJO events initiated in the Indian Ocean (IO) in boreal winter are objectively identified solely using outgoing longwave radiation data. The lagged-composite analysis of detected MJO events demonstrates that MJO convection is initiated in the southwestern IO (SWIO), where strong MRGTD–convection coupling is statistically found. Further classification of MJO cases in terms of intraseasonal convection and MRGTD activities in the SWIO suggests that 26 of 47 cases are related to more enhanced MRGTDs, although they can also be secondarily affected by Kelvin waves. For those MRGTD-enhanced MJO events, MJO convective initiation is primarily triggered by low-level MRGTD circulations that develop via the enhancement of downward energy dispersion in accordance with upper-tropospheric baroclinic conversion. This is supported by the modulation of MRGTD structure associated with zonal wave contraction due to upper-tropospheric zonal convergence, and plentiful moisture advected into the western IO. Following this MRGTD-induced MJO triggering and midtropospheric premoistening in the IO contributed by MRGTD shallow circulations as well as intraseasonal winds during the MJO-suppressed phase, low-level MRGTD winds with eastward group velocity successively trigger convection to the east, which helps MJO convective propagation over the IO. The interannual atmospheric variability may affect whether the presented MRGTD-related processes are effective or not.

Download Full-text

Does the Madden-Julian Oscillation modulate stratospheric gravity waves?

Geophysical Research Letters ◽

10.1002/2016gl068498 ◽

2016 ◽

Vol 43 (8) ◽

pp. 3973-3981 ◽

Cited By ~ 6

Author(s):

Andrew C. Moss ◽

Corwin J. Wright ◽

Nicholas J. Mitchell

Keyword(s):

Gravity Waves ◽

Madden Julian Oscillation

Download Full-text

Diurnal Lightning Variability over the Maritime Continent: Impact of Low-Level Winds, Cloudiness, and the MJO

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-13-021.1 ◽

2013 ◽

Vol 70 (10) ◽

pp. 3128-3146 ◽

Cited By ~ 22

Author(s):

Katrina S. Virts ◽

John M. Wallace ◽

Michael L. Hutchins ◽

Robert H. Holzworth

Keyword(s):

Gravity Waves ◽

Diurnal Cycle ◽

Tropical Rainfall Measuring Mission ◽

Madden Julian Oscillation ◽

Maritime Continent ◽

Mountain Ranges ◽

Low Level ◽

Westerly Winds ◽

Rainfall Anomalies ◽

Land Breezes

Abstract Lightning over the Maritime Continent exhibits a pronounced diurnal cycle. Daytime and evening lightning occurs near coastlines and over mountain slopes, driven by sea and valley breezes. Nocturnal and morning thunderstorms are touched off where land breezes or mountain breezes converge or by gravity waves propagating away from regions of vigorous afternoon convection. In this study, the modulation of the diurnal cycle of lightning and precipitation by 850-hPa winds, cloudiness, and the Madden–Julian oscillation (MJO) is investigated using observations from the World Wide Lightning Location Network (WWLLN) and the Tropical Rainfall Measuring Mission (TRMM) satellite. The 850-hPa wind speed and area-averaged cloudiness are shown to be negatively correlated with day-to-day lightning frequency over land, and thunderstorm occurrence is suppressed windward of, and enhanced leeward of, mountain ranges. Lightning and environmental conditions are similarly related in the MJO. During break periods, the regular diurnal cycle of lightning is enhanced where ambient low-level winds are easterly but abnormally weak—in the Strait of Malacca, over western and southern Borneo and the adjacent seas, and in the region of nocturnal thunderstorms to the west of Sumatra and Java. When the active, cloudy phase of the MJO, accompanied by low-level westerly winds, passes over the Maritime Continent, the regular diurnal cycle of lightning is enhanced leeward (to the east) of the mountains of Java, Borneo, and the Malay Peninsula. The spatial patterns of lightning and rainfall anomalies are broadly similar, but lightning anomalies tend to be more concentrated near coastlines.

Download Full-text