It is shown that genetic inversions can be used to recover lognormal aerosol size distributions from multiangle optical scattering cross-section data measured by a polar nephelometer at a wavelength of 0.532 μm. The inversions can also be used to recover the absolute calibration factor of the polar nephelometer. The method is demonstrated by applying it to polar nephelometer data measured during the Shoreline Environment Aerosol Study (SEAS) at Bellows Beach on the island of Oahu, Hawaii. Also, the inverted size distributions are compared with those inferred from direct measurements by particle sizers during SEAS. At 0.532 μm, the polar nephelometer data are dominated by the effect of coarse-mode hydrated sea salt. Although the inversion was unable to place constraints on the accumulation-mode size distribution, the modeled size distribution provides a good description of optical scattering at wavelengths of 0.532 μm and above.
The characteristics of a small, lightweight portable lidar system for measuring aerosol (Mie) scatter at wavelengths of 1064 and 532 nm are described. It uses a 20-Hz Nd:YAG pulsed laser as a source and a 12.7-cm-diameter telescope as a receiver. By using a minimal number of commercially available components, the cost of construction has been reduced. The lidar has a useable range of 60–3000 m for clean marine conditions. Its performance has been demonstrated using measurements of tropospheric aerosols on the island of Hawaii.
Abstract A new parameterization of sticking efficiency for aggregation of ice crystals onto snow and graupel is presented. This parameter plays a crucial role for the formation of ice precipitation and for electrification processes. The parameterization is intended to be used in atmospheric models simulating the aggregation of ice particles in glaciated clouds. It should improve the ability to forecast snow. Based on experimental results and general considerations of collision processes, dependencies of the sticking efficiency on temperature, surface area, and collision kinetic energy of impacting particles are derived. The parameters have been estimated from some laboratory observations by simulating the experiments and minimizing the squares of the errors of the prediction of observed quantities. The predictions from the new scheme are compared with other available laboratory and field observations. The comparisons show that the parameterization is able to reproduce the thermal behavior of sticking efficiency, observed in published laboratory studies, with a peak around −15°C corresponding to dendritic vapor growth of ice. Finally, a new theory of sticking efficiency is proposed. It explains the empirically derived parameterization in terms of a probability distribution of the work that would be required to separate two contacting particles colliding in all possible ways among many otherwise identical collisions of the same pair with a given initial collision kinetic energy. For each collision, if this work done would exceed the initial collision kinetic energy, then there is no separation after impact. The probability of that occurring equals the sticking efficiency.
On the windward side of Oahu, a multi-wavelength Mie-Rayleigh (MR) scanning lidar is used on a regular basis for measuring aerosol attenuation in the marine boundaiy layer. The lidar data are being used for investigathg dynamic effects of marine aerosol fields on electro-optical (EO) properties. The lidar has been operated mostly at 532 and 1064 nm, and recently at 355 nm. We have observed that the vertical aerosol distribution can be very non-uniform. Under certain atmospheric conditions, ascending and descending streaks of aerosols with high extinction (2x 1O-4 per meter) have been observed, indicating that both the surface and cloud drizzle effects are important. Horizontal lidar scans at 6 meters above the sea surface indicate that aerosol is fairly uniform on a large scale but can exhibit significant variability on small scales particularly close to protruding reefs and shorelines. Above the reefthe enhanced aerosol fields have been observed to rise as high as 100 meters. As expected there is a strong correlation between wind speed and sea salt extinction values. The temporal and spatial distribution ofthese aerosol fields and their dependence meteorological parameters and wave height are discussed.
A combination of aerosol and gas phase instrumentation was employed aboard the NASA‐P3B as part of the Pacific Exploratory Mission‐Tropics (PEM‐T) in the eastern equatorial Pacific during August‐October 1996. Recent particle production was found in cloud‐processed air over extended regions aloft (6–8 km). These were clearly associated with clean marine air lofted by deep convection and scavenged of most aerosol mass in the Intertropical Convergence Zone (ITCZ) and in more aged cloud‐scavenged air influenced by a distant continental combustion near the South Pacific Convergence Zone (SPCZ). Recent particle production was evident in regions where sulfuric acid concentrations were about 0.5 to 1 × l0 7 molecules cm −3 , when surface areas were near or below 5 µm 2 cm −3 , and when relative humidity (RH) was elevated over adjacent regions. In regions of recent particle production, the calculated critical sulfuric acid concentrations, based upon classical binary nucleation theory and corrected for in situ conditions near cloud, were generally consistent with nearby observed sulfuric acid concentrations. This indicates that classical binary nucleation theory and natural sources of sulfuric acid can account for nucleation in the near‐cloud environment. Data from six equatorial flights between 20°N and 20°S demonstrate that this process populates extensive regions of the equatorial free troposphere with new particles. Vertical profiles suggest that nucleation, subsidence, and mixing into the MBL can supply the MBL with new aerosol.
Abstract Two red paleosols, and the Mangaroa Ash which separates them, have stable components of magnetisation of order 10-3 to 10-2 A/m. They are normally magnetised and their age is considered to be within Paleomagnetic Epoch 1 (Brunhes Normal), i.e., less than 0·69 m.y.
The results of a self-potential survey in the Lambasa geothermal area, Fiji, are presented. Dipolar anomalies having peak-to-peak amplitudes as large as 100 mV were observed close to some, but not all of the hot spring localities. One of these anomalies was modeled with an electrokinetic thin sheet model. The results imply that the electrokinetic coupling coefficient difference must be greater than 70 mV/atm in order to explain the anomaly.
Abstract I have used the known epicenters and depths of 307 nuclear tests at the Nevada Test Site (NTS) and 75 tests at the East Kazakhstan Test Site to compare the distances between actual and calculated hypocenters (mislocations) with calculated location confidence limits (errors). Each test was located using its ISC-compiled P first arrivals, a starting depth of 33 km and the IASP91 velocity model. I also applied azimuth and incident angle-dependent station corrections to the arrival times. The most accurately located tests are those at the Kazakhstan Test Site, where all of the mislocations in latitude and longitude are less than ±10 km and 90% of the depth mislocations are less than 20 km. Bayesian confidence limits calculated from the least-squares covariance matrix satisfactorily account for these mislocations. At the Nevada Test Site, 90% of the mislocations are less than ±9 km in longitude, ±15 km in latitude, and 33 km in depth. The overestimates in depth are compensated for by origin times that are 2 to 5 sec late. The larger mislocations at NTS occur in spite of the fact that the closest recording sites are less than 200 km away, compared to 1800 km away at the Kazakhstan Test Site. A significant fraction of the depth mislocations at NTS are much larger than their calculated errors. I interpret this failure of the calculated errors to adequately account for the NTS mislocations as being due to systematically late arrivals at northwestern American stations relative to the predicted IASP91 values. By using a locally determined three-layer velocity model for the travel times of phases recorded at distances of less than 1500 km, I was able to reduce 90% of the depth mislocations to less than 11 km as well as significantly reducing the latitude, longitude, and origin time mislocations. I conclude that differences between the IASP91 model and velocities in the vicinity of the explosions may introduce a significant bias into the determined depths of nuclear tests. A similar bias would therefore be expected in the similarly determined depths of shallow earthquakes.
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