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At least 1,171 records · Page 65
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Explosive east coast cyclogenesis over the west-central North Atlantic Ocean - A composite study derived from ECMWF operational analyses

This paper describes the observational aspects of explosive east-coast cyclogenesis using composites constructed from the daily global analyses generated and archived by ECMWF. An explosively deepening storm or bomb is defined as an extratropical cyclone whose mean sea-level pressure falls at least 1 mb/h for 24 h. The ECMWF data sets are used to examine the three-dimensional kinematic and thermodynamic structure of bombs over the entire depth of the troposphere. The evolution and structure of the composite bomb is diagnosed using a moving coordinate system consisting of a box with dimensions of 35 x 35 deg of latitude-longitude. The results reveal that explosive cyclogenesis is a baroclinic phenomenon in which the rapid development in the presence of strong upper tropospheric forcing is most likely enhanced by a highly destabilized lower troposphere.

Manobianco, John↗
NASA NTRS1989

The role of diabatic heating in maintaining the upper-tropospheric baroclinic zone in the South Pacific

The four-dimensional structure of a region that encompasses the South Pacific Convergence Zone (SPCZ) is presently examined using a modified set of FGGE level III-b analyses, during the January 10-18, 1979 period when two cyclones formed in the tropics and propagated southeastward along the SPCZ to middle latitudes. An effort is made to ascertain the significance of kinematic and thermodynamic processes in maintaining the the upper baroclinic region coincident with the subtropical jet. A partitioned form of the frontogenetical function, used to diagnose the adiabatic and diabatic contributions to the maintenance of baroclinicity in the SPCZ's vicinity, indicates a major balance between the frontogenetical contribution by differential diabatic heating and the opposing diabatic tilting processes.

Robertson, Franklin R.↗
NASA NTRS1990

Mesoscale coastal processes during GALE IOP 2

Diagnostic calculations and detailed mesoscale analyses of data for the period January 24-26, 1986 during the second observation period of the Genesis of Atlantic Lows Experiment (GALE) were used to investigate mesoscale coastal processes during this period. Using a variety of National-Weather-Service and GALE surface and upper-air data, three physically related phenomena were studied: the coastal front; a shallow cyclone that propagated along the coastal front, modifying it as it moved northward; and a low-level jet that formed in the strong coastal pressure-gradient field.

Doyle, James D.↗
NASA NTRS1990

Relationship between tropical heating and subtropical westerly maxima in the Southern Hemisphere during SOP-1, FGGE

FGGE Level III-b analyses, produced by the Goddard Laboratory for Atmospheres, NASA, are used to investigate the relationship between tropical heating and subtropical westerly maxima in the Southern Hemisphere during SOP-1 (January 5 - March 4, 1979). The mean state of two 15-day periods is examined, as well as day-to-day variations for the entire 59-day period. In Period 1 (January 6-20), the central South Pacific was extremely active convectively, while in Period 2 (February 3-17), convective activity over the western Indian Ocean was enhanced. Episodes of strong outflow in the tropics, as measured by the upper tropospheric velocity potential, were found to be well correlated with the strengthening and propagation of westerly wind maxima in the subtropics. The average location of the westerly maximum over the South Pacific and Indian oceans was about 16 deg latitudes south, and slightly east, of its corresponding heat source. For a cyclone case study which is presented, however, this distance was considerably less. The response time between the upper level tropical outflow and subtropical westerly enhancement appears to be less than 12 hours; however, an exact temporal scale was difficult to identify.

Hurrel, James W.↗
NASA NTRS1990

Overview of the 27-28 October FIRE Cirrus IFO case: Meteorology and cloud fields

A detailed description of the meteorology of the 27 and 28 October FIRE Cirrus IFO case is presented. The progression of synoptic scale events over the region is reviewed including the evolution of surface and upper air features, i.e., the surface cyclone that formed to the west over Montana on the 27th and moved through Wisconsin late on the 28th and the associated short wave ridge aloft. A summary of the corresponding cloud conditions observed over the area of aircraft operations is given including characterization of the cloud forms and cloud heights based on information derived from debriefings of the aircrews, surface observations, airborne (ER-2) and surface lidars observations and satellite imagery (GOES). The correspondence between the resolved meteorological features (subsynoptic rawinsonde network) and the development of cloud layers is illustrated. In particular, the discussion emphasizes the relationship between vertical thermodynamic structure and the character and vertical structure of the cloud fields. The role of the larger scale in maintaining the observed vertical structure is quantified both with respect to its control via forced ascent and advective processes. Based on results of these analyses, conclusions are drawn with respect to the design of future field missions.

Starr, David OC.↗
NASA NTRS1990

Cloud and boundary layer structure over San Nicolas Island during FIRE

The temporal evolution of the structure of the marine boundary layer and of the associated low-level clouds observed in the vicinity of the San Nicolas Island (SNI) is defined from data collected during the First ISCCP Regional Experiment (FIRE) Marine Stratocumulus Intense Field Observations (IFO) (July 1 to 19). Surface, radiosonde, and remote-sensing measurements are used for this analysis. Sounding from the Island and from the ship Point Sur, which was located approximately 100 km northwest of SNI, are used to define variations in the thermodynamic structure of the lower-troposphere on time scales of 12 hours and longer. Time-height sections of potential temperature and equivalent potential temperature clearly define large-scale variations in the height and the strength of the inversion and periods where the conditions for cloud-top entrainment instability (CTEI) are met. Well defined variations in the height and the strength of the inversion were associated with a Cataline Eddy that was present at various times during the experiment and with the passage of the remnants of a tropical cyclone on July 18. The large-scale variations in the mean thermodynamic structure at SNI correlate well with those observed from the Point Sur. Cloud characteristics are defined for 19 days of the experiment using data from a microwave radiometer, a cloud ceilometer, a sodar, and longwave and shortwave radiometers. The depth of the cloud layer is estimated by defining inversion heights from the sodar reflectivity and cloud-base heights from a laser ceilometer. The integrated liquid water obtained from NOAA's microwave radiometer is compared with the adiabatic liquid water content that is calculated by lifting a parcel adiabatically from cloud base. In addition, the cloud structure is characterized by the variability in cloud-base height and in the integrated liquid water.

Albrecht, Bruce A.↗
NASA NTRS1989

Diagnostic analysis of observed and numerically simulated cloud and precipitation structures during pre-ERICA

A preliminary 140-km simulation of a rapid cyclogenesis, using the Limited Area Mesoscale Prediction System (LAMPS) is discussed. A three-dimensional version of LAMPS used in the simulation is described, along with a trajectory model utilizing the three-hourly output history files from the LAMPS model. Preliminary integrations of the LAMPS code as well as passive microwave digital data from SSM/I aboard the DMSP satellite are used for exploring the evolving baroclinic structure and moisture field of the cyclone event. A trajectory analysis of the model histories reveals a significant role for preconditioning of the low-level upstream air, which is then drawn into the ascending warm conveyor belt ahead of the storm.

Perkey, Donald J.↗
NASA NTRS1991

A numerical modeling study of the interaction between the tides and the circulation forced by high-latitude plasma convection

A spectral, time-varying thermospheric general circulation model has been used to study the nonlinear interaction at high latitudes between the tides propagating into the thermosphere from below and the circulation induced by magnetospheric forcing and in situ solar heating. The model is discrete in the vertical with 27 layers spaced by half a scale height. In the horizontal, the fields are expanded in a series of spherical harmonics using a triangular truncation at wave number 31, equivalent to a homogeneous global resolution with a minimum wavelength of 1270 km. A hypothetical uniform grid point model would require a horizontal spacing of 417 km to describe the same minimum wavelength. In the high-latitude F region the tides affect the dusk vortex of the neutral flow very little, but the dawn vortex is either suppressed or amplified dependent upon the universal time and tidal phase. In the E region neutral flow, both the dusk and dawn vortices are shifted in local time by the tides, again as a function of universal time and tidal phase. At dusk a nonlinear amplification of the sunward winds occurs for certain combinations of parameters, and at dawn the winds may be completely suppressed. Below 120 km altitude the magnetospheric forcing creates a single cyclonic vortex which is also sensitive to the high-latitude tidal structure.

Mikkelsen, I. S.↗
NASA NTRS1990

Stellar and Jovian vortices

The characteristics of 'Jovian' vortices (the large vortices observed in the atmospheres of Jupiter, Saturn, Neptune) are summarized, and the existence of similar structures in the atmospheres of stars is considered theoretically. The problem of vortex maintenance is addressed, including potential vorticity, numerical simulations of Jovian vortices, and cyclones and anticyclones; the Great Red Spot of Jupiter is described on the basis of Voyager data; the evidence for convective generation of vertical vorticity in the sun is examined; the possibly vortical nature of the large spots of RS CVn stars is discussed; and models of spots on rapidly rotating hot stars are surveyed.

Dowling, T. E.↗
NASA NTRS1991

Role of eddy pumping in enhancing primary production in the ocean

Eddy pumping is considered to explain the disparity between geochemical estimates and biological measurements of exported production. Episodic nutrient injections from the ocean into the photic zone can be generated by eddy pumping, which biological measurements cannot sample accurately. The enhancement of production is studied with respect to a cyclonic eddy in the subtropical Pacific. A pump-and-probe fluorimeter generates continuous vertical profiles of primary productivity from which the contributions of photochemical and nonphotochemical processes to fluorescence are derived. A significant correlation is observed between the fluorescence measurements and radiocarbon measurements. The results indicate that eddy pumping has an important effect on phytoplankton production and that this production is near the maximum relative specific growth rates. Based on the production enhancement observed in this case, eddy pumping increases total primary production by only 20 percent and does not account for all enhancement.

Falkowski, Paul G.↗
NASA NTRS1991

Advanced aircraft for atmospheric research

The development of aircraft for high-altitude research is described in terms of program objectives and environmental, technological limitations, and the work on the Perseus A aircraft. The need for these advanced aircraft is proposed in relation to atmospheric science issues such as greenhouse trapping, the dynamics of tropical cyclones, and stratospheric ozone. The implications of the study on aircraft design requirements is addressed with attention given to the basic categories of high-altitude, long-range, long-duration, and nap-of-the-earth aircraft. A strategy is delineated for a platform that permits unique stratospheric measurements and is a step toward a more advanced aircraft. The goal of Perseus A is to carry scientific air sampling payloads weighing at least 50 kg to altitudes of more than 25 km. The airfoils are designed for low Reynolds numbers, the structural weight is very low, and the closed-cycle power plant runs on liquid oxygen.

Russell, P.↗
NASA NTRS1991

Air mass origins and troposphere-to-stratosphere exchange associated with mid-latitude cyclogenesis and tropopause folding inferred from Be-7 measurements

The 1984 extratropical mission of NASA's Stratosphere-Troposphere Exchange Project (STEP) studied cross-jet transport in regions of cyclogenesis and tropopause folding. Correlations of Be-7, ozone, water vapor, and potential vorticity measured on a NASA U-2 research aircraft flying in high shear regions above the jet core are indicative of mixing between the cyclonic and the anticyclonic sides of the jet and are consistent with the hypothesis that small-scale entrainments of upper tropospheric air into the lower stratosphere during cyclogenesis are important in maintaining the vertical gradients of Be-7, ozone, water vapor and other trace constituents in the lower few kilometers of the midlatitude stratosphere. Correlations between Be-7, and ozone suggest a lower tropical stratospheric origin for the ozone-poor lamina observed above the jet core.

Kritz, Mark A.↗
NASA NTRS1990

Upper atmosphere dynamics

The spatial distribution of stratospheric ozone is useful in diagnosis of some features of the large scale atmospheric circulation, and the ozone may also interact with the atmospheric general circulation. Local maxima in the column ozone distribution are often associated with disturbances in the lower stratosphere and upper troposphere, which may herald cyclone development in the troposphere. One research objective is to explore these issues by means of time series analysis of a zonal index of total column ozone, to suggest the existence or nonexistence of relationships between column ozone and dynamical processes which are known to occur on various time scales. Another objective is to investigate the correlation between the ozone mixing ratio on the 350 K isentropic surface and the column integrated ozone, and to investigate the use of an easily derived parameter as a proxy for ozone mixing ratio, which is conserved in the stratosphere for time scales shorter than the photochemical time scale. The source of data for these studies is the Total Ozone Mapping Spectrometer (TOMS) data set.

Miller, Timothy L.↗
NASA NTRS1991

A Variational Assimilation Method for Satellite and Conventional Data: a Revised Basic Model 2B

A variational objective analysis technique that modifies observations of temperature, height, and wind on the cyclone scale to satisfy the five 'primitive' model forecast equations is presented. This analysis method overcomes all of the problems that hindered previous versions, such as over-determination, time consistency, solution method, and constraint decoupling. A preliminary evaluation of the method shows that it converges rapidly, the divergent part of the wind is strongly coupled in the solution, fields of height and temperature are well-preserved, and derivative quantities such as vorticity and divergence are improved. Problem areas are systematic increases in the horizontal velocity components, and large magnitudes of the local tendencies of the horizontal velocity components. The preliminary evaluation makes note of these problems but detailed evaluations required to determine the origin of these problems await future research.

Achtemeier, Gary L.↗
NASA NTRS1992

Inertial oscillation of a vertical rotating draft with application to a supercell storm

An analytic model (vertical rotating draft) which includes the gross features of a supercell storm on an f-plane, undergoes an inertial oscillation that appears to have been overlooked in previous analytic and numerical models. The oscillation is nonlinear and consists of a long quiescent phase and a short intense phase. During the intense phase, the rotating draft has the following features of a supercell: the diameter of the core contracts as it spins up and expands as it spins down; if vertical wind shear is included, the track of the rotating draft turns to the right (an anticyclonic rotating draft turns to the left); this turning point is followed by a predominantly upward flow; and the horizontal pressure gradient is very small (a property of most tornadoless supercells). The rapid spin-up during the intense phase and the high Rossby numbers obtainable establish the ability of the Coriolis force to spin up single cyclonic or anticyclonic supercells by means of this inertial oscillation. This surprising result has implications for numerical supercell simulations, which generally do not rely on the Coriolis force as a source of rotation. The physics and mathematics of the inertial oscillation are given, and the solution is applied to a documented supercell.

Supercell thunderstorm↗
NASA NTRS1992

Inertial Oscillation of a Vertical Rotating Draft with Application to a Supercell Storm: Video Supplement to NASA-TP-3230

In this video (8 min., color, sound, VHS), animation depicts the inertial oscillation of a new mathematical model ('vertical rotating draft') for spinning up a single supercell storm. The oscillation consists of a long quiescent phase when the draft is large in diameter and rotates anticyclonically and a short intense phase when the draft is small and cyclonic. During the intense phase, the rotating draft resembles a supercell. The physical basis for the oscillation is depicted by tracking air parcels in the draft as they move along inertial circles (projected on a horizontal plane), where the horizontal pressure gradient is zero and the Coriolis force balances the centrifugal force. A side view of the oscillation shows that contraction and expansion are linked, respectively, to buoyantly driven compressible downdraft and updraft. An aerial view tracks the draft as it moves above the surface of the Earth and turns to the right during the intense phase. Radar echoes from a supercell storm are superimposed for comparison. The data appear to support only the intense phase. A critical experiment would measure the predominantly downward flow that theoretically occurs before the right turn in a supercell track and causes contraction and spin-up.

Supercell thunderstorm↗
NASA NTRS1991

Chemical and biological structure and transport of a cool filament associated with a jet-eddy system of northern California in July 1986 (OPTOMA21)

The distributions of nutrient, pigment, bio-optical, and physical variables were mapped in a jet-eddy system off Point Reyes and Point Arena, California, from July 7 to 19, 1986, in order to describe the 3D variability of the filament and its relation to the nutrient and phytoplankton distributions offshore, to examine the interaction between the filament and coastal water, and to estimate the transport of nutrients and phytoplankton by the jet system. Several cool filaments were distinguishable at distances of more than 35-50 km from the coast in satellite imagery during this period. The juxtaposition of these features as well as the presence of an offshore anticyclone and a cyclone south of the filament anchored to the coast at Point Arena led to complex patterns in all variables, aided by the apparent alongshore variability in the source of upwelled water. This structure has implications for the fluxes of organic material in the region and is probably significant in organizing the interactions among different trophic levels within the system.

Jones, Burton H.↗
NASA NTRS1991

Diagnostic evaluation of numerical model simulations using the tendency equation

A procedure is proposed to expand the diagnostic capabilities of the pressure tendency equation of a primitive equation NWP model by computing the pressure tendency in physical coordinates. The advantages of isolating the density advection as a diagnostic tool to understand pressure changes is shown. By simple thermodynamic arguments it is demonstrated that in areas of synoptic-scale cyclonic development, the vertically integrated density advection is more than sufficient to explain the depletion of mass over a growing depression. Consequently, the joint contribution of the net divergence and vertical motion opposes the pressure fall. This is illustrated for a case of rapid cyclogenesis in southern South America.

Jusem, Juan C.↗