JPM7A

Numerical Modeling of Aerosol Production and CCN Formation in A Remote Marine Boundary Layer

Zhao Chunsheng and Qin Yu

Department of Geophysics, Peking University, CHINA

The objective of the research contained within this presentation includes two parts: first is development of a general framework for the modeling of general particulate systems, second is application to the production and development of atmospheric aerosols in a remote marine boundary layer. In this study, a size-resolved atmospheric aerosol model including the basic aerosol dynamic processes (coagulation, condensation, deposition and nucleation) is developed. Sectional equations of mass conservation during coagulation and number conservation during condensation are derived for describing aerosol dynamic mechanisms. Other processes such as deposition and nucleation are considered. Coupling with a simplified DMS chemical sub-module, production and growth of aerosols in the remote marine boundary layer are studied. Comparing with observational data, we discuss the interactions of the processes in the DMS-CCN system.

jpm7b

Air-sea CO₂ flux during mixed-layer development in the sub-polar North Pacific

Yoshikazu Sasai, Motoyoshi Ikeda and Noriyuki Tanaka

Graduate School of Environmental Earth Science, Hokkaido University, Sapporo, Japan

In the sub-polar and polar regions of the oceans, observations show that oceanic pCO₂ and the concentration of total CO₂ are higher during winter than summer. This seasonal evolution may be mainly accounted for by the winter mixing of deep waters, which are rich in total CO₂. We employ a bulk mixed-layer model, which is initialized with the historical data in the sub-polar North Pacific and forced by the observed atmospheric data for a period of 6 months (October-March). The model retains the following mechanisms: cooling and fresh water flux through the sea surface, kinetic energy input due to wind stresses, air-sea CO₂ flux as well as turbulent vertical mixing of heat, salt and total carbonate at the bottom of the mixed layer. This entrainment rate is determined from an energy balance between kinetic and potential energy input at the sea surface and a potential energy gain at the mixed-layer bottom. Total CO₂ and pCO₂ are related to each other under the assumption of the chemical equilibrium with a fixed alkalinity. Since biological processes are secondary for the pCO₂ evolution during winter, they are omitted.

The model reproduces the evolution of temperature, salinity and thickness of the mixed layer from fall to winter in the sub-polar North Pacific. The pCO₂ distribution is comparable with the ship of opportunity data. In fall, the upward flux of total CO₂ from the lower ocean to the mixed layer results in a rapid increase in pCO₂ from the low value in summer, while the ocean still absorbs CO2 from the atmosphere. The further increase in total CO₂ yields oceanic pCO₂ exceeding the atmospheric counter part and outgoing air-sea flux of CO₂ in winter. This air-sea flux would cease after CO₂ is reduced by biological production in spring. It is implied that the net air-sea CO2 flux must be sensitive to the timing of spring bloom.

Jpm7d

Laboratory experiments on free evaporative convection in various conditions

E.P. Anisimova¹, A.A. Speranskaya¹ and S.N. Dikarev²

¹Moscow State University, RUSSIA
²P.P. Shirshov Institute of Oceanology, Moscow, RUSSIA

The multifactoral nature of the small scale near-surface state of boundary layers is one of the main difficulties in studies of real ocean conditions. Mechanical turbulence in the air and water, vorticity of current, surface waves, solar radiation in the daytime, gas microbubbles (aeration) and spray, microbiological effects - is a far-from-complete list of the essential external parameters, which influence the thermodynamic state of the near-surface boundary layers. We put forward a laboratory method of construction or designing near-surface boundary layers with separate physical blocks, such as salt concentration in the water, aeration, uniform environmental rotation. The aim of our laboratory experiments is to determine who is starring in the sea surface physical performance?

It is obvious, that to determine the roles of different separate/combined physical factors in the process one has to have a background model to compare with. The fresh water body exposed to air cooling via evaporation in the free turbulent convection regime has been used as a background model in our investigations.

The results of the extended series of laboratory experiments produced in the P.P. Shirshov Institute of Oceanology (IO RAS, Moscow) and Moscow State University (MSU) will be presented. For example, contrary to expectations, free evaporative convection gets weaker with the increase of water salinity, but invisible aeration of water sufficiently enhances water-air mass and heat fluxes. It will be shown also, that convective cooling of small scale intensive vortices is slower than in the surrounding water. Theoretical treatment of experimental observations has been made on the basis of simple turbulent convective boundary layer approximation. Some numerical results from the extended system of Golitsin-Grachev integral relationships for multicomponent media will also be presented.

JPM7E

COASTWATCH'95: ERS-1/2 SAR Detection of Natural Film on the Ocean Surface

H.A. Espedal¹, O.M. Johannessen¹, D. Lyzenga², E. Dano³, J.A. Johannessen⁴,
J. Knulst⁵ and A. Jenkins¹

¹Nansen Environmental and Remote Sensing Center, Bergen, NORWAY
²Environmental Research Institute of Michigan, Ann Arbor, USA
³Department of Naval Architecture & Marine Engineering University of
Michigan, USA
⁴European Space Research and Technology Centre, Noordwijk,
THE NETHERLANDS
⁵Swedish Environmental Research Institute, Aneboda,
SWEDEN

Mesoscale phenomena on the ocean such as eddies and current convergence zones can often be seen in SAR images due to characteristic patterns caused by natural film induced damping of the waves. Such films have also been found to exert a first-order effect on air-sea gas exchange, which may be important for the global scale climate system. Satellite synthetic aperture radar (SAR) may prove very useful to quantify the extent of natural film. To investigate the composition of these films and their effect on radar return, samples of the sea surface were taken simultaneously with ERS-1/2 SAR coverage of a fjord (the Korsfjord experiment), and later in the open ocean (COASTWATCH'95). In the COASTWATCH'95 experiment simultaneous observations were made with a shipmounted C-band dual-polarized Doppler radar, and surface drifters were deployed to investigate the surface current variations in the vicinity of the slicks. The dependence of the existence of slicks on wind speed is also investigated, and an estimate of natural film distribution given, using a large number of ERS-1 and 2 images collected over the same area under a variety of wind conditions.

JPM7f

Wave Breaking as Periodic Event and its Effect on Momentum, Heat and Mass Transfer at the Sea-Atmosphere Interface.

Walter Eifler

CEC, JRC Ispra, SAI/Marine Enviroment Unit, Ispra, Italy

Breaking waves, visualised by oceanic whitecaps, cover only a limited part of the sea surface (typically 0.1 -1-10% for wind speeds of 5-10-20 m/s, e.g. Wu, 1979), but they have an important influence on transfer processes at the sea-atmosphere interface (e.g. Monahan and Spillane, 1984, showing a direct correlation between whitecap coverage and gas transfer). Since momentum and heat transfer are governed by airside transfer resistance, no direct correlation is considered but the effect of wave breaking is implicitly included using empirical correlations for the transfer coefficients (e.g. Smith, 1988) or using the roughness length concept (e.g. Charnok, 1955; Donelan et al, 1993). The effect of breaking waves in the upper ocean has been modelled as flux of turbulent kinetic energy, assumed to be continuous in time (e.g. Craig and Banner, 1994).

Here a model applying for momentum, heat and mass transfer is proposed. It is a 1-D "once through", i.e. directly coupled air-water model which allows the simulation of the time-depending, periodic breaking events. From a fixed position indeed a moving interface with periodic properties is seen. For most of the time between breaking events a continuous surface passes, only for a fraction of that time a disrupted surface passes. The latter time fraction is assumed to be given by the surface fraction of whitecaps. The model included transport equations for momentum, heat and passive tracers which are solved "once-through" between an atmospheric reference position and the sea bottom. Turbulent transport properties are determined separately for the air and water flow, solving transport equations for the turbulent kinetic energy and parametrizing the mixing length. The heart of the system is the interface submodel used as air-water coupling tool and described elsewhere (Eifler, 1993)*. This model, applied bothsides of the interface, replaces the information provided by the turbulence equations in the respective first interface adjacent grid elements and specifies the viscous layer resistance. During the passing of continuous surface the viscous layer resistance is present and generates high gradients of velocity, temperature and tracer concentration. Disruption of the sea surface destroys the viscous sublayers, i.e. during the passage of a disrupted surface the high viscous layer resistance is replaced by a low resistance. The short time of low transfer resistance is however not long enough to decrease significantly the high gradients, which therefore, in combination with the low transfer resistance, produce high fluxes. Comparing the time integrated fluxes with experimental data, it is shown that the transition between the low wind and high wind regime is well reproduced for (air side governed) heat and momentum transfer as well as for (water side governed) high Schmidt number gas transfer.

*Eifler, W., 1993, A Hypothesis on Momentum and Heat Transfer near the Sea-Atmosphere Interface and a Related Simple Model Journal of Marine Systems, 4, 133-153.

JPM7H

Spatial Variability of Heavy Metal fluxes into the Atmosphere over the Russian Arctic and Surrounded Regions.

S.A. Gromov

Institute of Global Climate and Ecology, Moscow, Russia

The methodology of estimating heavy metal emissions from natural and anthropogenic sources is presented. It is discussed from point of applicability to various type of sources, experimental data the assessment of and the ability to estimate regional and global scale emissions. The data on emissions of lead, cadmium, mercury and cooper are presented for large scale territory regions of the Arctic and its surroundings. There is a comparison with governmental reports and previous evaluations which were produced by both national researchers and others. First order assessment of atmospheric transport flows into Polar regions are carried out by performing backward trajectory set analysis of measured emission data.

Jpm7j

New understanding of ocean - atmosphere system interaction by means of skin-layer (physico-chemical structure) study

N. Kucherenko, V. Syhovey and B. Kapochkin

ODGMI , Odessa, UKRAINE

The investigation of processes in the ocean-atmosphere border relates to temperature and salinity especially. But the analysis of thin surface water skin-layer (SML) on the border of phase divisions shows that natural and laboratory measurements of SML, and also theoretical works concerning its formation, produce some contradictions. They concern, generally, the questions of density stability, structure and size of SML. But we still have not enough information about energetics of cold thermal microlayer formation processes, functions generality and SML, ice and foam connection. Our investigations data comes from the Indian Ocean and Black Sea. The present work was carried out for about ten years.

The physical and mathematical models of air-sea interactions based on the information about temperature in the surface layer 0–50 m. But interaction between air and sea take place in the skin-layer (0–0.5 mm). The temperature of the skin-layer is different to that in the deeper layers to 2–14ƒ. This mistake takes place in all mathematical models of air-sea interaction. This influences the quality of weather forecasts.

We proved that the stable stratification of the ocean’s skin-layer is the result of a particular water structure at the boundary line, low salinity and low density of frontier water at low temperature.

The role of evaporation is very small We estimated energetical appearance and barrier functions SML in self-regulation of ocean-atmosphere mass-heat exchange at different hydrometeorological conditions. We studied the influence of specific properties of ocean’s skin-layer on the results of temperature change of ocean surface from space.

JPM7k

Late Holocene palaeoclimates from lake sediments, North Island, New Zealand

D.N. Eden and M.J. Page

Manaaki Whenua-Landcare Research, Palmerston North,
New Zealand

A high-resolution lake sediment record from Lake Tutira on the east coast of the North Island, New Zealand contains a record of major storms spanning 2250 years. The record is largely one of natural variability without human impacts since first settlement occurred about 500 years ago.

Layers of sediment representing the products of individual storm events are clearly visible in cores from the lake. These storm sediment pulses, derived from soil erosion within the catchment, record the frequency and magnitude of storms. The presence of five tephra datums within the lake sediments provide a chronology.

Six periods of high sedimentation and associated erosion before European settlement (A.D. 1878) are identified from a clustering of sediment pulses. Two of these storm periods correspond to New Zealand-wide periods of increased erosion and sedimentation. At least five of the storm periods are interpreted to have resulted from periods of higher rainfall and probably warmer temperatures, since historic records show that most large storms are derived from the subtropics or tropics. The storm periods mostly occurred during warm climate intervals previously identified from New Zealand and Southern Hemisphere palaeoclimatic evidence. The Mapara 2 period (c.2090-1855 cal. yr B.P.) had the highest frequency of storms and lasted more than 200 years. Other periods were generally of shorter duration. The Mapara 2 period corresponds to warm intervals in the Chilean and Tasmanian tree-ring records which might indicate hemispheric warming around 2000 years ago.

The only storm period (Burrell) which occurred during the historical ENSO record corresponds to a time of moderate to high ENSO activity. Three earlier periods also appear to show responses to ENSO.

JPM7N

Breaking waves and whitecapping in coastal zone

J. Piazzola, O. Lecalve, J. Gourdeau and S. Despiau

LEPI, BP132, 83957 La Garde Cedex, FRANCE

The influence of sea surface state for the generation of particles and the transfer of gases at the interface is evident but, depending on the wind direction (of marine or continental origin), coastal regions are characterised by limited or unlimited fetch and consequently, the breaking wave and whitecap generation conditions can be very different from those prevailing in open ocean. Moreover, since the coast is often uneven, the problem is still complicated and the conditions which prevail to the break of the waves are very difficult to deal with. In order to estimate the surface percent covered by whitecapes in coastal zone, a simple model of breaking waves foresight, based on 10 m wind speed, fetch length and wave age has been developed and tested in the Mediterranean zone located off the coast of Toulon (France). At the same time, in that zone, a video and photo image processing developed in the laboratory is used to evaluate the same parameter. The results obtained by the two methods are presented and compared. Some results concerning aerosol particle concentrations and the DMS transfer obtained in the same zone are also presented. They show the great variability of these parameters with respect to the sea surface state.