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This study analyses the spatial and temporal distribution of heavy rainfall events (HREs) and its associated circulation anomalies over Tanzania during March to May (MAM) rainfall season of 1980–2010. A total of 822 HREs were revealed, concentrated over the northern sector (NS) of the country. Years with anomalous HREs are associated with low-level westerly convergence, advection of moisture from both the Indian Ocean and Congo basin, an upper warm temperature anomaly (UWTA), intensified and well-positioned Intertropical Convergence Zone (ITCZ), and pronounced rising motion since the ascending limb of the Walker type of circulation is centered over Tanzania. The analysis of the UWTA in this study has brought a key factor in exploring the possible likely cause and improved early warning system for the HREs during the MAM rainfall season in Tanzania. Making use of the thermal wind equation and the velocity divergent form of the continuity equation (DFCE), we found that the UWTA results into an upper-level horizontal wind divergence which significantly accelerates vertical ascent, deepening the surface low pressure for an enhanced convective process and HREs formation. [ABSTRACT FROM AUTHOR]

During the 2011 special observing period of the Dynamics of the Madden-Julian Oscillation (DYNAMO) field experiment, two sounding arrays were established over the central Indian Ocean, one north and one south of the equator, referred to here as the NSA and SSA, respectively. Three-hourly soundings from these arrays augmented by observations of radiation and rainfall are used to investigate the diurnal cycle of ITCZ convection during the MJO suppressed phase. During the first half of October, when convection was suppressed over the NSA but prominent over the SSA, the circulation over the sounding arrays could be characterized as a local Hadley cell. Strong rising motion was present within the ITCZ extending across the SSA with compensating subsidence over the NSA.Aprominent diurnal pulsing of this cell was observed, impacting conditions on both sides of the equator, with the cell running strongest in the early morning hours (0500-0800 LT) and notably weakening later in the day (1700-2000 LT). The declining daytime subsidence over the NSA may have assisted the moistening of the low to midtroposphere there during the pre-onset stage of the MJO. Apparent heating Q1 within the ITCZ exhibited a diurnal evolution from early morning bottom-heavy profiles to weaker daytime top-heavy profiles, indicating a progression from convective to stratiform precipitation. Making use of the weak temperature gradient approximation, results suggest that both horizontal radiative heating gradients and direct cloud radiative forcing have an important influence on diurnal variations of vertical motion and convection within the ITCZ. [ABSTRACT FROM AUTHOR]

The article focuses on the challenges in reducing the sea surface temperature (SST) biases in the Pacific and Atlantic Oceans. It mentions the impact of SST biases in the origin determination and precipitation biases in the Indian Ocean. Information regarding the intertropical convergence zone (ITCZ) precipitation bond, the contemporary coupled atmosphere-ocean general circulation models (CGCMs), and the El Niño-Southern Oscillation (ENSO), are discussed. INSET: A 30-YEAR HISTORY CONTINUES.

This study presents an analysis of the precursor environmental conditions related to the termination of Madden-Julian oscillation (MJO) events. A simple climatology is created using a real-time MJO monitoring index, documenting the locations and frequencies of MJO decay. Lead-lag composites of several atmospheric variables including temperature, moisture, and intraseasonal wind anomalies are generated from three reanalyses. There is remarkable agreement among the datasets with long-term, lower-tropospheric moisture deficits over the local domain best identifying termination events over the Indian Ocean. MJO termination in the Indian Ocean is also linked to a northward shift of the intertropical convergence zone (ITCZ) with possible lead times as much as 20 days prior to MJO decay. Statistically significant differences in the low-level vertical velocity and specific humidity are also identified more than 10 days in advance of MJO termination events in the western Pacific, though the differences here are more symmetric about the equator. Unlike the Indian Ocean and western Pacific, MJOs that terminate over the Maritime Continent appear to be related to their own intensity rather than the downstream conditions. As such, only the strongest MJOs tend to propagate into the warm pool region. Finally, a budget analysis is performed on the three-dimensional moisture advection equation in order to better elucidate what time scales and physical mechanisms are most important for MJO termination. The combination of intraseasonal vertical circulation anomalies coupled with the mean-state specific humidity best explain the anomalous moisture patterns associated with MJO termination, suggesting that the downstream influence of the MJO circulation can eventually lead to its future demise. [ABSTRACT FROM AUTHOR]

The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells. [ABSTRACT FROM AUTHOR]

The South China Sea summer monsoon (SCSSM) onset experiences evidently an interdecadal change around mid-1990s. Generally, the SCSSM broke out half a month earlier during 1994-2010 than IN 1978-1993. Possible causes are analyzed in this study. The results suggest that the earlier onset of the SCSSM is due to earlier retreat of the subtropical high (STH) over the western Pacific, which is closely related to enhanced intraseasonal oscillations of tropical convections. The enhanced convective activities can be found in three regions: the eastern tropical Indian Ocean (TIO), the equatorial SCS-Kalimantan (ESK) and the tropical western Pacific (TWP). Both convections in the TIO and the ESK are greatly influenced by the interaction of the westerly wind from the TIO and the easterly wind from the TWP. The convections in the TIO are never found to propagate to the east of 100°E, while those in the ESK are usually quite weak and not great help to the SCSSM onset. Our results suggest that the earlier retreat of the STH is mainly caused by the enhanced convections in the TWP, while the later may be the consequence of warming over the TWP on the interdecadal timescale. Therefore, the La Niña-like interdecadal change of the sea surface temperature (SST) in the Pacific is likely to be responsible for the interdecadal advance of the SCSSM onset. [ABSTRACT FROM AUTHOR]

This study examines wave disturbances on submonthly (6-30-day) timescales over the tropical Indian Ocean during Southern Hemisphere summer using Japanese Reanalysis (JRA25-JCDAS) products and National Oceanic and Atmospheric Administration outgoing longwave radiation data. The analysis period is December-February for the 29 years from 1979/1980 through 2007/2008. An extended empirical orthogonal function (EEOF) analysis of daily 850-hPa meridional wind anomalies reveals a well-organized wave-train pattern as a dominant mode of variability over the tropical Indian Ocean. Daily lagged composite analyses for various atmospheric variables based on the EEOF result show the structure and evolution of a wave train consisting of meridionally elongated troughs and ridges along the Indian Ocean Intertropical Convergence Zone (ITCZ). The wave train is oriented in a northeast-southwest direction from Sumatra toward Madagascar. The waves have zonal wavelengths of about 3,000-5,000 km and exhibit westward and southwestward phase propagation. Individual troughs and ridges as part of the wave train sequentially travel westward and southwestward from the west of Sumatra into Madagascar. Meanwhile, eastward and northeastward amplification of the wave train occurs associated with the successive growth of new troughs and ridges over the equatorial eastern Indian Ocean. This could be induced by eastward and northeastward wave energy dispersion from the southwestern to eastern Indian Ocean along the mean monsoon westerly flow. In addition, the waves modulate the ITCZ convection. Correlation statistics show the average behavior of the wave disturbances over the tropical Indian Ocean. These statistics and other diagnostic measures are used to characterize the waves obtained from the composite analysis. The waves appear to be connected to the monsoon westerly flow. The waves tend to propagate through a band of the large meridional gradient of absolute vorticity produced by the mean monsoon westerly flow. This suggests that the monsoon westerly flow provides favorable background conditions for the propagation and maintenance of the waves and acts as a waveguide over the tropical Indian Ocean. The horizontal structure of the wave train may be interpreted as that of a mixture of equatorial Rossby waves and mixed Rossby-gravity wavelike gyres. [ABSTRACT FROM AUTHOR]

We characterize the climatological features of the double inter-tropical convergence zones (DITCZs) over the western Indian Ocean during November–December by a synergistic analysis of the Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite (HOAPS III) data (1988–2005) and the National Aeronautics and Space Administration's (NASA's) A-Train data (2002–2009). We investigate rainfall, freshwater flux and cloud liquid water, cloud fraction and relative humidity over the DITCZs. In addition, the daily rainfall data from the Global Precipitation Climatology Project (GPCP) are used to document the DITCZs during the El Niño southern oscillation (ENSO) events. An analysis of the GPCP data shows that the DITCZs are clearly discernible during strong ENSO events (1997, 2002 and 2006), in sharp contrast to the DITCZs in the eastern Pacific Ocean, where they are absent during ENSOs. Further, these convergence zones on either side of the equator are of short duration, approximately 3–6 pentads during November and December. All satellite sensor data sets consistently capture the major features of DITCZs. As an accurate simulation of DITCZs in coupled global climate models remains a challenge, the results from the present study would provide a platform for evaluating these models. [ABSTRACT FROM AUTHOR]

Intense debate persists about the climatic mechanisms governing hydrologic changes in tropical and subtropical southeast Africa since the Last Glacial Maximum, about 20,000?years ago. In particular, the relative importance of atmospheric and oceanic processes is not firmly established. Southward shifts of the intertropical convergence zone (ITCZ) driven by high-latitude climate changes have been suggested as a primary forcing, whereas other studies infer a predominant influence of Indian Ocean sea surface temperatures on regional rainfall changes. To address this question, a continuous record representing an integrated signal of regional climate variability is required, but has until now been missing. Here we show that remote atmospheric forcing by cold events in the northern high latitudes appears to have been the main driver of hydro-climatology in southeast Africa during rapid climate changes over the past 17,000 years. Our results are based on a reconstruction of precipitation and river discharge changes, as recorded in a marine sediment core off the mouth of the Zambezi River, near the southern boundary of the modern seasonal ITCZ migration. Indian Ocean sea surface temperatures did not exert a primary control over southeast African hydrologic variability. Instead, phases of high precipitation and terrestrial discharge occurred when the ITCZ was forced southwards during Northern Hemisphere cold events, such as Heinrich stadial 1 (around 16,000?years ago) and the Younger Dryas (around 12,000?years ago), or when local summer insolation was high in the late Holocene, that is, during the past 4,000?years. [ABSTRACT FROM AUTHOR]

Convection over the tropical Indian Ocean is important to the global and regional climate. This study presents the monthly climatology of convection, inferred from the outgoing longwave radiation (OLR), over the tropical Indian Ocean. We also examine the impact of El Nino/La Nina events on the convection pattern and how variations in convection over the domain influence the spatial rainfall distribution over India. We used 35 recent years (1974-2008) of satellite-derived OLR over the area, the occurrence of El Nino/La Nina events and high resolution grid point rainfall data over India. The most prominent feature of the annual cycle of OLR over the domain is the movements of convection from south-east to north and north-west during the winter to the summer monsoon season. This feature represents the movement of the inter-tropical convergence zone (ITCZ). The climatology of OLR during the winter months (December-February) over the domain is characterized by high subsidence over central India with a decrease of OLR values towards the north and south. Moderate convection is also seen over the Himalayan Range and the south-east Indian Ocean. In contrast, during the summer (June-September) the OLR pattern indicates deep convection along the monsoon trough and over central India, with subsidence over the extreme north-west desert region. The annual march of convection over the Arabian Sea and Bay of Bengal sector shows that the Arabian Sea has a limited role, compared to the Bay of Bengal, in the annual cycle of the convection over the tropical Indian Ocean. The composite OLR anomalies for the El Nino cases during the summer monsoon season show suppressed convection over all of India and moderate convection over the central equatorial Indian Ocean and over the northern part of the Bay of Bengal. Meanwhile in La Nina events the OLR pattern is nearly opposite to the El Nino case, with deep convection over entire Indian region and adjoining seas and subsidence over the northern Bay of Bengal and extreme north-west region. The spatial variability of the 1° × 1° summer monsoon rainfall data over India is also examined during El Nino/La Nina events. The results show that rainfall of the summer monsoon season over the southern peninsular of India and some parts of central India are badly affected during El Nino cases, while the region lying along the monsoon trough and the west coast of India have received good amounts of rainfall. This spatial seasonal summer monsoon rainfall distribution pattern seems to average out the influence of El Nino events on total summer monsoon rainfall over India. It seems that, in El Nino events, the convection pattern over the Bay of Bengal remains unaffected during summer monsoon months and thus this region plays an important role in giving good summer monsoon rainfall over the northern part of India, which dilutes the influence of El Nino on seasonal scale summer monsoon rainfall over India. These results are also confirmed by using a monthly bias-corrected OLR dataset. [ABSTRACT FROM AUTHOR]

We investigated the seasonal march of the Intertropical Convergence Zone (ITCZ) shown by the 22 coupled general circulation models of the 20th Century Climate in Coupled Models experiment in seven regions (Africa, Indian Ocean, western Pacific, central Pacific, eastern Pacific, South America, and Atlantic Ocean). Inter-model differences in the seasonal march of the ITCZ over Africa (10-40°E) were significantly smaller than those over other regions. This finding indicates that the seasonal march of the ITCZ over Africa is insensitive to differences in model physics and resolution and suggests that the seasonal march of the African ITCZ is controlled by robust and simple mechanisms. Motivated by this result, we tried to understand the process of the seasonal march of the ITCZ over central Africa (15-30°E) based on an analysis of ERA-40 data. The analysis results revealed the following features of the ITCZ in this region: (1) The ITCZ itself produces large convective available potential energy that generates deep convection. (2) The abundant water vapor within the ITCZ is maintained by horizontal moisture flux. (3) Outside but near the ITCZ, shallow convection exists and may act to pre-moisten deep convection in spring and autumn. (4) The seasonal change of the ITCZ is preceded by that of the vertical moist instability in the lower free atmosphere caused by the seasonal change in insolation. [ABSTRACT FROM AUTHOR]

The north-south symmetry of the low level near-equatorial atmospheric flow is examined in relation to the position of the Intertropical Convergence Zone (ITCZ) over the Indian Ocean with the aid of satellite and reanalysis data. Absolute vorticity (AV) and convergence fields on temporal scales of 10 days are derived from 7 years of Quick Scatterometer (QuikSCAT) observations and related statistically to organized convection deduced from outgoing longwave radiation (OLR) measured by the National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellites. The AV observations reveal a belt of symmetric instability on the summer side of the equator. The evolution of this symmetric instability with respect to the cross-equatorial flow (CEF), the location of the ITCZ, and monsoonal forcing is investigated. We identify three distinct dominant convective regimes. We show that during the active Indian monsoon season, symmetric instability and the displacement of the zero-AV line off the equator are directly linked to organized convection and the off-equatorial location of the ITCZ. The advective (inertial) regime interacts with and is controlled by monsoon and CEF. In periods of transition between summer and winter monsoon, the lower atmosphere is symmetrically stable and two other convective regimes can be identified: a double ITCZ, and localized convection near the equator. [ABSTRACT FROM AUTHOR]

Abstract: Trace element and stable isotope ratios from an active stalagmite (LR06-B1) recovered from Liang Luar Cave on the island of Flores (eastern Indonesia) are used to reconstruct the position of the austral summer inter-tropical convergence zone and Australian-Indonesian summer monsoon variability during the Holocene. Uranium-series dating of the stalagmite shows that it commenced growth 12,640years ago, with hiatuses spanning 8,560 to 6,420 and 3,670 to 2,780years ago. Stalagmite Mg/Ca and Sr/Ca ratios correlate significantly with one another, and with δ 18O and δ 13C, throughout the record. This suggests that the Mg/Ca and Sr/Ca ratios are dominated by prior calcite precipitation, a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of Ca2+ ions (relative to Mg2+ and Sr2+) ‘upstream’ of the stalagmite. The degree of initial 234U/238U disequilibrium also appears to have been controlled by recharge to the overlying aquifer. Together with the Mg/Ca, Sr/Ca, and δ 18O values, the initial uranium isotope activity ratios ([234U/238U]I) imply a generally drier early Holocene, coincident with a lower sea level and lower Southern Hemisphere summer insolation. Comparison of speleothem δ 18O time-series from Flores and Borneo shows that they vary in unison for much of the Holocene. However, there is a significant decrease in the Borneo δ18O record ~6,000 to 4,000 years ago that does not occur in the Flores record. This anomaly may be related to a change in the Australian-Indonesian summer monsoon circulation in response to a protracted positive phase of the Indian Ocean Dipole. Under this scenario, stronger upwelling off of western Indonesia would, based on present-day effects, result in reduced summer convective activity over Flores and a subsequent northward shift of the intertropical convergence zone. [Copyright &y& Elsevier]

The article focuses on the changes in subsurface salinity in the Atlantic, Pacific, and India Ocean. Topics discussed include the anomalous eastward equatorial currents and enhanced precipitation along the intertropical convergence zone (ITCZ) in the Pacific Ocean, the positive salinity anomalies in the South Atlantic in 2015, and the salty and fresh anomalies of the Indian Ocean.

Effects of freshwater forcing from river discharge into the Indian Ocean on oceanic vertical structure and the Indian monsoons are investigated using a fully coupled, high-resolution, regional climate model. The effect of river discharge is included in the model by restoring sea surface salinity (SSS) toward observations. The simulations with and without this effect in the coupled model reveal a highly seasonal influence of salinity and the barrier layer (BL) on oceanic vertical density stratification, which is in turn linked to changes in sea surface temperature (SST), surface winds, and precipitation. During both boreal summer and winter, SSS relaxation leads to a more realistic spatial distribution of salinity and the BL in the model. In summer, the BL in the Bay of Bengal enhances the upper-ocean stratification and increases the SST near the river mouths where the freshwater forcing is largest. However, the warming is limited to the coastal ocean and the amplitude is not large enough to give a significant impact on monsoon rainfall. The strengthened BL during boreal winter leads to a shallower mixed layer. Atmospheric heat flux forcing acting on a thin mixed layer results in an extensive reduction of SST over the northern Indian Ocean. Relatively suppressed mixing below the mixed layer warms the subsurface layer, leading to a temperature inversion. The cooling of the sea surface induces a large-scale adjustment in the winter atmosphere with amplified northeasterly winds. This impedes atmospheric convection north of the equator while facilitating it in the austral summer intertropical convergence zone, resulting in a hemispheric-asymmetric response pattern. Overall, the results suggest that freshwater forcing from the river discharges plays an important role during the boreal winter by affecting SST and the coupled ocean–atmosphere interaction, with potential impacts on the broadscale regional climate. [ABSTRACT FROM AUTHOR]

The response of the seasonal tropical circulation to an 11-yr solar cycle forcing is studied with the Goddard Institute for Space Studies (GISS) ModelE, which includes fully interactive atmospheric chemistry. To identify characteristic solar signals in the tropical circulation, the model experiments are carried out with certain imposed conditions: a doubly amplified solar forcing and the present-day and preindustrial greenhouse gases and aerosol conditions, with the mixed layer or fully coupled dynamic ocean model. In both the model and the NCEP reanalysis, tropical humidity increases in response to enhanced solar irradiance are found to be statistically significant in both solstice seasons. Changes are also found in the vertical velocities for both the Hadley and Walker circulations in some areas of the Pacific region. With present-day greenhouse gas and aerosol conditions, the ascending branch of the Hadley cell is enhanced near the equator, and the intertropical convergence zone (ITCZ) is shifted northward in response to solar forcing during the boreal winter. Enhancement of the meridionally averaged vertical velocity over the western Pacific indicates strengthening of the Walker circulation in response to solar forcing in both solstice seasons. In present-day conditions, the tropical circulation response to an 11-yr solar forcing is generally consistent with that derived from previous observational works. [ABSTRACT FROM AUTHOR]

Abstract: The measurements of total number concentration and number size distribution of aerosols in size ranges of 16–700 nm and 0.5–20 μm diameters made from 14°N to 56°S in the Indian ocean during January 23 to March 31, 2004, are reported. The average values of total number (mass) concentration of micrometer aerosols (0.5–20 μm) are 7.2±3 cm− 3 (8.89 µg m− 3) from 14°N to the Inter-Tropical Convergence Zone (ITCZ), 4.6±2 cm− 3 (4.9 µg m− 3) in the ITCZ, 3.0±1.4 cm− 3 (5.78 µg m− 3) in the trade wind region from 8°–30°S, 3.8±2.6 cm−3 (7.9 µg m−3) from 30°–40°S, and 5.8±3.5 cm− 3 (9.65 µg m− 3) in the roaring forties from 40°–56°S. Latitudinal distribution of such aerosols shows that their number concentration is minimum (0.5 cm−3) at 11°S and increases on either side of this location. Size distributions of micrometer aerosols in all latitudinal belts show a maxima in coarse mode at 0.5–1.5 μm diameter. The correlation coefficient in the aerosol concentration–wind speed relations of these aerosols is observed to differ in different latitudinal belts and has maximum value in the belt of strongest winds. Also, diurnal variations of the average aerosol concentration and wind speed show some similarity in belts of strong winds. Total number concentration of submicrometer (16–700 nm) particles is also minimum in the southern trade wind region and their size distribution is bimodal with maxima in Aitken mode (~50 nm) and accumulation mode (~130 nm). South of the ITCZ, concentrations of both, total number and Aitken mode particles normally increase with latitude. The increase in Aitken mode particles at high latitudes is large enough for the Aitken mode maxima to superimpose the accumulation mode maxima. Observations suggest that addition of Aitken particles is so fast that process of coagulation is not able to reach equilibrium to develop a distinct accumulation maxima. Observations show that pristine air of the trade wind region in the Southern Hemisphere can be advected to mid-latitudes along the ridge developed between anticyclonic and cyclonic systems. [Copyright &y& Elsevier]

The article investigates the relationship between monthly sea-surface temperature (SST) in the tropical Pacific and the Indian Ocean and monthly precipitation over the Vietnamese central highlands by means of singular value decomposition. The seasonal variation of SST plays a critical role in the onset of the monsoon season and convective rain band movement in the inter-tropical convergence zone. The relationships between precipitation and SST in both oceans vary significantly through the rainy season.

The article presents a study on the interannual variability of rainfall in western equatorial Africa and its connections to sea-surface temperatures (SSTs). Among the factors which affect the interannual variability of rainfall in this region include SST anomalies along the Benguela Coast, the warming or cooling of the tropical oceans, the Pacific El Nñno-Southern Oscillation (ENSO), and the contrast between the Atlantic and Indian Oceans. Moreover, the role of the Atlantic appears to be the modulation of the north-south movement of the Intertropical Convergence Zone (ITCZ).

We have analyzed the stable oxygen isotopic composition of two Porites corals from the Chagos Archipelago, which is situated in the geographical center of the Indian Ocean. Coral δ18O at this site reliably records temporal variations in precipitation associated with the Intertropical Convergence Zone (ITCZ). Precipitation maxima occur in boreal winter, when the ITCZ forms a narrow band across the Indian Ocean. The Chagos then lies within the center of the ITCZ, and rainfall is strongly depleted in δ18O. A 120-yr coral isotopic record indicates an alternation of wet and dry intervals lasting 15 to 20 yr. The most recent 2 decades are dominated by interannual variability, which is tightly coupled to the El Niño–Southern Oscillation (ENSO). This is unprecedented in the 120 yr of coral record. As the ITCZ is governed by atmospheric dynamics, this provides evidence of a major change in the coupled ENSO–monsoon system. [Copyright &y& Elsevier]

Atmospheric moisture transport over southern Africa and surrounding oceans is considered during wet and dry conditions over the South African summer rainfall region. Wet and dry synoptic spells within wet and dry austral summers are examined. A link between synoptic and seasonal timescales is investigated using seasonal statistics of wet and dry spells. Dry synoptic spells exhibit divergent moisture flux over South Africa, within flow from the mid-latitude ocean regions to the south. Cyclonic features off the east coast may exist and attract moisture away from South Africa. For wet synoptic spells, there tends to be increased moisture flux from the tropical or subtropical southwest Indian Ocean (SWIO), either associated with ridging along the east coast or a deep low over the interior. Seasonal modulations of the intensity of the heat low over Angola/Namibia appear important for influencing early (OND) and late (JFM) summer rainfall over South Africa. This low may act as the tropical source for tropical temperate troughs and their associated cloudbands that are major synoptic rain-producing systems. Wet (dry) summers are often associated with a southward (northward) shift and strengthening (weakening) of the ITCZ over tropical southeastern Africa. Seasonal rainfall is found to be related to the distribution of wet and dry spells within the season, such that wetter seasons tend to have longer or more intense wet spells rather than a greater number of wet spells. [ABSTRACT FROM AUTHOR]

• Microplastics can long-range transport to a remote area through atmosphere. • Fiber was common shape of micropastic in atmospheric microplastic over the ocean. • Atmospheric microplastic was not major source of oceanic microplastic. • Intertropical Convergence Zone is probably a recipient for atmospheric microplastic. At present, microplastic (MP) is pervasive globally and has a regional difference. Recent studies have identified MP in the terrestrial atmospheric environment. However, the connection between terrigenous atmospheric MP emissions and impacts over the ocean is not well known. Here, we present the distribution of atmospheric MP abundance over the ocean based on a transoceanic survey conducted across 21 sampling transects from the Pearl River Estuary (PRE) to the South China Sea (SCS) and then to the East Indian Ocean (EIO). The abundance of atmospheric MP over the PRE (4.2 ± 2.5 items/100 m3) was significantly higher than that over the EIO (0.4 ± 0.6 items/100 m3). However, the abundance of atmospheric MP in the SCS (0.8 ± 1.3 items/100 m3) was not significantly different from the EIO and PRE. This result revealed that MP undergoes long-range transport, more than 1000 km away, through the atmosphere, but atmospheric MP transmission as the main source of oceanic MP based on transoceanic studies is not a plausible assumption. Furthermore, backward trajectory model analysis of 21 sampling transects preliminary showed the potential sources of atmospheric MP over the PRE, SCS, and EIO. [ABSTRACT FROM AUTHOR]

Satellite observations of the diurnal cycle of precipitation and cloud clusters show a dominant nighttime maximum over the tropical Indian Ocean, similar to other basins. The nighttime maximum is associated with the relatively long lifetime of large convective systems that initiated during the afternoon when the sea surface temperature (SST) reached its diurnal maximum as first showed in Chen and Houze (1997, https://doi.org/10.1002/qj.49712353806). Shipborne and island‐based radar data from Dynamics of the Madden‐Julian Oscillation show distinct characteristics of the diurnal cycle in the equatorial region and Intertropical Convergence Zone (ITCZ). A secondary afternoon precipitation maximum occurs under light surface winds (<5 m/s) when the diurnal cycle of SST is large (0.5–1.7 °C) in the equatorial region during the suppressed phase of the Madden‐Julian Oscillation (MJO). The afternoon maximum was from short‐lived convective systems with rain rates >10 mm/hr. In contrast, during the active MJO and in the ITCZ, the secondary afternoon maximum is mostly absent as the surface winds were generally >5 m/s and reduced afternoon SST warming to less than 0.5 °C. The Tropical Rainfall Measurement Mission Multiplatform Precipitation Analysis does not resolve the secondary afternoon maximum in heavier rain rates from short‐lived small systems, but it suggests a more pronounced night‐morning maximum in the ITCZ than in the MJO. Infrared 208‐K cloud cluster analysis show that this difference in the morning maximum was due to the greater number of long‐lasting, large convective systems (>~200 km in diameter) persisting into the morning in the ITCZ. Key Points: Satellite and radar data show a nighttime rain max with noticeable differences between the MJO and ITCZ over the equatorial Indian OceanThe nighttime precipitation max in the ITCZ is more pronounced than in the MJO, which is associated with large long‐lasting cloud clustersRadar data show a secondary afternoon rain max in the equatorial region when diurnal cycle of SST is > 0.5 °C and wind speed is <5 m/s [ABSTRACT FROM AUTHOR]