Tropical Precipitation Variability and Convectively Coupled Equatorial Waves on Submonthly Time Scales in Reanalyses and TRMM

2013 ◽  
Vol 26 (10) ◽  
pp. 3013-3030 ◽  
Author(s):  
Ji-Eun Kim ◽  
M. Joan Alexander
Keyword(s):  
Diurnal Cycle ◽  
Low Frequency ◽  
Tropical Rainfall Measuring Mission ◽  
Precipitation Variability ◽  
Department Of Energy ◽  
Equatorial Waves ◽  
Tropical Precipitation ◽  
Convectively Coupled Equatorial Waves ◽  
Precipitation Characteristics ◽  
Equatorial Wave

Abstract Tropical precipitation characteristics are investigated using the Tropical Rainfall Measuring Mission (TRMM) 3-hourly estimates, and the result is compared with five reanalyses including the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis (ERA-Interim), Modern Era Retrospective Analysis for Research and Applications (MERRA), National Centers for Environmental Prediction (NCEP)–National Center for Atmospheric Research (NCAR) reanalysis (NCEP1), NCEP–U.S. Department of Energy (DOE) reanalysis (NCEP2), and NCEP–Climate Forecast System Reanalysis (CFSR). Precipitation characteristics are evaluated in terms of the mean, convectively coupled equatorial wave activity, frequency characteristics, diurnal cycle, and seasonality of regional precipitation variability associated with submonthly scale waves. Generally the latest reanalyses such as ERA-Interim, MERRA, and CFSR show better performances than NCEP1 and NCEP2. However, all the reanalyses are still different from observations. Besides the positive mean bias in the reanalyses, a spectral analysis revealed that the reanalyses have overreddened spectra with persistent rainfall. MERRA has the most persistent rainfall, and CFSR appears to have the most realistic variability. The diurnal cycle in NCEP1 is extremely exaggerated relative to TRMM. The low-frequency waves with the period longer than 3 days are relatively well represented in ERA-Interim, MERRA, and CFSR, but all the reanalyses have significant deficiencies in representing convectively coupled equatorial waves and variability in the high-frequency range.

scholarly journals Variation of Radar-Observed Precipitation Characteristics in Relation to the Simultaneous Passages of a Madden-Julian Oscillation Event and Convectively Coupled Equatorial Waves during the Years of the Maritime Continent Pilot Study

2021 ◽  
Author(s):  
Biao Geng ◽  
Masaki Katsumata
Keyword(s):  
Pilot Study ◽  
Low Frequency ◽  
Radar Data ◽  
Frequency Variation ◽  
Equatorial Waves ◽  
Madden Julian Oscillation ◽  
Maritime Continent ◽  
Convectively Coupled Equatorial Waves ◽  
Precipitation Characteristics ◽  
Before And After

AbstractIn this study, we examined the variations of precipitation morphology and rainfall in relation to the simultaneous passages of a Madden-Julian Oscillation (MJO) event and convectively coupled equatorial waves (CCEWs) observed during the Years of the Maritime Continent pilot study. We utilized globally merged infrared brightness temperature data and the radiosonde and radar data observed aboard the research vessel Mirai at 4°4′S, 101°54′E. As well as the observed MJO event, equatorial Rossby waves (ERWs), Kelvin waves (KWs), and mixed Rossby-gravity waves (MRGWs) were identified. The radar data exhibited high-frequency variation, mainly caused by KWs and MRGWs, and low-frequency variation, mainly caused by the MJO and ERWs. The MRGWs predominantly modulated convective echo areas and both convective and stratiform volumetric rainfall. In contrast, the MJO event had little influence on the variance of convective echoes. Moreover, stratiform echo areas and volumetric rainfall were more strongly modulated by the combined effects of the MJO, ERWs, KWs, and MRGWs than their convective counterparts. The intense development of stratiform echo areas and volumetric rainfall was coherent with the superimposition of the active phases of the MJO event and all the analyzed CCEWs. The strongest development and a significant reduction of convective echo-top heights before and after the peak MJO date, respectively, were coherent with the passages of ERWs and MRGWs, which were the dominant wave types in modulating echo-top heights. Thus, it appears that the superimposition of the CCEWs on the MJO event exerted complex modulations on the convective activities within the MJO event.

scholarly journals Differences between Faster versus Slower Components of Convectively Coupled Equatorial Waves

2013 ◽  
Vol 71 (1) ◽  
pp. 98-111 ◽  
Author(s):  
Kazuaki Yasunaga ◽  
Brian Mapes
Keyword(s):  
Gravity Waves ◽  
Tropical Rainfall Measuring Mission ◽  
Space Time ◽  
Equatorial Waves ◽  
Convectively Coupled Equatorial Waves ◽  
Spectral Signal ◽  
Equatorial Wave ◽  
Significant Difference ◽  
Signal Peak ◽  
Inertia Gravity Waves

Abstract This paper describes an analysis of multiyear satellite datasets that subdivide two halves (faster and slower) of the space–time spectral signal peaks corresponding to convectively coupled equatorial waves such as Kelvin and inertia–gravity waves [n = 0 eastward inertia–gravity wave (EIGn0 wave), and n = 1 and n = 2 westward inertia–gravity waves (WIGn1 and WIGn2 waves, respectively)]. The faster (slower) component of an equatorial wave is defined as that which has a spectral signal peak in the regions with deeper (shallower) equivalent depths. The data obtained from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (TRMM-PR) are composited around space–time-filtered equatorial-belt data from the TRMM-3B42 rainfall product to separately estimate the convective and stratiform rainfall modulations. Results indicate that the faster components of WIGn1 and WIGn2 waves modulate convective rain relatively more (and stratiform rain relatively less) than their slower counterparts. For Kelvin and EIGn0 waves, however, there is no significant difference in the rainfall modulation between their faster and slower components. A space–time cospectral analysis of the satellite-retrieved rainfall and moisture shows that in the spectral regions corresponding to WIGn1 and WIGn2 waves, precipitation is significantly correlated with low-level moisture but not with midlevel moisture. In contrast, significant coherence between rainfall and moisture at these levels is found in the spectral regions corresponding to the Kelvin and EIGn0 waves. These results may bear on different convection–wave coupling mechanisms for these “divergent” waves (stratiform instability versus moisture–stratiform instability).

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

2007 ◽  
Vol 64 (10) ◽  
pp. 3406-3423 ◽  
Author(s):  
Gui-Ying Yang ◽  
Brian Hoskins ◽  
Julia Slingo
Keyword(s):  
Composite Structures ◽  
Wave Structure ◽  
Wave Theory ◽  
Western Hemisphere ◽  
Equatorial Waves ◽  
Kelvin Wave ◽  
Ambient Flow ◽  
Convectively Coupled Equatorial Waves ◽  
Eastern Hemisphere ◽  
Equatorial Wave

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.

The Diurnal Cycle of Rainfall and the Convectively Coupled Equatorial Waves over the Maritime Continent

2020 ◽  
Vol 33 (8) ◽  
pp. 3307-3331 ◽  
Author(s):  
Naoko Sakaeda ◽  
George Kiladis ◽  
Juliana Dias
Keyword(s):  
Diurnal Cycle ◽  
Large Scale ◽  
Vertical Motion ◽  
Equatorial Waves ◽  
Maritime Continent ◽  
Moisture Profile ◽  
Convectively Coupled Equatorial Waves ◽  
Large Scale Disturbance ◽  
Diurnal Rainfall ◽  
Equatorial Rossby Waves

AbstractPrecipitation variability over the Maritime Continent is predominantly explained by its diurnal cycle and large-scale disturbances such as the Madden–Julian oscillation (MJO) and convectively coupled equatorial waves (CCEWs). To advance our understanding of their interactions and physical processes, this study uses satellite data to examine changes in the diurnal cycle of rainfall associated with the MJO and CCEWs over the Maritime Continent. We find that diurnal cycle modulations associated with the passage of any type of large-scale disturbance are closely tied to changes in rain types and land–sea diurnal propagation of rainfall. When the amplitude of the diurnal cycle increases over the islands, the phase of the diurnal cycle is delayed by a few hours as clouds are more organized and rainfall from stratiform-anvil clouds increases. Enhanced amplitude of the diurnal cycle can alter the speed of land–sea diurnal propagation of rainfall, which then influences the timing of diurnal rainfall over coastal regions. These changes in the diurnal cycle occur asymmetrically across the island terrain associated with the MJO and equatorial Rossby waves, while such asymmetric modulations are not observed for other waves. Geographical and wave dependencies of the diurnal cycle are linked to differences in large-scale lower tropospheric wind, vertical motion, and moisture profile perturbations, which are in turn tied to differences in cloud population evolution. The results of this study highlight the importance of further improving our understanding of the sensitivity of cloud populations to varying large-scale phenomena.

scholarly journals Comparison of forecasting accuracy for Madden Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEW) using Tropical Rainfall Measuring Mission (TRMM) and ERA-Interim precipitation forecast data for Indonesia

2021 ◽  
Author(s):  
Ida Pramuwardani ◽  
Hartono ◽  
Sunarto ◽  
Arhasena Sopaheluwakan
Keyword(s):  
Tropical Rainfall Measuring Mission ◽  
Forecast Model ◽  
Precipitation Forecast ◽  
Poor Correlation ◽  
Equatorial Waves ◽  
Madden Julian Oscillation ◽  
Tropical Rainfall ◽  
Convectively Coupled Equatorial Waves ◽  
Zonal Wavenumber ◽  
Forecast Data

Tropical Rainfall Measuring Mission (TRMM) and ERA-Interim forecast data analyzed using second-order autoregressive AR(2) and space-time-spectra analysis methods (respectively) revealed contrasting results for predicting Madden Julian Oscillation (MJO) and Convectively Coupled Equatorial Waves (CCEW) phenomena over Indonesia. This research used the same 13-year series of daily TRMM 3B42 V7 derived datasets and ERA-Interim reanalysis model datasets from the European Center for Medium-Range Weather Forecasts (ECMWF) for precipitation forecasts. Three years (2016 to 2018) of the filtered 3B42 and ERA-Interim forecast data was then used to evaluate forecast accuracy by looking at correlation coefficients for forecast leads from day +1 through day +7. The results revealed that rainfall estimation data from 3B42 provides better results for the shorter forecast leads, particularly for MJO, equatorial Rossby (ER), mixed Rossby-gravity (MRG), and inertia-gravity phenomena in zonal wavenumber 1 (IG1), but gives poor correlation for Kelvin waves for all forecast leads. A consistent correlation for all waves was achieved from the filtered ERA-Interim precipitation forecast model, and although this was quite weak for the first forecast leads it did not reach a negative correlation in the later forecast leads except for IG1. Furthermore, Root Mean Square Error (RMSE) was also calculated to complement forecasting skills for both data sources, with the result that residual RMSE for the filtered ERA-Interim precipitation forecast was quite small during all forecast leads and for all wave types. These findings prove that the ERA-Interim precipitation forecast model remains an adequate precipitation model in the tropics for MJO and CCEW forecasting, specifically for Indonesia.

scholarly journals Identifying the MJO, Equatorial Waves, and Their Impacts Using 32 Years of HIRS Upper-Tropospheric Water Vapor

2013 ◽  
Vol 26 (4) ◽  
pp. 1418-1431 ◽  
Author(s):  
Carl J. Schreck ◽  
Lei Shi ◽  
James P. Kossin ◽  
John J. Bates
Keyword(s):  
Water Vapor ◽  
Rossby Waves ◽  
North Pacific Ocean ◽  
Low Frequency ◽  
Longwave Radiation ◽  
Equatorial Waves ◽  
Climate Data ◽  
Convectively Coupled Equatorial Waves ◽  
Intersatellite Calibration ◽  
The Tropics

Abstract The Madden–Julian oscillation (MJO) and convectively coupled equatorial waves are the dominant modes of synoptic-to-subseasonal variability in the tropics. These systems have frequently been examined with proxies for convection such as outgoing longwave radiation (OLR). However, upper-tropospheric water vapor (UTWV) gives a more complete picture of tropical circulations because it is more sensitive to the drying and warming associated with subsidence. Previous studies examined tropical variability using relatively short (3–7 yr) UTWV datasets. Intersatellite calibration of data from the High Resolution Infrared Radiation Sounder (HIRS) has recently produced a homogeneous 32-yr climate data record of UTWV for 200–500 hPa. This study explores the utility of HIRS UTWV for identifying the MJO and equatorial waves. Spectral analysis shows that the MJO and equatorial waves stand out above the low-frequency background in UTWV, similar to previous findings with OLR. The fraction of variance associated with the MJO and equatorial Rossby waves is actually greater in UTWV than in OLR. Kelvin waves, on the other hand, are overshadowed in UTWV by horizontal advection from extratropical Rossby waves. For the MJO, UTWV identifies subsidence drying in the subtropics, poleward of the convection. These dry anomalies are associated with the MJO’s subtropical Rossby gyres. MJO events with dry anomalies over the central North Pacific Ocean also amplify the 200-hPa flow pattern over North America 7 days later. These events cannot be identified using equatorial OLR alone, which demonstrates that UTWV is a useful supplement for identifying the MJO, equatorial waves.

scholarly journals Effect of Overturning Circulation on Long Equatorial Waves: A Low-Frequency Cutoff

2018 ◽  
Vol 75 (5) ◽  
pp. 1721-1739 ◽  
Author(s):  
Amanda Back ◽  
Joseph A. Biello
Keyword(s):  
Large Scale ◽  
Rossby Waves ◽  
Meridional Circulation ◽  
Low Frequency ◽  
Hadley Cell ◽  
Equatorial Waves ◽  
Kelvin Wave ◽  
Background Flow ◽  
Overturning Circulation ◽  
Equatorial Wave

Zonally long tropical waves in the presence of a large-scale meridional and vertical overturning circulation are studied in an idealized model based on the intraseasonal multiscale moist dynamics (IMMD) theory. The model consists of a system of shallow-water equations describing barotropic and first baroclinic vertical modes coupled to one another by the zonally symmetric, time-independent background circulation. To isolate the effects of the meridional circulation alone, an idealized background flow is chosen to mimic the meridional and vertical components of the flow of the Hadley cell; the background flow meridionally converges and rises at the equator. The resulting linear eigenvalue problem is a generalization of the long-wave-scaled version of Matsuno’s equatorial wave problem with the addition of meridional and vertical advection. The results demonstrate that the meridional circulation couples equatorially trapped baroclinic Rossby waves to planetary, barotropic free Rossby waves. The meridional circulation also causes the Kelvin wave to develop an equatorially trapped barotropic component, imparting a westward-tilted vertical structure to the wave. The total energy of the linear system is positive definite, so all waves are shown to be neutrally stable. A critical layer exists at latitudes where the meridional background flow vanishes, resulting in a minimum frequency cutoff for physically feasible waves. Therefore, linear Matsuno waves with periods longer than the vertical transport time of the meridional circulation do not exist in the equatorial waveguide. This implies a low-frequency cutoff for long equatorial waves.

scholarly journals Moist Hadley Circulation: Possible Role of Wave–Convection Coupling in Aquaplanet Experiments

2012 ◽  
Vol 69 (3) ◽  
pp. 891-907 ◽  
Author(s):  
Takeshi Horinouchi
Keyword(s):  
Angular Momentum ◽  
Baroclinic Instability ◽  
Hadley Circulation ◽  
Equatorial Region ◽  
Cumulus Parameterization ◽  
Tropical Precipitation ◽  
Convectively Coupled Equatorial Waves ◽  
Momentum Budget ◽  
Equatorial Wave ◽  
Wide Range

Abstract Aquaplanet simulations for a given sea surface temperature (SST) are conducted to elucidate possible roles of transient variability in the Hadley circulation and the intertropical convergence zone (ITCZ). Their roles are best illustrated with globally uniform SSTs. For such SSTs, an ITCZ and a Hadley circulation that are nearly equatorially symmetric emerge spontaneously. Their strength varies over a wide range from being faint to climatologically significant depending on a tunable parameter of the model’s cumulus parameterization. In some cases asymmetric Hadley circulations formed along with long-lived tropical cyclones. The tunable parameter affects the transient variability of tropical precipitation. In the runs in which well-defined near-symmetric ITCZs formed, tropical precipitation exhibited clear signatures of convectively coupled equatorial waves. The waves can explain the concentration of precipitation to the equatorial region, which induces the Hadley circulation. Also, the meridional structures of simulated ITCZs are consistent with the distribution of convergence/divergence associated with dominant equatorial wave modes. Even when the pole–equator temperature gradient is introduced, the dependence of the strength of the circulation to transient disturbances remains. Therefore, transient variability may have a broader impact on tropical climate and its numerical modeling than has been thought. The reason that a wide variety of circulation is possible when the SST gradient is weak is because the distribution of latent heating can be interactively adjusted while a circulation is formed. Angular momentum budget does not provide an effective thermodynamic constraint, since baroclinic instability redistributes the angular momentum.

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

2007 ◽  
Vol 64 (10) ◽  
pp. 3438-3451 ◽  
Author(s):  
Gui-Ying Yang ◽  
Brian Hoskins ◽  
Julia Slingo
Keyword(s):  
Lower Troposphere ◽  
Wave Activity ◽  
Equatorial Region ◽  
Western Hemisphere ◽  
Equatorial Waves ◽  
Kelvin Wave ◽  
Upper Troposphere ◽  
Convectively Coupled Equatorial Waves ◽  
Eastern Hemisphere ◽  
Equatorial Wave

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.

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