bluuebunny/crossref_metadata_2025 huggingface dataset:
Precipitation‐induced mesoscale wind perturbations in the melting layer
Authors: Atlas D. , Tatehira R. , Srivastava R. C. , Marker W. , Carbone R. E.
Published: February 2007

Doppler radar observations during widespread frontal precipitation in England on 20 February 1967 show significant perturbations of the wind in and near the melting layer. The analysis suggests the following hypotheses: (i) Mesoscale oscillations of the wind near the melting layer are produced by pressure perturbations due to horizontal variations in cooling by melting snow associated with the precipitation pattern. A simple theoretical analysis of the effect is presented. In simple patterns, the perturbed wind has a maximum on the low pressure side of the rainfall. The perturbations propagate with the velocity of the precipitation generators and their magnitude increases with the precipitation rate. This hypothesis is in accord with the finding that the oscillation in the tangential wind across hurricane rain bands is generally a maximum on the low pressure side of the bands. (ii) Smaller scale wind perturbations were also observed in the melting layer with scale of a few kilometers comparable to those reported by Harrold and Browning (1967). However, unlike their observations, these perturbations did not appear to move with the melting layer winds. A tentative suggestion is made that these may represent wave motions.
A ground‐based instrument for the continuous measurement of charges on cloud particles
Authors: Latham J. , Smith M. H.
Published: February 2007

An instrument has been devised which will measure continuously the charge and dimensions of individual ice crystals or water droplets within clouds at ground level. If its collection efficiency for cloud particles were established it could then also be used to determine particle‐size distributions and volume charge densities inside clouds.

A collimated beam of particles passes through a transverse electric field before impinging on a moving belt of 35 mm film coated with Formvar which has been softened immediately prior to exposure to the beam. Each particle is deflected by an amount proportional to its charge‐to‐mass ratio. The dimensions, type and charge of each collected particle can therefore be determined by subsequent analysis of the replicas using a stop‐motion projector allied to a data recording system. If required, the dimensions of selected particles can be determined more precisely using an electron scanning microscope. The minimum detectable charge on a droplet of radius r cm and terminal velocity V cm s−1 is given approximately by qmin ∼ 5 × 10−2 r3 V2 e.s.u.
The derivation of Swinbank's long‐wave radiation formula
Authors: Deacon E. L.
Published: February 2007

It is shown that Swinbank's empirical formula for the long‐wave radiation from clear skies can be derived from existing knowledge of atmospheric emission by taking account of the moderately strong correlation at most places between screen temperature and the amount of water vapour overhead.
Measurements of eddy‐fluxes over the sea from an off‐shore oil rig
Authors: Hicks B. B. , Dyer A. J.
Published: February 2007

Two eddy correlation instruments (Fluxatrons) and associated anemometers were installed on the Marlin natural gas platform, which stands in Bass Strait about 60 m deep and 40 km off the Victorian coast (lat. 38° 14′S, long. 148° 13′E). The sensing heads were mounted 5 m above the sea surface on a boom extending from the rig. At this height the rig did not appear to affect the wind flow.

The measured Reynolds stresses give an average value of 0.0011 ± 0.0001 for the drag coefficient referred to the 10 m wind speed (31 half hour observations over the wind speed range 2–10 m s−1). Below about 5 m s−1 the drag coefficient is not significantly different from that of an aerodynamically smooth surface. Above this speed, it increases with velocity, reaching about 0.0015 at 10 m s−1.

The measured sensible heat‐fluxes are small, showing that evaporation dominates sensible heat in the sea‐air energy budget. There is no reason to dispute the bulk aerodynamic approach, in which the heat‐flux is written as H = p cp d ua Δθa. The data do not allow an accurate estimate of the transfer coefficient, d, which is found here to be 0.0014 (±25 per cent), insignificantly different from the value found for the case of evaporation from inland lakes.

Heat budget considerations imply that about 60 per cent of the day‐time net radiation was used to heat the water body.

The success of the experiment suggests the feasibility of using oil rigs as platforms for further air‐sea interaction studies. The stability of such platforms, even at very high wind speeds, is particularly attractive.
Fluxes of momentum and mass from 2 km to 28 km at Laverton, Victoria, during the serial sounding experiment, Spring 1966
Authors: Brook R. R.
Published: February 2007

The Laverton Serial Sounding Experiment provided a comprehensive sounding of the atmosphere over a period of one month in the southern Spring of 1966. These data have been analysed to determine the variations of fluxes of mass and horizontal momentum at heights from 2 to 28 km, and the contributions to these fluxes by the mean flow and transient eddies. The co‐spectrum functions of the fluxes were evaluated to obtain contributions to them by eddies of different sizes. The partitioning of the Reynolds stresses (momentum fluxes) by various frequencies is examined for the existence of a ‘spectral gap’ and it is concluded that no definite gap exists in the frequency range examined. A strong quasi‐diurnal mass flux is found in the lower troposphere.
On the development of extratropical cyclones
Authors: Petterssen S. , Smebye S. J.
Published: February 2007

Certain synoptic aspects of cyclone development in the lower troposphere are reviewed and two types identified. Type A comprises the well‐known amplifying frontal wave, which is known to produce kinetic energy through a reduction of the baroclinicity within its own domain. Type B is found to be initiated through a finite disturbance in the upper troposphere, and its intensification is accompanied by an augmentation of the baroclinicity and import of kinetic energy, mainly from the jet‐stream region. The energy structures of two storms are described, one being a plain type B case, and, the other representing a type B development modified through the presence of strong fronts. The dissipation of kinetic energy in the surface air is computed and found to constitute an effective brake on cyclone development.
Some fog droplet size distributions obtained by an impaction method
Authors: Garland J. A.
Published: February 2007

A cascade impactor technique based on the methods of previous workers has been used to study the size distribution of water droplets in several fogs. Nomarski interference contrast, used as a method of microscopic examination of the samples revealed large numbers of small droplets which were not visible under phase contrast. In about one third of the fogs studied these droplets, smaller than 2 μm diameter, made a large contribution to the optical extinction coefficient. The use of interference contrast for assessment of samples has resulted in some reduction of the large deficit, frequently found by previous workers, in the extinction coefficient calculated from the droplet size distribution, as compared with that measured optically. The remaining discrepancy, however, is significant and sometimes exceeds a factor of two.

The small droplets are probably the result of condensation of water on hygroscopic nuclei whose critical supersaturation has not been exceeded. Their implications regarding the rate of clearance of fog are considered.
Wind profiles in and above a forest canopy
Authors: Oliver H. R.
Published: February 2007

Using an on‐line computer, measurements were made of wind speeds in and above a pine forest together with accurate potential temperature profiles over a wide range of stability conditions. It was found that between values of Richardson number of approximately –0.05 and +0.10 the wind profile above the canopy followed a pure log form with the measured roughness length increasing linearly from 0.75 to 1.23 m respectively. Outside this stability range a log‐linear profile could be fitted. The shape of the wind profile within the canopy was determined, and an increase of wind speed within the trunk space was noted.

A preliminary experiment to determine the effect of the anemometer tower structure upon wind speed readings is also described.
Eddy kinetic energy spectra in the Middle East sub‐tropical and easterly tropical jet streams
Authors: Gordon A. H.
Published: February 2007

An analysis is carried out of samples of time series of observations of wind components of the winter sub‐tropical and summer easterly jet streams in the Middle East. The periods covered by the samples are 60 days. Individual components showed peaks in the eddy kinetic energy with minimum periods of about 4 days. However, when both u and v components are combined or two separate 60 day samples are combined marked peaks diminish. There is probably a spectrum of preferred peak periods which can only be identified if a much larger population of individual series is analysed.
Aerodynamic properties of a plant of complex structure
Authors: Landsberg J. J. , Thom A. S.
Published: February 2007

Coefficients of momentum and vapour transfer of spruce shoots in a wind‐tunnel are measured, and are shown to depend on shoot density: transfer per unit needle area becomes less effective as shoot density increases. Comparisons with theoretical values derived from established coefficients for 1 mm and 3 mm diameter cylinders (representing needles and twigs, respectively) indicate that the magnitude of the implied shelter effect is the same for water vapour as for momentum.
On the dispersion of the sizes of droplets growing by condensation in turbulent clouds
Authors: Bartlett J. T. , Jonas P. R.
Published: February 2007

The effect of turbulence within a cloud on the distribution of the sizes of droplets growing by condensation has been examined in some detail with the aid of a scheme for simulating a fluctuating updraught numerically. It is found that, contrary to the conclusions previously reached by some Russian and Chinese workers, the spread in the radii of droplets at any given level which this mechanism produces is very small (generally < 0.2 γm). This result agrees with the conclusion of a similar analysis carried out by Warner.

Other factors which may account for the observed distributions of droplet sizes have been considered and the most important appear to be mixing between a cloud and its environment and the variable composition of condensation nuclei. It also appears that the absorption of organic surface active substances on to some condensation nuclei probably accounts for the existence of small droplets in the interiors of well‐developed clouds.
Ekman boundary layer interactions in a numerical model of the general circulation
Authors: Everson P. J. , Davies D. R.
Published: February 2007

A representation of an ‘Ekman’ type of boundary layer (assumed to extend from 1,000 mb to 900 mb) is inserted into a two‐level, quasi‐geostrophic, general circulation numerical model. An approximate time‐dependent analytic solution of this boundary layer is matched to the ‘free atmosphere’ régime of the model through the vertical velocities produced at the grid points. By using this analytic solution the essential physical characteristic of the observed continuous increase with height of scale length of turbulence in the boundary layer is represented. By comparing time integrations of two models, only one of which contains an Ekman layer, it is shown that large‐scale flow characteristics, expressed in terms of growth rate of zonal and eddy kinetic energy, are sensitively dependent on the presence of such a layer in a numerical model.
Studies of turbulence in the surface layer over water (Lough Neagh). Part I. Instrumentation, programme, profiles
Authors: Sheppard P. A. , Tribble D. T. , Garratt J. R.
Published: February 2007

Instrumentation is described which has been used over a body of deep water, with fetches of 8 km to 22 km, to provide (i) vertical profiles of mean wind u, potential temperature ø and specific humidity q from the water surface to 16 m height and (ii) turbulent fluctuations of temperature and of the longitudinal and vertical components of wind and hence the vertical fluxes of momentum and sensible heat.

Logarithmic wind profiles in near‐neutral conditions lead to a drag‐coefficient CD of the water surface as a function of the wind speed u10 at 10 m height given by 103 CD = 0.36 + 0.10u10 (3 m s−1 < u10 < 16 m s−1). Corresponding bulk transfer coefficients for heat and water vapour are not distinguishably different from CD in the observed range of u*z0/ν < 102 (conventional nomenclature).

An analysis, following Webb (1970), of profiles in stable conditions (0 < Ri4 ≤ 0.16) lends support to the utility of the log‐linear form. Using the Monin‐Oboukhov relation ∂X/∂z = X*ø (z/L)/(kz) where × is either u, ø, or q and taking ø(z/L) = 1 + α z/L, so that z/L = Ri/(1− α Ri), we find α ≃ 6. In unstable conditions (0 > Ri4 ≥ −0.6) the profile shape factor Sx = (X4 − X1)/(X16 − X1) is greater for ø than for u, implying øH < øM (KH > KM) but Sq has less well defined behaviour. The data on Su,ø are not inconsistent with øM = (1 − 16 z/L)−1/4, øH = ø, as proposed by Dyer and Hicks (1970) and others but the shape factor is very insensitive to the numerical factor multiplying z/L in these relations.

Analysis of the measurements of turbulent fluctuations and derived fluxes will be presented in later papers.
The variability of the onset of spring in Britain
Authors: Davis N. E.
Published: February 2007

The first day of spring is defined in terms of daily maximum temperatures. Spring at Oxford as defined begins some time between the third week of February and the last week of April. The average date shows a secular change over the last hundred years.

The date of the first day of spring is shown to be related to ice conditions in the Baltic and in the Iceland area, to the sea temperature pattern in the North Atlantic, the circulation patterns at 500 mb and to various atmospheric indices. Rules developed from these relationships enable ‘statistical’ forecasts for the first day of spring to be made.
The estimation of ground‐level pressure fields from computer analyses and their application to large‐scale atmospheric mass transfer
Authors: Lewis R. P. W.
Published: February 2007

A method is presented for estimating mean ground‐level pressure over most of the Northern Hemisphere using objectively analysed fields of 1,000 mb and 500 mb height together with suitable grid‐point values of mean topographic height. A limited sample of data indicates that estimates of the seasonal transfer of mass between the Hemispheres using fields of mean sea‐level pressure are too large by a factor of about 4.
Zonal wind quasi‐biennial oscillations at 25–60 km altitude, 1962–69
Authors: Groves G. V.
Published: February 2007

Meteorological rocket observations of zonal winds at thirteen sites (or pairs of sites) have been analysed for amplitudes and phases of their quasi‐biennial oscillation. The period of the oscillation was taken to be 32 months because from 1962–69 the period was relatively constant, not varying by more than ±3 months. Amplitudes and phases of the oscillation over a wide range of latitude are presented and discussed. The low‐latitude part of the oscillation is well‐defined with maximum amplitudes at 25 to 30 km altitude, which reach about 25 ms−1 at the Equator and decrease to a few ms−1 at 20° latitude. At other latitudes, amplitudes are less than 5 ms−1 except above 50 km at two sites between 50° and 60° latitude, where another main part of the oscillation is indicated. More observations and sites are needed at mid and high latitudes. Observations at the highest latitude site (77°) show no evidence of a diminished amplitude. Phases also depend on height and latitude and may reach gradients of 1 month km−1 with height and 2 months deg−1 with latitude respectively.
Air motion within Kelvin‐Helmholtz billows determined from simultaneous Doppler radar and aircraft measurements
Authors: Browning K. A. , Bryant G. W. , Starr J. R. , Axford D. N.
Published: February 2007

A new linked mode of operation has been used to obtain virtually simultaneous measurements by a fully instrumented aircraft and a ground‐based high power radar within a train of large amplitude Kelvin‐Helmholtz billows in the optically clear atmosphere. Both sets of data were analysed to show the detailed distribution of air motion and turbulence within the billows. The resulting pattern was consistent with a train of vortices each of which was characterized by a vertical wind shear of 6 m s−1 over 100 m, with downward motion of about 1 m s−1 on the downshear side and upward motion of about 1 m s−1 on the upshear side. Between the vortices the vertical shear decreased to almost half the maximum value. The most intense radar echoes occurred within inclined layers connecting the top of one region of maximum vorticity to the bottom of the next. The aircraft, which flew through the upper parts of the billows, encountered turbulence of up to moderate intensity as it penetrated the crests of the billows. Between successive penetrations of the billow crests the aircraft flew close to but just above the region of intense radar echo and encountered smooth air with a slowly varying vertical component of motion.
Coalescence in a weakly turbulent cloud
Authors: Tennekes H. , Woods J. D.
Published: February 2007

In a recent paper on the effect of turbulence on droplet collisions in clouds, Woods, Drake and Goldsmith (1972) proposed that the principal factor was the strong spectral peak of shear near the Kolmogoroff micro‐scale. This hypothesis led to an important simplification, namely that spatial and temporal fluctuations in the turbulent shear field could be ignored during an encounter between a pair of cloud droplets. However, the authors pointed out that their simple model of (isotropic, homogeneous) turbulence contained an assumption, namely that the shears are normally distributed, which would have to be re‐examined if it turned out that droplet collision efficiency increased rapidly after a threshold value is exceeded. Subsequent measurements by Jonas and Goldsmith (1972) showed that this is indeed the case. In this paper we reconsider the efficiency of turbulent coalescence in the light of the new experimental data, and taking account of the intermittency of shear distribution. It is concluded that significant increases of collection efficiency will occur in clouds which are only weakly turbulent. For example, the collection efficiency for droplets of radii R = 20 μm and γ = 9 μm in a cloud with energy dissipation rate ε = 55·5 cm2 s−3 will be approximately 14 per cent compared with 2 per cent for the same droplets falling though still air. The shear zone in the wind tunnel experiment designed by Woods et al. (1972) is a realistic approximation to the shear zones in cloud turbulence.
The production of secondary ice particles during riming
Authors: Mossop S. C. , Brownscombe J. L. , Collins G. J.
Published: February 2007

Two series of experiments were undertaken to investigate whether secondary ice particles are thrown off during the accretion of supercooled water drops upon an ice surface. Riming took place in cloud at a temperature of about −9°C, and the accreted droplets were of various diameters up to 100 μm. Drops were accreted upon targets moving at velocities from 0·15 to 2·1 m s−1. The number of secondary ice particles produced per unit mass of rime appears to be far too low to account for the high concentrations of ice particles observed in some natural clouds.

Footnote added in proof. Subsequent work by J. Hallett and S. C. Mossop (Nature, 1974, 249, pp. 26‐27) has shown that high concentration of secondary ice particles can be produced by riming under certain special conditions.
Storm surges in the Bay of Bengal
Authors: Das P. K. , Sinha M. C. , Balasubramanyam V.
Published: February 2007

Estimates of the surge generated by a model storm impinging on three coastal areas of north Bay of Bengal are presented. A linear shallow‐water long‐wave model was used to evaluate the surge. Surge amplitudes were computed for different values of storm intensity and speed. The effect of the astronomical tide was estimated by specifying initial boundary conditions on the open boundary of the computational grid. For a devastating storm, which struck Bangladesh (formerly East Pakistan) on 12/13 November 1970, we show that superposition of the surge on the tide leads to an overestimate of sea level elevation at the time of landfall.
Electrical conditions near the bases of thunderclouds over New Mexico
Authors: Rust W. D. , Moore C. B.
Published: February 2007

Measurements of atmospheric electricity were made at a mountain‐top observatory with some instruments at the earth's surface and with others carried aloft by captive balloons into the bases of thunderclouds overhead. The properties measured included the charge on individual precipitation particles, the electric current density carried by precipitation, the local electric field vector, and the electrical conductivity of the air.

The electric fields aloft, near cloud base, were often twice the intensity of the surface fields and had large horizontal components that indicated non‐uniform distributions of charge. The polar electrical conductivity of cloudy air was found to be about 2 times; 10−15 per ohm m which is about 1/10 that of the clear air at the same altitude.

The polarity of charge on the precipitation aloft was almost invariably that of the local potential gradient; it did not show the well‐known ‘mirror‐image’ relation that is observed between the precipitation electricity at the ground and the local potential gradient during periods of point discharge. Use of our charge and conductivity data in Wormell's analysis of Wilson's ion capture mechanism suggests that ion capture in the subcloud region may explain adequately the precipitation charge arriving at the earth.

There was little correlation between the magnitudes of the precipitation charge aloft and the intensity of the electric field. We could not identify the origin of the charges found on precipitation aloft although one possible explanation is that they were derived from that residing on the cloud droplets from which the raindrops were formed.

Calculations of the electrical power transfer in the lower regions of developing thunderclouds by the fall of charged precipitation indicate local energy dissipation as predicted by Vonnegut, with rates of about 5 times; 10−6 watts m−3.
The mean meridional temperature behaviour of the stratosphere from November 1970 to November 1971 derived from measurements by the Selective Chopper Radiometer on Nimbus IV
Authors: Barnett J. J.
Published: February 2007

Zonal means of radiance originating in the stratosphere and measured by the Selective Chopper Radiometer are given for the period November 1970 to November 1971. Results are presented as latitude‐time sections and as monthly means. Equatorial cooling of several degrees was found to be associated with a major warming in the Northern Hemisphere. In the lower stratosphere the annual variation of temperature near the South Pole was approximately twice that near the North Pole, but in the upper stratosphere the variations were almost equal. At the Equator a semi‐annual oscillation of 2.5 K amplitude was present near the stratopause, while there was an annual oscillation of 1.7 K near the tropopause. Global mean temperatures exhibited little variation but the annual component for the upper stratosphere was consistent with the variation of solar heating. The upper stratosphere of the Southern Hemisphere had a pole warmer than midlatitudes during most of the winter, unlike the Northern Hemisphere winter. Height‐latitude sections of retrieved temperature are given for days representative of each season.
Sponginess in ice grown by accretion
Authors: Roos D. V. D. S. , Pum H.‐D. R.
Published: February 2007

Ice was grown by accretion on rotating embryos at air temperatures of −6, −12 and −24°C while the liquid water content ranged approximately between 1 and 4 g m−3. The air speed in the wind tunnel and the modal droplet diameter were, respectively, 20 m s−1 and 13 μm. Details of the structure of the spongy ice were studied in thin sections after elimination of internal liquid water by centrifuging. Sponginess occurred in radial zones associated with surface protuberances but did not necessarily coincide with the indentations between them. Radial striations and tangential microlayers of some 200 μm thickness were found and point to a complex original ice‐water interface. About half of the spongy specimens were allowed to freeze undisturbed. The subsequent transparent ice contained patches of air bubbles mostly of some 20 μm in diameter showing distinctive arrangements and a log‐normal size distribution. Crystals were elongated in the growth direction while optic axes tended to lie normal to it, 67° being the average value of the angle between the projection of the c‐axis on the plane of the hailstone section and the growth direction. This tendency confirms epitaxial growth during the later stages of freezing.
Determination of optical parameters of atmospheric particulates from ground‐based polarimeter measurements
Authors: Kuriyan J. G. , Phillips D. H. , Willson R. C.
Published: February 2007

This paper describes the theoretical analysis that is required to infer, from polarimeter measurements of skylight, the size distribution, refractive index and abundance of particulates in the atmosphere. To illustrate the viability of the method, some data obtained at UCLA is analysed and the atmospheric parameters are derived. The explicit demonstration of the redundancy in the description of aerosol distributions suggests that radiation field measurements will not uniquely determine the modal radius of the size distribution. In spite of this non‐uniqueness information useful to heat budget calculations can be derived.
What property of a haze is determined by light scattering?
Authors: McKellar Bruce H. J.
Published: February 2007

We develop a criterion for estimating the conditions under which two polydisperse hazes will give identical scattering of light in the single scattering approximation. This criterion, that equivalent hazes have the one value of the parameter p2 = R8/R6, is derived from the Rayleigh‐Gans approximation to small angle scattering. We find that it is well satisfied by hazes which have been found to give identical scattering.
Long‐wave radiation at the ground. II. Geometry of interception by slopes, solids, and obstructed planes
Authors: Unsworth M. H.
Published: February 2007

At the earth's surface, long‐wave radiation received from the atmosphere in the absence of cloud may be expressed as the sum of the flux density from an isotropic source and the flux density due to anisotropy of atmospheric radiation. Separation of these components facilitates calculations of the radiative flux received by obstructed horizontal surfaces (near walls or in valleys), by sloping planes, by solid cylinders, and by spheres and prisms. Radiation received from adjacent surfaces is also considered.

As the angular distribution of radiation is the same for overcast skies as for clear skies, the relationships for clear skies may be extended to derive climatological mean values for the long‐wave irradiances of slopes, solids, etc.
A quasi‐biennial standing wave in the Southern Hemisphere and interrelations with sea surface temperature
Authors: Trenberth Kevin E.
Published: February 2007

An empirical orthogonal function analysis is performed on monthly mean sea level pressure (SLP) deviations from normal (anomalies) in the Australasian area and monthly mean sea surface temperature (SST) anomalies in the Tasman Sea for 14 years of data.

Only the five components of each that explain most of the variance appear to be significant. Spectral and cross‐spectral analysis of the time series of the coefficients reveals significant relations at a quasi‐biennial periodicity. An empirical model of the SLP and SST fields for this period is constructed and the amplitudes of the oscillation are found to be about 2 1/2 mb in the monthly mean SLP anomaly field and 0·4 degC in the monthly mean SST anomaly field. Physical and statistical indications are that the SST field is largely caused by the SLP field but some interdependence is present.

The quasi‐biennial SLP oscillation is related to Pittock's L‐index and appears to correspond to a change in wavenumber 3 in the Southern Hemisphere atmospheric circulation. A phase change occurred at the end of 1970, but in even years prior to 1971, and in odd years since 1970, there were increased meridional transports throughout the troposphere and lower stratosphere by the large‐scale eddies. A suggestion is made that changes in land–sea heating contrasts may be an important part of the mechanism.
Air bubbles in accreted ice
Authors: Carras J. N. , Macklin W. C.
Published: February 2007

On the assumption that the concentration of air bubbles formed in freezing water is a function of the freezing rate, an expression for the concentration of air bubbles in accreted ice has been deduced. This expression has been confirmed by measurements of the bubble concentrations and size distributions in frozen bulk water and in ice accreted on rotating cylinders. Consequently, in both the wet and dry growth regimes it is the rate of freezing which essentially determines the bubble concentration. The size distribution of bubbles is determined by the amount of air available for bubble growth. This depends on the rate at which air diffuses out of the individual droplets during the freezing process. In the wet growth regime the freezing rate depends on the rate at which heat is dissipated from the accreting object by forced convection and also, depending on the fraction of unfrozen water, on the way in which the spongy deposits are finally frozen. In the dry growth regime the freezing rate of the accreted droplets depends on their size and speed of impact, since these determine the extent to which the droplets spread, and on the temperature of the deposit.

The air bubble concentrations and size distributions were determined using ordinary optical microscopy so that only bubbles of radius greater than 1μm were counted and sized. In the dry growth regime the visible bubble concentrations range from about 106 to 108cm−3, depending primarily on the deposit temperature. The mean radii of the bubbles in the deposits range from 1 to 4μm. In the wet growth regime the bubble concentrations generally lie between 105 and 106cm−3 while the mean radii of the bubbles range from 10 to 50μm. Consequently, the two growth regimes may be readily distinguished.
Laboratory Experimental check of radiative air cooling theory
Authors: Corradini C. , Severini M.
Published: February 2007

Experimental evidence of air mass cooling in the laboratory by infrared radiative exchanges is given.

The experiments were carried out in a 50m3 chamber, with relative humidities less than 70%, in the absence of turbulent motions and haze. The measured values of the air temperature as a function of the height and time with decreasing floor temperature are compared with calculated values for which the radiative contribution is determined by the emissivity method.

The difference, less than 10%, between experimental and theoretical coolings, gives evidence that the method of computing radiation flux divergence is sufficiently accurate for many meteorological purposes.
Baroclinic instability of a simple flow on the sphere
Authors: Hollingsworth A.
Published: February 2007

We examine the baroclinic instability problem in some simple two‐level models on a sphere. We find that there are large momentum transports associated with the growing waves. These transports are induced by aspects of the spherical geometry other than those included in the beta‐plane analysis. On the other hand, the beta‐plane gives a good description of the essential dynamics of the waves.
Periodic variations in stratospheric meridional wind from 20 to 65km: 80°N to 70°S
Authors: Nastrom G. D. , Belmont A. D. , Dartt D. G.
Published: February 2007

Height‐latitude sections for January along 70°E and 90°W in the northern hemisphere show a divergence zone above 50km near 60°N 70°E, and an intense, persistent (October–April) convergence zone above 40km near 50°N 90°W. Tidal meridional winds dominate circulation features in summer at all latitudes, and throughout the year at low latitudes. As most rocket data are taken in late morning and as there is an appreciable diurnal tide at rocket levels, all results given here apply only to late morning.

Long‐term periodic features in the meridional wind are analysed. No appreciable periodic waves are found in the tropics. The quasi‐biennial oscillation, annual wave, and four‐month wave have maximum amplitudes of about 10, 20, and 10m/s respectively in the arctic near 45km. The phase of the annual wave changes by nearly 180° in a narrow zone near 45°N. The semiannual wave has an amplitude of 10m/s near 50°N above 50km with equinoctial phase dates in the region of maximum amplitude. The location of this polar semiannual wave corresponds closely to that previously found in the zonal wind.
On the eddy structure of hurricanes
Authors: Robock Alan
Published: February 2007

Given the general conditions present in a mature hurricane, this paper seeks to show by observational and theoretical means that the circulation regime within a hurricane, beyond a certain radius, must be of the eddy type rather than axisymmetric. This is done by first pointing out, following recent results of Starr, that mean radial circulations cannot transport angular momentum across surfaces of constant mean values of this quantity. A diagram is constructed showing such momentum surfaces obtained from data for a mean hurricane, and it is demonstrated that there must be a flux of momentum across these closed surfaces. This flux, therefore, can only be produced by an eddy type circulation regime.
A split semi‐implict reformulation of the Bushby‐Timpson 10‐level model
Authors: Burridge D. M.
Published: February 2007

A split semi‐implicit reformulation of the Bushby‐Timpson 10–level model is described. The integration cycle is split into two main parts. Firstly, the dependent variables are advected by the wind using the explicit two‐step Lax‐Wendroff integration scheme with the grid staggered in time and space. Secondly, these advected values are adjusted to account for the terms that govern the motion of small amplitude inertio‐gravity waves in the model, using a combination of an unconditionally stable implicit scheme and a conditionally stable explicit scheme. A novel feature of the scheme is the implicit treatment of only two of the model's ten gravity wave modes. This split semi‐implicit scheme is more than four times as efficient as the original explicit scheme designed by Bushby and Timpson. The results of one semi‐implicit integration to 36 hours are described and compared with an integration made with Bushby and Timpson's original explicit scheme.
A numerical model of cumulonimbus convection generating a protected core
Authors: Berson F. A. , Baird G.
Published: February 2007

The theory of buoyant motion in a turbulent environment due to Priestley (1953) is applied to steady‐state Cb updraught. An axisymmetric numerical model of columnar convection is modified to allow for radial cloud structure and internal turbulence. In this model the net vertical body force on a fluid element is the buoyancy relative to adjacent elements, and represents a residual of environment‐referred buoyancy and non‐hydrostatic pressure gradient.

Moisture exchange and lateral transfer of momentum and heat by mass exchange with the environment on the scale of the cloud are disregarded, yet the model gives realistic updraught velocities and cloud depth. It simulates such features as a dome rising from a protected core of the cloud, oscillating motion of cloud tops and penetration of the tropopause. In some respects the predicted behaviour compares favourably with actual measurements.

An incidental result concerns the generating gross buoyancy which is determined by the ambient and pseudo‐adiabatic temperature lapse rates. It appears that the values of the latter rate published in Smithonian Meteorological Tables and incorporated in pseudo‐adiabats on aerological diagrams, are in error.
On the components of time series; the removal of spatial dependence
Authors: Dyer T. G. J.
Published: February 2007

A linear model is fitted to the precipitation series of each group of stations formed by principal component analysis on 157 precipitation records (Dyer 1975). Precipitation can thus be decomposed into independent components one each for regional temporal effect, regional spatial effect, and a residual or micro‐effect. Each region has a temporal effect which is analysed for trend, enabling the conclusion to be made that Southern Africa's precipitation budget is stationary. On the other hand, trend on a microscale is present over randomly distributed parts of the country. Spectral analysis shows the oscillatory behaviour of the regional temporal effects, and provides information useful to the fitting of stochastic forecasting models to the data. The technique solves the problem of dependence between meteorological time series, and can be applied to any variable.
Statistics of vertical motion over land and water
Authors: Merry M. , Panofsky H. A.
Published: February 2007

Observations from many sources have been brought together to study the relationship between the ratio of standard deviation of vertical velocity to friction velocity, and z/L where z is the height and L the Monin‐Obukhov length. A good compromise for this relationship is:

where ϕM is the normalized wind shear.

This equation has been combined with theoretical expressions for the wind profile to derive a nomogram for the standard deviation of vertical angle as function of z/L and z/z0, where z0 is the roughness length.
Some observations and analysis of wind over non‐uniform terrain
Authors: Peterson Ernest W. , Kristensen Leif , Su Chang‐Chun
Published: February 2007

Continuous measurements of wind were made throughout a layer extending from the surface to a depth of 12m over a distance along the direction of the wind of about 150 metres. It has been found that the variation in the elevation of the underlying terrain has a profound effect, larger than that of the variation in surface roughness. The shape of the downwind profiles is consistent with the prediction of second‐order‐closure change‐of‐roughness models. Another observational site has been selected for comparison and the study of flow over non‐uniform terrain is continuing.
Boundary layer flow over gentle curvilinear topography with a sudden change in surface roughness
Authors: Lo A. K. , McBean G. A.
Published: February 2007

A new approach using a curvilinear coordinate system that enables incorporation of a change of roughness with a zero‐plane displacement or elevation change in a boundary‐layer model is presented. the effect of topography together with the rapid development of an internal boundary layer produce vertical wind speeds that reach a maximum value of about 25 % of the horizontal component. It is found that perturbations due to a smooth‐to‐rough transition together with an increase of elevation are stronger than those generated from a rough‐to‐smooth transition with a decrease of elevation.
Cover Picture: Fluorescent Electrospun Nanofibers Embedding Dye‐Loaded Zeolite Crystals (Small 2/2007)
Authors: Cucchi Ilaria , Spano Fabrice , Giovanella Umberto , Catellani Marinella , Varesano Alessio , Calzaferri Gion , Botta Chiara
Published: February 2007

The cover picture shows composite nanofibers obtained by electrospinning a polymer doped with a blue‐light‐emitting dye, containing fluorescent zeolite L crystals. Even in small‐diameter (150 nm) nanowires, zeolites of about 600–800 nm in diameter and 1 μm in length are well embedded into the fibers, with their crystal axis parallel to the fiber axis. Since zeolite L crystals impose a specific orientation on the organic dyes inserted into their parallel nanochannels, the reported procedure provides a simple method to hierarchically organize an ensemble of emissive molecules. Dye‐loaded zeolites, integrated into fluorescent nanowires, form very bright nanometric light sources emitting polarized light in the visible region of the spectrum that can be exploited in advanced nanophotonic applications. For more information, please read the Communication, “Fluorescent Electrospun Nanofibers Embedding Dye‐Loaded Zeolite Crystals” by C. Botta and co‐workers on page 305.
Depth of edge influence of the agricultural‐forest landscape boundary, Southwestern China
Authors: Li Liguang , He Xingyuan , Li Xiuzhen , Wen Qingchun , He Hong S.
Published: February 2007

The landscape boundary is an important component of a landscape and often plays an indispensable role in regulating ecological flows. The primary objective of this study was to estimate how far the edge effects on agricultural‐forest landscape boundaries can penetrate into the forest and agricultural field. This will serve as a basis for understanding the interaction between forest and agricultural fields in the mountainous area of southwestern China and provide scientific basis for the practice of the policy of “returning agricultural field to forest.” Based on field investigations, three types of boundaries with six sampling transects were selected. We investigated the soil moisture, soil nutrients and vegetation diversity along the transect gradient and explored the depth of edge influence (DEI) with moving split‐window techniques for analyzing the data. DEI for soil moisture changed with the seasons, ranging from 6 m in the pepper field to 2 m in the forest during the dry season, and from 12 m in the pepper field to 2 m in the forest after heavy rain. DEI based on soil organic matter ranged from 1.5 to 10 m in the forest field, while it was not detected based on other soil nutrient factors. DEI based on vegetation diversity varied from 4 to 26 m and from 10 to 31 m in the forest and agricultural fields, respectively. These results provide the scientific basis for the policy “returning agricultural field to forest”. Based on these field observations, reducing human disturbance and revegetating with natural shrubs and meadows could be more effective for vegetation conservation in terms of soil moisture and soil nutrient content in the arid valley of the Minjiang River.
The complexity of the afterpotential of rabbit A-type horizontal
cells
Authors: HANITZSCH R. , KÜPPERS-TIEDT L.
Published: February 2007

Afterpotentials of A-type horizontal cells (HCs) are believed to be
rod-induced. They are, however, complex potentials and evidently of
multiple causation. That part of the HC potential immediately after
light-off is not entirely rod-determined because it has the same spectral
sensitivity as the response to light-on, which is cone-induced with only
some rod influence. It persists during a strong blue adapting light, which
suppresses rod activity. The afterpotential may also be influenced by
feedback from HCs to photoreceptors. The later part of the afterpotentials
of A-type HCs is, however, rod dominated, as are the afterpotentials of
axon terminals of B-type HCs.
Reduced synaptic vesicle density and aberrant synaptic localization
caused by a splice site mutation in the Rs1h gene
Authors: JOHNSON BRITT A. , IKEDA SAKAE , PINTO LAWRENCE H. , IKEDA AKIHIRO
Published: February 2007

X-linked retinoschisis (XLRS) is a common form of inherited macular
degeneration caused by mutations in the RS1 gene. Whereas the
role of RS1 has been implicated in the synaptic structure as well
as layer organization in the retina, the pathological effect of a
defective RS1 gene on the synaptic interaction between
photoreceptor cells and second-order neurons has not been thoroughly
investigated. In this study, we perform a detailed characterization of the
retinal synaptic phenotypes caused by a splice site mutation in the murine
RS1 homolog (Rs1htmgc1). Electron
microscopic analysis showed that presynaptic terminals of photoreceptor
cells contain a lower areal density of synaptic vesicles in the
Rs1htmgc1 retina. Examination of the synaptic
interactions in the outer plexiform layer also revealed ectopic
localization of photoreceptor cell presynaptic markers and elongation of
neurites from postsynaptic neurons (bipolar and horizontal cells), which
are observed in other mouse models with defective photoreceptor cell
molecules. Consistent with these synaptic abnormalities, ERG analysis of
young Rs1htmgc1 mice revealed attenuation of
the b-wave with preservation of the a-wave. These results demonstrate that
RS1H has functional significance in the morphology and function of the
synapse between photoreceptors and second-order neurons. A developmental
study from postnatal day (P) 15 through P19 showed that synaptic
interactions form normally, and structural abnormalities occur after
completion of synaptic formation suggesting that RS1H is important for the
maintenance of this synaptic interaction. Thus,
Rs1htmgc1 mice may serve as a new genetic
model for human XLRS and other synaptic disorders.
The transcription factorNr2e3functions in retinal progenitors to suppress cone cell generation
Authors: HAIDER NEENA B. , DEMARCO PAUL , NYSTUEN ARNE M. , HUANG XIAONA , SMITH RICHARD S. , MCCALL MAUREEN A. , NAGGERT JÜRGEN K. , NISHINA PATSY M.
Published: February 2007

The transcription factorNr2e3is an essential component for development and specification of rod and cone photoreceptors; however, the mechanism through which it acts is not well understood. In this study, we useNr2e3rd7/rd7mice that harbor a mutation inNr2e3, to serve as a model for the human retinal disease Enhanced S Cone Syndrome. Our studies reveal that NR2E3 is expressed in late retinal progenitors and differentiating photoreceptors of the developing retina and localized to the cell bodies of mature rods and cones. In particular, we demonstrate that the abnormal increase in cone photoreceptors observed inNr2e3rd7/rd7mice arise from ectopic mitotic progenitor cells that are present in the outer nuclear layer of the matureNr2e3rd7/rd7retina. A prolonged phase of proliferation is observed followed by abnormal retinal lamination with fragmented and disorganized photoreceptor synapses that result in a progressive loss of rod and cone function. An extended and pronounced wave of apoptosis is also detected at P30 and temporally correlates with the phase of prolonged proliferation. Approximately twice as many apoptotic cells were detected compared to proliferating cells. This wave of apoptosis appears to affect both rod and cone cells and thus may account for the concurrent loss of rod and cone function. We further show thatNr2e3rd7/rd7cones do not express rod specific genes andNr2e3rd7/rd7rods do not express cone specific genes. Our studies suggest that, based on its temporal and spatial expression, NR2E3 acts simultaneously in different cell types: in late mitotic progenitors, newly differentiating post mitotic cells, and mature rods and cones. In particular, this study reveals the function of NR2E3 in mitotic progenitors is to repress the cone generation program. NR2E3 is thus one of the few genes known to influence the competency of retinal progenitors while simultaneously directing the rod and cone differentiation.
Existentialism, Eschatology and Wisdom: Canon Law as an Interim Agent of the Kingdom
Authors: Homfray Kenyon
Published: February 2007

Using methods of analysis suggested by existentialism, existential eschatology and the wisdom tradition, this paper seeks to offer an understanding of what canon law is and why canon law is necessary for the church, in a philosophical and theological sense. The paper concludes that canon law may be seen as an interim agent of the Kingdom. The analysis is grounded in the phenomenological, stoic and platonic schools of thought, formed as ontological questions.