New Particle Formation in the Mid-Latitude Upper Troposphere

Primary aerosol production due to new particle formation (NPF) in the upper troposphere and the impact that this might have on cloud condensation nuclei (CCN) concentration can be of sufficient magnitude to contribute to the uncertainty in radiative forcing. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Therefore, new particle formation must be accurately defined, parametrized and accounted for in models. This research involved the deployment of instruments, data analysis and interpretation of particle formation events during the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) campaign. The approach combined field measurements and observations with extensive data analysis and modeling to study the process of new particle formation and growth to CCN active sizes. Simultaneous measurements of O3, CO, ultrafine aerosol particles and surface area from a high-altitude research aircraft were used to study tropospheric-stratospheric mixing as well as the frequency and location of NPF. It was found that the upper troposphere was an active region in the production of new particles by gas-to-particle conversion, that nucleation was triggered by convective clouds and mixing processes, and that NPF occurred in regions with high relative humidity and low surface area. In certain cases, mesoscale and synoptic features enhanced mixing and facilitated the formation of new particles in the northern mid-latitudes. A modeling study of particle growth and CCN formation was done based on measured aerosol size distributions and modeled growth. The results indicate that when SO2 is of sufficient concentration NPF is a significant source of potential CCN in the upper troposphere. In conditions where convective cloud outflow eject high concentrations of SO2, a large number of new particles can form especially in the instance when the preexisting surface area is low. The fast growth of nucleated clusters produces a particle mode that becomes CCN active within 24-hours

Aircraft Observations of Sub-cloud Aerosol and Convective Cloud Physical Properties

This research focuses on aircraft observational studies of aerosol-cloud interactions in cumulus clouds. The data were collected in the summer of 2004, the spring of 2007 and the mid-winter and spring of 2008 in Texas, central Saudi Arabia and Istanbul, Turkey, respectively. A set of 24 pairs of sub-cloud aerosol and cloud penetration data are analyzed. Measurements of fine and coarse mode aerosol concentrations from 3 different instruments were combined and fitted with lognormal distributions. The fit parameters of the lognormal distributions are compared with cloud droplet effective radii retrieved from 260 cloud penetrations. Cloud condensation nuclei (CCN) measurements for a subset of 10 cases from the Istanbul region are compared with concentrations predicted from aerosol size distributions. Ammonium sulfate was assumed to represent the soluble component of aerosol with dry sizes smaller than 0.5 mm and sodium chloride for aerosol larger than 0.5 mm. The measured CCN spectrum was used to estimate the soluble fraction. The correlations of the measured CCN concentration with the predicted CCN concentration were strong (R2 > 0.89) for supersaturations of 0.2, 0.3 and 0.6%. The measured concentrations were typically consistent with an aerosol having a soluble fraction between roughly 0.5 and 1.0, suggesting a contribution of sulfate or some other similarly soluble inorganic compound. The predicted CCN were found to vary by +or-3.7% when the soluble fraction was varied by 0.1. Cumulative aerosol concentrations at cutoff dry diameters of 1.1, 0.1 and 0.06 mm were found to be correlated with cloud condensation nuclei concentrations but not with maximum cloud base droplet concentrations. It is also shown that in some cases the predominant mechanisms involved in the formation of precipitation were altered and modified by the aerosol properties. This study suggests that CCN-forced variations in cloud droplet number concentration can change the effective radius profile and the type of precipitation hydrometeors. These differences may have a major impact on the global hydrological cycle and energy budget

17th Conference on Planned and Inadvertent Weather Modification (AMS/WMA 2008)

Preliminary results from the Queensland Government Cloud Seeding Research program were presented to the American Meteorological Society's 17th Weather Modification Conference (in powerpoint format)

Interim report on the Southeast Queensland Cloud Seeding Research Program

Water stresses are occurring in Southeast Queensland. In order to assess the feasibility of any future precipitation enhancement potential in clouds in the Southeast Queensland region, it is extremely important to obtain observations in a well-designed measurement program. Aerosol and microphysical measurements, in particular, can help determine if seeding could be beneficial and also help determine what the optimal seeding method would be with regards to potential for enhancing precipitation in local clouds. The potential for such manmade increases is strongly dependent on the natural microphysics and dynamics of the clouds that are being seeded (in this case microphysics means the size and concentration of water droplets and ice inside clouds). These factors can differ significantly from one geographical region to another, as well as during and between seasons in the same region. In some instances, clouds may not be suitable for seeding, or the frequency of occurrence of suitable clouds may be too low to warrant the investment in a cloud seeding program. Both factors need to be evaluated from a climatological perspective. It is therefore important to conduct preliminary studies on the microphysics and dynamics of the naturally forming clouds prior to commencing a larger, operational experiment. It is also important to conduct hydrological studies relating rainfall with river flows and reservoir levels, and to determine hydrological regions where reservoir catchments are most efficient. Seeding could then be optimized by preferentially targeting the most efficient watersheds. The following is a summary of key preliminary results derived from the analysis of data collected during the 2007-2008 season in Southeast Queensland

Processing of Ice Cloud In-Situ Data Collected by Bulk Water, Scattering, and Imaging Probes: Fundamentals, Uncertainties and Efforts towards Consistency

In-situ observations of cloud properties made by airborne probes play a critical role in ice cloud research through their role in process studies, parameterization development, and evaluation of simulations and remote sensing retrievals. To determine how cloud properties vary with environmental conditions, in-situ data collected during different field projects processed by different groups must be used. However, due to the diverse algorithms and codes that are used to process measurements, it can be challenging to compare the results. Therefore it is vital to understand both the limitations of specific probes and uncertainties introduced by processing algorithms. Since there is currently no universally accepted framework regarding how in-situ measurements should be processed, there is a need for a general reference that describes the most commonly applied algorithms along with their strengths and weaknesses. Methods used to process data from bulk water probes, single particle light scattering spectrometers and cloud imaging probes are reviewed herein, with emphasis on measurements of the ice phase. Particular attention is paid to how uncertainties, caveats and assumptions in processing algorithms affect derived products since there is currently no consensus on the optimal way of analyzing data. Recommendations for improving the analysis and interpretation of in-situ data include the following: establishment of a common reference library of individual processing algorithms; better documentation of assumptions used in these algorithms; development and maintenance of sustainable community software for processing in-situ observations; and more studies that compare different algorithms with the same benchmark data sets

Modern and prospective technologies for weather modification activities: A look at integrating unmanned aircraft systems

AbstractPresent-day weather modification technologies are scientifically based and have made controlled technological advances since the late 1990s, early 2000s. The technological advances directly related to weather modification have primarily been in the decision support and evaluation based software and modeling areas. However, there have been some technological advances in other fields that might now be advanced enough to start considering their usefulness for improving weather modification operational efficiency and evaluation accuracy. We consider the programmatic aspects underlying the development of new technologies for use in weather modification activities, identifying their potential benefits and limitations. We provide context and initial guidance for operators that might integrate unmanned aircraft systems technology in future weather modification operations

The Queensland cloud seeding research program

In late 2006 the Queensland government decided to establish the Queensland Cloud Seeding Research Program (QCSRP) in southeastern Queensland to determine the feasibility of cloud seeding as a component of its long-term water management strategy. The Queensland water management strategy recognizes the need for a broad portfolio of water sources to account for the uncertainties and costs associated with each type of source. While it was not expected that cloud seeding would restore southeastern Queensland's water supply levels to pre-drought values, it seemed valuable to determine whether certain types of seeding techniques might impact rainfall and water supplies in the region and whether that impact could be quantified. The project was developed as a collaboration between a number of institutions from Australia, the United States, and South Africa, and included field measurements over the course of two wet seasons. A two-pronged approach was taken to a) conduct a randomized cloud seeding experiment and b) assemble state-of-the-art instrumentation systems to collect data on the complete physical process from cloud formation to seeding to precipitation