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At least 577 records · Page 32
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NASA NTRS1986

The possible influence of upstream upper-level baroclinic processes on the development of the QE II storm

An analysis of the QE II storm of September 9-11, 1978 presents evidence for the existence of upper-level baroclinic processes upstream of the rapidly developing cyclone. The analysis shows that a deepening shortwave trough was located 400 to 500 km upstream of the site of the storm 12 h prior to rapid cyclogenesis. The trough was associated with: (1) a polar jet marked by 65 m/s winds in its core and significant vertical and horizontal wind shear, (2) positive vorticity advection and divergence at the 300 mb level, and (3) an intense frontal zone that extended from 300 mb down to the surface. It also appears that a tropopause fold likely extruded stratospheric air down to the 700-800 mb level, 400-500 km upstream of the surface low and 12 h prior to the explosive development phase of the cyclone. These findings raise questions about Gyakum's (1983) assertion that the QE II storm developed in an area in which the baroclinic support was confined to the lower troposphere and the related assertion by Anthes et al. (1983) that upper-level forcing upstream of the area of rapid cyclogenesis was weak and apparently not important in this case.

Uccellini, L. W.↗
NASA NTRS1985

Dynamics and energetics of the South Pacific Convergence Zone during FGGE SOP-1

The major research objectives are to diagnose the physical processes responsible for the maintenance of the South Pacific Convergence Zone (SPCZ) and to examine the role of the SPCZ in the large-scale circulation patterns of the Southern Hemisphere. To accomplish these objectives researchers used several data sources which include: a modified set of Level III-b upper air analyses, originally produced by ECMWF (Vincent, 1982); subjectively analyzed surface analyses for the South Pacific based on island station reports (Vincent, 1985); outgoing longwave radiation values supplied to us by NOAA/NESDIS; and equivalent black body temperatures and precipitation rates derived by Robertson. In the past year researchers found that wave number four plays an inportant role in the Southern Hemisphere tropics during the 15-day period when the sPCZ was a dominant feature, particularly with regard to the baroclinic conversion of potential to kinetic energy (Huang and Vincent, 1985). The convectively-active SPCZ area was found to make a significant contribution to this conversion process; thus, it appears that baroclinic effects and latent heating are important in maintaining the SPCZ. Recently efforts concentrated on two research tasks, an examination of cyclone activity within the SPCZ (Kann, 1985; Vincent, 1985; Vincent and Kann, 1985) and a study of the heat and moisture budgets in the South Pacific (Miller, et al., 1985). It was found that cyclonic disturbances occurred with regularity in the Zone from 10 to 17 January.

Vincent, D. G.↗
NASA NTRS1986

Comparative energetics of the observed and simulated global circulation during the special observing periods of FGGE

Energetics of the observed and simulated global circulation are evaluated in the zonal spectral domain for the special observing periods of FGGE. The study utilizes GLA analyses of FGGE observational data and parallel simulation experiments. There are noticeable differences in energy transformations between the observation and simulation during SOP-1. These include the baroclinic conversion C(n) by the zonal mean motion and short-wave disturbances, and the nonlinear wave-wave interaction L(n) at the long and short waves. The energy transformations of the short-wave disturbances are much more intense in the simulated circulation than in the observation. However, good agreement is noted in the conversion and dissipation of kinetic energy in the large- and cyclone-wave range n = 1-10. Spectral distributions of global energy transformations at the long- and cyclone-wave range indicate that the SOP-2 simulation agrees more closely with the observed fields than the SOP-1 simulation. Other pertinent points of energetics diagnosis are also included in the discussion.

Kung, E. C.↗
NASA NTRS1985

A study of GLAS and UCLA model forecasts of explosive maritime cyclogenesis

The explosive development of a maritime cyclone was examined with a numeric model of a cyclone which occurred during the FGGE Special Observing Period One in January 1979. The storm exhibited a Petterssen type-system frontal wave development. The model used was a nine-level, fourth-order coarse-mesh GLAS model initialized with FGGE level II-B data. Two versions of 72 hr synoptic-scale predictions were performed for the storm: with and without the input of meteorological satellite data. Attention was focused on the heat, mass and vorticity budgets of the storm, starting 24 hr before storm onset. The inclusion of satellite data, due to the poor quality of remotely sensed wind fields, degraded the performance of the model.

Peak, J. E.↗
NASA NTRS1986

Comparative energetics diagnosis of the observed and simulated blockings in the Northern Hemisphere

The blocking phenomena, in particular winter blocking, are stuided using energetic diagnostics. Sequences of blockings during the FGGE winter and summer in observed and simulated circulations, and energy transformations associated with blockings are examined. It is observed that the simulation of the Northern Hemisphere circulation correlates better with the observed circulation during summer than during winter. It is noted that the observed winter blockings are maintained by the supply of kinetic energy to the ultralong waves from the shorter cyclone scales through nonlinear wave-wave interaction; in the simulated winter blocking, the energy converted at the cyclone scale cascades down to the shorter wave range; and the summer blockings are supported by the baroclinic conversion of long waves in both the observed and simulated circulations.

Kung, Ernest C.↗
NASA NTRS1987

Suggested hurricane operational scenario for GOES I-M

Improvements in tropical cyclone forecasts require optimum use of remote sensing capabilities, because conventional data sources cannot provide the necessary spatial and temporal data density over tropical and subtropical oceanic regions. In 1989, the first of a series of geostationary weather satellites, GOES 1-M, will be launched with the capability for simultaneous imaging and sounding. Careful scheduling of the GOES 1-M will enable measurements of both the wind and mass fields over the entire tropical cyclone activity area. The document briefly describes the GOES 1-M imager and sounder, surveys the data needs for hurricane forecasting, discusses how geostationary satellite observations help to meet them, and proposes a GOES 1-M schedule of observations and hurricane relevant derived products.

Menzel, W. P.↗
NASA NTRS1988

The use of available potential energy to evaluate the impact of satellite data on numerical model analysis during FGGE

To evaluate the effect of the FGGE satellite observing system, the following two data sets were compared by examining the available potential energy (APE) and extratropical cyclone activity within the entire global domain during the first Special Observing Period: (1) the complete FGGE IIIb set, which incorporates satellite soundings, and (2) a NOSAT set which incorporates only conventional data. The time series of the daily total APEs indicate that NOSAT values are larger than the FGGE values, although in the Northern Hemisphere the differences are negligible. Analyses of cyclone scale features revealed only minor differences between the Northern Hemisphere FGGE and NOSAT analyses. On the other hand, substantial differences were revealed in the two Southern Hemisphere analyses, where the satellite soundings apparently add detail to the FGGE set.

Horn, Lyle H.↗
NASA NTRS1988

Diagnostic study of explosive cyclogenesis during FGGE

Two rapidly developing extratropical maritime cyclones (one, developed during January 13-15, 1979, along an intense frontal zone south of Japan, the other, of January 26-27, 1979, in a polar mass over the North Atlantic) were investigated using the FGGE data and ECMWF level IIIb analyses to describe the structure and dynamics of these events. Although the cyclones evolved from a strong low-level baroclinic zone without initial large midtropospheric vorticity advection, thus resembling the Petterssen type A development, rapid deepening occurred in both cases when an approaching upper tropospheric jet with appreciable shear vorticity advection became favorably superposed over the surface low. During the development period, stability decreased in the low troposphere, aiding in the rapid development of an intense mass-circulation and low tropospheric vorticity production by the divergence term. The results suggest that upper-level forcing plays a greater role in the initiation of explosive oceanic development than is suggested by the Petterssen and Smebye (1971) description.

Wash, Carlyle H.↗
NASA NTRS1988

Bangladesh Agro-Climatic Environmental Monitoring Project

The Agro-Climatic Environmental Monitoring Project (ACEMP) is based on a Participating Agency Service Agreement (PASA) between the Agency for International Development (AID) and the National Oceanic and Atmospheric Administration (NOAA). In FY80, the Asia Bureau and Office of Federal Disaster Assistance (OFDA), worked closely to develop a funding mechanism which would meet Bangladesh's needs both for flood and cyclone warning capability and for application of remote sensing data to development problems. In FY90, OFDA provided for a High Resolution Picture Transmission (HRPT) receiving capability to improve their forecasting accuracy for cyclones, flooding and storm surges. That equipment is primarily intended as a disaster prediction and preparedness measure. The ACEM Project was designed to focus on the development applications of remote sensing technology. Through this Project, AID provided to the Bangladesh Government (BDG) the equipment, technical assistance, and training necessary to collect and employ remote sensing data made available by satellites as well as hydrological data obtained from data collection platforms placed in major rivers. The data collected will enable the BDG to improve the management of its natural resources.

Vermillion, C.↗
NASA NTRS1988

Fiji South Pacific Severe Storm Detection and Warning System Project (SPSSD/WS)

In August 1986, a South Pacific Severe Storm Detection and Warning System (SPSSD/WS) was installed by NASA at the Fiji Meteorological Service (FMS) in Nadi, Fiji. The system consists of a 6.1 meter parabolic dish antenna, a satellite ground station, and computer and image processing facilities. The system allows tracking of all South Pacific tropical cyclones with real-time, high resolution reception of visible and infrared cloud images from both the Japanese Geostationary Meteorological Satellite (GMS) and the U.S. Geostationary Operational Environmental Satellite (GOES-WEST). Training was also provided in system usage and operations. In December 1986, the U.S. AID Office of U.S. Foreign Disaster Assistance (OFDA) commissioned an evaluation of the SPSSD/WS. The system was recognized as one of the most advanced of its kind in the Pacific Basin. It has functioned successfully since installation with only minor interruptions, and it has become the prime tool in supporting the FMS' role as the regional tropical cyclone warning center for the Southwest Pacific. However, it was noted that there are needed enhancements to the system.

Vermillion, C.↗
NASA NTRS1989

Identification of atmospheric fronts over the ocean with microwave measurements of water vapor and rain

This paper describes some basic research techniques and algorithms developed to diagnose fronts in cyclonic storms over the ocean with data from satellite-borne microwave radiometers. Methods are developed for flagging strong gradients in integrated atmospheric water vapor and the presence of rain by using data from the SSMR on board the polar orbiting Seasat and Nimbus-7 satellites. Examination of 65 frontal systems showed that the water vapor gradient flag correctly identified 86 percent of the fronts, while the precipitation flagged 91 percent. The two types of flags emphasize different portions of the cyclone and are therefore complementary. Ultimately, these techniques are intended for operational use with data from the Special Sensor Microwave Imager which was launched in June 1987 on a satellite in the Defense Meteorological Satellite Program (DMSP).

Katsaros, Kristina B.↗
NASA NTRS1991

Annular denuders for use in global climate and stratospheric measurements of acidic gases and particles

Measurements of acidic and basic gases that coexist with fine particle (less than 2.5 micron) may be useful for determining the impact of these species on global climate changes and determining species that influence stratospheric ozone levels. Annular denuders are well suited for this purpose. A new concentric annular denuder system, consisting of a three channel denuder, a Teflon coated cyclone preseparator, and a multistage filter pack was developed, evaluated, and shown to provide reliable atmospheric measurements of SO2, HNO2, HNO3, NH3, SO4(=), NH4(+), NO3(-), and H(+). For example, the precision of the annular denuder for the ambient measurements of HNO3 and nitrates at concentrations between 0.1 to 3 microgram/cu m was + or - 12 and 16 pct., respectively. The 120 x 25 mm three channel denuder is encased in a stainless steel sheath and has annular spaces that are 1 mm wide. This design was shown to have nearly identical capacity for removal of SO2 as conventional 210 x 25 mm single channel denuder configurations. The cyclone preseparator was designed and tested to have a D sub 50 cutoff diameter of 2.5 micron and minimal retention of HNO3.

Stevens, Robert K.↗
NASA NTRS1991

Synoptic/planetary-scale interactions and blocking over the North Atlantic Ocean

One segment of work in the past year focused on the diagnosis of a major blocking anticyclone and its interacting synoptic scale circulations that occurred during January 1979 over the North Atlantic Ocean. Another segment focused on the diagnosis of a second explosive cyclone development that occurred over the southeastern United States during the time of block formation. The diagnoses were accomplished using the diagnostic relationship known as the Zwack-Okossi (Z-O) development equation. Results indicate that in both cyclone cases the development occurred as a result of the favorable influence of positive vorticity advection, warm air advection, and latent heat release and ceased when one or more of these influences diminished. The advantages of the Z-O equation are described.

Smith, Phillip J.↗
NASA NTRS1990

The importance of non-quasigeostrophic forcing during the development of a blocking anticyclone

This study examines the impact of non-quasigeostrophic (NQG) processes during the development of a blocking anticyclone (January 21, 1979 over the southern tip of Greenland) and a precursor, upstream intense cyclone (January 18, 1979). Energy quantities and height tendencies determined from quasigeostrophic estimates are compared with the same quantities obtained from more general formulations. GLA FGGE Level III-b analysis on a 4 deg lat by 5 deg long grid was used to obtain energetics results. It is concluded that NQG processes strengthened the intensity of the block and a precursor explosive cyclone and that a portion of this increase resulted from enhanced baroclinic conversion of eddy potential to eddy kinetic energy and reduced barotropic energy conversion from eddy to zonal flow. It is suggested that NQG vorticity advection, instead of moderating wave developments, enhanced the block development, and it is also suggested that QG forcing might not have been adequate to produce the observed block development.

Tsou, Chih-Hua↗
NASA NTRS1989

A frontal cyclogenesis case study from Seasat scatterometer data

In June 1978, the Seasat satellite was launched carrying, among other instruments, the Seasat-A scatterometer system (SASS), which produced ambiguous wind speed and direction data at the ocean surface. A fifteen day subset of dealiased wind vector data with the inherent ambiguities removed was produced for the period of September 6-20, 1978. On September 8, SASS began to observe a development of frontal cyclogenesis in the South Pacific off the east coast of New Zealand, in an area of few surface observations. A large mature cyclone contained weak warm and cold fronts and an occlusion with a strong horizontal wind shear. Satellite imagery shows that a strong upper-level jet streak was moving rapidly over the area of the surface frontal occlusion and as the jet passed over this area a new vortex formed. This cyclogenesis event was studied using 50-km resolution scatterometer surface wind data. High-resolution fields of wind vectors, divergence and vorticity are computed and plotted from the scatterometer data to study the structure and development of the newly formed cyclonic vortex, not otherwise possible using conventional observations.

Cunningham, Glenn F.↗
NASA NTRS1990

Entrainment instability and vertical motion as causes of stratocumulus breakup

Entrainment instability is thought to be a cause of stratocumulus breakup. At the interface between the cloud and the overlying air, mixtures may form which are negatively buoyant because of cloud droplet evaporation. Quantities devised to predict breakup are obtained from aircraft observations and are tested against cloud observations from satellite. Often, the parameters indicate that breakup should occur but the clouds remain, sometimes for several days. One possible explanation for breakup is vertical motion from passing synoptic cyclones. Several cases suggest that breakup is associated with the downward vertical motion from the cold air advected behind an eastward moving cyclone.

Weaver, C. J.↗
NASA NTRS1991

Measurements of condensation nuclei above the jet stream - Evidence for cross jet transport by waves and new particle formation at high altitudes

Condensation nuclei were used as a tracer in midlatitude NASA Stratosphere-Troposphere Exchange Project (STEP) experiments in April and May 1984 in order to study transport in the stratosphere. The very large scale, mean CN distribution was distorted by waves which had the effect of transporting air with anticyclonic properties several degrees to the cyclonic side of the jet and created a strongly layered structure in the CN distribution. Unfiltered CN data revealed short-wavelength oscillations in the CN distribution at the interface between the transported anticyclonic air parcel and the adjacent cyclonic air mass. These oscillations were also seen in the ozone data and increase the potential for mixing along that interface. If the mixing does occur, a wave mechanism for cross-jet transport has been observed.

Wilson, J. C.↗
NASA NTRS1990

Stratospheric dynamics

A global circulation model is being used to study the dynamical behavior of stratospheric planetary waves (waves having horizontal wavelengths of tens of thousands of kilometers) forced by growing cyclonic disturbances of intermediate scale, typically with wavelengths of a few thousand kilometers, which occur in the troposphere. Planetary scale waves are the dominant waves in the stratosphere, and are important for understanding the distribution of atmospheric trace constituents. Planetary wave forcing by intermediate scale tropospheric cyclonic disturbances is important for producing eastward travelling planetary waves of the sort which are prominent in the Southern Hemisphere during winter. The same global circulation model is also being used to simulate and understand the rate of dispersion and possible stratospheric climatic feedbacks of the El Chichon volcanic aerosol cloud. By comparing the results of the model calculation with an established data set now in existence for the volcanic cloud spatial and temporal distribution, stratospheric transport processes will be better understood, and the extent to which the cloud modified stratospheric wind and temperature fields can be assessed.

Young, Richard E.↗