scholarly journals The Synoptic Regulation of Dryline Intensity

2007 ◽  
Vol 135 (5) ◽  
pp. 1699-1709 ◽  
Author(s):  
David M. Schultz ◽  
Christopher C. Weiss ◽  
Paul M. Hoffman
Keyword(s):  
United States ◽  
Boundary Layer ◽  
New Mexico ◽  
Short Wave ◽  
Synoptic Scale ◽  
West Texas ◽  
Long Wave ◽  
Surface Cyclone ◽  
The Difference ◽  
Upper Level

Abstract To investigate the role of synoptic-scale processes in regulating the strength of the dryline, a dataset is constructed of all drylines occurring within the West Texas Mesonet (WTM) during April, May, and June of 2004 and 2005. In addition, dewpoint and wind data were collected from stations on the western (Morton; MORT) and eastern (Paducah; PADU) periphery of the WTM domain (230 km across), generally oriented east–west across the typical location of the dryline in west Texas. Drylines were characterized by two variables: the difference in dewpoint between MORT and PADU (hereafter, dryline intensity) and the difference in the eastward component of the wind between MORT and PADU (hereafter, dryline confluence). A high degree of correlation existed between the two variables, consistent with a strong role for dryline confluence in determining dryline intensity. Some cases departing from the strong correlation between these variables represent synoptically quiescent drylines whose strength is likely dominated by boundary layer mixing processes. Composite synoptic analyses were constructed of the upper and lower quartiles of dryline intensity, termed STRONG and WEAK, respectively. STRONG drylines were associated with a short-wave trough in the upper-level westerlies approaching west Texas, an accompanying surface cyclone over eastern New Mexico, and southerly flow over the south-central United States. This synoptic environment was favorable for enhancing the dryline confluence responsible for strengthening the dryline. In contrast, WEAK drylines were associated with an upper-level long-wave ridge over Texas and New Mexico, broad surface cyclogenesis over the southwestern United States, and a weak lee trough—the dryline confluence favorable for dryline intensification was much weaker. A third composite termed NO BOUNDARY was composed of dates with no surface airstream boundary (e.g., front, dryline) in the WTM domain. The NO BOUNDARY composite featured an upper-level long-wave ridge west of Texas and no surface cyclone or lee trough. The results of this study demonstrate the important role that synoptic-scale processes (e.g., surface lee troughs, upper-level short-wave troughs) play in regulating the strength of the dryline. Once such a favorable synoptic pattern occurs, mesoscale and boundary layer processes can lead to further intensification of the dryline.

scholarly journals The Behavior of Synoptic-Scale Errors in the Eta Model

2006 ◽  
Vol 134 (11) ◽  
pp. 3355-3366 ◽  
Author(s):  
Kimberly L. Elmore ◽  
David M. Schultz ◽  
Michael E. Baldwin
Keyword(s):  
United States ◽  
Large Scale ◽  
The United States ◽  
Short Wave ◽  
Relative Vorticity ◽  
Synoptic Scale ◽  
The West ◽  
Long Wave ◽  
Eta Model ◽  
Grid Points

Abstract A previous study of the mean spatial bias errors associated with operational forecast models motivated an examination of the mechanisms responsible for these biases. One hypothesis for the cause of these errors is that mobile synoptic-scale phenomena are partially responsible. This paper explores this hypothesis using 24-h forecasts from the operational Eta Model and an experimental version of the Eta run with Kain–Fritsch convection (EtaKF). For a sample of 44 well-defined upper-level short-wave troughs arriving on the west coast of the United States, 70% were underforecast (as measured by the 500-hPa geopotential height), a likely result of being undersampled by the observational network. For a different sample of 45 troughs that could be tracked easily across the country, consecutive model runs showed that the height errors associated with 44% of the troughs generally decreased in time, 11% increased in time, 18% had relatively steady errors, 2% were uninitialized entering the West Coast, and 24% exhibited some other kind of behavior. Thus, landfalling short-wave troughs were typically underforecast (positive errors, heights too high), but these errors tended to decrease as they moved across the United States, likely a result of being better initialized as the troughs became influenced by more upper-air data. Nevertheless, some errors in short-wave troughs were not corrected as they fell under the influence of supposedly increased data amount and quality. These results indirectly show the effect that the amount and quality of observational data has on the synoptic-scale errors in the models. On the other hand, long-wave ridges tended to be underforecast (negative errors, heights too low) over a much larger horizontal extent. These results are confirmed in a more systematic manner over the entire dataset by segregating the model output at each grid point by the sign of the 500-hPa relative vorticity. Although errors at grid points with positive relative vorticity are small but positive in the western United States, the errors become large and negative farther east. Errors at grid points with negative relative vorticity, on the other hand, are generally negative across the United States. A large negative bias observed in the Eta and EtaKF over the southeast United States is believed to be due to an error in the longwave radiation scheme interacting with water vapor and clouds. This study shows that model errors may be related to the synoptic-scale flow, and even large-scale features such as long-wave troughs can be associated with significant large-scale height errors.

scholarly journals Synoptic-Scale Flow and Valley Cold Pool Evolution in the Western United States

2009 ◽  
Vol 24 (6) ◽  
pp. 1625-1643 ◽  
Author(s):  
Heather Dawn Reeves ◽  
David J. Stensrud
Keyword(s):  
United States ◽  
Large Scale ◽  
Numerical Models ◽  
Western United States ◽  
Cold Pool ◽  
Synoptic Scale ◽  
Temperature Changes ◽  
Cold Pools ◽  
Upper Level ◽  
Forecast Problem

Abstract Valley cold pools (VCPs), which are trapped, cold layers of air at the bottoms of basins or valleys, pose a significant problem for forecasters because they can lead to several forms of difficult-to-forecast and hazardous weather such as fog, freezing rain, or poor air quality. Numerical models have historically failed to routinely provide accurate guidance on the formation and demise of VCPs, making the forecast problem more challenging. In some case studies of persistent wintertime VCPs, there is a connection between the movement of upper-level waves and the timing of VCP formation and decay. Herein, a 3-yr climatology of persistent wintertime VCPs for five valleys and basins in the western United States is performed to see how often VCP formation and decay coincides with synoptic-scale (∼200–2000 km) wave motions. Valley cold pools are found to form most frequently as an upper-level ridge approaches the western United States and in response to strong midlevel warming. The VCPs usually last as long as the ridge is over the area and usually only end when a trough, and its associated midlevel cooling, move over the western United States. In fact, VCP strength appears to be almost entirely dictated by midlevel temperature changes, which suggests large-scale forcing is dominant for this type of VCP most of the time.

Micro-Meteorological Conditions for Snow Melt

1987 ◽  
Vol 33 (113) ◽  
pp. 24-26 ◽  
Author(s):  
M. Kuhn
Keyword(s):  
Boundary Layer ◽  
Transfer Coefficient ◽  
Air Temperature ◽  
Short Wave ◽  
Wave Radiation ◽  
Free Atmosphere ◽  
Alpine Glacier ◽  
Long Wave ◽  
Air Temperatures ◽  
Long Wave Radiation

AbstractThe energy budget of a snow or ice surface is determined by atmospheric variables like solar and atmospheric long-wave radiation, air temperature, and humidity; the transfer of energy from the free atmosphere to the surface depends on the stability of the atmospheric boundary layer, where vertical profiles of wind speed and temperature determine stability, and on surface conditions like surface temperature (and thus surface humidity), roughness, and albedo.This paper investigates the conditions exactly at the onset or the end of melting using air temperature, humidity, and as the radiation term the sum of global and reflected short-wave plus downward long-wave radiation. For the turbulent exchange in the boundary layer, examples are computed with a transfer coefficient of 18.5 W m−2K−1which corresponds to the average over the ablation period on an Alpine glacier. Ways to estimate the transfer coefficient for various degrees of stability are indicated in the Appendix.It appears from such calculations that snow may melt at air temperatures as low as –10°C and may stay frozen at +10°C.

Permian Gastropoda of the southwestern United States: Subulitacea

1988 ◽  
Vol 62 (01) ◽  
pp. 56-69 ◽  
Author(s):  
Douglas H. Erwin
Keyword(s):  
United States ◽  
New Species ◽  
New Mexico ◽  
New Genus ◽  
Southwestern United States ◽  
New Family ◽  
West Texas ◽  
Permian System ◽  
The Family ◽  
The Status

The composition of Permian members of the superfamily Subulitacea is considered, and 12 new species of Subulitacea are described from the silicified fauna of the Permian System of West Texas and New Mexico. Other elements of the gastropod fauna were previously described by Yochelson (1956a, 1960) and Batten (1958).The new genusIschnoptygmais established for subulitaceans possessing a plate-like columellar fold, and includes the new speciesIschnoptygma archibaldiandI. valentinei.The genus is placed within the new family Ischnoptygmidae. New species of Subulitidae areCeraunocochlis deformis, C. elongata, C. kidderi, C. trekensis, Strobeus girtyi, Soleniscus diminutus, S. variabilis, Cylindritopsis hamiltonae, andC. spheroides.The status of the genusLabridensis questioned, but provisionally retained. The assignment of the family Meekospiridae to the Subulitacea is questioned, and a single new species,Meekospira mimiae, is described.

scholarly journals Feedbacks of dust and boundary layer meteorology during a dust storm in the eastern Mediterranean

2015 ◽  
Vol 15 (22) ◽  
pp. 12909-12933 ◽  
Author(s):  
S. Rémy ◽  
A. Benedetti ◽  
A. Bozzo ◽  
T. Haiden ◽  
L. Jones ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Radiative Forcing ◽  
Eastern Mediterranean ◽  
Surface Wind ◽  
Short Wave ◽  
Radiative Fluxes ◽  
Aerosol Radiative Forcing ◽  
Wind Speeds ◽  
Long Wave ◽  
Boundary Layer Meteorology

Abstract. Aerosols affect the atmosphere through direct interaction with short-wave and long-wave radiation and the microphysical properties of clouds. In this paper we report in detail on several mechanisms by which the short-term impact of dust on surface radiative fluxes can affect the dust loading of the atmosphere via modification of boundary-layer meteorology. This in turn affects the aerosol radiative forcing itself. Examples of these feedbacks between dust and boundary layer meteorology were observed during a series of dust storms in the Sahara and the eastern Mediterranean in April 2012. These case studies have been analysed using the Monitoring Atmospheric Composition and Climate – Interim Implementation (MACC-II) system. The radiative fluxes in the short-wave and long-wave spectra were both significantly affected by the prognostic aerosol–radiation interaction, which in turn impacted the meteorological simulation. Reduced incoming solar radiation below the aerosol layers led to a decrease in maximum surface temperatures and to a more stable thermal stratification of the lower atmosphere. This in turn forced weaker surface wind speeds and eventually smaller dust emissions. Moreover, we also observed a secondary impact of the aerosol radiative forcing, whereby horizontal gradients of surface temperature were increased at the edge of the dust plume, which led to local increases of surface wind speeds due to the thermal wind effect. The differentiated impact of the aerosol layer on surface pressure also contributed to the increase in surface wind speed and dust production in the same area. Enhanced long-wave radiative fluxes by the dust mass were associated with opposite processes. Less stable thermal stratification at night, brought mainly by higher minimum temperatures at the surface, caused stronger surface winds. At the edge of the dust storm, weaker horizontal temperature and pressure gradients forced lower winds and reduced dust production. Regarding dust emissions, short-wave radiative forcing had a larger impact than long-wave radiative forcing, corroborating several previous studies. For surface temperature, short-wave and long-wave contribution were close in intensity. These feedbacks were amplified when using data assimilation to build the aerosol analysis of the MACC-II global system. This led to an improvement in the short-term forecasts of thermal radiative fluxes and surface temperatures.

scholarly journals The Integral Role of a Diabatic Rossby Vortex in a Heavy Snowfall Event

2008 ◽  
Vol 136 (6) ◽  
pp. 1878-1897 ◽  
Author(s):  
Richard W. Moore ◽  
Michael T. Montgomery ◽  
Huw C. Davies
Keyword(s):  
Mesoscale Model ◽  
Heavy Precipitation ◽  
Short Wave ◽  
Low Level ◽  
Wave Trough ◽  
Surface Cyclone ◽  
Integral Role ◽  
Surface Disturbance ◽  
Upper Level ◽  
Inversion Techniques

Abstract On 24–25 February 2005, a significant East Coast cyclone deposited from 4 to nearly 12 in. (∼10–30 cm) of snow on parts of the northeastern United States. The heaviest snowfall and most rapid deepening of the cyclone coincided with the favorable positioning of an upper-level, short-wave trough immediately upstream of a preexisting surface cyclone. The surface cyclone in question formed approximately 15 h before the heaviest snowfall along a coastal front in a region of frontogenesis and heavy precipitation. The incipient surface cyclone subsequently intensified as it moved to the northeast, consistently generating the strongest convection to the east-northeast of the low-level circulation center. The use of potential vorticity (PV) inversion techniques and a suite of mesoscale model simulations illustrates that the early intensification of the incipient surface cyclone was primarily driven by diabatic effects and was not critically dependent on the upper-level wave. These facts, taken in conjunction with the observed structure, energetics, and Lagrangian evolution of the incipient surface disturbance, identify it as a diabatic Rossby vortex (DRV). The antecedent surface vorticity spinup associated with the DRV phase of development is found to be integral to the subsequent rapid growth. The qualitative similarity with a number of observed cases of explosive cyclogenesis leaves open the possibility that a DRV-like feature comprises the preexisting positive low-level PV anomaly in a number of cyclogenetic events that exhibit a two-stage evolution.

Short-wave instability of an elastic plate in supersonic flow in the presence of the boundary layer

2016 ◽  
Vol 802 ◽  
pp. 528-552 ◽  
Author(s):  
Vsevolod Bondarev ◽  
Vasily Vedeneev
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Elastic Plate ◽  
Inflection Point ◽  
Short Wave ◽  
Uniform Flow ◽  
Rayleigh Equation ◽  
Panel Flutter ◽  
Convex Boundary ◽  
Long Wave

Panel flutter is a dangerous aeroelastic instability of the skin panels of supersonic flight vehicles. Though the linear stability of panels in uniform flow has been studied in detail, the influence of the boundary layer is still an open question. Most studies of panel flutter in the presence of the boundary layer are devoted to the ($1/7$)th-power velocity law and yield a stabilising effect of the boundary layer. Recently, Vedeneev (J. Fluid Mech., vol. 736, 2013, pp. 216–249) considered arbitrary velocity and temperature profiles and showed that, for a generalised convex boundary layer profile, a decrease of the growth rates of ‘supersonic’ perturbations (responsible for single-mode panel flutter) is accompanied by destabilisation of ‘subsonic’ perturbations that are neutral in uniform flow. However, this result is not self-consistent, as the long-wave expansion for solutions of the Rayleigh equation was used, whereas subsonic perturbations, generally speaking, cannot be considered as long waves. More surprising results are obtained for the boundary layer profile with a generalised inflection point, where the effect of the layer is destabilising even for ‘supersonic’ perturbations, and such waves can also have short lengths. In order to overcome this inconsistency, in this paper, we solve the Rayleigh equation numerically and investigate the stability of short-wave perturbation of the elastic plate in the presence of the boundary layer. As before, two problem formulations are investigated. First, we study running waves in an infinite plate. Second, we analyse eigenmodes of the plate of large finite length and use Kulikovskii’s global instability criterion. Based on the results of calculations, we confirm that the effect of the boundary layer with a generalised inflection point can be essentially destabilising. On the other hand, for generalised convex boundary layers, calculations show that, unlike the prediction of the long-wave approximation, the finite plate is fully stabilised for sufficiently thick boundary layers.

scholarly journals Micro-Meteorological Conditions for Snow Melt

1987 ◽  
Vol 33 (113) ◽  
pp. 24-26 ◽  
Author(s):  
M. Kuhn
Keyword(s):  
Boundary Layer ◽  
Transfer Coefficient ◽  
Air Temperature ◽  
Short Wave ◽  
Wave Radiation ◽  
Free Atmosphere ◽  
Alpine Glacier ◽  
Long Wave ◽  
Air Temperatures ◽  
Long Wave Radiation

AbstractThe energy budget of a snow or ice surface is determined by atmospheric variables like solar and atmospheric long-wave radiation, air temperature, and humidity; the transfer of energy from the free atmosphere to the surface depends on the stability of the atmospheric boundary layer, where vertical profiles of wind speed and temperature determine stability, and on surface conditions like surface temperature (and thus surface humidity), roughness, and albedo.This paper investigates the conditions exactly at the onset or the end of melting using air temperature, humidity, and as the radiation term the sum of global and reflected short-wave plus downward long-wave radiation. For the turbulent exchange in the boundary layer, examples are computed with a transfer coefficient of 18.5 W m−2 K−1 which corresponds to the average over the ablation period on an Alpine glacier. Ways to estimate the transfer coefficient for various degrees of stability are indicated in the Appendix.It appears from such calculations that snow may melt at air temperatures as low as –10°C and may stay frozen at +10°C.

Permian Gastropoda of the southwestern United States: Subulitacea

1988 ◽  
Vol 62 (1) ◽  
pp. 56-69 ◽  
Author(s):  
Douglas H. Erwin
Keyword(s):  
United States ◽  
New Species ◽  
New Mexico ◽  
New Genus ◽  
Southwestern United States ◽  
New Family ◽  
West Texas ◽  
Permian System ◽  
The Family ◽  
The Status

The composition of Permian members of the superfamily Subulitacea is considered, and 12 new species of Subulitacea are described from the silicified fauna of the Permian System of West Texas and New Mexico. Other elements of the gastropod fauna were previously described by Yochelson (1956a, 1960) and Batten (1958).The new genus Ischnoptygma is established for subulitaceans possessing a plate-like columellar fold, and includes the new species Ischnoptygma archibaldi and I. valentinei. The genus is placed within the new family Ischnoptygmidae. New species of Subulitidae are Ceraunocochlis deformis, C. elongata, C. kidderi, C. trekensis, Strobeus girtyi, Soleniscus diminutus, S. variabilis, Cylindritopsis hamiltonae, and C. spheroides. The status of the genus Labridens is questioned, but provisionally retained. The assignment of the family Meekospiridae to the Subulitacea is questioned, and a single new species, Meekospira mimiae, is described.

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