The Impact of MJO, Kelvin, and Equatorial Rossby Waves on the Diurnal Cycle over the Maritime Continent

The impacts of the Madden–Julian Oscillation (MJO), Kelvin waves, and Equatorial Rossby (ER) waves on the diurnal cycle of rainfall and types of deep convection over the Maritime Continent are investigated using rainfall from the Tropical Rainfall Measurement Mission Multisatellite Precipitation Analysis and Infrared Weather States (IR–WS) data from the International Satellite Cloud Climatology Project. In an absolute sense, the MJO produced its strongest modulations of rainfall and organized deep convection over the islands, when and where convection is already strongest. The MJO actually has a greater percentage modulation over the coasts and seas, but it does not affect weaker diurnal cycle there. Isolated deep convection was also more prevalent over land during the suppressed phase, while organized deep convection dominated the enhanced phase, consistent with past work. This study uniquely examined the effects of Kelvin and ER waves on rainfall, convection, and their diurnal cycles over the Maritime Continent. The modulation of convection by Kelvin waves closely mirrored that by the MJO, although the Kelvin wave convection continued farther into the decreasing phase. The signals for ER waves were also similar but less distinct. An improved understanding of how these waves interact with convection could lead to improved subseasonal forecast skill.

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Cycles and Propagation of Deep Convection over Equatorial Africa

Monthly Weather Review ◽

10.1175/2011mwr3500.1 ◽

2011 ◽

Vol 139 (9) ◽

pp. 2832-2853 ◽

Cited By ~ 53

Author(s):

Arlene G. Laing ◽

Richard E. Carbone ◽

Vincenzo Levizzani

Keyword(s):

Deep Convection ◽

Active Phase ◽

Kelvin Waves ◽

Convective Precipitation ◽

Atmospheric Conditions ◽

Kelvin Wave ◽

Mesoscale Convection ◽

Diurnal Cycles ◽

Continental Scale ◽

Equatorial Africa

Long-term statistics of organized convection are vital to improved understanding of the hydrologic cycle at various scales. Satellite observations are used to understand the timing, duration, and frequency of deep convection in equatorial Africa, a region with some of the most intense thunderstorms. Yet little has been published about the propagation characteristics of mesoscale convection in that region. Diurnal, subseasonal, and seasonal cycles of cold cloud (proxy for convective precipitation) are examined on a continental scale. Organized deep convection consists of coherent structures that are characteristic of systems propagating under a broad range of atmospheric conditions. Convection is triggered by heating of elevated terrain, sea/land breezes, and lake breezes. Coherent episodes of convection result from regeneration of convection through multiple diurnal cycles while propagating westward. They have an average 17.6-h duration and 673-km span; most have zonal phase speeds of 8–16 m s−1. Propagating convection occurs in the presence of moderate low-level shear that is associated with the southwesterly monsoonal flow and midlevel easterly jets. Convection is also modulated by eastward-moving equatorially trapped Kelvin waves, which have phase speeds of 12–22 m s−1 over equatorial Africa. Westward propagation of mesoscale convection is interrupted by the dry phase of convectively coupled Kelvin waves. During the wet phase, daily initiation and westward propagation continues within the Kelvin wave and the cold cloud shields are larger. Mesoscale convection is more widespread during the active phase of the Madden–Julian oscillation (MJO) but with limited westward propagation. The study highlights multiscale interaction as a major source of variability in convective precipitation during the critical rainy seasons in equatorial Africa.

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A local-to-large scale view of Maritime Continent rainfall: control by ENSO, MJO and equatorial waves

Journal of Climate ◽

10.1175/jcli-d-21-0263.1 ◽

2021 ◽

pp. 1-52

Author(s):

Simon C. Peatman ◽

Juliane Schwendike ◽

Cathryn E. Birch ◽

John H. Marsham ◽

Adrian J. Matthews ◽

...

Keyword(s):

Diurnal Cycle ◽

Large Scale ◽

Deep Convection ◽

Extreme Rainfall ◽

Equatorial Waves ◽

Maritime Continent ◽

Local Circulation ◽

Wind Regimes ◽

Equatorial Rossby Waves

AbstractThe canonical view of the Maritime Continent (MC) diurnal cycle is deep convection occurring over land during the afternoon and evening, tending to propagate offshore overnight. However, there is considerable day-to-day variability in the convection, and the mechanism of the offshore propagation is not well understood. We test the hypothesis that large-scale drivers such as ENSO, the MJO and equatorial waves, through their modification of the local circulation, can modify the direction or strength of the propagation, or prevent the deep convection from triggering in the first place. Taking a local-to-large scale approach we use in situ observations, satellite data and reanalyses for five MC coastal regions, and show that the occurrence of the diurnal convection and its offshore propagation is closely tied to coastal wind regimes we define using the k-means cluster algorithm. Strong prevailing onshore winds are associated with a suppressed diurnal cycle of precipitation; while prevailing offshore winds are associated with an active diurnal cycle, offshore propagation of convection and a greater risk of extreme rainfall. ENSO, the MJO, equatorial Rossby waves and westward mixed Rossby-gravity waves have varying levels of control over which coastal wind regime occurs, and therefore on precipitation, depending on the MC coastline in question. The large-scale drivers associated with dry and wet regimes are summarised for each location as a reference for forecasters.

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Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-17-793-2017 ◽

2017 ◽

Vol 17 (2) ◽

pp. 793-806 ◽

Cited By ~ 9

Author(s):

Barbara Scherllin-Pirscher ◽

William J. Randel ◽

Joowan Kim

Keyword(s):

Large Scale ◽

Deep Convection ◽

Wave Activity ◽

Kelvin Waves ◽

Temperature Variability ◽

Stationary Waves ◽

Kelvin Wave ◽

Quasi Biennial Oscillation ◽

Tropical Tropopause ◽

Tropopause Region

Abstract. Tropical temperature variability over 10–30 km and associated Kelvin-wave activity are investigated using GPS radio occultation (RO) data from January 2002 to December 2014. RO data are a powerful tool for quantifying tropical temperature oscillations with short vertical wavelengths due to their high vertical resolution and high accuracy and precision. Gridded temperatures from GPS RO show the strongest variability in the tropical tropopause region (on average 3 K2). Large-scale zonal variability is dominated by transient sub-seasonal waves (2 K2), and about half of sub-seasonal variance is explained by eastward-traveling Kelvin waves with periods of 4 to 30 days (1 K2). Quasi-stationary waves associated with the annual cycle and interannual variability contribute about a third (1 K2) to total resolved zonal variance. Sub-seasonal waves, including Kelvin waves, are highly transient in time. Above 20 km, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO) in stratospheric zonal winds, with enhanced wave activity during the westerly shear phase of the QBO. In the tropical tropopause region, however, peaks of Kelvin-wave activity are irregularly distributed in time. Several peaks coincide with maxima of zonal variance in tropospheric deep convection, but other episodes are not evidently related. Further investigations of convective forcing and atmospheric background conditions are needed to better understand variability near the tropopause.

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The Diurnal Cycle of Land–Atmosphere Interactions across Oklahoma’s Winter Wheat Belt

Monthly Weather Review ◽

10.1175/mwr-2842.1 ◽

2005 ◽

Vol 133 (1) ◽

pp. 120-130 ◽

Cited By ~ 15

Author(s):

Matthew J. Haugland ◽

Kenneth C. Crawford

Keyword(s):

Soil Moisture ◽

Winter Wheat ◽

Surface Pressure ◽

Diurnal Cycle ◽

Wheat Crop ◽

Near Surface ◽

Diurnal Cycles ◽

Dewpoint Temperature ◽

Before And After ◽

The Impact

Abstract This manuscript documents the impact of Oklahoma’s winter wheat belt (WWB) on the near-surface atmosphere by comparing the diurnal cycle of meteorological conditions within the WWB relative to conditions in adjacent counties before and after the wheat harvest. To isolate the impact of the winter wheat belt on the atmosphere, data from several meteorological parameters were averaged to create a diurnal cycle before and after the wheat harvest. Observations from 17 Oklahoma Mesonet sites within the WWB (during a period of 9 yr) were compared with observations from 22 Mesonet sites in adjacent counties outside the winter wheat belt. The average diurnal cycles of dewpoint, temperature, and surface pressure exhibited patterns that revealed a distinct mesoscale impact of the wheat fields. The diurnal patterns were consistent with the status of the wheat crop and the grassland in adjacent counties. The impact of the WWB was shown to be more significant during a month when soil moisture was abundant, and minimal during a month when soil moisture was limited. Statistically significant, hydrostatically consistent afternoon surface pressure anomalies suggest that there is a strong possibility of weak mesoscale circulations induced by the WWB.

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Ice injected into the tropopause by deep convection – Part 2: Over the Maritime Continent

10.5194/acp-2019-800 ◽

2019 ◽

Author(s):

Iris-Amata Dion ◽

Cyrille Dallet ◽

Philippe Ricaud ◽

Fabien Carminati ◽

Peter Haynes ◽

...

Keyword(s):

Deep Convection ◽

Companion Paper ◽

Horizontal Resolution ◽

Horizontal Distribution ◽

High Temporal Resolution ◽

Vertical Resolution ◽

Maritime Continent ◽

Diurnal Cycles ◽

Tropical Tropopause ◽

Study Zone

Abstract. The amount of ice injected up to the tropical tropopause layer has a strong radiative impact on climate. In the tropics, the Maritime Continent (MariCont) region presents the largest injection of ice by deep convection into the upper troposphere (UT) and tropopause level (TL) (from results presented in the companion paper Part 1). This study focuses on the MariCont region and aims to assess the processes, the areas and the diurnal amount and duration of ice injected by deep convection over islands and over seas using a 2° × 2° horizontal resolution during the austral convective season of December, January and February. The model presented in the companion paper is used to estimate the amount of ice injected (∆IWC) up to the TL by combining ice water content (IWC) measured twice a day in tropical UT and TL by the Microwave Limb Sounder (MLS; Version 4.2), from 2004 to 2017, and precipitation (Prec) measurement from the Tropical Rainfall Measurement Mission (TRMM; Version 007) at high temporal resolution (1 hour). The horizontal distribution of ∆IWC estimated from Prec (∆IWCPrec) is presented at 2° × 2° horizontal resolution over the MariCont. ∆IWC is also evaluated by using the number of lightnings (Flash) from the TRMM-LIS instrument (Lightning Imaging Sensor, from 2004 to 2015 at 1-h and 0.25° × 0.25° resolutions). ∆IWCPrec and ∆IWC estimated from Flash (∆IWCFlash) are compared to ∆IWC estimated from the ERA5 reanalyses (∆IWCERA5) degrading the vertical resolution to that of MLS observations (). Our study shows that, while the diurnal cycles of Prec and Flash are consistent to each other in timing and phase over lands and different over offshore and coastal areas of the MariCont, the observational ∆IWC range between ∆IWCPrec and ∆IWCFlash is small (to within 4–20 % over land and to within 6–50 % over ocean) in the UT and TL. The reanalysis ∆IWC range between ∆IWCERA5 and has been also found to be small in the UT (22–32 %) but large in the TL (68–71 %), highlighting the stronger impact of the vertical resolution on the TL than in the UT. Combining observational and reanalysis ∆IWC ranges, the total ∆IWC range is estimated in the UT between 4.17 and 9.97 mg m−3 (20 % of variability per study zone) over land and between 0.35 and 4.37 mg m−3 (30 % of variability per study zone) over sea, and, in the TL, between 0.63 and 3.65 mg m−3 (70 % of variability per study zone) over land and between 0.04 and 0.74 mg m−3 (80 % of variability per study zone) over sea. Finally, from IWCERA5, Prec and Flash, this study highlights (1) ∆IWC over land has been found larger than ∆IWC over sea, and (2) the Java Island is the area of the largest ∆IWC in the UT (7.89–8.72 mg m−3 daily mean).

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

Journal of Climate ◽

10.1175/jcli-d-19-0043.1 ◽

2020 ◽

Vol 33 (8) ◽

pp. 3307-3331 ◽

Cited By ~ 3

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.

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Diurnal Cycles of Synthetic Microwave Sounding Lower-Stratospheric Temperatures from Radio Occultation Observations, Reanalysis, and Model Simulations

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-21-0071.1 ◽

2021 ◽

Author(s):

Aodhan J Sweeney ◽

Qiang Fu

Keyword(s):

Diurnal Cycle ◽

Radio Occultation ◽

Lower Stratosphere ◽

Deep Convection ◽

Winter Season ◽

Boreal Winter ◽

Diurnal Cycles ◽

Stratospheric Temperature ◽

Diurnal Range ◽

Microwave Sounding

AbstractAn observationally-based global climatology of the temperature diurnal cycle in the lower stratosphere is derived from eleven different satellites with Global Positioning System-Radio Occultation (GPS-RO) measurements from 2006-2020. Methods used in our analysis allow for accurate characterization of global stratospheric temperature diurnal cycles, even in the high latitudes where the diurnal signal is small but longer timescale variability is large. A climatology of the synthetic Microwave Sounding Unit (MSU) and Advanced MSU (AMSU) Temperature in the Lower Stratosphere (TLS) is presented to assess the accuracy of diurnal cycle climatologies for the MSU and AMSU TLS observations, which have traditionally been generated by model data. The TLS diurnal temperature ranges are typically less than 0.4 K in all latitude bands and seasons investigated. It is shown that the diurnal range (maximum minus minimum temperature) of TLS is largest over southern hemisphere tropical land in the boreal winter season, indicating the important role of deep convection. The range, phase, and seasonality of the TLS diurnal cycle are generally well captured by the WACCM6 simulation and ERA5 reanalysis. We also present an observationally-based diurnal cycle climatology of temperature profiles from 300-10 hPa for various latitude bands and seasons and compare the ERA5 reanalysis with the observations.

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Observed Structure of Convectively Coupled Waves as a Function of Equivalent Depth: Kelvin Waves and the Madden–Julian Oscillation

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-12-03.1 ◽

2012 ◽

Vol 69 (7) ◽

pp. 2097-2106 ◽

Cited By ~ 42

Author(s):

Paul E. Roundy

Keyword(s):

Shallow Water ◽

Deep Convection ◽

Longwave Radiation ◽

Kelvin Waves ◽

Water Model ◽

Madden Julian Oscillation ◽

Kelvin Wave ◽

Easterly Wind ◽

Equivalent Depth ◽

Westerly Winds

Abstract The view that convectively coupled Kelvin waves and the Madden–Julian oscillation (MJO) are distinct modes is tested by regressing data from the Climate Forecast System Reanalysis against satellite outgoing longwave radiation data filtered for particular zonal wavenumbers and frequencies by wavelet analysis. Results confirm that nearly dry Kelvin waves have horizontal structures consistent with their equatorial beta-plane shallow-water-theory counterparts, with westerly winds collocated with the lower-tropospheric ridge, while the MJO and signals along Kelvin wave dispersion curves at low shallow-water-model equivalent depths are characterized by geopotential troughs extending westward from the region of lower-tropospheric easterly wind anomalies through the region of lower-tropospheric westerly winds collocated with deep convection. Results show that as equivalent depth decreases from that of the dry waves (concomitant with intensification of the associated convection), the ridge in the westerlies and the trough in the easterlies shift westward. The analysis therefore demonstrates a continuous field of intermediate structures between the two extremes, suggesting that Kelvin waves and the MJO are not dynamically distinct modes. Instead, signals consistent with Kelvin waves become more consistent with the MJO as the associated convection intensifies. This result depends little on zonal scale. Further analysis also shows how activity in synoptic-scale Kelvin waves characterized by particular phase speeds evolves with the planetary-scale MJO.

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Role of Diurnal Cycle in the Maritime Continent Barrier Effect on MJO Propagation in an AGCM

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-20-0112.1 ◽

2021 ◽

Vol 78 (5) ◽

pp. 1545-1565

Author(s):

R. S. Ajayamohan ◽

Boualem Khouider ◽

V. Praveen ◽

Andrew J. Majda

Keyword(s):

Diurnal Cycle ◽

General Circulation ◽

Dominant Role ◽

Circulation Model ◽

Striking Difference ◽

Barrier Effect ◽

Maritime Continent ◽

Stochastic Case ◽

The Impact

AbstractThe barrier effect of the Maritime Continent (MC) in stalling or modifying the propagation characteristics of the MJO is widely accepted. The strong diurnal cycle of convection over the MC is believed to play a dominant role in this regard. This hypothesis is studied here, with the help of a coarse-resolution atmospheric general circulation model (AGCM). The dry dynamical core of the AGCM is coupled to the multicloud parameterization piggybacked with a dynamical bulk boundary layer model. A set of sensitivity experiments is carried out by systematically varying the strength of the MC diurnal flux to assess the impact of the diurnal convective variability on the MJO propagation. The effects of deterministic and stochastic diurnal forcings on MJO characteristics are compared. It is found that the precipitation and zonal wind variance, on the intraseasonal time scales, over the western Pacific region decreases with the increase in diurnal forcing, indicating the blocking of MC precipitation. An increase in precipitation variance over the MC associated with the weakening of precipitation variance over the west Pacific is evident in all experiments. The striking difference between deterministic and stochastic diurnal forcing experiments is that the strength needed for the deterministic case to achieve the same degree of blocking is almost double that of stochastic case. The stochastic diurnal flux over the MC seems to be more detrimental in blocking the MJO propagation. This hints at the notion that the models with inadequate representation of organized convection tend to suffer from the MC-barrier effect.

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Ice injected into the tropopause by deep convection – Part 2: Over the Maritime Continent

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-2191-2021 ◽

2021 ◽

Vol 21 (3) ◽

pp. 2191-2210

Author(s):

Iris-Amata Dion ◽

Cyrille Dallet ◽

Philippe Ricaud ◽

Fabien Carminati ◽

Thibaut Dauhut ◽

...

Keyword(s):

Water Content ◽

Deep Convection ◽

Companion Paper ◽

Horizontal Resolution ◽

High Temporal Resolution ◽

Vertical Resolution ◽

Maritime Continent ◽

Ice Water Content ◽

Ice Water ◽

The Impact

Abstract. The amount of ice injected into the tropical tropopause layer has a strong radiative impact on climate. A companion paper (Part 1) used the amplitude of the diurnal cycle of ice water content (IWC) as an estimate of ice injection by deep convection, showed that the Maritime Continent (MariCont) region provides the largest injection to the upper troposphere (UT; 146 hPa) and to the tropopause level (TL; 100 hPa). This study focuses on the MariCont region and extends that approach to assess the processes, the areas and the diurnal amount and duration of ice injected over islands and over seas during the austral convective season. The model presented in the companion paper is again used to estimate the amount of ice injected (ΔIWC) by combining ice water content (IWC) measured twice a day by the Microwave Limb Sounder (MLS; Version 4.2) from 2004 to 2017 and precipitation (Prec) measurements from the Tropical Rainfall Measurement Mission (TRMM; Version 007) binned at high temporal resolution (1 h). The horizontal distribution of ΔIWC estimated from Prec (ΔIWCPrec) is presented at 2∘×2∘ horizontal resolution over the MariCont. ΔIWC is also evaluated by using the number of lightning events (Flash) from the TRMM-LIS instrument (Lightning Imaging Sensor, from 2004 to 2015 at 1 h and 0.25∘ × 0.25∘ resolution). ΔIWCPrec and ΔIWC estimated from Flash (ΔIWCFlash) are compared to ΔIWC estimated from the ERA5 reanalyses (ΔIWCERA5) with the vertical resolution degraded to that of MLS observations (ΔIWCERA5). Our study shows that the diurnal cycles of Prec and Flash are consistent with each other in phase over land but different over offshore and coastal areas of the MariCont. The observational ΔIWC range between ΔIWCPrec and ΔIWCFlash, interpreted as the uncertainty of our model in estimating the amount of ice injected, is smaller over land (where ΔIWCPrec and ΔIWCFlash agree to within 22 %) than over ocean (where differences are up to 71 %) in the UT and TL. The impact of the MLS vertical resolution on the estimation of ΔIWC is greater in the TL (difference between ΔIWCERA5 and 〈ΔIWCERA5〉 of 32 % to 139 %, depending on the study zone) than in the UT (difference of 9 % to 33 %). Considering all the methods, in the UT, estimates of ΔIWC span 4.2 to 10.0 mg m−3 over land and 0.4 to 4.4 mg m−3 over sea, and in the TL estimates of ΔIWC span 0.5 to 3.9 mg m−3 over land and 0.1 to 0.7 mg m−3 over sea. Finally, based on IWC from MLS and ERA5, Prec and Flash, this study highlights that (1) at both levels, ΔIWC estimated over land can be more than twice that estimated over sea and (2) small islands with high topography present the largest ΔIWC (e.g., island of Java).

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