Engineering topics

Vincent, Dayton G.

Publications and source records attributed to Vincent, Dayton G..

At least 19 records

NASA NTRS1995

A composite study of the quasi-periodic subtropical wind maxima over the South Pacific during November 1984-April 1985

A composite of 10 cases of zonal wind maxima at 200 hPa over the subtropical region stretching from Australia to the central Pacific is examined for the six-month period, November 1984-April 1985. This region is unique in that distinct westerly jets frequently form and propagate eastward at latitudes between 20 deg and 35 deg S in the summer season. Some statistical tests were applied and suggest that the flow patterns are quasi periodic, consisting of a tendency for new jet streaks to develop over the eastern Australian region approximately every one to two weeks. These jets then take about 10 days to propagate across the western Pacific before dissipating or, perhaps, moving toward higher latitudes. Their average propagation speed is approximately 4 m/s. An examination of the case-to-case variability of the jets provides additional evidence that they are significant features. A diagnosis of the trough/ridge systems at 200 and 850 hPa, together with calculations of the vertically integrated mean and shear kinetic energies suggests that baroclinic processes dominate in the entrance and center regions of the jet, whereas barotropic processes dominate in the exit and downstream regions.

Ko, Ken-Chung↗

NASA NTRS1995

Computation of vertical profiles of longwave radiative cooling over the equatorial Pacific

An important quantity whose magnitude has not been throughly examined is the vertical distribution of heating in the Tropics. The details of the vertical distribution of heating have a significant impact on a number of phenomena, including the 30-60 day oscillation, sometimes known as the intraseasonal oscillation. Prior attempts to establish the structure of the heating relied on limited field data or assimilated data, coupled with climatological radiative heating parameters. The availability of high quality global-scale datasets has made it possible to make more accurate calculations than were possible a few years ago. An important component of the apparent heat budget is the longwave radiative cooling, which in this paper is found by using the ECMWF/WCRP/TOGA Archive 2 and ISCCP C1 datasets, together with a well-established parameterization scheme. A method is developed that can be used to estimate the vertical structure of cloud amounts based on top-of-atmosphere cloud observations, and the results are used with a wide-band longwave parameterization to produce longwave cooling rates over the tropical Pacific Ocean. Outgoing longwave radiation is calculated and compared the ERBE results. The calculated values are generally higher than those from ERBE, though the spatial distributions are similar. Some significant problems exist with the ECMWF upper-tropospheric water vapor amounts, which could imply uncertainties of 0.5 C/day in the calculated cooling rates. This is comparable to the differences associated with the minimum or random overlap assumptions used to generate cloud profiles.

Ramsey, Perry G.↗

NASA NTRS1994

The South Pacific convergence zone (SPCZ): A review

The circulation features associated with the South Pacific convergence zone (SPCZ) and its accompanying cloud band are reviewed and discussed. The paper focuses on the following topics: location, structure, and characteristics of the SPCZ; theories and observations concerning its existence; the significance and scope of the SPCZ in global-scale circulation patterns; quasi-periodic changes in its location and strength; and synoptic-scale features within its regional influence (e.g., cyclones, subtropical jets). It concludes with some challenging problems for the future.

Vincent, Dayton G.↗

NASA NTRS1994

Rainfall rates and the vertical distribution of diabatic heating components over tropical oceans

During the fall of 1993, nearly all of the emphasis on this project was devoted to the completion of Ph.D. research. In January 1994, a poster summarizing research was presented at the 8th Conference on Atmospheric Radiation held in Nashville, TN. In February 1994, we submitted two papers for publication. Finally, we learned that we have had a paper accepted for poster presentation at the European Conference on the Global Energy and Water Cycle to be held in London, England in July 1994. Titles for all these papers are provided.

Vincent, Dayton G.↗

NASA NTRS1994

Observational and modeling studies of heat, moisture, precipitation and global-scale circulation patterns

This research grant was a revised version of an original proposal. The period of the grant was for three years with a six-month no-cost extension; thus, it was from 20 July 1990 to 19 January 1994. The objectives of the grant were to identify periods and locations of active convection centers, primarily over the Southern Hemisphere tropical Indian and Pacific Oceans; determine reasons for any periodic behavior found in the first objective; identify cases where subtropical jets over the South Pacific persisted for several days and examine the influences of tropical versus extra-tropical mechanisms in maintaining them; obtain estimates of precipitation by Q(sub 1) and Q(sub 2) budgets, including the importance of terms in each of the respective budgets, and compare these estimates to those obtained by other methods; and diagnose the distributions of moisture and precipitable water over the North Atlantic Ocean using routine analyses and satellite microwave data. To accomplish these objectives, we used grant funds to purchase several data sets, including the Global Precipitation Climate Project (GPCP) observations of station precipitation, ECMWF WCRP/TOGA archive two analyses for January 1985 - December 1990, ECMWF WMO analyses for January 1980 - December 1987, and OLR data for July 1974 - December 1991. We already had some SSM/I data and GLA analyses from a previous grant. In addition, to improve our computing power, we also used grant funds to purchase an IBM PS/2 with accessories, a NEC laser jet printer, and a microcomputer system for word processing. This report is organized as follows. Our research team is listed first. Section two contains a summary of our significant accomplishments; however, a detailed discussion of research results is not included since this information can be found in the accompanying reprints and preprints. Section three offers some concluding remarks, and a complete bibliographic summary is given in Section four.

Vincent, Dayton G.↗

NASA NTRS1993

A review of the South Pacific convergence zone (SPCZ)

The paper summarizes the information obtained on the South Pacific convergence zone (SPCZ) since it was first depicted in the surface analyses by Bergeron (1930). Particular attention is given to the average structure and characteristics of the SPCZ, the current theories regarding its origin and maintenance, and its relation to global-scale circulations. Some of the findings related to the quasi-periodic behavior of the SPCZ are presented.

Vincent, Dayton G.↗

NASA NTRS1993

Some climatological variables for TOGA-COARE domains - 1985-1990

Results are presented of the Tropical Oceans Global Atmosphere-Coupled Ocean Atmosphere Response Experiment (TOGA-COARE) conducted in the western Pacific, with particular attention given to the atmospheric component of the experiment. The climatological variables explored are the mean sea level pressure, precipitable water, sea surface-air temperature difference, zonal wind component at 200 mb and 10 m, vertical motion at 500 mb, and precipitation rates. The paper provides some of the large-scale flow patterns in which other circulation features reside. Results are presented for three of the TOGA-COARE domains bounded by the following: (1) the Upper Air Network, 30 deg N-30 deg S, 90 deg E-70 deg W; (2) the Large-Scale Array, 10 deg N-10 deg S, 140 deg E-180 deg; and (3) the Equatorial Synoptic Array, 5 deg N-5 deg S, 150 deg E-180 deg.

Vincent, Dayton G.↗

NASA NTRS1993

Observational and modeling studies of heat, moisture, precipitation, and global-scale circulation patterns

The research sponsored by this grant is a continuation and an extension of the work conducted under a previous contract, 'South Pacific Convergence Zone and Global-Scale Circulations'. In the prior work, we conducted a detailed investigation of the South Pacific convergence zone (SPCZ), and documented many of its significant features and characteristics. We also conducted studies of its interaction with global-scale circulation features through the use of both observational and modeling studies. The latter was accomplished toward the end of the contract when Dr. James Hurrell, then a Ph.D. candidate, successfully ported the NASA GLA general circulation model (GCM) to Purdue University. In our present grant, we have expanded our previous research to include studies of other convectively-driven circulation systems in the tropics besides the SPCZ. Furthermore, we have continued to examine the relationship between these convective systems and global-scale circulation patterns. Our recent research efforts have focused on three objectives: (1) determining the periodicity of large-scale bands of organized convection in the tropics, primarily synoptic to intraseasonal time scales in the Southern Hemisphere; (2) examining the relative importance of tropical versus mid-latitude forcing for Southern Hemisphere summertime subtropical jets, particularly over the Pacific Ocean; and (3) estimating tropical precipitation, especially over oceans, using observational and budget methods. A summary list of our most significant accomplishments in the past year is given.

Vincent, Dayton G.↗

NASA NTRS1993

A case study of the intraseasonal oscillation traversing the TOGA-COARE LSD

The paper presents examination of tree intraseasonal (30-60 day) oscillations (ISOs) that occurred during the southern summer season (December 1, 1985 - February 28, 1986) traversing the Large-Scale Domain (LSD) TOGA-COARE, the region which also plays an important role in ENSO, Australian monsoon, and extratropical circulations. Data presented include Hovmoeller diagrams of 5-day running means of 250-mb velocity potential anomalies and OLR anomalies; graphs of five-day running means of OLR in precipitable water (W) per sq m, averaged over 10 x 10 deg boxes centered on 5 S and (1) 145 E, (2) 155 E, (3) 165 E, and (4) 165 D, indicating the midpoint of each ISO; and vertical profiles of zonal wind in m/s averaged over the time period that each ISO spends in the 10 x 10 deg box centered at 5 S, and 175 E and 145 E.

Vincent, Dayton G.↗

NASA NTRS1993

A climatological study of the TOGA-COARE region

The tropical western pacific 'warm pool' region, which plays a significant role in the initiation and/or enhancement of several atmospheric and oceanic phenomena on a variety of time and space scales, was seleted for the TOGA-COARE field program conducted in the northern winter season of 1992-1993. This paper provides some of the recent background climatology for the TOGA-COARE region. The variables illustrated and discussed represent a sample of those taken from an atlas being prepared (e.g., the mean sea level pressure for July 1985 and January 1986; three-month running means of precipitable water (W) and zonal wind at selected grid points; monthly mean averages of W and zonal wind for April 1986-1990, April 1987 anomaly, and January 1989 anomaly; and three-month running means of precipitation rate in mm/day for selected equatorial grid points and a grid point at 10 S, 150 E). Graphs and charts presented are constructed using data sets from the WCRP/TOGA archive II ECMWF global analyses.

Sliwinski, L. D.↗

NASA NTRS1992

A GCM case study on the maintenance of short-term subtropical wind maxima in the summer hemisphere during SOP-1, FGGE

In order to substantiate earlier findings of pronounced short-term deviations in Southern Hemisphere tropical convection during the first Special Observing Period (SOP-1) of FGGE, the hypothesis that the observed summertime subtropical wind maxima were strengthened by episodes of enhanced tropical divergence is numerically tested using a fourth-order GCM. FGGE observational data for January 6-20, 1979 suggested that strong convection over the South Pacific helped to maintain a nearby subtropical jet. The dominant term in the zonal momentum budget was the Coriolis force applied to the diabatically driven meridional circulation. The present GCM study simulates these processes to a reasonable degree of accuracy. Experimental reduction of the latent energy supplied to the GCM is used to substantiate that summertime subtropical westerly maxima are largely forced by divergent outflow from the tropics.

Hurrell, James W.↗

NASA NTRS1992

A case study of analyzed versus satellite-derived water vapor distributions over the Atlantic Ocean

The paper compares two estimates (one derived from the ECMF analysis and the other from the DMSP Special Sensor Microwave/Imager, SSM/I) of precipitable water content (PWC) over the North Atlantic Ocean during a period of intense cyclone and frontal activity between September 20 and 29, 1987, when two tropical cyclones, Dennis and Emily, moved into midlatitudes and took on extratropical characteristics. The values from the ECMWF analyses consisted of vertical integrals of specific humidity from 1000-300 mb, on a 2.5-deg latitude/longitude grid. The PWC values from the SSM/I were computed using the technique described by Wentz (1983) and were based on retrievals at increments of 25 km. The two distributions of PWC showed very good agreement with each other and with the synoptic patterns depicted.

Vincent, Dayton G.↗

NASA NTRS1991

Precipitation rates in the tropics based on the Q1-budget method - 1 June 1984-31 May 1987

The 'apparent' heat source method (Q1 budget) is used to compute the total derivative of dry static energy from 30 deg N to 30 deg S for the period June 1, 1984-May 31, 1987. The dataset is produced from the ECMWF global analyses and consists of twice-daily values of temperature, geopotential height, horizontal wind components, and vertical velocity at increments of 2.5 x 2.5 deg lat/long at seven pressure levels. Vertically integrated values of ds/dt, which are equal to total diabatic heating, Q1, are combined with estimates of net columnar radiation and surface sensible heat exchange to compute mean monthly precipitation rates, P0, as the residual in the Q1 budget. The accuracy of these P0 values is thoroughly examined, and it is suggested that the technique produces reliable estimates of precipitation over tropical oceanic areas on a monthly basis. Time series of mean monthly P0 for several geographic regions of the Southern Hemisphere tropics and the equatorial western Pacific (TOGA-COARE region) reveal that (1) the South Pacific convergence zone has the highest precipitation rates in the Southern Hemisphere; (2) a clear and distinct seasonal cycle is prominent in all regions; and (3) the 1986-87 ENSO event is easily identified, particularly in the TOGA-COARE region.

Vincent, Dayton G.↗

NASA NTRS1991

On the maintenance of short-term subtropical wind maxima in the Southern Hemisphere during SOP-1, FGGE

The extent to which divergent circulations, induced by tropical heating, help to maintain westerly maxima in the Southern Hemisphere subtropics during the SOP-1 of FGGE is explored using Level III-b analyses from the Goddard Laboratory for Atmospheres. The contribution of the divergent wind component to the total ageostrophic flow in the subtropics is examined, as are the roles of other forcing terms in the localized Eliassen-Palm (1961) flux zonal momentum equation. Throughout the summertime subtropics, it is generally found that the dominant term in the zonal momentum budget is the Coriolis force applied to the diabatically driven meridional circulation. The largest positive tendencies due to this term are found in the entrance regions of the subtropical westerly maxima, and divergent circulations account for nearly all of the total ageostrophic flow. In the SPCZ region, however, it is found that transient eddies play an important role by partially offsetting the strong Coriolis acceleration in the entrance region of the local jet, and they help accelerate the westerly flow in the exit region through both barotropic and baroclinic processes. Energetically, the dominant term in the rotational kinetic energy budget throughout the subtropical belt is the conversion of divergent to rotational kinetic energy. The evidence supports the view that tropical heating in transient events drives or enhances local meridional overturning in the atmosphere, which, in turn, strengthens the summer subtropical westerly jet stream.

Hurrell, James W.↗

NASA NTRS1991

South Pacific convergence zone and global scale circulations (Jul. 1987 - Jul. 1991). Observational and modeling studies of heat, moisture, precipitation, and global-scale circulation patterns (Jul. 1990 - Jul. 1993)

Several research projects were worked on between August 1990 and May 1991. Topics covered included observational and modeling studies of relationships between tropical heat sources and subtropical jet streams, the intraseasonal (30 to 60 day) oscillation near the equator, and precipitation over tropical oceans. Current research activities and plans for the coming year are outlined.

Vincent, Dayton G.↗

NASA NTRS1991

South Pacific convergence zone and global-scale circulations

The major goals of the research can be classified under three categories: (1) heat and moisture budget studies in the tropics; (2) the role of tropical forcing on subtropical wind maxima in the Southern Hemisphere; and (3) general circulation modeling of low latitude circulations. Research related to the first goal included budget estimates of precipitation, as well as a comparison to rainfall rates observed at numerous island stations. It also included a comparison between observed and satellite estimates of precipitable water. Results and methods used to achieve this goal are given. Included in the second research goal were diagnostic studies of the intraseasonal oscillation which is known to be an important component of organized tropical convection. Also, the role of extratropical forcing on subtropical wind maxima was examined through the use of Eliassen-Palm (EP) fluxes. Again, results and procedural details are discussed in section 3. To accomplish the third research goal, the GLA general circulation model (GCM) was ported to Purdue University and successfully used in a number of control and experimental runs to investigate the significance of tropical heating on subtropical and extratropical circulation features. As with the first two research goals, results and methodology are detailed. Documentation of publications, theses, conference preprint papers, and other scientific information relevant to the research results and significant accomplishments achieved under the contract are given. Finally, the conclusions of the sponsored research are given.

Vincent, Dayton G.↗

NASA NTRS1991

Intraseasonal oscillation of convective activity in the tropical Southern Hemisphere - May 1984-April 1986

This paper studies the intraseasonal oscillation of convection and related variables in the Southern Hemisphere tropics utilizing European Centre for Medium-range Weather Forecasts analyses of 1984 to 1986. One aspect of the research was that the original, unfiltered, time series of various variables was first analyzed to determine if a statistically significant signal occurred on the intraseasonal time scale. The analysis showed that two variables, outgoing longwave radiation and velocity potential at 200 hPa, provided the best evidence of an intraseasonal oscillation. The oscillation propagated eastward, and the convective activity for both years was more intense over the Indian Ocean-Indonesia-western Pacific region than elsewhere.

Vincent, Dayton G.↗

NASA NTRS1991

Precipitation rates in the tropics - June 1984-May 1987

A study aimed at gaining better understanding of the heating potential of the tropics by examining the 'apparent' heat source (Q1), i.e. dry static energy budget, is presented. The Q1 budget and precipitation rates over a three year period are analyzed using a routine data set: the European Center for Medium-range Weather Forecasts analyses. A noticeable increase in the values of Q1 during years 2 and 3 compared to year 1 was observed, which is considered to be due to the changes in the ECMWF model physics that produced larger values of upper level divergence after May 1985. There is a slow eastward progression of maximum values across the Western Pacific during the calendar year 1986 and into early 1987.

North, Keith H.↗