Sea salt aerosol (SSA) exerts a major influence over a broad reach of geophysics. It is important to the physics and chemistry of the marine atmosphere and to marine geochemistry and biogeochemistry generally. It affects visibility, remote sensing, atmospheric chemistry, and air quality. Sea salt aerosol particles interact with other atmospheric gaseous and aerosol constituents by acting as sinks for condensable gases and suppressing new particle formation, thus influencing the size distribution of these other aerosols and more broadly influencing the geochemical cycles of substances with which they interact. As the key aerosol constituent over much of Earth's surface at present, and all the more so in pre-industrial times, SSA is central to description of Earth's aerosol burden.

Sea Salt Aerosol Production: Mechanisms, Methods, Measurements, and Models - A Critical Review

Radiative effects of natural aerosols: A review

Recent work on mid-latitude and equatorial sporadic-E

. Southern Asia, extending from Pakistan and Afghanistan to Indonesia and Papua New Guinea, is one of the most heavily populated regions of the world. Biofuel and biomass burning play a disproportionately large role in the emissions of most key pollutant gases and aerosols there, in contrast to much of the rest of the Northern Hemisphere, where fossil fuel burning and industrial processes tend to dominate. This results in polluted air masses which are enriched in carbon-containing aerosols, carbon monoxide, and hydrocarbons. The outflow and long-distance transport of these polluted air masses is characterized by three distinct seasonal circulation patterns: the winter monsoon, the summer monsoon, and the monsoon transition periods. During winter, the near-surface flow is mostly northeasterly, and the regional pollution forms a thick haze layer in the lower troposphere which spreads out over millions of square km between southern Asia and the Intertropical Convergence Zone (ITCZ), located several degrees south of the equator over the Indian Ocean during this period. During summer, the heavy monsoon rains effectively remove soluble gases and aerosols. Less soluble species, on the other hand, are lifted to the upper troposphere in deep convective clouds, and are then transported away from the region by strong upper tropospheric winds, particularly towards northern Africa and the Mediterranean in the tropical easterly jet. Part of the pollution can reach the tropical tropopause layer, the gateway to the stratosphere. During the monsoon transition periods, the flow across the Indian Ocean is primarily zonal, and strong pollution plumes originating from both southeastern Asia and from Africa spread across the central Indian Ocean. This paper provides a review of the current state of knowledge based on the many observational and modeling studies over the last decades that have examined the southern Asian atmospheric pollutant outflow and its large scale effects. An outlook is provided as a guideline for future research, pointing out particularly critical issues such as: resolving discrepancies between top down and bottom up emissions estimates; assessing the processing and aging of the pollutant outflow; developing a better understanding of the observed elevated pollutant layers and their relationship to local sea breeze and large scale monsoon circulations; and determining the impacts of the pollutant outflow on the Asian monsoon meteorology and the regional hydrological cycle, in particular the mountain cryospheric reservoirs and the fresh water supply, which in turn directly impact the lives of over a billion inhabitants of southern Asia.

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Atmospheric pollutant outflow from southern Asia: a review

Systematic characterization of aerosol over the oceans is needed to understand the aerosol effect on climate and on transport of pollutants between continents. Reported are the results of a comprehensive optical and physical characterization of ambient aerosol in five key island locations of the Aerosol Robotic Network (AERONET) of sun and sky radiometers, spanning over 2‐5 yr. The results are compared with aerosol optical depths and size distributions reported in the literature over the last 30 yr. Aerosol found over the tropical Pacific Ocean (at three sites between 208S and 208N) still resembles mostly clean background conditions dominated by maritime aerosol. The optical thickness is remarkably stable with mean value of ta(500 nm) 5 0.07, mode value at tam

/pdf/optical-properties-of-atmospheric-aerosol-in-maritime-3h70wjoyvh.pdf

Optical Properties of Atmospheric Aerosol in Maritime Environments

Results of the studies on the characteristics of marine aerosol optical depths made in remote regions of the tropical Indian Ocean using a multiwavelength solar radiometer, taken on a scientific cruise, are presented. The dependence of the aerosol optical depths on prevailing winds in marine boundary layer and on deck level relative humidity (RH) are examined. Aerosol optical depths (τp) in far oceanic regions with marine air mass prevailing, in general, are found to increase nearly exponentially with average wind speed (Ua) as τp=τo exp(a Ua), where a = 0.16 ± 0.04. No association is seen with deck level relative humidity, as the effects of wind appear to offset the effects due to RH. The columnar size distributions retrieved from aerosol spectral optical depths reveal two modes, one at ∼0.04 μm and a secondary mode at ∼0.8 μm. The columnar mass loading estimated from the size distributions increases exponentially with wind speed and has a wind independent value of ∼28 mg m−2.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97JD01121

Investigations of marine aerosols over the tropical Indian Ocean

Nighttime equatorial thermospheric meridional winds have been derived using h′F data from two equatorial stations nearly on the same magnetic meridian. It is shown that the winds derived are quite consistent with earlier observations.

Nighttime equatorial thermospheric meridional winds from ionospheric h'F data

Evaluation of hypoglycemic and antihyperglycemic effects of Datura metel (Linn.) seeds in normal and alloxan-induced diabetic rats

. Sources and propagation characteristics of high-frequency gravity waves observed in the mesosphere using airglow emissions from Gadanki (13.5° N, 79.2° E) and Hyderabad (17.5° N, 78.5° E) are investigated using reverse ray tracing. Wave amplitudes are also traced back, including both radiative and diffusive damping. The ray tracing is performed using background temperature and wind data obtained from the MSISE-90 and HWM-07 models, respectively. For the Gadanki region, the suitability of these models is tested. Further, a climatological model of the background atmosphere for the Gadanki region has been developed using nearly 30 years of observations available from a variety of ground-based (MST radar, radiosondes, MF radar) and rocket- and satellite-borne measurements. ERA-Interim products are utilized for constructing background parameters corresponding to the meteorological conditions of the observations. With the reverse ray-tracing method, the source locations for nine wave events could be identified to be in the upper troposphere, whereas for five other events the waves terminated in the mesosphere itself. Uncertainty in locating the terminal points of wave events in the horizontal direction is estimated to be within 50–100 km and 150–300 km for Gadanki and Hyderabad wave events, respectively. This uncertainty arises mainly due to non-consideration of the day-to-day variability in the tidal amplitudes. Prevailing conditions at the terminal points for each of the 14 events are provided. As no convection in and around the terminal points is noticed, convection is unlikely to be the source. Interestingly, large (~9 m s−1km−1) vertical shears in the horizontal wind are noticed near the ray terminal points (at 10–12 km altitude) and are thus identified to be the source for generating the observed high-phase-speed, high-frequency gravity waves.

/pdf/evidence-for-tropospheric-wind-shear-excitation-of-high-42pe9cvs2b.pdf

Evidence for tropospheric wind shear excitation of high-phase-speed gravity waves reaching the mesosphere using the ray-tracing technique

Aerosol spectral optical depths (τpλ) estimated at 10 wavelengths in the visible and near infrared range over oceanic regions covering near and far coastal regions of the Arabian Sea and remote areas of the equatorial Indian Ocean adjoining the Indian peninsula have been used to study the spatial variation of aerosol optical depths over the ocean. Size parameters and concentrations of aerosols along the downwind direction have been derived with a view to studying the effect of the continent on aerosol properties over the ocean. The studies showed a gradual decrease in τpλ with fetch distance D with an e−l scaling distance in the range of 1700 to 2400 km under calm to moderate wind conditions. The scaling distance increases with increase in wind speed. A significant increase in the relative concentration of small (accumulation size range) particles is seen as the continent is approached from deeper oceanic regions downwind, indicating increased influence of anthropogenic activities. The coarse-particle concentration appears to be of oceanic origin and remains nearly steady over the entire region when the winds are low to moderate.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/98JD00803

B. V. Krishna Murthy

Papers

Investigations of marine aerosols over the tropical Indian Ocean

Nighttime equatorial thermospheric meridional winds from ionospheric h'F data

Evaluation of hypoglycemic and antihyperglycemic effects of Datura metel (Linn.) seeds in normal and alloxan-induced diabetic rats

Evidence for tropospheric wind shear excitation of high-phase-speed gravity waves reaching the mesosphere using the ray-tracing technique

Spatial Gradients in Aerosol Characteristics over the Arabian Sea and Indian Ocean