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Abstract
Typhoon Winnie (1997) was the fourth supertyphoon in the western North Pacific in 1997. In its mature stage, an outer eyewall, consisting of deep convection with a diameter of 370 km, was observed by satellite and radar. Within this unusually large outer eyewall existed an inner eyewall, which consisted of a ring of shallow clouds with a diameter of ∼50 km. In this study, Typhoon Winnie is simulated using a nested-grid version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) with an inner grid length of 9 km. The model reproduces an outer cloud eyewall with a diameter of ∼350 km. The simulated radar reflectivity and hourly precipitation are verified with satellite microwave, infrared, and cloud brightness temperature images.
Analysis of the model results indicates that the large outer eyewall in many ways possesses the structure of a typical hurricane eyewall. This includes strong tangential winds and radial inflow outside the eyewall as well as an extremely large horizontal wind shear right at the eyewall. The outer eyewall is characterized with a ring of high vorticity (RHV). This RHV is closely related to a ring of high convergence (RHC). This RHC is caused by organized convective systems along the eyewall. The eye simulated by Winnie is characterized by a broad region of warm, dry slowly sinking air.
The factors determining the diameter of eyes in tropical cyclones are discussed by considering the scale of the environmental angular momentum and the maximum kinetic energy achieved by parcels of air originating in the environment and reaching the radius of maximum wind. It is hypothesized that the formation of a large eye is favored by large circulations in which parcels of air are drawn in toward the center of the storm from great distances, and trajectories of air in Winnie that support this hypothesis are shown.
Abstract
Typhoon Winnie (1997) was the fourth supertyphoon in the western North Pacific in 1997. In its mature stage, an outer eyewall, consisting of deep convection with a diameter of 370 km, was observed by satellite and radar. Within this unusually large outer eyewall existed an inner eyewall, which consisted of a ring of shallow clouds with a diameter of ∼50 km. In this study, Typhoon Winnie is simulated using a nested-grid version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) with an inner grid length of 9 km. The model reproduces an outer cloud eyewall with a diameter of ∼350 km. The simulated radar reflectivity and hourly precipitation are verified with satellite microwave, infrared, and cloud brightness temperature images.
Analysis of the model results indicates that the large outer eyewall in many ways possesses the structure of a typical hurricane eyewall. This includes strong tangential winds and radial inflow outside the eyewall as well as an extremely large horizontal wind shear right at the eyewall. The outer eyewall is characterized with a ring of high vorticity (RHV). This RHV is closely related to a ring of high convergence (RHC). This RHC is caused by organized convective systems along the eyewall. The eye simulated by Winnie is characterized by a broad region of warm, dry slowly sinking air.
The factors determining the diameter of eyes in tropical cyclones are discussed by considering the scale of the environmental angular momentum and the maximum kinetic energy achieved by parcels of air originating in the environment and reaching the radius of maximum wind. It is hypothesized that the formation of a large eye is favored by large circulations in which parcels of air are drawn in toward the center of the storm from great distances, and trajectories of air in Winnie that support this hypothesis are shown.
Abstract
The spatial and temporal variability of the marine boundary layer (MBL) over the southeastern Pacific is studied using high-resolution radiosonde data from the VAMOS Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx), lidar cloud measurements from the CALIOP instrument on the CALIPSO satellite, radio occultation (RO) data from the COSMIC satellites, and the ERA-Interim. The height of the MBL (MBLH) is estimated using three RO-derived parameters: the bending angle, refractivity, and water vapor pressure computed from the refractivity derived from a one-dimensional variational data inversion (1D-VAR) procedure. Two different diagnostic methods (minimum gradient and break point method) are compared. The results show that, although a negative bias in the refractivity exists as a result of superrefraction, the spatial and temporal variations of the MBLH determined from the RO observations are consistent with those from CALIOP and the radiosondes. The authors find that the minimum gradient in the RO bending angle gives the most accurate estimation of the MBL height.
Abstract
The spatial and temporal variability of the marine boundary layer (MBL) over the southeastern Pacific is studied using high-resolution radiosonde data from the VAMOS Ocean–Cloud–Atmosphere–Land Study Regional Experiment (VOCALS-REx), lidar cloud measurements from the CALIOP instrument on the CALIPSO satellite, radio occultation (RO) data from the COSMIC satellites, and the ERA-Interim. The height of the MBL (MBLH) is estimated using three RO-derived parameters: the bending angle, refractivity, and water vapor pressure computed from the refractivity derived from a one-dimensional variational data inversion (1D-VAR) procedure. Two different diagnostic methods (minimum gradient and break point method) are compared. The results show that, although a negative bias in the refractivity exists as a result of superrefraction, the spatial and temporal variations of the MBLH determined from the RO observations are consistent with those from CALIOP and the radiosondes. The authors find that the minimum gradient in the RO bending angle gives the most accurate estimation of the MBL height.
This article summarizes the activities of the past year's 40th anniversary celebration for the University Corporation for Atmospheric Research and the National Center for Atmospheric Research (NCAR). NCAR's High Altitude Observatory celebrated its 60th anniversary, and NCAR's sponsor, the National Science Foundation, celebrated their 50th. These anniversaries provided the opportunity to reflect on past accomplishments as well as look to the future. The article also relates the year-long community dialogue about issues important to the future of these organizations and the university community.
This article summarizes the activities of the past year's 40th anniversary celebration for the University Corporation for Atmospheric Research and the National Center for Atmospheric Research (NCAR). NCAR's High Altitude Observatory celebrated its 60th anniversary, and NCAR's sponsor, the National Science Foundation, celebrated their 50th. These anniversaries provided the opportunity to reflect on past accomplishments as well as look to the future. The article also relates the year-long community dialogue about issues important to the future of these organizations and the university community.
Abstract
The development of mesoscale features in numerical model forecasts of the environment of severe local storms is examined for two of the SESAME-1979 cases. The results show that a 10-layer model with a horizontal resolution of about 100 km, simple physics and initialized with essentially synoptic-scale data, is capable of generating and maintaining mesoscale phenomena in the 0–24 h time period. These results indicate that some mesoscale phenomena are predictable for periods of time longer than the lifetime of the mesoscale feature itself. Mesoscale features produced in the forecasts of the 10–11 April and 25–26 April cases include low-level jets, mesoscale convective complexes, upper-level jet streaks, cold and warm frontogenesis, drylines, mountain waves and capping inversions (lids). The development and structure of these phenomena in the model forecast are examined in detail and the interactions among the phenomena are emphasized. The results strongly confirm the conclusions from earlier studies that improved forecasts of mesoscale weather systems are possible through the use of fine-mesh models. Improved results can be expected with the incorporation of better surface and boundary-layer physics and with the use of mesoscale observations in the initial conditions.
Abstract
The development of mesoscale features in numerical model forecasts of the environment of severe local storms is examined for two of the SESAME-1979 cases. The results show that a 10-layer model with a horizontal resolution of about 100 km, simple physics and initialized with essentially synoptic-scale data, is capable of generating and maintaining mesoscale phenomena in the 0–24 h time period. These results indicate that some mesoscale phenomena are predictable for periods of time longer than the lifetime of the mesoscale feature itself. Mesoscale features produced in the forecasts of the 10–11 April and 25–26 April cases include low-level jets, mesoscale convective complexes, upper-level jet streaks, cold and warm frontogenesis, drylines, mountain waves and capping inversions (lids). The development and structure of these phenomena in the model forecast are examined in detail and the interactions among the phenomena are emphasized. The results strongly confirm the conclusions from earlier studies that improved forecasts of mesoscale weather systems are possible through the use of fine-mesh models. Improved results can be expected with the incorporation of better surface and boundary-layer physics and with the use of mesoscale observations in the initial conditions.
Abstract
Emerging networks of Global Positioning System (GPS) receivers can be used in the remote sensing of atmospheric water vapor. The time-varying zenith wet delay observed at each GPS receiver in a network can be transformed into an estimate of the precipitable water overlying that receiver. This transformation is achieved by multiplying the zenith wet delay by a factor whose magnitude is a function of certain constants related to the refractivity of moist air and of the weighted mean temperature of the atmosphere. The mean temperature varies in space and time and must be estimated a priori in order to transform an observed zenith wet delay into an estimate of precipitable water. We show that the relative error introduced during this transformation closely approximates the relative error in the predicted mean temperature. Numerical weather models can be used to predict the mean temperature with an rms relative error of less than 1%.
Abstract
Emerging networks of Global Positioning System (GPS) receivers can be used in the remote sensing of atmospheric water vapor. The time-varying zenith wet delay observed at each GPS receiver in a network can be transformed into an estimate of the precipitable water overlying that receiver. This transformation is achieved by multiplying the zenith wet delay by a factor whose magnitude is a function of certain constants related to the refractivity of moist air and of the weighted mean temperature of the atmosphere. The mean temperature varies in space and time and must be estimated a priori in order to transform an observed zenith wet delay into an estimate of precipitable water. We show that the relative error introduced during this transformation closely approximates the relative error in the predicted mean temperature. Numerical weather models can be used to predict the mean temperature with an rms relative error of less than 1%.
severe local storms
Papers presented to the U.S. House of Representatives Subcommittee on Environment and the Atmosphere at a special review session of the AMS Ninth Conference on Severe Local Storms, Norman, Okla., 23 October 1975
This paper provides an overview of applications of the Global Positioning System (GPS) for active measurement of the Earth's atmosphere. Microwave radio signals transmitted by GPS satellites are delayed (refracted) by the atmosphere as they propagate to Earth-based GPS receivers or GPS receivers carried on low Earth orbit satellites.
The delay in GPS signals reaching Earth-based receivers due to the presence of water vapor is nearly proportional to the quantity of water vapor integrated along the signal path. Measurement of atmospheric water vapor by Earth-based GPS receivers was demonstrated during the GPS/STORM field project to be comparable and in some respects superior to measurements by ground-based water vapor radiometers. Increased spatial and temporal resolution of the water vapor distribution provided by the GPS/STORM network proved useful in monitoring the moisture-flux convergence along a dryline and the decrease in integrated water vapor associated with the passage of a midtropospheric cold front, both of which triggered severe weather over the area during the course of the experiment.
Given the rapid growth in regional networks of continuously operating Earth-based GPS receivers currently being implemented, an opportunity exists to observe the distribution of water vapor with increased spatial and temporal coverage, which could prove valuable in a range of operational and research applications in the atmospheric sciences.
The first space-based GPS receiver designed for sensing the Earth's atmosphere was launched in April 1995. Phase measurements of GPS signals as they are occluded by the atmosphere provide refractivity profiles (see the companion article by Ware et al. on page 19 of this issue). Water vapor limits the accuracy of temperature recovery below the tropopause because of uncertainty in the water vapor distribution. The sensitivity of atmospheric refractivity to water vapor pressure, however, means that refractivity profiles can in principle yield information on the atmospheric humidity distribution given independent information on the temperature and pressure distribution from NWP models or independent observational data.
A discussion is provided of some of the research opportunities that exist to capitalize on the complementary nature of the methods of active atmospheric monitoring by GPS and other observation systems for use in weather and climate studies and in numerical weather prediction models.
This paper provides an overview of applications of the Global Positioning System (GPS) for active measurement of the Earth's atmosphere. Microwave radio signals transmitted by GPS satellites are delayed (refracted) by the atmosphere as they propagate to Earth-based GPS receivers or GPS receivers carried on low Earth orbit satellites.
The delay in GPS signals reaching Earth-based receivers due to the presence of water vapor is nearly proportional to the quantity of water vapor integrated along the signal path. Measurement of atmospheric water vapor by Earth-based GPS receivers was demonstrated during the GPS/STORM field project to be comparable and in some respects superior to measurements by ground-based water vapor radiometers. Increased spatial and temporal resolution of the water vapor distribution provided by the GPS/STORM network proved useful in monitoring the moisture-flux convergence along a dryline and the decrease in integrated water vapor associated with the passage of a midtropospheric cold front, both of which triggered severe weather over the area during the course of the experiment.
Given the rapid growth in regional networks of continuously operating Earth-based GPS receivers currently being implemented, an opportunity exists to observe the distribution of water vapor with increased spatial and temporal coverage, which could prove valuable in a range of operational and research applications in the atmospheric sciences.
The first space-based GPS receiver designed for sensing the Earth's atmosphere was launched in April 1995. Phase measurements of GPS signals as they are occluded by the atmosphere provide refractivity profiles (see the companion article by Ware et al. on page 19 of this issue). Water vapor limits the accuracy of temperature recovery below the tropopause because of uncertainty in the water vapor distribution. The sensitivity of atmospheric refractivity to water vapor pressure, however, means that refractivity profiles can in principle yield information on the atmospheric humidity distribution given independent information on the temperature and pressure distribution from NWP models or independent observational data.
A discussion is provided of some of the research opportunities that exist to capitalize on the complementary nature of the methods of active atmospheric monitoring by GPS and other observation systems for use in weather and climate studies and in numerical weather prediction models.
Abstract
Global positioning system (GPS) radio occultation (RO) observations, first made of Earth’s atmosphere in 1995, have contributed in new ways to the understanding of the thermal structure and variability of the tropical upper troposphere–lower stratosphere (UTLS), an important component of the climate system. The UTLS plays an essential role in the global radiative balance, the exchange of water vapor, ozone, and other chemical constituents between the troposphere and stratosphere, and the transfer of energy from the troposphere to the stratosphere. With their high accuracy, precision, vertical resolution, and global coverage, RO observations are uniquely suited for studying the UTLS and a broad range of equatorial waves, including gravity waves, Kelvin waves, Rossby and mixed Rossby–gravity waves, and thermal tides. Because RO measurements are nearly unaffected by clouds, they also resolve the upper-level thermal structure of deep convection and tropical cyclones as well as volcanic clouds. Their low biases and stability from mission to mission make RO observations powerful tools for studying climate variability and trends, including the annual cycle and intraseasonal-to-interannual atmospheric modes of variability such as the quasi-biennial oscillation (QBO), Madden–Julian oscillation (MJO), and El Niño–Southern Oscillation (ENSO). These properties also make them useful for evaluating climate models and detection of small trends in the UTLS temperature, key indicators of climate change. This paper reviews the contributions of RO observations to the understanding of the three-dimensional structure of tropical UTLS phenomena and their variability over time scales ranging from hours to decades and longer.
Abstract
Global positioning system (GPS) radio occultation (RO) observations, first made of Earth’s atmosphere in 1995, have contributed in new ways to the understanding of the thermal structure and variability of the tropical upper troposphere–lower stratosphere (UTLS), an important component of the climate system. The UTLS plays an essential role in the global radiative balance, the exchange of water vapor, ozone, and other chemical constituents between the troposphere and stratosphere, and the transfer of energy from the troposphere to the stratosphere. With their high accuracy, precision, vertical resolution, and global coverage, RO observations are uniquely suited for studying the UTLS and a broad range of equatorial waves, including gravity waves, Kelvin waves, Rossby and mixed Rossby–gravity waves, and thermal tides. Because RO measurements are nearly unaffected by clouds, they also resolve the upper-level thermal structure of deep convection and tropical cyclones as well as volcanic clouds. Their low biases and stability from mission to mission make RO observations powerful tools for studying climate variability and trends, including the annual cycle and intraseasonal-to-interannual atmospheric modes of variability such as the quasi-biennial oscillation (QBO), Madden–Julian oscillation (MJO), and El Niño–Southern Oscillation (ENSO). These properties also make them useful for evaluating climate models and detection of small trends in the UTLS temperature, key indicators of climate change. This paper reviews the contributions of RO observations to the understanding of the three-dimensional structure of tropical UTLS phenomena and their variability over time scales ranging from hours to decades and longer.
Abstract
Over a two-year period beginning in 2015, a panel of subject matter experts, the Space Platform Requirements Working Group (SPRWG), carried out an analysis and prioritization of different space-based observations supporting the National Oceanic and Atmospheric Administration (NOAA)’s operational services in the areas of weather, oceans, and space weather. NOAA leadership used the SPRWG analysis of space-based observational priorities in different mission areas, among other inputs, to inform the Multi-Attribute Utility Theory (MAUT)-based value model and the NOAA Satellite Observing Systems Architecture (NSOSA) study. The goal of the NSOSA study is to develop candidate satellite architectures for the era beginning in approximately 2030. The SPRWG analysis included a prioritized list of observational objectives together with the quantitative attributes of each objective at three levels of performance: a threshold level of minimal utility, an intermediate level that the community expects by 2030, and a maximum effective level, a level for which further improvements would not be cost effective. This process is believed to be unprecedented in the analysis of long-range plans for providing observations from space. This paper describes the process for developing the prioritized objectives and their attributes and how they were combined in the Environmental Data Record (EDR) Value Model (EVM). The EVM helped inform NOAA’s assessment of many potential architectures for its future observing system within the NSOSA study. However, neither the SPRWG nor its report represents official NOAA policy positions or decisions, and the responsibility for selecting and implementing the final architecture rests solely with NOAA senior leadership.
Abstract
Over a two-year period beginning in 2015, a panel of subject matter experts, the Space Platform Requirements Working Group (SPRWG), carried out an analysis and prioritization of different space-based observations supporting the National Oceanic and Atmospheric Administration (NOAA)’s operational services in the areas of weather, oceans, and space weather. NOAA leadership used the SPRWG analysis of space-based observational priorities in different mission areas, among other inputs, to inform the Multi-Attribute Utility Theory (MAUT)-based value model and the NOAA Satellite Observing Systems Architecture (NSOSA) study. The goal of the NSOSA study is to develop candidate satellite architectures for the era beginning in approximately 2030. The SPRWG analysis included a prioritized list of observational objectives together with the quantitative attributes of each objective at three levels of performance: a threshold level of minimal utility, an intermediate level that the community expects by 2030, and a maximum effective level, a level for which further improvements would not be cost effective. This process is believed to be unprecedented in the analysis of long-range plans for providing observations from space. This paper describes the process for developing the prioritized objectives and their attributes and how they were combined in the Environmental Data Record (EDR) Value Model (EVM). The EVM helped inform NOAA’s assessment of many potential architectures for its future observing system within the NSOSA study. However, neither the SPRWG nor its report represents official NOAA policy positions or decisions, and the responsibility for selecting and implementing the final architecture rests solely with NOAA senior leadership.
Abstract
Launched in 2006, the Formosa Satellite Mission 3–Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) was the first constellation of microsatellites carrying global positioning system (GPS) radio occultation (RO) receivers. Radio occultation is an active remote sensing technique that provides valuable information on the vertical variations of electron density in the ionosphere, and temperature, pressure, and water vapor in the stratosphere and troposphere. COSMIC has demonstrated the great value of RO data in ionosphere, climate, and meteorological research and operational weather forecasting. However, there are still challenges using RO data, particularly in the moist lower troposphere and upper stratosphere. A COSMIC follow-on constellation, COSMIC-2, was launched into equatorial orbit in 2019. With increased signal-to-noise ratio (SNR) from improved receivers and digital beam steering antennas, COSMIC-2 will produce at least 5,000 high-quality RO profiles daily in the tropics and subtropics. In this paper, we summarize 1) recent (since 2011 when the last review was published) contributions of COSMIC and other RO observations to weather, climate, and space weather science; 2) the remaining challenges in RO applications; and 3) potential contributions to research and operations of COSMIC-2.
Abstract
Launched in 2006, the Formosa Satellite Mission 3–Constellation Observing System for Meteorology, Ionosphere and Climate (FORMOSAT-3/COSMIC) was the first constellation of microsatellites carrying global positioning system (GPS) radio occultation (RO) receivers. Radio occultation is an active remote sensing technique that provides valuable information on the vertical variations of electron density in the ionosphere, and temperature, pressure, and water vapor in the stratosphere and troposphere. COSMIC has demonstrated the great value of RO data in ionosphere, climate, and meteorological research and operational weather forecasting. However, there are still challenges using RO data, particularly in the moist lower troposphere and upper stratosphere. A COSMIC follow-on constellation, COSMIC-2, was launched into equatorial orbit in 2019. With increased signal-to-noise ratio (SNR) from improved receivers and digital beam steering antennas, COSMIC-2 will produce at least 5,000 high-quality RO profiles daily in the tropics and subtropics. In this paper, we summarize 1) recent (since 2011 when the last review was published) contributions of COSMIC and other RO observations to weather, climate, and space weather science; 2) the remaining challenges in RO applications; and 3) potential contributions to research and operations of COSMIC-2.
