Fig 1 - available via license: CC BY
Content may be subject to copyright.
Topography of Sumatra Island and its surroundings and the locations of Bengkulu Meteorological Observatory (cross) and the research vessel Mirai (closed circle). Shading denotes terrain elevation. MSL is meters above sea level
Source publication
The land-sea surface temperature contrast on the western coast of Sumatra Island was examined using observation data obtained from the pre-Years of the Maritime Continent (YMC) field campaign from November to December 2015. Surface observations showed that, on most days, strong daytime solar radiation caused a pronounced diurnal cycle in surface ai...
Context in source publication
Context 1
... observations were conducted at Bengkulu on the western coast of Sumatra Island, and ship-based observations were conducted over the sea 50 km off the western coast (Fig. 1). Surface meteorological observa- tions, radar observations, and balloon soundings at inter- vals of 3 h were performed at Bengkulu Meteorological Observatory for 47 successive days from 9 November to 25 December 2015. The observation site is located on the coastal plain about 4 km from the shore, at an elevation of 16 m above sea level. Surface meteorological variables, including atmospheric pressure, temperature, relative humidity, wind direction and speed, rainfall, and global solar radiation, were measured at intervals of 1 min using an automatic weather station (MAWS 201, Vaisala, Finland). Rainfall was measured by a tipping bucket rain gauge, with a sensitivity of 1 tip per 0.2 ...
Similar publications
A 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 t...
Citations
... Range. The study was conducted from August to November 2021 in three locations with different elevations in Bengkulu Province, namely the coastland of Bengkulu City (10 m), the midland of Kepahiang Regency (600 m), and the highland of Rejang Lebong Regency (1050 m). Figure 4, as adapted from Wu et al. (2018) shows the geographical position of the experimental sites. The weather data during the growing season for each location are presented in Suppl Table 1 and summarized in Table 4, indicating that temperature was the main discriminating weather component among the locations. ...
Temperature plays a determinant role in the rate of plant metabolic activities and, accordingly, dictates the plant's phenological stages, growth, and productivity. The objective of this study was to evaluate the phenological, growth, and ear yield behavior of ten sweet corn hybrids in response to elevational temperature changes in the humid tropics. Seeds of ten hybrids were grown in three elevations (coastland, midland, and highland). Results show that the hybrids belonged to the same maturity group with comparable accumulated growing degree days, but they varied in green ear yield, harvest index, and heat use efficiency. It was also found that higher elevations lead to longer plant growth and fewer growing degree-day requirements, resulting in increased in biomass accumulation for ear and overall vegetative growth but more efficient in the heat use. These findings will be useful as a guide for crop management scheduling, including fertilizers application, pest control, diseases control, and weed control, to maximize sweet corn yield at different elevations in the humid tropics.
... The intensity of CAPE during AMJO was lower than the mean, especially during the day (Fig. 3a). This result is consistent with that of Wu et al. (2018), who found that during the active MJO, afternoon convection over the island was suppressed because of strong prevailing winds and lower solar insolation. The result is also supported by Zhao et al. (2022), who found that during the active MJO, afternoon convection over the island was delayed and suppressed, and midnight convection was also suppressed. ...
This study aims to investigate the effect of large-scale phenomena, particularly Cross Equatorial Northerly Surge (CENS) and Madden–Julian Oscillation (MJO), on the diurnal cycle of local convection, moisture convergence, and rainfall over the land, coast, and sea in the western part of Java Island. The data used in this study were the CENS and MJO indices, Convective Available Potential Energy (CAPE), convective inhibition (CINH), Vertically Integrated Moisture Flux Convergence (VIMFC), and rainfall from atmospheric reanalysis of the global climate (ERA-5) for 18 years (2001–2018). The average diurnal profiles of CAPE, CINH, VIMFC, and rainfall over five different locations (mountain, coastal land, coast, coastal sea, non-coastal sea) were plotted to see their patterns under five different large-scale conditions: CENS, Active MJO (AMJO), CENS + Active MJO (CAMJO), CENS + Inactive MJO (CIMJO), and the mean condition. The results showed a distinctive and regular character of diurnal profiles of CAPE, CINH, VIMFC, and rainfall in the five locations caused by the specific responses of different underlying surface properties to the diurnal cycle of incoming solar radiation. Furthermore, CENS tended to reduce CAPE (~ 33% reduction, averaged over all locations), which might suppress free (natural) convection. CENS also tended to reduce CINH (~ 41%), which might facilitate convection. Conversely, CENS tended to increase VIMFC significantly (~ 174%), probably through its interaction with the land breezes, which could induce forced convection. As a result, rainfall significantly increased (~ 63%) during CENS. AMJO showed similar effects to CENS but with much weaker influences. On average, AMJO reduced CAPE (~ 14%), slightly reduced CINH (~ 2%), increased VIMFC (~ 28%), and slightly reduced rainfall (~ 3%). However, the effects were the strongest when CENS and AMJO coincided (CAMJO), during which CAPE reduced (~ 37%), CINH reduced (~ 31%), VIMFC increased (~ 334%), and rainfall increased (~ 123%). The effect of CENS and AMJO was strongest over the coastal area, where rainfall increased by ~ 215%. Therefore, one of the most important results from this study was that the increase in rainfall during CENS and AMJO was not caused primarily by the increase of free convection (indicated by the CAPE), which tended to decrease. The increase of rainfall during CENS and AMJO was found mainly due to the increase of moisture convergence (indicated by the VIMFC), which might induce forced convection. We also found that a relatively high value of CINH tended to coincide with a lower value of rainfall, indicating a possible role of CINH in preventing convection. The results of the analysis of the effects of CENS and MJO on the diurnal cycle of CAPE, CINH, and VIMFC have given a better understanding of the detailed mechanisms that produce rainfall increase, which have not been much discussed in previous studies. During CENS/MJO, CAPE decreased, so its role was reducing free convection. CINH also generally decreased, so its role was increasing the potential for convective initiation. VIMFC tended to increase significantly, especially around the coast, so its role was increasing the potential for convection. The role of VIMFC tended to be dominant in increasing rainfall. Conversely, the role of CAPE was less important since it was reduced. The effects of MJO were similar to but weaker than CENS in reducing CAPE, reducing CINH, and increasing VIMFC.
... The soil skin temperature at a given instant is the result of a balance between the net radiative flux, vertical heat flux (sensible and latent heat flux), and ground heat flux, while the near-surface air temperature depends on the soil skin temperature and sensible heat flux (Fan et al. 2019;Liu and Pu 2019). In addition to the above, over coastal regions, the advection of marine air can significantly reduce the air temperature (Wang et al. 2017;Wu et al. 2018;Reddy et al. 2020). Studies on the variability of ABL height carried out using the National Oceanic and Atmospheric Administration (NOAA) wind-profiler network data showed a significant dependence of ABL height on surface temperature and moisture content, with a deeper ABL for warmer and drier areas (Molod et al. 2015). ...
... The results presented here are in agreement with the observations carried out at several coastal regions in the world, though the magnitude of the impacts vary (Kuwagata et al. 1994;Wang et al. 2017;Wu et al. 2018;Anjos and Lopes 2019). Over the south-east coast of the Indian Peninsula, observations suggest that T air continues to increase till about 1400-1500 LT (in phase with soil temperature) when the sea breeze onset is late (post-noon), while it shows a broad peak during 1200-1400 LT when sea-breeze onset occurs by 0900 LT (Reddy et al. 2020). ...
The height of the atmospheric boundary layer (ABL) plays a crucial role in the vertical transport of energy, moisture, and pollutants from the surface. We investigate the development of the convective ABL (CABL) height over a tropical coastal station and quantify its variations with the shortwave radiative flux, near-surface air temperature (Tair), soil skin temperature, soil moisture content, lower tropospheric thermal structure, and virtual potential temperature lapse rate (VPLR) during onshore and offshore flows, based on multi-year (2012–2017) observations carried out using a microwave radiometer profiler and in situ probes at Thumba (8.5° N, 77° E), located in the south-west of Indian Peninsula. The maximum CABL height increases linearly with the VPLR at the rate of 140 to 200 m per °C km⁻¹ (correlation coefficient of 0.82 to 0.92) during different seasons. The delayed onset of daytime onshore flow results in a greater CABL height as continental conditions persist longer, allowing more CABL growth, whereas the earlier arrival of the onshore flow leads to early development of a thermal internal boundary layer with a lower CABL height. When offshore flow prevails, the CABL develops like the continental CABL, with a peak CABL height greater than that during onshore flow by about 300 m. The onset of onshore flow lowers the daytime increase in Tair by about 2 °C. Such quantifications for distinct flow conditions are very sparse over tropical coastal regions and would be useful for understanding coastal air-pollution dispersal as well as validation and improvements in numerical modelling of the CABL under different wind conditions.
... 3a and 3c). Meanwhile, the solar radiation reduced about 30% at Bengkulu and even became only one-third of its previous level over the sea as we observed aboard the R/V Mirai (e.g., Wu et al. 2018;Suzuki et al. 2018). However, due to the larger heat capacity of the water, the temperature over the land and the sea experienced similar reductions, resulting in the similar diurnal amplitude of the land-sea temperature contrast as the PRE period (but was 12 File generated with AMS Word template 2.0 ...
... Prior to the MJO, convection was initiated over the mountainous areas of the island in the afternoon (06 UTC/13 LT), while the peak precipitation over mountains was observed a few hours later at approximately 09 UTC (16 LT; Fig. 8e). Then, mountainous convection migrated offshore toward the sea in the subsequent late afternoon to evening hours, presenting a typical pattern of the diurnal cycle of convection over the western coast of Sumatra Island (Wu et al. 2017(Wu et al. , 2018Yokoi et al. 2017). As a result, the precipitation over the land decreased during the evening but increased over the sea (see solid lines in Figs. ...
This study investigated the diurnal cycle of convection over Sumatra Island in an active phase of the Madden-Julian Oscillation (MJO) during the Pre-Years of the Maritime Continent (YMC) observation campaign in December 2015 based on in-situ and satellite observations and a convection-permitting numerical model. Observations suggest that before the active phase of the MJO in early December, convection occurred frequently over the island during the afternoon and at midnight. By contrast, during the active phase of the MJO in mid-December, afternoon convection over the island was delayed and suppressed, and midnight convection was suppressed. Numerical experiments also successfully replicated the main features of the observed modulations. In general, during the active phase of the MJO, the troposphere became drier in the Sumatra region. While the clouds reduced the solar radiation over the land, the sea breeze was also found to be delayed and weakened. As a result, the afternoon convection initiation was delayed and weakened. Further analyses suggested that the sea breeze was weakened mainly due to the orographic stagnation effect rather than the slightly reduced land-sea temperature contrast. On the other hand, the increased stratiform-anvil clouds induced the anomalous evaporative cooling in the mid-troposphere and generated island-scale subsidence during the nighttime, which finally led to the suppression of inland convection. Overall, our study reveals the modulation of diurnal convection over Sumatra Island by an active phase of the MJO and also shows the potential role of land-sea interaction in convection initiation and maintenance.
... With few YMC field campaigns conducted and others still pending, the limited in situ observations available from YMC start to provide detailed depictions of MJO modulations of the local diurnal cycle (P. Wu et al., 2017Wu et al., , 2018Yokoi et al., 2017Yokoi et al., , 2019, oceanic barrier layers (Moteki et al., 2018), andCCEWs (Kubokawa et al., 2016;Takasuka et al., 2019) over the MC region. With the progress of YMC, these observations will provide unprecedented data sets to identify model deficiencies in representing MC-MJO interactions and to advance our understanding and prediction of MC weather-climate systems and their remote teleconnections. ...
Plain Language Summary
The Madden‐Julian Oscillation (MJO), first discovered by Madden and Julian in 1971, is a prominent tropical phenomenon with a typical period of 30–60 days and featured by a large‐scale envelope of cloud clusters and rain systems moving eastward along the equator. The MJO significantly influences not only intense tropical rainstorms, such as hurricanes, but also extreme weather over the middle to high latitudes. Skillful prediction of the MJO several weeks ahead, therefore, will be greatly valuable for disaster mitigation purposes. However, many present‐day climate models have great difficulty in realistically simulating the MJO for reasons that are not well understood. This article provides a comprehensive review of the recent progress in the observational, modeling, and theoretical study of the MJO, with a particular focus on the most recent decade. Several future research directions are also suggested to further advance our understanding and prediction capability of the MJO.
... This asymmetric temperature cycle seems consistent with the diurnal cycle rainfall being heavier in the morning on the sea-side than in the evening on the land-side (contrary to the cloud top height shown in Fig. 6) as observed in various coastal areas (Sumatera, Jawa, and Kalimantan) over the IMC (Mori et al. 2004. For the case shown in Fig. 9, detailed features including those associated with an MJO landing are also shown elsewhere (Wu et al. , 2018Yokoi et al. 2017). On land, these processes lead to rapid land/hydrosphere −atmosphere water exchange (Sulistyowati et al. 2014) and local air pollutant washout. ...
... In the next step called Years of the Maritime Continent (YMC; 2017−9), Indonesia as a G20 country should take observations under a more completely multinational framework (see YMC (Years of the Maritime Continent) 2017). As a preliminary activity, pre-YMC campaign observations have been carried out in and off Bengkulu (Wu et al. , 2018Yokoi et al. 2017), which is located about 400 km south of Padang (Sumatera Barat area in Table 2). The Bengkulu area has not yet been observed well and is almost free from small islands distributed off Padang. ...
... The abscissas of b−d are in UT (= LT−7 h). Details of the observations are described inYokoi et al. (2017) andWu et al. (2018) mean value of 2700 mm/year ≈ 7 mm/day (see IPCC report values in ...
During the Monsoon Asian Hydro−Atmosphere Scientific Research and Prediction Initiative (MAHASRI; 2006–16), we carried out two projects over the Indonesian maritime continent (IMC), constructing the Hydrometeorological Array for Intraseasonal Variation−Monsoon Automonitoring (HARIMAU; 2005–10) radar network and setting up a prototype institute for climate studies, the Maritime Continent Center of Excellence (MCCOE; 2009–14). Here, we review the climatological features of the world’s largest “regional” rainfall over the IMC studied in these projects. The fundamental mode of atmospheric variability over the IMC is the diurnal cycle generated along coastlines by land−sea temperature contrast: afternoon land becomes hotter than sea by clear-sky insolation before noon, with the opposite contrast before sunrise caused by evening rainfall-induced “sprinkler”-like land cooling (different from the extratropical infrared cooling on clear nights). Thus, unlike the extratropics, the diurnal cycle over the IMC is more important in the rainy season. The intraseasonal, seasonal to annual, and interannual climate variabilities appear as amplitude modulations of the diurnal cycle. For example, in Jawa and Bali the rainy season is the southern hemispheric summer, because land heating in the clear morning and water vapor transport by afternoon sea breeze is strongest in the season of maximum insolation. During El Niño, cooler sea water surrounding the IMC makes morning maritime convection and rainfall weaker than normal. Because the diurnal cycle is almost the only mechanism generating convective clouds systematically near the equator with little cyclone activity, the local annual rainfall amount in the tropics is a steeply decreasing function of coastal distance (e-folding scale 100–300 km), and regional annual rainfall is an increasing function of “coastline density” (coastal length/land area) measured at a horizontal resolution of 100 km. The coastline density effect explains why rainfall and latent heating over the IMC are twice the global mean for an area that makes up only 4% of the Earth’s surface. The diurnal cycles appearing almost synchronously over the whole IMC generate teleconnections between the IMC convection and the global climate. Thus, high-resolution (<< 100 km; << 1 day) observations and models over the IMC are essential to improve both local disaster prevention and global climate prediction.
The mechanisms regulating the relationship between the tropical island diurnal cycle and large-scale modes of tropical variability such as the Boreal Summer Intraseasonal Oscillation (BSISO) are explored in observations and an idealized model. Specifically, the local environmental conditions associated with diurnal cycle variability are explored. Using Luzon island in the northern Philippines as an observational test case, a novel probabilistic framework is applied to improve the understanding of diurnal cycle variability. High amplitude diurnal cycle days tend to occur with weak to moderate offshore low-level wind and near to above average column moisture in the local environment. The transition from the BSISO suppressed phase to the active phase is most likely to produce the wind and moisture conditions supportive of a substantial diurnal cycle over western Luzon and the South China Sea (SCS). Thus, the impact of the BSISO on the local diurnal cycle can be understood in terms of the change in the probability of favorable environmental conditions. Idealized high-resolution 3-D Cloud Model 1 (CM1) simulations driven by base-states derived from BSISO composite profiles are able to reproduce several important features of the observed diurnal cycle variability with BSISO phase, including the strong, land-based diurnal cycle and offshore propagation in the transition phases. Background wind appears to be the primary variable controlling the diurnal cycle response, but ambient moisture distinctly reduces precipitation strength in the suppressed BSISO phase, and enhances it in the active phase.
The impact of quasi-biweekly variability in the monsoon southwesterly winds on the precipitation diurnal cycle in the Philippines is examined using CMORPH precipitation, ERA5 reanalysis, and outgoing longwave radiation (OLR) fields. Both a case study during the 2018 Propagation of Intraseasonal Tropical Oscillations (PISTON) field campaign and a 23-year composite analysis are used to understand the effect of the QBWO on the diurnal cycle. QBWO events in the west Pacific, identified with an extended EOF index, bring increases in moisture, cloudiness, and westerly winds to the Philippines. Such events are associated with significant variability in daily mean precipitation and the diurnal cycle. It is shown that the modulation of the diurnal cycle by the QBWO is remarkably similar to that by the boreal summer intraseasonal oscillation (BSISO). The diurnal cycle reaches a maximum amplitude on the western side of the Philippines on days with average to above average moisture, sufficient insolation, and weakly offshore prevailing wind. This occurs during the transition period from suppressed to active large-scale convection for both the QBWO and BSISO.Westerly monsoon surges associated with QBWO variability generally exhibit active precipitation over the South China Sea (SCS), but a depressed diurnal cycle. These results highlight that modes of large-scale convective variability in the tropics can have a similar impact on the diurnal cycle if they influence the local scale environmental background state similarly.
Plain Language Summary
Years of the Maritime Continent is a multiyear international program to study the weather climate system of the Indo‐Pacific Maritime Continent and its global impacts. Systematic biases in regional rainfall produced by numerical forecast and climate models and incomplete knowledge of the regional weather climate system motivated this program. This program conducts field campaigns to collect atmospheric and oceanic observations. Its preliminary results reveal new information that encourage further researches by combining observations with numerical models. This article also serves as a solicitation for contributions to a cross‐organization special collection of publications in journals of seven professional organizations. This special collection is intended to promote further studies on the diverse nature of the weather climate system of the Maritime Continent.
