Scale Interactions between the MJO and the Western Maritime Continent

Abstract State-of-the-art regional climate model simulations that are able to resolve key mesoscale circulations are used, for the first time, to understand the interaction between the large-scale convective environment of the MJO and processes governing the strong diurnal cycle over the islands of the Maritime Continent (MC). Convection is sustained in the late afternoon just inland of the coasts because of sea breeze convergence. Previous work has shown that the variability in MC rainfall associated with the MJO is manifested in changes to this diurnal cycle; land-based rainfall peaks before the active convective envelope of the MJO reaches the MC, whereas oceanic rainfall rates peak while the active envelope resides over the region. The model simulations show that the main controls on oceanic MC rainfall in the early active MJO phases are the large-scale environment and atmospheric stability, followed by high oceanic latent heat flux forced by high near-surface winds in the later active MJO phases. Over land, rainfall peaks before the main convective envelope arrives (in agreement with observations), even though the large-scale convective environment is only moderately favorable for convection. The causes of this early rainfall peak are strong convective triggers from land–sea breeze circulations that result from high surface insolation and surface heating. During the peak MJO phases cloud cover increases and surface insolation decreases, which weakens the strength of the mesoscale circulations and reduces land-based rainfall, even though the large-scale environment remains favorable for convection at this time. Hence, scale interactions are an essential part of the MJO transition across the MC.

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Diurnal cycle of precipitation and near-surface atmospheric conditions over the maritime continent: land–sea contrast and impacts of ambient winds in cloud-permitting simulations

Climate Dynamics ◽

10.1007/s00382-021-06012-3 ◽

2021 ◽

Author(s):

Yuntao Wei ◽

Zhaoxia Pu

Keyword(s):

Diurnal Cycle ◽

Large Scale ◽

Deep Convection ◽

Vertical Motion ◽

Sea Breeze ◽

Return Flow ◽

Atmospheric Conditions ◽

Maritime Continent ◽

Regional Variability ◽

Near Surface

AbstractA set of cloud-permitting-scale numerical simulations during January–February 2018 is used to examine the diurnal cycle (DC) of precipitation and near-surface variables (e.g., 2 m temperature, 10 m wind and convergence) over the Indo-Pacific Maritime Continent under the impacts of shore-orthogonal ambient winds (SOAWs). It is found that the DC of these variables and their variabilities of daily maxima, minima, and diurnal amplitudes vary over land, sea, and coastal regions. Among all variables, the DC of precipitation has the highest linear correlation with near-surface convergence (near-surface temperature) over coastal (noncoastal) regions. The correlations among the DCs of precipitation, wind, and heating are greater over the ocean than over land. Sine curves can model accurately the DCs of most variables over the ocean, but not over land. SOAWs act to influence the DC mainly by affecting the diurnal amplitude of the considered variables, with DC being stronger under more strengthened offshore SOAWs, though variable dependence and regional variability exist. Composite analysis over Sumatra reveals that under weak SOAWs, shallow clouds are dominant and cause a pre-moistening effect, supporting shallow-to-deep convection transition. A sea breeze circulation (SBC) with return flow aloft can develop rapidly. Cold pools are better able to trigger new updrafts and contribute to the upscale growth and inland migration of deep convection. In addition, warm gravity waves can propagate upward throughout the troposphere, thereby supporting a strong DC. In contrast, under strong SOAWs, both shallow and middle-high clouds prevail and persist throughout the day. The evolution of moistening and SBC is reduced, leading to weak variation in vertical motion and rainwater confined to the boundary layer. Large-scale winds, moisture, and convection are discussed to interpret how strong SOAWs affect the DC of Sumatra.

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MJO-Induced Variability of the Diurnal Cycle of Precipitation over the Maritime Continent

10.5194/egusphere-egu2020-19432 ◽

2020 ◽

Author(s):

Ajda Savarin ◽

Shuyi Chen

Keyword(s):

Diurnal Cycle ◽

Large Scale ◽

Complex Nature ◽

Madden Julian Oscillation ◽

Maritime Continent ◽

Convective Envelope ◽

Modes Of Variability ◽

Complex Interactions ◽

The Indian Ocean ◽

The Western Pacific

Large-scale convection associated with the Madden-Julian Oscillation (MJO) initiates over the Indian Ocean and propagates eastward across the Maritime Continent (MC) into the western Pacific. As an MJO enters the MC, it often weakens or completely dissipates due to complex interactions between the large-scale MJO and the MC landmass and its topography. This is referred to as the MC barrier effect, and it is responsible for the dissipation of 40-50% of observed MJO events. One of the main reasons for the MJO&#8217;s weakening and dissipation over the MC is the diurnal cycle (DC), one of the strongest modes of variability in the region. Due to the complex nature of the MJO and the MC&#8217;s complicated topography, the interaction between the DC and the MJO is not well understood.In this study, we examine the MJO-induced variability of the DC of precipitation over the MC. We use gridded satellite precipitation products (TRMM 3B42 and GPM IMERG) to: (1) track the MJO convective envelope using the Large-scale Precipitation Tracking algorithm (LPT), (2) analyze the changes in the DC of precipitation over the MC relative to the passage of the MJO. We find that the presence of an MJO not only increases the amount of precipitation over the MC, but that the increase is more pronounced over water than over land. The results from observations are compared to those from two reanalysis datasets (ERA5, MERRA-2). The reanalysis datasets are then used to examine the dynamic and thermodynamic changes that drive the variability in the DC of precipitation relative to the MJO. In addition, we separate MJO events into two groups based on whether they cross the MC, and independently examine their influences on the evolution of the DC of precipitation.

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Detecting and Tracking Coastal Precipitation in the Tropics: Methods and Insights into Multiscale Variability of Tropical Precipitation

Journal of Climate ◽

10.1175/jcli-d-19-0321.1 ◽

2020 ◽

Vol 33 (15) ◽

pp. 6689-6705

Author(s):

David Coppin ◽

Gilles Bellon ◽

Alexander Pletzer ◽

Chris Scott

Keyword(s):

Diurnal Cycle ◽

Large Scale ◽

Madden Julian Oscillation ◽

Maritime Continent ◽

Total Rainfall ◽

Tropical Precipitation ◽

Precipitation Estimates ◽

Summer Hemisphere ◽

The Tropics ◽

Climate Prediction Center

AbstractWe propose an algorithm to detect and track coastal precipitation systems and we apply it to 18 years of the high-resolution (8 km and 30 min) Climate Prediction Center CMORPH precipitation estimates in the tropics. Coastal precipitation in the Maritime Continent and Central America contributes to up to 80% of the total rainfall. It also contributes strongly to the diurnal cycle over land with the largest contribution from systems lasting between 6 and 12 h and contributions from longer-lived systems peaking later in the day. While the diurnal cycle of coastal precipitation is more intense over land in the summer hemisphere, its timing is independent of seasons over both land and ocean because the relative contributions from systems of different lifespans are insensitive to the seasonal cycle. We investigate the hypothesis that coastal precipitation is enhanced prior to the arrival of the Madden–Julian oscillation (MJO) envelope over the Maritime Continent. Our results support this hypothesis and show that, when considering only coastal precipitation, the diurnal cycle appears reinforced even earlier over islands than previously reported. We discuss the respective roles of coastal and large-scale precipitation in the propagation of the MJO over the Maritime Continent. We also document a shift in diurnal cycle with the phases of the MJO, which results from changes in the relative contributions of short-lived versus long-lived coastal systems.

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Diurnal and Seasonal Lightning Variability over the Gulf Stream and the Gulf of Mexico

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-14-0233.1 ◽

2015 ◽

Vol 72 (7) ◽

pp. 2657-2665 ◽

Cited By ~ 17

Author(s):

Katrina S. Virts ◽

John M. Wallace ◽

Michael L. Hutchins ◽

Robert H. Holzworth

Keyword(s):

Gulf Of Mexico ◽

Diurnal Cycle ◽

Gulf Stream ◽

Land Surface ◽

Southeastern United States ◽

Surface Wind ◽

Tropical Rainfall Measuring Mission ◽

Sea Breeze ◽

Near Surface ◽

Early Evening

Recent observations from the World Wide Lightning Location Network (WWLLN) reveal a pronounced lightning maximum over the warm waters of the Gulf Stream that exhibits distinct diurnal and seasonal variability. Lightning is most frequent during summer (June–August). During afternoon and early evening, lightning is enhanced just onshore of the coast of the southeastern United States because of daytime heating of the land surface and the resulting sea-breeze circulations and convection. Near-surface wind observations from the Quick Scatterometer (QuikSCAT) satellite indicate divergence over the Gulf of Mexico and portions of the Gulf Stream at 1800 LT, at which time lightning activity is suppressed there. Lightning frequency exhibits a broad maximum over the Gulf Stream from evening through noon of the following day, and QuikSCAT wind observations at 0600 LT indicate low-level winds blowing away from the continent and converging over the Gulf Stream. Over the northern Gulf of Mexico, lightning is most frequent from around sunrise through late morning. During winter, lightning exhibits a weak diurnal cycle over the Gulf Stream, with most frequent lightning during the evening. Precipitation rates from a 3-hourly gridded dataset that incorporates observations from Tropical Rainfall Measuring Mission (TRMM), as well as other satellites, exhibit a diurnal cycle over the Gulf Stream that lags the lightning diurnal cycle by several hours.

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Intraseasonal Variability of the Diurnal Cycle of Precipitation in the Philippines

Journal of the Atmospheric Sciences ◽

10.1175/jas-d-19-0152.1 ◽

2019 ◽

Vol 76 (11) ◽

pp. 3633-3654 ◽

Cited By ~ 2

Author(s):

Michael B. Natoli ◽

Eric D. Maloney

Keyword(s):

Diurnal Cycle ◽

Coastal Waters ◽

Intraseasonal Oscillation ◽

Sea Breeze ◽

Active Phase ◽

The Philippines ◽

Boreal Summer ◽

Breeze Circulation ◽

Convective Envelope ◽

Cycle Amplitude

Abstract Precipitation in the region surrounding the South China Sea over land and coastal waters exhibits a strong diurnal cycle associated with a land–sea temperature contrast that drives a sea-breeze circulation. The boreal summer intraseasonal oscillation (BSISO) is an important modulator of diurnal precipitation patterns, an understanding of which is a primary goal of the field campaign Propagation of Intraseasonal Tropical Oscillations (PISTON). Using 21 years of CMORPH precipitation for Luzon Island in the northern Philippines, it is shown that the diurnal cycle amplitude is generally maximized over land roughly 1 week before the arrival of the broader oceanic convective envelope associated with the BSISO. A strong diurnal cycle in coastal waters is observed in the transition from the inactive to active phase, associated with offshore propagation of the diurnal cycle. The diurnal cycle amplitude is in phase with daily mean precipitation over Mindanao but is nearly out of phase over Luzon. The BSISO influence on the diurnal cycle on the eastern side of topography is nearly opposite to that on the western side. Using wind, moisture, and radiation products from the ERA5 reanalysis, it is proposed that the enhanced diurnal cycle west of the mountains during BSISO suppressed phases is related to increased insolation and weaker prevailing onshore winds that promote a stronger sea-breeze circulation when compared with the May–October mean state. Offshore propagation is suppressed until ambient midlevel moisture increases over the surrounding oceans during the transition to the active BSISO phase. In BSISO enhanced phases, strong low-level winds and increased cloudiness suppress the sea-breeze circulation.

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Interannual Variability in the Large-Scale Dynamics of the South Asian Summer Monsoon

Journal of Climate ◽

10.1175/jcli-d-14-00612.1 ◽

2015 ◽

Vol 28 (9) ◽

pp. 3731-3750 ◽

Cited By ~ 22

Author(s):

Jennifer M. Walker ◽

Simona Bordoni ◽

Tapio Schneider

Keyword(s):

Interannual Variability ◽

South Asian ◽

Summer Monsoon ◽

Large Scale ◽

Asian Summer Monsoon ◽

Sea Breeze ◽

South Asian Summer Monsoon ◽

The South ◽

Near Surface ◽

Asian Summer

Abstract This study identifies coherent and robust large-scale atmospheric patterns of interannual variability of the South Asian summer monsoon (SASM) in observational data. A decomposition of the water vapor budget into dynamic and thermodynamic components shows that interannual variability of SASM net precipitation (P − E) is primarily caused by variations in winds rather than in moisture. Linear regression analyses reveal that strong monsoons are distinguished from weak monsoons by a northward expansion of the cross-equatorial monsoonal circulation, with increased precipitation in the ascending branch. Interestingly, and in disagreement with the view of monsoons as large-scale sea-breeze circulations, strong monsoons are associated with a decreased meridional gradient in the near-surface atmospheric temperature in the SASM region. Teleconnections exist from the SASM region to the Southern Hemisphere, whose midlatitude poleward eddy energy flux correlates with monsoon strength. Possible implications of these teleconnection patterns for understanding SASM interannual variability are discussed.

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Influence of ENSO on the Diurnal Cycle of Rainfall over the Maritime Continent and Australia

Journal of Climate ◽

10.1175/jcli-d-12-00124.1 ◽

2013 ◽

Vol 26 (4) ◽

pp. 1304-1321 ◽

Cited By ~ 34

Author(s):

Surendra P. Rauniyar ◽

Kevin J. E. Walsh

Keyword(s):

Diurnal Cycle ◽

El Niño ◽

Large Scale ◽

El Nino ◽

Walker Circulation ◽

La Niña ◽

Boreal Winter ◽

Maritime Continent ◽

La Nina ◽

Rainfall Anomalies

Abstract This study examines the influence of ENSO on the diurnal cycle of rainfall during boreal winter for the period 1998–2010 over the Maritime Continent (MC) and Australia using Tropical Rainfall Measuring Mission (TRMM) and reanalysis data. The diurnal cycles are composited for the ENSO cold (La Niña) and warm (El Niño) phases. The k-means clustering technique is then applied to group the TRMM data into six clusters, each with a distinct diurnal cycle. Despite the alternating patterns of widespread large-scale subsidence and ascent associated with the Walker circulation, which dominates the climate over the MC during the opposing phases of ENSO, many of the islands of the MC show localized differences in rainfall anomalies that depend on the local geography and orography. While ocean regions mostly experience positive rainfall anomalies during La Niña, some local regions over the islands have more rainfall during El Niño. These local features are also associated with anomalies in the amplitude and characteristics of the diurnal cycle in these regions. These differences are also well depicted in large-scale dynamical fields derived from the interim ECMWF Re-Analysis (ERA-Interim).

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An oceanic pathway for Madden–Julian Oscillation influence on Maritime Continent Tropical Cyclones

npj Climate and Atmospheric Science ◽

10.1038/s41612-021-00208-4 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Karthik Balaguru ◽

L. Ruby Leung ◽

Samson M. Hagos ◽

Sujith Krishnakumar

Keyword(s):

Numerical Model ◽

Tropical Cyclones ◽

Large Scale ◽

Sea Surface ◽

Madden Julian Oscillation ◽

Surface Cooling ◽

Maritime Continent ◽

Large Scale Circulation ◽

Model Simulations ◽

Sea Surface Cooling

AbstractWhile the Madden–Julian Oscillation (MJO) has been shown to affect tropical cyclones (TCs) worldwide through its modulation of large-scale circulation in the atmosphere, little or no role for the ocean has been identified to date in this influence of MJO on TCs. Using observations and numerical model simulations, we demonstrate that MJO events substantially impact TCs over the Maritime Continent (MC) region through an oceanic pathway. While propagating across the MC region, MJO events cause significant sea surface cooling with an area-averaged value of about 0.35 ± 0.12 °C. Hence, TCs over the MC region immediately following the passage of MJO events encounter considerably cooler sea surface temperatures. Consequently, the enthalpy fluxes under the storms are reduced and the intensification rates decrease by more than 50% on average. These results highlight an important role played by the ocean in facilitating MJO-induced sub-seasonal variability in TC activity over the MC region.

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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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Precipitation scaling in the tropics with a convection-permitting model

10.5194/egusphere-egu2020-6890 ◽

2020 ◽

Author(s):

Daniel Argüeso ◽

Alejandro Di Luca ◽

Nicolas Jourdain ◽

Romualdo Romero ◽

Victor Homar

Keyword(s):

Water Vapor ◽

Large Scale ◽

Potential Temperature ◽

Lower Troposphere ◽

Dew Point ◽

Precipitation Extremes ◽

Maritime Continent ◽

Near Surface ◽

Intense Precipitation ◽

Precipitation Events

The Maritime Continent is a major convective area and precipitation processes in the region pose great challenges to atmospheric models. A combination of large-scale drivers, such as the Madden-Julian Oscillation and ENSO, and fine-scale processes, such as orographically-forced precipitation, land-sea circulations and tropical convection, governs rainfall in the Maritime Continent. The use of convection-permitting models in the region has shown improved performance in the simulation of precipitation characteristics that are key for the region (i.e. diurnal cycle).Most of the rainfall occurring over land is concentrated in the late afternoon and precipitation extremes often occur over short periods of time. The availability of water vapor in the lower troposphere and the high water-holding capacity of a warm atmosphere favors very intense precipitation events, according to the Clausius-Clapeyron relationship. In a warming climate, a full understanding of the so-called precipitation scaling with temperature is thus crucial. However, this potential generally requires the atmosphere be saturated and convection be initiated to become effective. Using a regional climate model operating at convection-permitting scales over 3 consecutive wet seasons, we investigate the response of intense precipitation to temperature.In this presentation, we examine different approaches to relate precipitation extremes to near-surface temperature and dew-point temperature. We show that the relationship breaks at certain thresholds that are relatively uniform across islands. The region is well supplied with water vapor and the break is not explained by a deficit in water vapor, unlike previously proposed for other water-limited regions. We identify possible reasons for this behavior, such as the lack of environmental conditions that trigger convection. In this context, we explore the sensitivity of the modelling system to the convection representation (explicit vs. parameterized) and discuss the implications for future changes in intense precipitation events. Finally, we put forward the use of specific variables, such as temperature and equivalent potential temperature integrated in the vertical. These variables not only are coherent with the CC equation but also acknowledge the different warming rates near the surface and at higher tropospheric levels, where precipitating processes actually occur.

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