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- Author or Editor: S. D. Burk x
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Abstract
When radiative transfer is the dominant mechanism cooling the lower thermosphere of Jupiter, CH4, (7.7μ) is probably the dominant cooling agent; however, its low turbopause mixing ratio (10−4, as compared to 10−3 in the lower atmosphere) contributes to a cooling rate small (≲10−4) compared to CO2 on Mars. This results in a Javian mesopause density ∼10 times the Martian density or ∼1014 cm−3, if radiative cooling is the primary heat transfer mechanism in the lower thermosphere. An alternate method for transporting heat is convection (forced or free), which apparently emerges as the dominant transport mechanism as the effective eddy diffusion coefficient (Kv ) approaches values similar to those anticipated in the earth's lower thermosphere (106 cm see−1). Over the solar cycle, with a high heating efficiency (0.86), the temperature rise above the turbopause ranges between 19 and 53K for weak convective activity (Kv =105 cm see−1) and 7–19K for strong activity (107 cm see−1), suggesting that satellite measurements of the exospheric temperature could be used to estimate the degree of convective activity present in the upper atmosphere. Reasonable variations in the H2-He ratio and the mesopause height (∼300 km), temperature (140K) and cooling rate are of minor importance compared to the heating efficiency and the incident flux in establishing the thermospheric temperature profile via the heat conduction equation. The diurnal temperature variation in the Jovian exosphere over the solar cycle is small, probably less than 5–10K.
Abstract
When radiative transfer is the dominant mechanism cooling the lower thermosphere of Jupiter, CH4, (7.7μ) is probably the dominant cooling agent; however, its low turbopause mixing ratio (10−4, as compared to 10−3 in the lower atmosphere) contributes to a cooling rate small (≲10−4) compared to CO2 on Mars. This results in a Javian mesopause density ∼10 times the Martian density or ∼1014 cm−3, if radiative cooling is the primary heat transfer mechanism in the lower thermosphere. An alternate method for transporting heat is convection (forced or free), which apparently emerges as the dominant transport mechanism as the effective eddy diffusion coefficient (Kv ) approaches values similar to those anticipated in the earth's lower thermosphere (106 cm see−1). Over the solar cycle, with a high heating efficiency (0.86), the temperature rise above the turbopause ranges between 19 and 53K for weak convective activity (Kv =105 cm see−1) and 7–19K for strong activity (107 cm see−1), suggesting that satellite measurements of the exospheric temperature could be used to estimate the degree of convective activity present in the upper atmosphere. Reasonable variations in the H2-He ratio and the mesopause height (∼300 km), temperature (140K) and cooling rate are of minor importance compared to the heating efficiency and the incident flux in establishing the thermospheric temperature profile via the heat conduction equation. The diurnal temperature variation in the Jovian exosphere over the solar cycle is small, probably less than 5–10K.
Abstract
Monthly averages of numerical model fields are beneficial for depicting patterns in surface forcing such as sensible and latent heat fluxes, wind stress, and wind stress curl over data-sparse ocean regions. Grid resolutions less than 10 km provide the necessary mesoscale detail to characterize the impact of a complex coastline and coastal topography. In the present study a high-resolution mesoscale model is employed to reveal patterns in low-level winds, temperature, relative humidity, sea surface temperature as well as surface fluxes, over the eastern Pacific and along the U.S. west coast. Hourly output from successive 12-h forecasts are averaged to obtain monthly mean patterns from each season of 1999. The averages yield information on interactions between the ocean and the overlying atmosphere and on the influence of coastal terrain forcing in addition to their month-to-month variability.
The spring to summer transition is characterized by a dramatic shift in near-surface winds, temperature, and relative humidity as offshore regions of large upward surface fluxes diminish and an alongshore coastal flux gradient forms. Embedded within this gradient, and the imprint of strong summertime topographic forcing, are small-scale fluctuations that vary in concert with local changes in sea surface temperature. Potential feedbacks between the low-level wind, sea surface temperature, and the wind stress curl are explored in the coastal regime and offshore waters. In all seasons, offshore extensions of colder coastal waters impose a marked influence on low-level conditions by locally enhancing stability and reducing the wind speed, while buoy measurements along the coast indicate that sea surface temperatures and wind speeds tend to be negatively correlated.
Abstract
Monthly averages of numerical model fields are beneficial for depicting patterns in surface forcing such as sensible and latent heat fluxes, wind stress, and wind stress curl over data-sparse ocean regions. Grid resolutions less than 10 km provide the necessary mesoscale detail to characterize the impact of a complex coastline and coastal topography. In the present study a high-resolution mesoscale model is employed to reveal patterns in low-level winds, temperature, relative humidity, sea surface temperature as well as surface fluxes, over the eastern Pacific and along the U.S. west coast. Hourly output from successive 12-h forecasts are averaged to obtain monthly mean patterns from each season of 1999. The averages yield information on interactions between the ocean and the overlying atmosphere and on the influence of coastal terrain forcing in addition to their month-to-month variability.
The spring to summer transition is characterized by a dramatic shift in near-surface winds, temperature, and relative humidity as offshore regions of large upward surface fluxes diminish and an alongshore coastal flux gradient forms. Embedded within this gradient, and the imprint of strong summertime topographic forcing, are small-scale fluctuations that vary in concert with local changes in sea surface temperature. Potential feedbacks between the low-level wind, sea surface temperature, and the wind stress curl are explored in the coastal regime and offshore waters. In all seasons, offshore extensions of colder coastal waters impose a marked influence on low-level conditions by locally enhancing stability and reducing the wind speed, while buoy measurements along the coast indicate that sea surface temperatures and wind speeds tend to be negatively correlated.
Abstract
The conditions under which atmospheric island wakes form leeward of Kauai, Hawaii, are investigated using idealized numerical simulations and real data forecasts from the U.S. Navy's Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). Nondimensional mountain height ĥ is varied in a series of idealized simulations by altering the island's terrain height; with increasing ĥ, the wake configuration varies from two small counterrotating vortices to a straight wake to a meandering wake to a von Kármán vortex street. In both the idealized and real data forecasts, stability changes across the wake alter the surface layer temperature and moisture profiles, thereby modifying the refractivity and evaporation duct height (EDH) fields. An electromagnetic (EM) propagation model and a radar clutter model are used to demonstrate that the alterations to the refractivity field created by the wake are capable of strongly affecting near-surface EM propagation. Substantial azimuthal variability in radar sea clutter was observed during radar performance tests conducted by the USS O'Kane leeward of Kauai in December of 1999; these anomalies were postulated to result from an island wake. Results from the linkage of COAMPS output with the two EM codes are compared with the radar returns collected aboard the O'Kane, and metrics are developed for comparing COAMPS forecast EDH values with those calculated directly from the shipboard observations.
Abstract
The conditions under which atmospheric island wakes form leeward of Kauai, Hawaii, are investigated using idealized numerical simulations and real data forecasts from the U.S. Navy's Coupled Ocean–Atmosphere Mesoscale Prediction System (COAMPS). Nondimensional mountain height ĥ is varied in a series of idealized simulations by altering the island's terrain height; with increasing ĥ, the wake configuration varies from two small counterrotating vortices to a straight wake to a meandering wake to a von Kármán vortex street. In both the idealized and real data forecasts, stability changes across the wake alter the surface layer temperature and moisture profiles, thereby modifying the refractivity and evaporation duct height (EDH) fields. An electromagnetic (EM) propagation model and a radar clutter model are used to demonstrate that the alterations to the refractivity field created by the wake are capable of strongly affecting near-surface EM propagation. Substantial azimuthal variability in radar sea clutter was observed during radar performance tests conducted by the USS O'Kane leeward of Kauai in December of 1999; these anomalies were postulated to result from an island wake. Results from the linkage of COAMPS output with the two EM codes are compared with the radar returns collected aboard the O'Kane, and metrics are developed for comparing COAMPS forecast EDH values with those calculated directly from the shipboard observations.
Abstract
A new very narrow band model (VNBM) approach has been developed and incorporated into the MODTRAN atmospheric transmittance–radiance code. The VNBM includes a computational spectral resolution of 1 cm−1, a single-line Voigt equivalent width formalism that is based on the Rodgers–Williams approximation and accounts for the finite spectral width of the interval, explicit consideration of line tails, a statistical line overlap correction, a new sublayer integration approach that treats the effect of the sublayer temperature gradient on the path radiance, and the Curtis–Godson (CG) approximation for inhomogeneous paths. A modified procedure for determining the line density parameter 1/d is introduced, which reduces its magnitude. This results in a partial correction of the VNBM tendency to overestimate the interval equivalent widths. The standard two parameter CG approximation is used for H2O and CO2, while the Goody three parameter CG approximation is used for O3. Atmospheric flux and cooling rate predictions using a research version of MODTRAN, MODR, are presented for H2O (with and without the continuum), CO2, and O3 for several model atmospheres. The effect of doubling the CO2 concentration is also considered. These calculations are compared to line-by-line (LBL) model calculations using the AER, GLA, GFDL, and GISS codes. The MODR predictions fall within the spread of the LBL results. The effects of decreasing the band model spectral resolution are illustrated using CO2 cooling rate and flux calculations.
Abstract
A new very narrow band model (VNBM) approach has been developed and incorporated into the MODTRAN atmospheric transmittance–radiance code. The VNBM includes a computational spectral resolution of 1 cm−1, a single-line Voigt equivalent width formalism that is based on the Rodgers–Williams approximation and accounts for the finite spectral width of the interval, explicit consideration of line tails, a statistical line overlap correction, a new sublayer integration approach that treats the effect of the sublayer temperature gradient on the path radiance, and the Curtis–Godson (CG) approximation for inhomogeneous paths. A modified procedure for determining the line density parameter 1/d is introduced, which reduces its magnitude. This results in a partial correction of the VNBM tendency to overestimate the interval equivalent widths. The standard two parameter CG approximation is used for H2O and CO2, while the Goody three parameter CG approximation is used for O3. Atmospheric flux and cooling rate predictions using a research version of MODTRAN, MODR, are presented for H2O (with and without the continuum), CO2, and O3 for several model atmospheres. The effect of doubling the CO2 concentration is also considered. These calculations are compared to line-by-line (LBL) model calculations using the AER, GLA, GFDL, and GISS codes. The MODR predictions fall within the spread of the LBL results. The effects of decreasing the band model spectral resolution are illustrated using CO2 cooling rate and flux calculations.
Meteorological data from over 2800 automated environmental monitoring stations in the western United States are collected, processed, archived, integrated, and disseminated as part of the MesoWest program. MesoWest depends upon voluntary access to provisional observations from environmental monitoring stations installed and maintained by federal, state, and local agencies and commercial firms. In many cases, collection and transmission of these observations are facilitated by NWS forecast offices, government laboratories, and universities. MesoWest augments the Automated Surface Observing System (ASOS) network maintained by the NWS, Federal Aviation Administration, and Department of Defense. MesoWest increases the coverage of observations in remote locations and helps capture many of the local and mesoscale weather phenomena that impact the public.
The primary goal of MesoWest is to improve timely access to automated observations for NWS forecasters at offices throughout the western United States. In addition, integration of the observations into analyses of surface conditions at high spatial and temporal resolution provides additional tools for nowcasts and forecast verification. MesoWest observations are being used for many other applications, including input to operational and research models and research and education on weather processes in the western United States.
Meteorological data from over 2800 automated environmental monitoring stations in the western United States are collected, processed, archived, integrated, and disseminated as part of the MesoWest program. MesoWest depends upon voluntary access to provisional observations from environmental monitoring stations installed and maintained by federal, state, and local agencies and commercial firms. In many cases, collection and transmission of these observations are facilitated by NWS forecast offices, government laboratories, and universities. MesoWest augments the Automated Surface Observing System (ASOS) network maintained by the NWS, Federal Aviation Administration, and Department of Defense. MesoWest increases the coverage of observations in remote locations and helps capture many of the local and mesoscale weather phenomena that impact the public.
The primary goal of MesoWest is to improve timely access to automated observations for NWS forecasters at offices throughout the western United States. In addition, integration of the observations into analyses of surface conditions at high spatial and temporal resolution provides additional tools for nowcasts and forecast verification. MesoWest observations are being used for many other applications, including input to operational and research models and research and education on weather processes in the western United States.
