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Recent advances in the technology of the optical radar (lidar) are reviewed. Its use as a remote probe for the study of atmospheric parameters, such as water vapor, density, temperature and aerosols at altitudes above 10 km is discussed. The lidar data on the reflectivity of the 20 km sulfate layer is used to determine the most likely size distribution of the particulates in that layer.
Recent advances in the technology of the optical radar (lidar) are reviewed. Its use as a remote probe for the study of atmospheric parameters, such as water vapor, density, temperature and aerosols at altitudes above 10 km is discussed. The lidar data on the reflectivity of the 20 km sulfate layer is used to determine the most likely size distribution of the particulates in that layer.
Abstract
Historical records of aviation turbulence encounters above Greenland are examined for the period from 2000 to 2006. These data identify an important flow regime that contributes to the occurrence of aircraft turbulence encounters, associated with the passage of surface cyclones that direct easterly or southeasterly flow over Greenland’s imposing terrain. The result of this incident flow is the generation of mountain waves that may become unstable through interactions with the background directional wind shear. It is shown that this regime accounted for approximately 40% of the significant turbulent events identified in the 7-yr database. In addition, two specific cases from the database are examined in more detail using a high-resolution mesoscale model. The model simulations highlight the important role of three-dimensional gravity wave–critical level interactions and demonstrate the utility of high-resolution forecasts in the prediction of such events.
Abstract
Historical records of aviation turbulence encounters above Greenland are examined for the period from 2000 to 2006. These data identify an important flow regime that contributes to the occurrence of aircraft turbulence encounters, associated with the passage of surface cyclones that direct easterly or southeasterly flow over Greenland’s imposing terrain. The result of this incident flow is the generation of mountain waves that may become unstable through interactions with the background directional wind shear. It is shown that this regime accounted for approximately 40% of the significant turbulent events identified in the 7-yr database. In addition, two specific cases from the database are examined in more detail using a high-resolution mesoscale model. The model simulations highlight the important role of three-dimensional gravity wave–critical level interactions and demonstrate the utility of high-resolution forecasts in the prediction of such events.
Abstract
Cloud-to-ground lightning flash characteristics of a series of four mesoscale convective systems (MCS) that occurred in Oklahoma and Kansas on 3–4 June 1985 during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central project are described. A total of 23 490 flashes were detected by the network from all four MCSs; 96% of them lowered negative charge to ground. Because the second MCS (MCS II) spent nearly all of its lifetime within the optimal region of coverage of the lightning and radar networks, trends in ground-flash characteristics could be documented throughout the system's life cycle. Lightning trends were analyzed relative to rainfall parameters based on radar network data and were stratified by the flashes’ polarity and locations according to their association with convective and stratiform radar echoes.
Most flashes in the second MCS were negative ground strikes within convective radar echoes. In convective regions the flashes were primarily negative; in stratiform regions the negatives were somewhat more than half the flashes. Positive flashes were much less frequent than negative ground strikes for the entire storm. Positive strikes in stratiform echoes during the last half of the storm exceeded the number of negative flashes, but positive ground strikes were always scarce in convective regions. For the second MCS, time series of flashes were developed for flash density, flash rate per rain volume, and number according to radar echo type. Severe weather tended to occur during the growth and mature stages of the storm and was located on the southern and western sides of the MCS's lightning activity. During the growth stage, smaller elements within the new storm had a somewhat linear organization of frequent negative flashes in convective echoes. During the mature stage, negative flashes were in a large cluster, their rates peaked, and then began to decrease. During the decay stage, negative flash rates rapidly decreased but continued to cluster in convective regions. At most, a few percent of the flashes in convective regions lowered positive charge to ground, and positive flash rates in convective regions followed trends very similar to those of negative flash rates. Positive flash rates in the stratiform region, however, tended to increase until early in the decay stage. In the stratiform region during the decay stage, positive flashes were spread over a much larger area than negative flashes.
Abstract
Cloud-to-ground lightning flash characteristics of a series of four mesoscale convective systems (MCS) that occurred in Oklahoma and Kansas on 3–4 June 1985 during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central project are described. A total of 23 490 flashes were detected by the network from all four MCSs; 96% of them lowered negative charge to ground. Because the second MCS (MCS II) spent nearly all of its lifetime within the optimal region of coverage of the lightning and radar networks, trends in ground-flash characteristics could be documented throughout the system's life cycle. Lightning trends were analyzed relative to rainfall parameters based on radar network data and were stratified by the flashes’ polarity and locations according to their association with convective and stratiform radar echoes.
Most flashes in the second MCS were negative ground strikes within convective radar echoes. In convective regions the flashes were primarily negative; in stratiform regions the negatives were somewhat more than half the flashes. Positive flashes were much less frequent than negative ground strikes for the entire storm. Positive strikes in stratiform echoes during the last half of the storm exceeded the number of negative flashes, but positive ground strikes were always scarce in convective regions. For the second MCS, time series of flashes were developed for flash density, flash rate per rain volume, and number according to radar echo type. Severe weather tended to occur during the growth and mature stages of the storm and was located on the southern and western sides of the MCS's lightning activity. During the growth stage, smaller elements within the new storm had a somewhat linear organization of frequent negative flashes in convective echoes. During the mature stage, negative flashes were in a large cluster, their rates peaked, and then began to decrease. During the decay stage, negative flash rates rapidly decreased but continued to cluster in convective regions. At most, a few percent of the flashes in convective regions lowered positive charge to ground, and positive flash rates in convective regions followed trends very similar to those of negative flash rates. Positive flash rates in the stratiform region, however, tended to increase until early in the decay stage. In the stratiform region during the decay stage, positive flashes were spread over a much larger area than negative flashes.
The Convective Storm Initiation Project (CSIP) is an international project to understand precisely where, when, and how convective clouds form and develop into showers in the mainly maritime environment of southern England. A major aim of CSIP is to compare the results of the very high resolution Met Office weather forecasting model with detailed observations of the early stages of convective clouds and to use the newly gained understanding to improve the predictions of the model.
A large array of ground-based instruments plus two instrumented aircraft, from the U.K. National Centre for Atmospheric Science (NCAS) and the German Institute for Meteorology and Climate Research (IMK), Karlsruhe, were deployed in southern England, over an area centered on the meteorological radars at Chilbolton, during the summers of 2004 and 2005. In addition to a variety of ground-based remote-sensing instruments, numerous rawinsondes were released at one- to two-hourly intervals from six closely spaced sites. The Met Office weather radar network and Meteosat satellite imagery were used to provide context for the observations made by the instruments deployed during CSIP.
This article presents an overview of the CSIP field campaign and examples from CSIP of the types of convective initiation phenomena that are typical in the United Kingdom. It shows the way in which certain kinds of observational data are able to reveal these phenomena and gives an explanation of how the analyses of data from the field campaign will be used in the development of an improved very high resolution NWP model for operational use.
The Convective Storm Initiation Project (CSIP) is an international project to understand precisely where, when, and how convective clouds form and develop into showers in the mainly maritime environment of southern England. A major aim of CSIP is to compare the results of the very high resolution Met Office weather forecasting model with detailed observations of the early stages of convective clouds and to use the newly gained understanding to improve the predictions of the model.
A large array of ground-based instruments plus two instrumented aircraft, from the U.K. National Centre for Atmospheric Science (NCAS) and the German Institute for Meteorology and Climate Research (IMK), Karlsruhe, were deployed in southern England, over an area centered on the meteorological radars at Chilbolton, during the summers of 2004 and 2005. In addition to a variety of ground-based remote-sensing instruments, numerous rawinsondes were released at one- to two-hourly intervals from six closely spaced sites. The Met Office weather radar network and Meteosat satellite imagery were used to provide context for the observations made by the instruments deployed during CSIP.
This article presents an overview of the CSIP field campaign and examples from CSIP of the types of convective initiation phenomena that are typical in the United Kingdom. It shows the way in which certain kinds of observational data are able to reveal these phenomena and gives an explanation of how the analyses of data from the field campaign will be used in the development of an improved very high resolution NWP model for operational use.
