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Larry Vardiman and James A. Moore

Abstract

An a posteriori analysis was conducted utilizing precipitation, rawinsonde and seeding generator data from seven randomized winter cloud-seeding research projects conducted in orographic settings in the Rocky Mountain West and on the Pacific Coast of the United States. Variables were developed and investigated to establish generalized seedability criteria that are applicable to a variety of meteorological and topographic conditions. The variables were divided into four general categories: time available, water available, nuclei available and mixing available. This approach established stratifications under which positive (increases) or negative (decreases) seeding effects occurred. The study showed that positive seeding effects occurred at the crest under stable or unstable conditions when a “crest” trajectory was present, moderate-to-high cloud moisture was present and the cloud-top temperature was between −10 and −30°C. Decreases occurred at the crest for unstable clouds with a “blow-over” trajectory, with low cloud moisture and cloud-top temperature colder than −30°C. The precipitation for upwind and downwind regions of a barrier was also increased or decreased depending on stability, trajectory, cloud moisture and cloud-top temperature. Other stratifications are discussed in the paper.

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Larry Vardiman and James A. Moore

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No abstract available.

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James T. Moore and William A. Abeling

Abstract

Terms of the balance equation were calculated at 300 mb to diagnose unbalanced flow in the upper troposphere both prior to and during a period of strong convection which took place during the AVE-SESAME I period. The sum of the balance equation terms displayed large imbalances(>50×10−10s−2)over the Red River Valley as early as 2100 UTC. This region grew in magnitude, expanding over Oklahoma during the next 3–6 hours. The vorticity and Laplacian terms in the balance equation dominated this imbalance.

An examination of ageostrophic, geostrophic and actual 300 mb winds at 2100 UTC revealed that the ageostrophic winds over Oklahoma were directed towards lower geopotential heights, indicating that the flow was neither in geostrophic balance nor merely responding to curved flow as described by the gradient wind equation. Such imbalance led to substantial increases in divergence and midlevel upward vertical motion.

The remaining terms of the divergence equation were computed and summed. These terms partially compensated for the strong divergence tendencies created from the balance equation. In this way, the divergence and vertical motion terms of the divergence equation checked the growth of divergence in upper levels.

Finally, an error assessment was conducted on the terms of the divergence equation. Although balance equation terms are susceptible to substantial error due to random errors in wind and height data, the patterns of these terms are more reliable, thereby permitting the conclusions of this case study.

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Donald Rottner, Larry Vardiman, and James A. Moore

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No abstract available.

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Donald Rottner, Larry Vardiman, and James A. Moore

Abstract

A serious systematic bias of the data set used in the original Vardiman and Moore (1978) work was detected while performing a continuing investigation of seeding “windows.” This bias occurred because a large number of no-seed cases were used in the Climax I and Climax II data sets that were not within the original strict randomization. Removal of this systematic bias produced a significant change in both the overall and stratified results. The nature of the bias and its impact on the original results are discussed.

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Scot M. Loehrer, Todd A. Edmands, and James A. Moore

One of the most important datasets to come from the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) is the most complete, high-resolution upper-air sounding dataset ever collected in the equatorial western Pacific Ocean. The University Corporation for Atmospheric Research/Office of Field Project Support&UCAR/OFPS (recently combined with the UCAR/Joint International Climate Projects Planning Office and renamed the Joint Office for Science Support); was given the responsibility of processing, quality controlling, and archiving the dataset. OFPS, in consultation with the TOGA COARE scientific community, developed a four-stage process to provide the community with a thoroughly quality controlled dataset.

The TOGA COARE sounding dataset includes over 14 000 soundings, collected from 14 countries, in over 20 different original formats. The first OFPS processing step was the conversion of all soundings to a single, easy to use format, the OFPS quality control format. The second stage was a series of automated internal consistency checks on each sounding. This stage was particularly important as it directly led to the improvement of several of the datasets. The third step was a visual examination of each sounding to provide another layer of internal consistency checks, for dewpoint and wind in particular. The final process used spatial quality control checks to put each station into context with its neighboring stations as well as the network as a whole. These checks provided statistics from which both systematic and individual sounding problems could be determined. Finally, some derived sounding parameters such as convective available potential energy (CAPE) were calculated for each sounding. The CAPE calculations provided a quick method to qualitatively examine the high-resolution sounding data for low-level humidity problems. A composite dataset of all soundings at a uniform vertical resolution of 5 hPa was created to provide the community with a sounding dataset that has been found to be useful in certain modeling studies.

The processed TOGA COARE sounding data, as well as statistical output from the OFPS spatial quality control procedures, are available on-line via the Internet using the World Wide Web (WWW) through the OFPS data management system. Access via the WWW allows a full range of on-line data browsing and ordering capabilities.

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Martin A. Baxter, Charles E. Graves, and James T. Moore

Abstract

A 30-yr climatology of the snow-to-liquid-equivalent ratio (SLR) using the National Weather Service (NWS) Cooperative Summary of the Day (COOP) data is presented. Descriptive statistics are presented for 96 NWS county warning areas (CWAs), along with a discussion of selected histograms of interest. The results of the climatology indicate that a mean SLR value of 13 appears more appropriate for much of the country rather than the often-assumed value of 10, although considerable spatial variation in the mean exists. The distribution for the entire dataset exhibits positive skewness. Histograms for individual CWAs are both positively and negatively skewed, depending upon the variability of the in-cloud, subcloud, and ground conditions.

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James W. Wilson, James A. Moore, G. Brant Foote, Brooks Martner, Alfred R. Rodi, Taneil Uttal, and James M. Wilczak

The Convection Initiation and Downburst Experiment (CINDE) was conducted in the Denver, Colorado area from 22 June to 7 August 1987 to study processes leading to the formation of deep convection and the physics of downbursts. A total of 6 Doppler radars, 87 mesonet stations, 3 research aircraft, 8 sounding systems and numerous photographic facilities were deployed within an 85 km × 85 km area. A comprehensive data set was obtained including measurements of convergence lines, downbursts, and tornadoes that occurred on 35, 22, and 11 days, respectively.

This paper describes the objectives of the experiment and the specific facilities employed. Highlights and preliminary results are presented for several studies underway to show the type of data collected and to illustrate the sorts of analyses being pursued. Examples chosen include the topics of cloud initiation on stationary convergence lines, terrain-induced circulations, downbursts, tornadoes, and tracking chaff in precipitation-filled regions.

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Fred L. Moore, Eric A. Ray, Karen H. Rosenlof, James W. Elkins, Pieter Tans, Anna Karion, and Colm Sweeney

A stratospheric trace gas measurement program using balloon-based sonde and AirCore sampler techniques is proposed as a way to monitor the strength of the stratospheric mean meridional or Brewer–Dobson circulation. Modeling work predicts a strengthening of the Brewer–Dobson circulation in response to increasing greenhouse gas concentrations; such a change will likely impact tropospheric climate. Because the strength of the Brewer–Dobson circulation is an unmeasureable quantity, trace gas measurements are used to infer characteristics of the circulation. At present, stratospheric trace gas measurements are sporadic in time and/or place, primarily associated with localized aircraft or balloon campaigns or relatively short-lived satellite instruments. This program would consist of regular trace gas profile measurements taken at multiple latitudes covering tropical, midlatitude, and polar regimes. The program would make use of the relatively low-cost AirCore and sonde techniques, allowing more frequent measurements given the significantly lower cost than with current techniques. The program will provide a means of monitoring changes in the strength and redistribution of the stratospheric circulation. The goals are to monitor the strength of the Brewer–Dobson circulation and to improve understanding of the reasons for stratospheric circulation changes, ultimately resulting in more realistic model predictions of climate change for the coming decades.

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Tammy M. Weckwerth, David B. Parsons, Steven E. Koch, James A. Moore, Margaret A. LeMone, Belay B. Demoz, Cyrille Flamant, Bart Geerts, Junhong Wang, and Wayne F. Feltz

The International H2O Project (IHOP_2002) is one of the largest North American meteorological field experiments in history. From 13 May to 25 June 2002, over 250 researchers and technical staff from the United States, Germany, France, and Canada converged on the Southern Great Plains to measure water vapor and other atmospheric variables. The principal objective of IHOP_2002 is to obtain an improved characterization of the time-varying three-dimensional water vapor field and evaluate its utility in improving the understanding and prediction of convective processes. The motivation for this objective is the combination of extremely low forecast skill for warm-season rainfall and the relatively large loss of life and property from flash floods and other warm-season weather hazards. Many prior studies on convective storm forecasting have shown that water vapor is a key atmospheric variable that is insufficiently measured. Toward this goal, IHOP_2002 brought together many of the existing operational and new state-of-the-art research water vapor sensors and numerical models.

The IHOP_2002 experiment comprised numerous unique aspects. These included several instruments fielded for the first time (e.g., reference radiosonde); numerous upgraded instruments (e.g., Wyoming Cloud Radar); the first ever horizontal-pointing water vapor differential absorption lidar (DIAL; i.e., Leandre II on the Naval Research Laboratory P-3), which required the first onboard aircraft avoidance radar; several unique combinations of sensors (e.g., multiple profiling instruments at one field site and the German water vapor DIAL and NOAA/Environmental Technology Laboratory Doppler lidar on board the German Falcon aircraft); and many logistical challenges. This article presents a summary of the motivation, goals, and experimental design of the project, illustrates some preliminary data collected, and includes discussion on some potential operational and research implications of the experiment.

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