Maritime Convection Research Articles

Evaluation of bulk microphysics parameterizations for simulating the vertical structure of heavy rainfall between Korea and the United States

The Korean Peninsula and the United States (US) have many contrasting precipitation characteristics that are part of the oceanic monsoon and continental convection. This study evaluated 11 microphysics schemes in the Weather Research and Forecasting model in terms of vertical reflectivity structure for heavy rainfall during the summer in Korea and the US. Compared to satellite radar observation, the correlation coefficients for the reflectivity structure for 11 microphysics schemes were 0.581–0.906 and 0.745–0.918 for the Korean and US domains, respectively. We observed that a simple scheme (such as the use of single moment and limited ice categories) does not always fail, and complex methods do not always succeed. The relatively low correlation over Korea versus the US was assumed because many microphysics parameterizations were developed and tuned over the US. Consequently, some microphysics schemes exhibited a severe overestimation of reflectivity in both the upper and lower levels over the Korean Peninsula. In contrast, a microphysics scheme that was evaluated and improved for both continental and maritime convection regions, showed the best performance on the Korean Peninsula too. This highlights the importance of evaluation for various regions with different precipitation characteristics to improve parameterization of cloud microphysics. Because Korean and US domains are representative areas of oceanic monsoon and continental convection, we expect that this study can serve as a conceptual guide to suggest which microphysics parameterizations should be used for a realistic simulation in continental and oceanic monsoon precipitation regimes.

Diurnal Differences in Tropical Maritime Anvil Cloud Evolution

AbstractSatellite observations of tropical maritime convection indicate an afternoon maximum in anvil cloud fraction that cannot be explained by the diurnal cycle of deep convection peaking at night. We use idealized cloud-resolving model simulations of single anvil cloud evolution pathways, initialized at different times of the day, to show that tropical anvil clouds formed during the day are more widespread and longer lasting than those formed at night. This diurnal difference is caused by shortwave radiative heating, which lofts and spreads anvil clouds via a mesoscale circulation that is largely absent at night, when a different, longwave-driven circulation dominates. The nighttime circulation entrains dry environmental air that erodes cloud top and shortens anvil lifetime. Increased ice nucleation in more turbulent nighttime conditions supported by the longwave cloud-top cooling and cloud-base heating dipole cannot compensate for the effect of diurnal shortwave radiative heating. Radiative–convective equilibrium simulations with a realistic diurnal cycle of insolation confirm the crucial role of shortwave heating in lofting and sustaining anvil clouds. The shortwave-driven mesoscale ascent leads to daytime anvils with larger ice crystal size, number concentration, and water content at cloud top than their nighttime counterparts.Significance StatementDeep convective activity and rainfall peak at night over the tropical oceans. However, anvil clouds that originate from the tops of deep convective clouds reach their largest extent in the afternoon hours. We study the underlying physical mechanisms that lead to this discrepancy by simulating the evolution of anvil clouds with a high-resolution model. We find that the absorption of sunlight by ice crystals lofts and spreads the daytime anvil clouds over a larger area, increasing their lifetime, changing their properties, and thus influencing their impact on climate. Our findings show that it is important not only to simulate the correct onset of deep convection but also to correctly represent anvil cloud evolution for skillful simulations of the tropical energy balance.

Strong day-to-day variability of the Asian Tropopause Aerosol Layer (ATAL) in August 2016 at the Himalayan foothills

Abstract. The South Asian summer monsoon is associated with a large-scale anticyclonic circulation in the upper troposphere and lower stratosphere (UTLS), which confines the air mass inside. During boreal summer, the confinement of this air mass leads to an accumulation of aerosol between about 13 and 18 km (360 and 440 K potential temperature); this accumulation of aerosol constitutes the Asian Tropopause Aerosol Layer (ATAL). We present balloon-borne aerosol backscatter measurements of the ATAL performed by the Compact Optical Backscatter Aerosol Detector (COBALD) instrument in Nainital in northern India in August 2016, and compare these with COBALD measurements in the post-monsoon time in November 2016. The measurements demonstrate a strong variability of the ATAL's altitude, vertical extent, aerosol backscatter intensity and cirrus cloud occurrence frequency. Such a variability cannot be deduced from climatological means of the ATAL as they are derived from satellite measurements. To explain this observed variability we performed a Lagrangian back-trajectory analysis using the Chemical Lagrangian Model of the Stratosphere (CLaMS). We identify the transport pathways as well as the source regions of air parcels contributing to the ATAL over Nainital in August 2016. Our analysis reveals a variety of factors contributing to the observed day-to-day variability of the ATAL: continental convection, tropical cyclones (maritime convection), dynamics of the anticyclone and stratospheric intrusions. Thus, the air in the ATAL is a mixture of air masses coming from different atmospheric altitude layers. In addition, contributions from the model boundary layer originate in different geographic source regions. The location of the strongest updraft along the backward trajectories reveals a cluster of strong upward transport at the southern edge of the Himalayan foothills. From the top of the convective outflow level (about 13 km; 360 K) the air parcels ascend slowly to ATAL altitudes within a large-scale upward spiral driven by the diabatic heating in the anticyclonic flow of the South Asian summer monsoon at UTLS altitudes. Cases with a strong ATAL typically show boundary layer contributions from the Tibetan Plateau, the foothills of the Himalayas and other continental regions below the Asian monsoon. Weaker ATAL cases show higher contributions from the maritime boundary layer, often related to tropical cyclones, indicating a mixing of clean maritime and polluted continental air. On the one hand increasing anthropogenic emissions in the future are expected due to the strong growth of Asian economies; on the other hand the implementation of new emission control measures (in particular in China) has reduced the anthropogenic emissions of some pollutants contributing to the ATAL substantially. It needs to be monitored in the future whether the thickness and intensity of the ATAL will further increase, which will likely impact the surface climate.

Aerosol Effects on Lightning Characteristics: A Comparison of Polluted and Clean Regimes

AbstractOceanic lightning can be a sensitive indicator of aerosol effects on lightning characteristics as thermodynamic contrast is indistinct over adjacent oceanic regions. The study presents discernable aerosol impacts on lightning characteristics by analyzing 2 years (2017–2018) of intracloud (IC) and cloud‐to‐ground (CG) lightning data from Earth Networks Total Lightning Network over two key regions in southern South China Sea. Mean stroke density, IC/CG ratio, +IC fraction, and +CG fraction in polluted conditions are respectively 3.7, 2, 1.2, and 5.8‐fold larger than unpolluted counterparts. Total stroke contrast is further confirmed with the GLD360 network. Thermodynamic parameters conversely support slightly stronger convection over clean ocean. Clear evidence shows cloud droplet size diminishes with added aerosol. Aerosol invigorates more frequent and robust mixed‐phase development, endowing maritime convection with continental characteristics. Modifications in the charge reversal temperature and lower and upper positive charge regions are speculated on as means for stimulating more positive ICs and CGs.

Small ice particles at slightly supercooled temperatures in tropical maritime convection

Abstract. In this paper we show that the origin of the ice phase in tropical cumulus clouds over the sea may occur by primary ice nucleation of small crystals at temperatures just between 0 and −5 ∘C. This was made possible through use of a holographic instrument able to image cloud particles at very high resolution and small size (6 µm). The environment in which the observations were conducted was notable for the presence of desert dust advected over the ocean from the Sahara. However, there is no laboratory evidence to suggest that these dust particles can act as ice nuclei at temperatures warmer than about −10 ∘C, the zone in which the first ice was observed in these clouds. The small ice particles were observed to grow rapidly by vapour diffusion, riming, and possibly through collisions with supercooled raindrops, causing these to freeze and potentially shatter. This in turn leads to the further production of secondary ice in these clouds. Hence, although the numbers of primary ice particles are small, they are very effective in initiating the rapid glaciation of the cloud, altering the dynamics and precipitation production processes.

Evaluation of Simulated Drop Size Distributions and Microphysical Processes Using Polarimetric Radar Observations for Landfalling Typhoon Matmo (2014)

AbstractThe Morrison (Morr), Thompson (Thom), Thompson aerosol‐aware (ThomA), and WRF double‐moment 6‐class (WDM6) microphysics schemes within the WRF model are used to simulate landfalling Typhoon Matmo (2014) and evaluated against polarimetric radar observations in terms of raindrop size distribution (RSD) and microphysical processes. Focus is placed on the inner rainband convection. Only ThomA is able to reproduce observed RSD characteristics having even smaller mean raindrop sizes and larger number concentrations than those of typical maritime convection, when measured in terms of mass‐weighted mean diameter and normalized RSD intercept parameter. The diagnoses of microphysical transfer terms show that warm rain processes are dominant in all experiments. The accretion and autoconversion processes dominate the production of rainwater content and raindrop number concentration, respectively. Examinations of vertical profiles of hydrometeor masses and number concentrations as well as rainwater‐related microphysical transfer rates suggest that raindrop total number concentration NTr near the freezing level, mainly produced by the autoconversion process, plays an important role in determining the near‐surface RSD characteristics. Morr and Thom assume fixed values of cloud droplet number concentration NTc that are much larger than those predicted by ThomA, leading to much smaller NTr near the freezing level produced by the autoconversion process. Sensitivity experiments using much reduced NTc substantially increase predicted NTr, mainly through invigoration of autoconversion. These results indicate that adequately predicting NTc is very important for capturing the right RSD characteristics for landfalling typhoons over East China where Typhoon Matmo is one of the representative examples.

Maritime convection and fluctuation between Vietnam and China: A data-driven study

A network is usually embedded in a larger network and interacts with other networks simultaneously, while the networks in network science literature are generally examined independently. The trade values can generally reflect periodical (annual or monthly) flows of cargo types and values between two economies, while the geographical and transportation details cannot be embodied although they are important for national logistics and supply chains. We investigate the vessel flows between two national maritime networks activated by possible implications to trade and shipping investments. The maritime network of flows between China and Vietnam is figured as a typical example under the consideration that the two countries are both typical maritime countries and the development of China is slowing down while Vietnam's economy and trade are booming. Using five years' mutual connectivity data between Vietnam and China, the flow directions and amounts are estimated and examined by network and flow analyzing methods. Maritime convection is introduced to investigate the changing cargo flows that represents supply chains between the two countries. Maritime fluctuation is used to study the strength and tendencies of seaborne trade between the two countries. These two aspects are visualized and conceptualized in the context of China's Belt and Road Initiative. New maritime interconnection facilities and opportunities are then discussed based on the results from this analysis. All methods for developing the networks and metrics of convection and fluctuation are incorporated into a system framework. So, the proposed method can be used for general network relation analysis, especially when the networks are connected by flows.

Drop Size Distribution Characteristics of Seven Typhoons in China

AbstractThis study is the first attempt to investigate the characteristics of the drop size distribution (DSD) and drop shape relation (DSR) of seven typhoons after making landfall in China. Four typhoons were sampled by a C‐band polarimetric radar (CPOL) and a two‐dimensional video disdrometer (2DVD) in Jiangsu Province (East China) while three typhoons were sampled by two 2DVDs in Guangdong Province (south China). Although the DSD and DSR are different in individual typhoons, the computed DSD parameters in these two groups of typhoons possess similar characteristics. The DSR is more spherical, and the shape‐slope (μ‐Λ) relation has a significantly lower value of μ for a given Λ than that in typhoons in the Taiwan area, indicating different microphysical processes of typhoons between continental China and other regions (western Pacific and Atlantic). The convective precipitation of typhoons contains higher raindrop concentration and lower raindrop diameter than that of the maritime convection. A Z (reflectivity factor)‐R (rain rate) relationship, Z = 147.28R1.38, is derived for typhoons over land in China. The contoured frequency by altitude diagrams of CPOL polarimeteric parameters and the vertical distributions of hydrometeors and retrieved DSD parameters are further investigated to better reveal the microphysical processes of two typhoons (Matmo and Soudelor). Despite the differences in DSDs and polarimetric parameters, microphysical characteristics in both typhoons are similar. The CPOL‐derived microphysical properties, in conjunction with high freezing level, suggest that warm rain accretion processes dominate typhoon rainfall after landfall in China.

Sticky Thermals: Evidence for a Dominant Balance between Buoyancy and Drag in Cloud Updrafts

Abstract The vertical velocities of convective clouds are of great practical interest because of their influence on many phenomena, including severe weather and stratospheric moistening. However, the magnitudes of forces giving rise to these vertical velocities are poorly understood, and the dominant balance is in dispute. Here, an algorithm is used to extract thousands of cloud thermals from a large-eddy simulation of deep and tropical maritime convection. Using a streamfunction to define natural boundaries for these thermals, the dominant balance in the vertical momentum equation is revealed. Cloud thermals rise with a nearly constant speed determined by their buoyancy and the standard drag law with a drag coefficient of 0.6. Contrary to suggestions that cloud thermals might be slippery, with a dominant balance between buoyancy and acceleration, cloud thermals are found here to be sticky, with a dominant balance between buoyancy and drag.

Cloud Conditions Favoring Secondary Ice Particle Production in Tropical Maritime Convection

Abstract Progress in understanding the formation of ice in lower-tropospheric clouds is slowed by the difficulties in characterizing the many complex interactions that lead to ice initiation and to the dynamic, non-steady-state nature of the clouds. The present study characterizes the conditions where secondary ice particles, specifically identified as needle or thin columnar types, are observed in tropical maritime convection with modest liquid water contents during the Ice in Clouds Experiment-Tropical (ICE-T), based out of St. Croix, U.S. Virgin Islands, and the NASA African Monsoon Multidisciplinary Analyses (NAMMA) in 2006 sampling from Cape Verde, Africa. The properties of the cloud droplet populations relevant to the secondary ice production process and the ice particle populations are characterized as a function of temperature and vertical velocity. These secondary ice particles are observed primarily in regions of low liquid water content and weak vertical velocities. Two situations are examined in detail. First, ice formation is examined by following the tops of a group of ICE-T chimney clouds as they ascend and cool from a temperature of +7° to −8°C, examining the production of the first ice. Then, using the data from a cloud system sampled during NAMMA, the authors elucidate a process that promotes ice multiplication. The intention is that this study will lead both to a better understanding of how secondary ice production proceeds in natural clouds and to more realistic laboratory studies of the processes involved.

Microphysical characteristics of cumulus clouds as observed in some African countries

This paper analyses airborne measurements of several midlevel and mixed-phase cumulus clouds observed in different environments (maritime, continental, shallow and deep convection) obtained during the scientific experiments performed by national weather modification programs in Morocco and Burkina Faso. Three cases are documented in this paper presenting the synoptic meteorological situation leading to the formation and the development of the sampled clouds and the results of the measurements collected using instrumental aircrafts. Several passes were made at the top of the sampled clouds and reported data were collected and analysed describing the variability of the measured parameters at various altitudes and thus different temperature values (negative and positive temperatures). The dependency of the liquid water content to the temperature has been studied but also its variation with regard to the vertical velocity and to the total concentration number of cloud particles. Keywords: Aircraft Measurements, Cloud Microphysics, Liquid Water Content, West African Monsoon.

Analyzing dynamical circulations in the tropical tropopause layer through empirical predictions of cirrus cloud distributions

We explore the use of nonlinear empirical predictions of thin cirrus for diagnosing transport through the tropical tropopause layer (TTL). Thirty day back trajectories are calculated from the locations of CALIPSO cloud observations to obtain Lagrangian dry and cold points associated with each observation. These historical values are combined with “local” (at the location of the CALIPSO observation) temperature and specific humidity to predict cloud probability using multivariate polynomial regression. We demonstrate that our statistical sample (seven seasons) is sufficient to retrieve the full nonlinear relationship between cloud probability and its predictors and that substantial information is lost in a purely linear analysis. The best cloud prediction is obtained by the two-variable combination of local temperature and humidity, which reflects the close relationship between clouds and relative humidity. However, single-variable predictions involving air parcel histories are better than those based solely on the individual local fields, indicating the existence of reliable dynamical information content within parcel trajectories. Thermal fields are better cirrus predictors during boreal winter than summer primarily due to poor predictions over the Asian summer monsoon region, revealing that the functional relationship over southern Asia differs from the rest of the tropics; in short, TTL cirrus formation over regions of active maritime convection, such as the West Pacific, is thermally dominated, indicating an environment in which in situ cirrus are readily formed, while TTL cirrus of southern Asia is moisture dominated, indicating a more direct connection between convective injection of moisture and thin cirrus.

Aerosol Effects on Cumulus Congestus Population over the Tropical Pacific: A Cloud-Resolving Modeling Study

This study examines the significance of aerosol serving as cloud condensation nuclei (CCN) in modulating strengths of tropical maritime convection. Through a Tropical Ocean Global Atmosphere Couple OceanAtmosphere Response Experiment (TOGA COARE) case study using a cloud-resolving model (the Goddard Cumulus Ensemble Model with a horizontal mesh interval of 750 m) anda d etailedspectral bin microphysical scheme, it is foundthat low aerosol concentration acts to reduce convection strengths. Over the tropical western Pacific where low-level water vapor is abundant and a ubiquitous weak stable level exists near 0° C, the low backgroundmaritime aerosol concentration is conducive for forming cumulus congestus. Sensitivity tests show that the main mechanism of convection damping in a clean maritime environment is through reduced condensational growth, although the freezing of supercooled water, cloudtop evaporation, andrain evaporation also contribute to the simulatedeffects. Consid ering the importance of congestus in tropical dynamics and the MaddenJulian oscillation (MJO) lifecycle, we further propose a hypothesis that aerosolcloudprecipitation interactions in an ultraclean marine environment may serve as a damping mechanism for tropical convection.

Radar characteristics of continental, coastal, and maritime convection observed during AMMA/NAMMA

AbstractGround‐based radar observations at three distinct geographical locations in West Africa along a common latitudinal band (Niamey, Niger (continental), Kawsara, Senegal (coastal), and Praia, Republic of Cape Verde (maritime)) are analyzed to determine convective system characteristics in each domain during a 29‐day period in 2006. Ancillary datasets provided by the African Monsoon Multidisciplinary Analyses (AMMA) and NASA‐AMMA (NAMMA) field campaigns are also used to place the radar observations in context. Results show that the total precipitation is dominated by propagating mesoscale convective systems. Convective characteristics vary according to environmental properties, such as vertical shear, CAPE, and the degree of synoptic forcing. Data are bifurcated based on the presence or absence of African easterly waves. In general, African easterly waves appear to enhance mesoscale convective system strength characteristics (e.g. total precipitation and vertical reflectivity profiles) at the inland and maritime sites. The wave regime also resulted in an increased population of the largest observed mesoscale convective systems observed near the coast, which led to an increase in stratiform precipitation. Despite this increase, differentiation of convective strength characteristics was less obvious between wave and no‐wave regimes at the coast. Owing to the propagating nature of these advecting mesoscale convective systems, interaction with the regional thermodynamic and dynamic environment appears to result in more variability than enhancements due to the wave regime, independent of location. Copyright © 2011 Royal Meteorological Society

A Synthetic Aperture Radar–Based Climatology of Open-Cell Convection over the Northeast Pacific Ocean

Abstract This paper presents an 8-yr (1999–2006) climatology of the frequency of open-cell convection over the northeastern Pacific Ocean and the thermodynamic and kinematic environment associated with its development. The climatology is based on synthetic aperture radar–derived wind speed images and reanalysis data. The climatology shows that open-cell convection was a cold-season phenomenon, having occurred in environments in which the difference in temperature between the near-surface air and the sea surface is negative and in environments with positive surface sensible and latent heat fluxes. Within the region between the surface and 500 hPa, the 700–850-hPa layer median static stability was near moist adiabatic while that for the remainder was conditionally unstable. The median magnitude of the vertical wind shear was largest in the 925-hPa–near-surface and 500–700-hPa layers while that at midlevels was relatively weak. Similarities are highlighted between the organization of open-cell convection over the northeastern Pacific Ocean and tropical deep moist maritime convection in terms of cold-pool dynamics. Avenues for future work are discussed.

Microphysical and radiative properties of tropical clouds investigated in TC4 and NAMMA

The size, shape and concentration of ice particles in tropical anvil cirrus and in situ cirrus clouds have a significant impact on cloud radiative forcing, and hence on global climate change. Data collected in tropical anvil and cirrus clouds with a 2D‐S probe, an optical imaging probe with improved response characteristics and the ability to remove shattered artifacts, are analyzed and discussed. The data were collected with NASA DC‐8 and WB‐57F research aircraft near Costa Rica during the 2007 Tropical Composition, Cloud and Climate Coupling (TC4) field project, and with the DC‐8 near Cape Verde during the 2006 NASA African Monsoon Multidisciplinary Analyses (NAMMA) campaign. Data were collected in convective turrets, anvils still attached to convection, aged anvils detached from convection and cirrus formed in situ. Unusually strong maritime convection was encountered, with peak updrafts of 20 m s−1, ice water contents exceeding 2 g m−3 and total particle concentrations exceeding 10 cm−3 at 12.2 km. Ice water contents in the anvils declined outward from the center of convection, decreasing to <0.1 g m−3 in aged anvil cirrus. The data show that microphysical and radiative properties of both tropical anvils and cirrus are most strongly influenced by ice particles in the size range from about 100 to 400 μm. This is contrary to several previous investigations that have suggested that ice particles less than about 50 μm control radiative properties in anvils and cirrus. The 2D‐S particle area and mass size distributions, plus information on particle shape, are input into an optical properties routine that computes cloud extinction, asymmetry parameter and single scattering albedo. These optical properties are then input into two‐stream radiative code to compute radiative heating profiles within the various cloud types. The results produce short‐ and long‐wave heating/cooling vertical profiles in these tropical clouds. A simple parameterization based on 2D‐S measurements is derived from the particle mass size distribution that yields an area size distribution. The parameterized area size distribution can then be used in large‐scale numerical simulations that include radiative transfer packages.

Aerosol composition of the tropical upper troposphere

Abstract. Aerosol composition was measured by the NOAA single-particle mass spectrometer (PALMS) aboard the NASA WB-57 high altitude aircraft platform during two Aura Validation Experiment (AVE) campaigns based in Costa Rica in 2004 and 2006. These studies yielded the most complete set of aerosol composition measurements to date throughout the tropical tropopause layer (TTL) and tropical lower stratosphere. We describe the aerosol properties of the tropical atmosphere and use composition tracers to examine particle sources, the role of recent convection, and cirrus-forming potential in the TTL. Tropical dynamics and regional air sources played principal roles in dictating tropospheric aerosol properties. There was a sharp change in aerosol chemical composition at about 12 km altitude coincident with a change in convective influence. Below this level, maritime convection lofted condensable material that generated acidic, sulfate-rich aerosol. These particles contained significant amounts of methanesulfonic acid (MSA) and showed evidence of cloud processes. In contrast, continental convection injected particles and precursors directly into the TTL, yielding a population of neutralized, organic-rich aerosol. The organics were often highly oxidized and particles with oxidized organics also contained nitrate. Above the tropopause, chemical composition gradually changed toward sulfuric acid particles but neutralized particles were still abundant 2 km above the tropopause. Deep continental convection, though sporadic and geographically localized, may strongly influence TTL aerosol properties on a global scale. The abundance of organic-rich aerosol may inhibit ice nucleation and formation of tropopause level cirrus.

Convective Systems of the North Australian Monsoon

Abstract The climatology of convection over northern Australia and the surrounding oceans, based on six wet seasons (September–April), is derived from the Japanese Meteorological Agency Geostationary Meteorological Satellite-5 (GMS-5) IR1 channel for the years from 1995/96 to 2000/01. This is the first multiyear study of this kind. Clouds are identified at two cloud-top temperature thresholds: 235 and 208 K. The annual cycle of cloudiness over northern Australia shows an initial (October–November) buildup over the Darwin region before widespread cloudiness develops over the entire region during the monsoon months (December–February), followed by a northward contraction during March and April. Tracking mesoscale convective systems (MCSs) reveals that both the size of the cloud systems and their lifetimes follow power-law distributions. For short-lived MCSs (less than 12 h), the initial expansion of the cloudy area is related to the lifetime, with mergers important for long-lived MCSs (greater than 24 h). During periods of deep zonal flow, which coincide with the active phase of the monsoon, the number of convective elements in the Darwin region peaks in the early afternoon, which is characteristic of the diurnal cycle over land. In contrast, when the zonal flow is deep and easterly and the monsoon is in a break phase, the areal extent of the convective elements in the Darwin region is greatest in the late morning, which is more typical of maritime convection.

ATMOSPHERIC MOIST CONVECTION

▪ Abstract Various forms of atmospheric moist convection are reviewed through a consideration of three prevalent regimes: stratocumulus; trade-wind; and deep, precipitating, maritime convection. These regimes are chosen because they are structural components of the general circulation of the atmosphere and because they highlight distinguishing features of this polymorphous phenomenon. In particular, the ways in which varied forms of moist convection communicate with remote parts of the flow through mechanisms other than the rearrangement of fluid parcels are emphasized. These include radiative, gravity wave, and/or microphysical (precipitation) processes. For each regime, basic aspects of its phenomenology are presented along with theoretical frameworks that have arisen to help rationalize the phenomenology. Recent developments suggest that the increased capacity for numerical simulation and increasingly refined remote sensing capabilities bodes well for major advances in the coming years.

Semiannual NO2plumes during the monsoon transition periods over the central Indian Ocean

[1] In this study we identify recurring plumes of tropospheric NO2 originating from Africa and Indonesia during the monsoon transition periods over the central Indian Ocean (CIO, 5°N–30°S, 55°E–95°E), based on GOME satellite observations and global model (MATCH-MPIC) simulations. Despite the relatively short lifetime of NOx, these strong plumes can develop due to the pronounced anti-cyclonic circulation over the CIO, and the weak maritime convection, which limits vertical mixing. Model results indicate that the plumes are mainly transported in the middle troposphere (MT). Thus, the CIO in the Southern Hemisphere (SH) is not always as pristine as found in INDOEX during the winter monsoon.