Characteristics of cloud drop spectra in tropical warm clouds

Characteristics of cloud drop spectra were studied using 400 samples obtained from 120 warm cumulus clouds formed during the summer monsoon season.The total concentration of cloud drops (N _T) varied from 384 to 884 cm^–3 and the maximum concentration was observed in the layer below the cloud-top. The width of the drop spectrum was broader in the cloud-base region and in the region below the cloud-top. The spectrum was multimodal at all levels except in the cloud-top region where it was unimodal. The concentration of drops with diameter greater than 50 m (N _L) varied from 0.0 to 0.674 cm^–3.N _L was larger in the cloud-base region.N _L decreased with height up to the middle level and thereafter showed an increase. In the cloud-top region no large drops were present. The computed values of the liquid water varied between 0.132 and 0.536 g m^–3 and the mean volume diameter (MVD) varied between 8.1 and 12.0 m. The LWC and MVD showed a decrease with height except in the middle region of the cloud where the values were higher than the adjacent levels. The dispersion of the cloud drops was lower (0.65) in the cloud-top region and higher (1.01) in the cloud-base region.The observed cloud microphysical characteristics were attributed to vertical mixing in clouds induced by the cloud-top gravity oscillations (buoyancy oscillations) generated by the intensification of turbulent eddies due to the buoyant production of energy by the microscale-fractional-condensation (MFC) in turbulent eddies.     

A comparative study on the growth of cloud drops by condensation using an air parcel model with and without entrainment

During a study of the growth of cloud drops by condensation the evolution of cloud drop size spectra with height above cloud base was determined for maritime aerosols, and for continental aerosols containing aerosol particles of mixed composition. Air parcel models were used in which the parcel was either completely closed to mass and heat transfer (strictly adiabatic models), or open to heat transfer and to partial or complete mass transfer (entrainment models). It was found that adiabatic models and models which consider the entraining of air devoid of aerosol particles predict drop size distributions which are considerably narrower than those observed in non-precipitating cumulus clouds, and have only a single maximum. On the other hand, relative broad drop size distributions and distributions with a double maximum — as they are observed in atmospheric clouds — are predicted if the entrainment of both air and aerosol particles are considered in the condensation model. Our results support the findings ofWarner (1973) which were obtained for a purely maritime aerosol.     

Do Cloud Properties in a Puerto Rican Tropical Montane Cloud Forest Depend on Occurrence of Long-Range Transported African Dust?

We investigated cloud properties of warm clouds in a tropical montane cloud forest at Pico del Este (1,051 m a.s.l.) in the northeastern part of Puerto Rico to address the question of whether cloud properties in the Caribbean could potentially be affected by African dust transported across the Atlantic Ocean. We analyzed data collected during 12 days in July 2011. Cloud droplet size spectra were measured using the FM-100 fog droplet spectrometer that measured droplet size distributions in the range from 2 to 49 µm, primarily during fog events. The droplet size spectra revealed a bimodal structure, with the first peak (D < 6 µm) being more pronounced in terms of droplet number concentrations, whereas the second peak (10 µm < D < 20 µm) was found to be the one relevant for total liquid water content (LWC) of the cloud. We identified three major clusters of characteristic droplet size spectra by means of hierarchical clustering. All clusters differed significantly from each other in droplet number concentration ( \(N_{\rm tot}\) ), effective diameter (ED), and median volume diameter (MVD). For the cluster comprising the largest droplets and the lowest droplet number concentrations, we found evidence of inhomogeneous mixing in the cloud. Contrastingly, the other two clusters revealed microphysical behavior, which could be expected under homogeneous mixing conditions. For those conditions, an increase in cloud condensation nuclei—e.g., from processed African dust transported to the site—is supposed to lead to an increased droplet concentration. In fact, one of these two clusters showed a clear shift of cloud droplet size spectra towards smaller droplet diameters. Since this cluster occurred during periods with strong evidence for the presence of long-range transported African dust, we hypothesize a link between the observed dust episodes and cloud characteristics in the Caribbean at our site, which is similar to the anthropogenic aerosol indirect effect.     

Observations of condensation growth determined by entity type mixing

It has been speculated for many years that the development of the droplet spectra in cloud is probably influenced by mixing processes. Various theoretical attempts to broaden the droplet spectra by mixing parcels with different velocity histories has shown that that particular effect is small. Similarly, very simpleuniform entrainment procedures did not lead to cloud drop size spectra which were broad enough, although by producing cloud drop size distributions with a double mode these models did substantially improve the drop size spectra of earlier adiabatic models which only exhibited a single mode.Recently a model based on entraining entities representing moving parcels of cloud air within the cloud was detailed byTelford andChai (1980). This study showed that the mixing in of dry air at cumulus turrets could lead to vertical cycling of diluted parcels, and that this cycling, with continual entrainment across the parcel boundaries, will produce much larger drops, as well as smaller drops of all sizes, in the droplet spectra. The entity entrainment concept studied there appears to apply to the observations of stratus cloud discussed in this paper.This paper presents data taken in marine stratus off the California coast which give a particularly clear example of how such droplet spectra modification occurs in practice. Both large drops, and the spread of the spectra to smaller sizes, occur in relation to other variables in such a way as to be consistent with an entity entrainment explanation, with no other obvious possibility.In a marine stratus cloud just over 200 m thick and many tens of miles in extent we find clear evidence that dry air is mixing in at cloud tops. Strong vertical motion is to be found in the cloud, large sized drops are found in cloud parcels where the mixing gives lower droplet concentrations, and there is evidence that newly formed cloud parcels are warmer and contain many more smaller droplets.The observations show that immediately following entrainment of dry air drop diameters are not reduced appreciably, but, in the same parcels, drop concentrations have been reduced by a factor of ten or more. Further down in the cloud big drops, able to start growth by coalescence, are found associated with low total droplet concentrations.Overall, it seems likely from the consideration of these observations that the formation of the large drops which lead to precipitation processes in clouds depends critically on the mixing in of dry air at cloud tops, and very little on the size of the small drops resulting from the condensation nucleus counts. As a conclusion it appears reasonable to state that if entrainment occurs at cloud tops, then big drops will be formed!     

Relocation of Swarm Events in the June 1987 Earthquake Sequence from the Lake Aswan Area in Egypt

--We have examined the digital waveform data and relocated a number of events within the June 1987 earthquake swarm, which occurred beneath the northern part of Lake Aswan, 70 km southwest of the Aswan High Dam in Egypt. This swarm occurred between June 17th and 19th with a maximum magnitude event of "M_L"=3.5.¶Cross correlation between a chosen master and the analyzed events has been carried out on seismograms from stations of the Aswan network. The cross correlation demonstrates the presence of a difference in both the P wave ((t_p) and the S wave ((t_s) arrival times at each station in the network relative to the arrival times of the master event at the same stations. (t_p ranges between т.15 and 0.11 second, while (t_s ranges between т.17 and 0.11 second.¶The primary interpretation is that the se time differences represent an error in the manually picking arrival times. Then, (t_p and (t_s values for each event result from a change in the hypocentral parameters from those of the master event, assuming the P- and S-wave velocity distribution remains constant during the swarm activity. This interpretation enables us to determine the relative distribution of hypocenters with respect to the hypocentral location of the master event. We present the results from a swarm of 9 events demonstrating they originate from a nearly unique location, rather than the zone identified from the preliminary locations which used manually picked onset times.     

Direct Assessment of Wood’s Metal Wettability on Quartz

--A tensiometric method (Wilhelmy plate) is used to study Wood's metal dynamic wettability on specially prepared surfaces of quartz single crystals at low velocities of immersion (2 to 16 wm/s). After correction for buoyancy, the force exerted on the plate by the molten metal is used to derive the unit work of wetting n cos Š where n is the Wood's metal surface tension and Š is the interfacial contact angle. Tests at different temperatures (85, 120 and 200°C) show that below 120°C, viscosity effects cannot be neglected. At an immersion/emersion rate of 2 wm/s, n cos Š is in the range 0.417-0.444 N/m at 120°C, and 0.432-0.458 N/m at 200°C. These figures allow the conversion of injection pressures into capillary diameters during Wood's metal injection tests. The method is promising since it may be used in porous materials to check the sensitivity of the unit work of wetting n cos Š to parameters such as roughness and mineralogy, which are known to vary in a wide range within the pores and cracks of rocks.     

A Study of Chloride Aerosol, Total Aerosol and Ice Nuclei in the Indian Regions

--Atmospheric aerosols were sampled from aircraft at various levels over Rihand in northern India during the monsoon season of 1974 and at surface levels at Calcutta, Delhi, Varanasi and Jodhpur during different seasons of 1970 and 1971. Millipore filter assembly was used for this purpose. Chloride nuclei, total aerosol and ice nuclei concentrations were evaluated from millipore filters. At Rihand/Varanasi, during the monsoon, the chloride size spectrum was broader and the distribution bimodal at cloud base level while the spectra were narrower and the distributions unimodal at other levels. At Rihand, chloride mass and larger giant chloride number were considerably higher, total aerosol higher while ice nuclei concentrations were lower on the days with moderate rain as compared to those with light rain. Calcutta (maritime) showed maximum while Varanasi (well-inland) showed minimum chloride number concentrations. As compared with Calcutta, Delhi (continental) had lower chloride and total aerosol, and markedly higher ice nuclei concentrations. Varanasi (high rainfall region) showed all the values, except for small-sized chlorides, notably higher with respect to Jodhpur (low rainfall region). Ice nuclei concentration was lowest in winter and highest in summer at Delhi. Variations of the aerosols during different parts of the day/night are also discussed.     

Changes in the photosynthetic coefficients α and Pm of Planktothrix rubescens grown on light-dark cycles

The relationship between photosynthesis and irradiance was investigated in a strain of the cyanobacterium Planktothrix rubescens isolated from Lake Zürich, using cultures grown on a 12:12-h light-dark cycle. From the photosynthesis-irradiance (P/I) curves, values of the light-affinity coefficient, f, and the maximum rate of photosynthesis, P_m, were determined: in different cultures f ranged from 0.02-0.08 7mol mg^-1 h^-1 (7mol m^-2 s^-1)^-1 and P_m from 0.6-2.6 7mol mg^-1 h^-1 (rates of O₂ production related to dry biomass). Comparisons made at different phases of the light-dark cycle in individual cultures showed that in the first hour of the light phase f rose by an average of 21 % and P_m by 7 %. In cultures that had been grown in many light-dark cycles, however, the rise occurred only if light was given at the beginning of the notional light phase; cultures kept in darkness showed no rise. It is concluded that the observed increases in f and P_m after dawn were in response to the exogenous irradiance rather than due to endogenous rhythms. These findings are discussed in relation to diel variations in the photosynthetic coefficients of natural populations of P. rubescens in Lake Zürich.     

Effects of collision-induced breakup on drop size distributions in steady state rainshafts

New equations and techniques for dealing with drop breakups are developed and applied to the modelling of the evolution of raindrop spectra in rainshafts. Breakup experiments byMcTaggart-Cowan andList (1975) served as data base.No matter what the original size distribution, the spectrum evolution will always lead to a Marshall-Palmer type equilibrium di tributionN=N ₀e^–D, with =constant andN ₀ proportional to the rainfall rateR. (D stands for raindrop diameter.) ForR29 mm h^–1 and an original Marshall-Palmer distribution, the required fall height to reach equilibrium is 2 km.The equilibrium distributions are characterized by linear relationships betweenR, the radar reflectivity factorZ, the liquid water content LWC and theN ₀ of the Marshall-Palmer distribution. Possible explanations for the discrepancy with observations are given.The fact that the all-water processes cannot produce drops withD2.5 mm (as confirmed by observations) leads to the conclusion that observed large raindrops withD5 mm represent melted hailstones and have not yet reached an equilibrium distribution. These latter conclusions were reached within the original assumption of videspread, steady state precipitation.     

Observation of Double-mixing Line Structure in the Convective Boundary Layer During the Summer Monsoon Season

v--vThe special aerological observations carried out as a part of Land Surface Processes Experiment (LASPEX) were used to investigate the thermodynamic structure of the convective boundary layer during the summer monsoon of 1997. The analysis suggested that the convective boundary layer top was found at 700 hPa which was associated with Š_e minimum and Š_es maximum values. Double-mixing line structure was noticed in the conserved variable diagrams which was possibly attributed to the radiative warming/evaporation of falling precipitation.     

Biochemical characteristics of alga-bacterial mats and invertebrates from shallow-water hydrothermal fields of the West Pacific Ocean

In this study we assessed the biochemical adaptations of biotic specimens from the hydrothermal vent fields from different geographical zones. Algabacterial and bacterial mats and specimens of bivalves (9 species) and sea urchins (2 species) from different coastal shallow-water fields of hydrothermal activity along the West Rift zones of the Pacific Ocean were sampled to compare biochemical activities to volcanogenic chemical characteristics. The algabacterial and bacterial mat cells and subcellular fractions of bivalve gills and sea urchin guts were measured for 5-aminolevulinic acid (ALA), cytochromes b, (c + c₁), (a + a₃) and P450 (CYP), and activities of ALA synthetase and CYP-dependent aminopyrine N-demethylase (APND). The algabacterial mats from the Kuril Islands and New Zealand displayed comparable ALA and cytochrome levels and enzyme activities. Similar ALA synthesis, APND activity, and levels of cytochromes b and (c + c₁) were observed in bacterial mats from hydrothermal fields from Kuriles, New Britain Island and New Zealand. More active ALA synthesis, APND activity and enhanced content of cytochromes b and (c + c₁) and lower levels of CYP were found in bacterial mats than in algabacterial mats. Further, all bivalves influenced by hydrothermal discharges had elevated CYP levels and APND activity as well as a significant increase in ALA content and ALA synthesis (P < 0.05). Statistically sufficient (P < 0.05) alterations in ALA synthesis, APND activity and total CYP level were found in sea urchins under hydrothermal influence. Our findings contribute to the global assessment of hydrothermal effluents on biota and indicate that living conditions near hydrothermal vents accelerate metabolism of bivalves and sea urchins in examined hydrothermal zones in the northern and southern West Pacific Ocean.     

Die Erforschung der Natürlichen Radioaktivität von Wolkenelementen und einige damit verbundene Probleme

Summary During a number of years at Vilnius the sounding of clouds has been carried out from airplanes in order to study the contents of radioactive materials accumulated in cumuli. Two methods for taking samples have been used: 1) the collection on cooled surfaces and 2) using the method of filter paper covered with erythrosin and kept in a special collector within the Venturi tube. In the first case radioactivity has been measured with the help of Geiger-Müller counter and in the second by means of nuclear photo emulsion (sensitive to -particles) which was brought into contact with the filter paper moistened in the cloud. This method has made it possible: 1) to measure radioactivity in local zones of a cloud, 2) to measure radioactivity of separate big drops and 3) to study the composition of -radioactivity contained in cloud particles.The magnitude of specific radioactivity of cloud elements appears to be of the same order with the rain drops and at times even greater than that of the rain samples.There exist two types of the distribution of radioactivity in a cumulus according to the height: 1) an increase of radioactivity from the bottom to maximum at the height of 0.6 part of the cloud's thickness and 2) two maxima of radioactivity at the bottom and in the centre. The latter phenomenon is characteristic of thick cumuli where big radioactive drops apparently fall out from the centre. The distribution of radioactivity at different heights correlates well with cloud's liquid-water.In a cumulus there takes a place a process of accumulation of radioactive aerosol with the accumulation coefficient of 1000. This circumstance points to a very important part played by clouds as accumulators of radioactive materials from the air which continuously filters itself through them. And just by this is expressed one of the properties of clouds as purifiers of the atmosphere from radioactive aerosol, for, as theoretical calculations indicate, the ability of drops to absorbe radioactive aerosol diminishes with the process of cloud droplets growing to the size of rain drops.The composition of radioactive materials in cloud elements is very complex. In drogs there appear nearly all the natural radioactive elements (emitting -particles) which exist in the earth's crust.     

Application of Regional Phase Amplitude Tomography to Seismic Verification

v--vWe have applied tomographic techniques to amplitude data to quantify regional phase path effects for use in source discrimination studies. Tomography complements interpolation (kriging) methods by extending our ability to apply path corrections into regions devoid of calibration events, as well as raising levels of confidence in the corrections because of their more physical basis. Our tomography technique solves for resolvable combinations of attenuation, source-generation, site and spreading terms. First difference regularization is used to remove singularities and reduce noise effects.¶In initial tests the technique was applied to a data set of 1488, 1.0 Hz, P_g/L_g amplitude ratios from 13 stations for paths inside a 30° by 40° box covering western China and surrounding regions. Tomography reduced variance 60%, relative to the power-law distance correction traditionally applied to amplitude ratios. Relative P_g/L_g attenuation varied with geologic region, with low values in Tibet, intermediate values in basins and high values for platforms and older crust. Spatial patterns were consistent with previous path effect studies in Asia, especially local earthquake coda-Q. Relative spreading was consistent with expected values for P_g and L_g. Relative site terms were similar to one another, yet some tradeoff with attenuation was evident.¶Tomography residuals followed systematic trends with distance, which may result from the evolution from direct to coda phases, focusing, model tradeoff or data windowing effects. Examination of the residuals using a kriging interpolator showed coherent geographical variations, indicating unmodeled path effects. The residual patterns often follow geological boundaries, which could result from attenuating zones or minor blockages that are too thin to be resolved, or that have anisotropic effect on regional phases. These results will guide efforts to reparameterize tomography models to more effectively represent regional wave attenuation and blockage. The interpolated residuals also can be combined with predictions of the tomographic model to account for path effects in discrimination studies on a station by station basis.     

Earthquake Hazard Parameters in Crete Island and its Surrounding Area Inferred from Bayes Statistics: An Integration of Morphology of the Seismically Active Structures and Seismological Data

-- The study addresses the evaluation of earthquake hazard parameters such as maximum regional magnitude (M_max) and the slope of Gutenberg-Richter law # (where b=# log e) for the Hellenic Wadati-Benioff zone and the overriding lithospheric plate in the area of Crete and its surroundings. The seismicity of the area is divided in a cellular (1.0° 2 1.0°) manner allowing analysis of the localized earthquake hazard parameters and graphical representation of their spatial variation. Our approach incorporates the recently updated earthquake catalogue for Greece and the adjacent areas, the consideration of the morphology of the deep seismically active structures in the studied area and use of a probabilistic procedure for estimating the earthquake hazard parameters.¶One of the main inconsistencies in the earthquake hazard assessment is the estimation of the maximum magnitude and the related uncertaint y. The Bayesian approach, applied in the present, is a straightforward technique for evaluating the earthquake hazard parameters and is based on the following assumptions: Poissonian character of seismic events flow, a frequency-magnitude law of Gutenberg-Richter's type with cutoff maximal value for estimated parameter and a seismic catalogue, having a rather sizeable number of events (i.e., 50 events at least per cell). For five cells in which the number of events is less than 50, an effort is made to produce synthetic data. The re-assessed parameters obtained from the synthetic data show no significant difference and the real data (of the five cells) are finally taken into account although the estimated uncertainty is high.¶For four random cells we constructed hazard curves showing the probabilities that a certain magnitude M will be exceeded in one year and the return periods (in years) that are expected for a given magnitude. These are particularly useful for the mapping of earthquake hazard in regions of either low or high seismic activity, as is Crete and the adjacent area.¶The obtained results show that the W and E parts of both subducting and overriding plates differ in the spatial distribution of all the estimated earthquake hazard parameters. The M_max distribution indicates strong coupling between the western portions of the interacting plates (M_max > 6.3) to the south of 36°N. The smaller values of M_max (M_max < 6.3) estimated in the SE part of the studied area indicate weak coupling between the eastern portions of the subducting and overriding plates.¶Values of b > 1.0 are found to the south and east of Crete for the Wadati-Benioff zone, and over the central part of the island and the area to the northeast of it (cell 11) for the continental wedge, which suggests nonuniform stress field and/or heterogeneous material.     

3-D Simulation of Earthquake Generation Cycles and Evolution of Fault Constitutitve Properties

--The earthquake generation cycle consists of tectonic loading, quasi-static rupture nucleation, dynamic rupture propagation and stop, and subsequent stress redistribution and fault restrengthening. From a macroscopic point of view, the entire process of earthquake generation cycles should be consistently described by a coupled nonlinear system of a slip-response function, a fault constitutive law and a driving force. On the basis of such a general idea, we constructed a realistic 3-D simulation model for earthquake generation cycles at a transcurrent plate boundary by combining the viscoelastic slip-response function derived for a two-layered elastic-viscoelastic structure model, the slip- and time-dependent fault constitutive law that has an inherent mechanism of fault restrengthening, and the steady relative plate motion as a driving force into a single closed system. With this model we numerically simulated the earthquake generation cycles repeated in a seismogenic region on a plate interface, and examined space-time changes in shear stress, slip deficits and fault constitutive properties during one complete cycle in detail. The occurrence of unstable dynamic slip brings about decrease both in fault strength and shear stress to a constant residual level. After the arrest of dynamic slip, the breakdown strength drop j†_p of fault is restored rapidly and the process of stress accumulation resumes in the seismogenic region. On the other hand, the restoration of the critical weakening displacement D_c proceeds gradually with time through the interseismic period. The restoration of D_c can be regarded as the macroscopic manifestation of the microscopic recovery process of fractal fault surface structure. Through numerical simulation with a multi-segmented fault model, we examined the effects of viscoelastic fault-to-fault interaction. The effect of transient viscoelastic stress transfer through the asthenosphere is significant as well as the direct effect of elastic stress transfer, and it possibly explains the time lag of the sequential occurrence of large events along a plate boundary.     

Interception,drop size distributions and rainfall kinetic energy in four colombian forest ecosystems

Interception losses, rain and throughfall drop size spectra and kinetic energy were studied in four relatively undisturbed tropical forest ecosystems along a transect across the Central Andean Cordillera of Colombia at altitudes between 3000 and 1000 m above sea level. Interception amounts ranged from 11 to more than 20 per cent of the total rainfall and fell within the normal range of interception figures observed in natural tropical forests. Drop size spectra were established using the filter paper method; the drop size distributions of the open field rainfall were unimodal while the throughfall had bimodal distributions, with a higher percentage of the volume of rain falling as large drops. Disturbance of the natural forests, for example by logging activities or cattle grazing, will further increase the throughfall kinetic energy and may lead to higher splash erosion rates inside the forests than in the open field. The kinetic energy of the throughfall was higher than that of the open field rainfall (20-70 per cent), even after correcting for interception losses (4-30 per cent). Splash-cup experiments, conducted both in the field and in the laboratory, indicated that the kinetic energy is a good index of rainfall erosivity. Inside the forests the amounts of sand splashed from the splash-cups was, after correction for interception losses, 2-16 per cent higher than outside the forests.     

Thermal-mechanical Coupling in Shear Deformation of Viscoelastic Material as a Model of Frictional Constitutive Relations

-- We propose a thermal-mechanical model of shear deformation of a viscoelastic material to describe the temperature-dependence of friction law. We consider shear deformation of one-dimensional layer composed of a Maxwell linear viscoelastic material under a constant velocity V and temperature T_w at the boundary. The strain rate due to viscous deformation depends both on temperature and shear stress. The temperature inside the layer changes owing to frictional heating and conductive cooling. Steady-state calculations show that the sign of d†^ss/dV, where †^ss is steady-state stress, changes from positive to negative as V increases, and that the threshold velocity above which the sign of d†^ss/dV is negative increases with increasing T_w. These results are in accordance with the conjecture that the downdip limit of seismogenic zones is marked by the transition in the sign of d†^ss/dV due to temperature rise with depth. We also find that the response of steady state to a step change in V is quite similar to the response of frictional slip with constitutive laws which employ state variables. These findings suggest that by further improving the present model a model of constitutive relations along faults or plate boundaries can be developed which contains temperature-dependence in a physically-sound manner.     

Optimized Seismic Threshold Monitoring – Part 1: Regional Processing

v--v Continuous seismic threshold monitoring is a technique that has been developed over the past several years to assess the upper magnitude limit of possible seismic events that might have occurred in a geographical target area. The method provides continuous time monitoring at a given confidence level, and can be applied in a site-specific, regional or global context.¶In this paper (Part 1) and a companion paper (Part 2) we address the problem of optimizing the site-specific approach in order to achieve the highest possible automatic monitoring capability of particularly interesting areas. The present paper addresses the application of the method to cases where a regional monitoring network is available. We have in particular analyzed events from the region around the Novaya Zemlya nuclear test site to develop a set of optimized processing parameters for the arrays SPITS, ARCES, FINES, and NORES. From analysis of the calibration events we have derived values for beam-forming steering delays, filter bands, short-term average (STA) lengths, phase travel times (P and S waves), and amplitude-magnitude relationships for each array. By using these parameters for threshold monitoring of the Novaya Zemlya testing area, we obtain a monitoring capability varying between m_b 2.0 and 2.5 during normal noise conditions.¶The advantage of using a network, rather than a single station or array, for monitoring purposes becomes particularly evident during intervals with high global seismic activity (aftershock sequences), high seismic noise levels (wind, water waves, ice cracks) or station outages. For the time period November-December 1997, all time intervals with network magnitude thresholds exceeding m_b 2.5 were visually analyzed, and we found that all of these threshold peaks could be explained by teleseismic, regional, or local signals from events outside the Novaya Zemlya testing area. We could therefore conclude within the confidence level provided by the method, that no seismic event of magnitude exceeding 2.5 occurred at the Novaya Zemlya test site during this two-month time interval.¶As an example of particular interest in a monitoring context, we apply optimized threshold processing of the SPITS array for a time interval around 16 August 1997 m_b 3.5 event in the Kara Sea. We show that this processing enables us to detect a second, smaller event from the same site (m_b 2.6), occurring about 4 hours later. This second event was not defined automatically by standard processing.     

Simulating Z–LWC Relations in Natural Fogs with Radiative Transfer Calculations for Future Application to a Cloud Radar Profiler

The vertical distribution of liquid water content (LWC) in natural fog and low stratus is a crucial variable in many applications, e.g. the development of satellite based retrievals of ground fog. Unfortunately, there is very little data concerning fog LWC-profiles, mainly due to the lack of suitable operational instrumentation. A novel ground-based 94?GHz FMCW cloud radar could fill this gap if radar reflectivity Z could be converted to LWC by using appropriate Z–LWC relations. However, this relation strongly depends on drop size distribution (DSD) and is hardly known for natural fog types. In this sensitivity study, the influence of the DSD on the Z–LWC relation in different types and life cycle stages of natural fogs is analyzed using a radiative transfer code (RTC) and published fog drop size distributions. It could be shown that there is a direct but nonlinear relationship between LWC and radar reflectivity. The proportionality factor of the Z–LWC equation in particular reveals specific ranges for the different life cycle stages. If a proper classification of fog life cycle in the field is possible, the results could be used to properly convert Z to LWC.     

Soluble iron sulfide species in natural waters: Reappraisal of their stoichiometry and stability constants

A wide range of stoichiometries has been previously proposed for soluble iron sulfide species and there is no general agreement on their importance in natural waters. The solubility of Fe(II) in 0.1 M NaClO₄ equilibrated at 20 - 0.1°C with various partial pressures of H₂S (0.1, 0.001, 0.0001, 0.00001 MPa) was measured in the pH range 3.1-7.9. Equilibrium was established within 1-6 h when amorphous FeS was the solid phase. The results could all be fitted using values for the solubility product constant (I = 0) of p*K_s = 3.00 - 0.12 and of the stability constant for a soluble Fe(HS) ₂ species (I = 0) of p#₂ = -6.45 - 0.12 where *K_s = aFe²⁺ · aHS-/aH⁺ and #₂ = aFe(HS) ₂/aFe²⁺ · (aHS^-)². Any soluble species of the form Fe_x (HS) _2x where x = &gif1; would fit the data equally well. Measurements at different partial pressures are inconsistent with labile species of the form Fe_xS_x. There was no evidence for a Fe(HS) ⁺ species. When a solution is saturated with respect to amorphous FeS, Fe(HS) ₂ will only be a significant proportion of Fe(II) when S(-II) is higher than 0.2mmoll^-1. The constants for Fe(HS) ₂ or Fe_x (HS) _2x (x S 2) are consistent with all freshwater data where constant values of measured ion activity products provide no evidence for soluble complex formation. For marine waters with high sulfide concentrations (S 6mmol l^-1), measured concentrations of Fe(II) are consistent with there being negligible soluble iron sulfide. The data are better fitted if the dissolved species are polymeric as predicted concentrations of the monomer Fe(HS) ₂ are significant. These findings suggest that rather than the dissolved species being Fe(HS) ₂, it is probably polymeric, that is Fe_x (HS) _2x (x S 2).