First GARP Global Experiment Research Articles

Lidar measurements of Asian dust storms and dust cloud interactions

Long‐range transport of Asian dust storms has been investigated by using lidar at Chungli (24.6°N, 121.1°E) in 2002–2004. One of the dust storms that occurred in the period of 27–31 March 2002 was also observed by lidar at Hefei (31.9°N, 117.16°E). The lidar height distributions of dust extinction were compared with back trajectory calculation and atmospheric data including First Global GARP Experiment (FGGE)‐type ground observations and National Center for Environment Prediction/Atmospheric Research (NCEP/NCAR) reanalysis. Dust layers had an average total (aerosol and molecular) depolarization ratio (DR) about 0.2; however, formation of droplets with near‐zero depolarization ratio (0.02) was also measured. The cloud condensation nuclei (CCN) activities of dust particles were considered based on chemical properties observed from the ground. We observed that dust transport to the south may interact strongly with the moisture from the active weather system in the region producing significant climate effects.

Recovery of Near-Surface Velocity from Undrogued Drifters

Abstract The authors have quality controlled six global datasets of drifting buoy data, made comparisons of 15-m drogued and undrogued buoy observations, and developed a 2D linear regression model of the difference between drogued and undrogued drifter velocity as a function of wind. The data were acquired from 2334 Surface Velocity Program (SVP) drifters, including 1845 SVP drifters after they lost their drogues; 704 AN/WSQ-6 Navy drifter buoys; and 503 First Global GARP Experiment (FGGE) drifter buoys. Meridional and zonal surface wind velocity components from the global synoptic FNMOC model, the global synoptic ECMWF model, and the global synoptic NCEP model were interpolated to naval AN/WSQ-6, WOCE–TOGA buoy, or FGGE buoy positions and date/times in the datasets. Two-day mean buoy drift velocities and positions were computed: 122 101 SVP drifter mean velocities before they lost their drogues and 58 201 SVP drifter mean velocities after they lost their drogues, 21 799 Navy drifter mean velocities, and ...

Use of satellite tracked oceanographic buoys in Brazil

Satellite tracked drifting buoys have become an important field component in several international studies of ocean circulation and related marine climate programs over the past 19 years. The First GARP Global Experiment (FGGE) took place in 1978-1979 and utilized about 365 drifting buoys in the southern hemisphere oceans. About 10 years then passed, during which time the buoy technology underwent significant improvements that were used in smaller scale research activities. The first large program to use modern drifting buoys, or drifters as they are often called, occurred during the Surface Velocity Programme (SVP) of the World Ocean Circulation Experiment (WOCE), during the early to mid 1990's. In contrast, buoy development and use in Brazilian field studies began in the mid 1980's, within the national antarctic research program (PROANTAR). Brazilian participation in international programs began with SVP/WOCE and is continuing within CLIVAR, the follow-on program to WOCE. Because of its interest in Antarctica, Brazil is also a member of the International Program for Antarctic Buoys (IPAB) and more recently of the International South Atlantic Buoy Programme (ISABP). A new national buoy program (PNBOIA) has been approved and acquisition and deployment of WOCE/TOGA type drifters should begin in 1997. In another large project, PETROBRAS, the national oil company, will be collaborating with INPE in the launch of similar drifters, also planned for 1997.

ノーマルモード関数展開を用いたECMWF, NMC, JMA全球解析データのエネルギー比較解析

In this study, normal-mode energetics diagnosis was carried out for the 9-year period of ECMWF (European Center for Medium-Range Weather Forecasts) analysis during winters (DJF) of 1986 to 1994. The diagnosis was performed also for operational global analyses by JMA (Japan Meteorological Agency) and NMC (National Meteorological Center) during the winter of 1988/89 for comparison. Special attention is focussed on the total energy spectra for Rossby and gravity modes over the 3-D scale index. The result was compared with our former studies for other datasets, including original and re-analyses of the First GARP Global Experiment (FGGE). The result for the 9-year average of ECMWF shows that the slopes of the Rossby-mode energy spectra in the eigenfrequency domain are estimated as 2.2, 2.1, 3.5, 5.0, 5.5 for vertical modes m=0 to 4, respectively, whereas the corresponding slopes are -1.8, -1.7, -1.6, -1.3, -1.0, respectively, for the gravity mode. We confirm that the energy spectra of Rossby and gravity modes are connected with each other in the high-frequency range, at least for the vertical modes m=1 to 4. However, the mechanism to create the spectral peaks within the Rossby modes is not known. The intercomparison of the normal-mode energetics for JMA, NMC, and ECMWF shows that the Rossby-mode energy levels are virtually the same, having a minor discrepancy less than 8%. We find that the total energy level pertaining to the gravity modes is about 45 (1O3 Jm-2) and shows a minor discrepancy of only about 8% between the analyses. According to our former studies for the FGGE reanalyses, the corresponding energy levels for the gravity modes are 90 and 41 (103 Jm-2) for GFDL and ECMWF, respectively. Hence, we can conclude that the total energy levels of the gravity modes in the recent operational analyses are converging to the value of ECMWF FGGE data. Since the amount of the total energy of the atmosphere is about 6800 (103 Jm-2), the energy level of the gravity mode is found to be only 0.7% of the total energy.

Tropical-Midlatitude Interaction on the Time Scale of 30 to 60 Days during the Northern Summer of 1979

Abstract The relationship between the low-frequency oscillation of convective activity in the tropics and the intensity of planetary-scale upper-tropospheric (200 mb) systems in the subtropics during the Northern Hemisphere (NH) summer is studied using data obtained in the First GARP Global Experiment (FGGE). The mid-Pacific trough and the South Asian (Tibetan) and Mexican anticyclones undergo cycles of amplification and decay with the 30–60 day fluctuation of convective activities in the Indonesia-western Pacific (IWP) region and in the intertropical covergence zone (ITCZ) over Central America. The thermal contrast between the Asian continent and the North Pacific and the resulting east-west circulation show similar time variations. This circulation regulates the intensity of the South Asian anticyclone and the mid-Pacific trough. Divergent circulation associated with convection over Central America maintains the Mexican anticyclone. The low-frequency transients in the upper troposphere around the mid-Pa...

Physical and biological processes in the North Atlantic during the first GARP Global Experiment

The seasonal cycle of the phytoplankton biomass in the North Atlantic Ocean (20°S to 70°N) is discussed using monthly mean surface pigment concentration fields from the Nimbus 7 coastal zone color scanner (CZCS) for the period of December 1978 through December 1979. The temporal and spatial distributions of surface pigments are compared with quantities derived from the First GARP Global Experiment (FGGE) wind data set (1000‐mbar streamlines, Ekman upwelling, horizontal Ekman transport and |τ|3/2), Climate Analysis Center (CAC) sea surface temperature (SST) fields, concurrent hydrographic station data, and climatological mixed‐layer depths and heat fluxes. The objective of the analysis is to clarify the role of some physical mechanisms that regulate the supply of nutrients to the euphotic zone at different locations in the basin and at different times of the year. It is observed that during this period, the spring bloom was, in most locations, sustained for 2 to 3 months. At a given latitude the onset of the spring bloom varied by several months and, in some cases, could be referred to as a fall bloom. In other cases there were both spring and fall blooms. Time series at 11 selected sites throughout the basin are used to illustrate, in detail, the relation of phytoplankton biomass to local physical forcing. Finally, separate analyses of the mean pigment concentrations for the shelf and open ocean regions indicate that the phytoplankton of both regimes had spring and fall blooms of equal magnitude, the spring bloom being located at northern latitudes and the fall bloom in the equatorial region. Analysis of the open ocean Ekman upwelling field shows similar peaks approximately 2 months in advance of the surface pigment concentration peaks.

Intercomparison of daily values of atmospheric variables, including diabatic heating rates, from the ECMWF, GFDL, and Goddard Laboratory for Atmospheres FGGE level IIIb analyses

In order to assess the agreement among three First GARP Global Experiment (FGGE) Level IIIb analysis data sets produced by the European Centre for Medium Range Weather Forecasts, the Geophysical Fluid Dynamics Laboratory, and the Goddard Laboratory for Atmospheres, the intercomparisons of daily values of large‐scale vorticity ζ, divergence δ, temperature T, static stability Γ, vertical motion ω, and diabatic heating rate Q/Cp are performed during the period January 26 to February 11, 1979. The ζ, δ, and ω fields are calculated from the velocity components u and v after interpolation of Level IIIb analyses onto the National Center for Atmospheric Research Community Climate Model, version 0B (NCAR CCM0B) grid. The Q/Cp is obtained as a residual of the thermodynamic energy balance. Using standard descriptive and comparative statistics, we intercompare the three analyses in three geographic regions: NH (60°N–30°N), TR (30°N–30°S) and SH (30°S–60°S). The agreement among the ζ analyses is excellent, though a slight disagreement is found in the lower troposphere of the TR and SH. However, the agreement among the δ analyses is generally weaker, except for the lower troposphere of the NH. Intercomparison of the T analyses shows significant systematic differences, though the agreement in their geographical distributions is generally good. This influences the Γ analyses, which show weak agreement particularly in the lower troposphere. The intercomparison of kinematic and thermodynamic fields for the different analyses gives an indication of the degree of agreement among the Q/Cp analyses whose calculations involve many highly sensitive quantities. The intercomparison statistics provide us with a quantitative assessment of the systematic differences, spatial coherence, and quantitative agreement between the different analyses for each meteorological field, but they do not provide a measure of the relative accuracy. To provide such a measure, we compare the heating rates and vertical motion with equivalent blackbody emission temperatures observed by TIROS‐N in the TR. Through this technique, we infer the relative accuracy of the three FGGE Level IIIb analyses. It is clear that the method of objective analysis for meteorological observations must be refined to improve the quality of the divergent wind analysis and the temperature analysis in the tropics.

Observing System Experiments Using the AFGL Four-Dimensional Data Assimilation System

Abstract Five observing system experiments have been performed with the Air Force Geophysics Laboratory (AFGL) global data assimilation system (GDAS). Each experiment includes one week of data assimilation during each of the two special observing periods of the First GARP Global Experiment (FGGE) of 1979, and three 4-day forecasts. The first experiment (STATSAT) provides a baseline for comparison. It uses all the available level II-b FGGE data, except surface observations. Comparisons with the National Meteorological Center (NMC) level III-A analyses show that the AFGL GDAS performs adequately. In the second experiment (NOSAT) all satellite data are removed from the dataset, showing the sensitivity of the AFGL GDAS to satellite data. As expected the impact on the analysis is small in the Northern Hemisphere, but large in the Southern Hemisphere. In the third experiment (GLASAT), the effect of a physical satellite retrieval method is tested by using the temperature profiles provided by NASA Goddard laborat...

Nonmigrating thermal tides detected in data analysis and a general circulation model simulation

Nonmigrating thermal tides, which do not move in synchrony with the Sun, are detected in the analyses of the First GARP Global Experiment (FGGE) Level IIIb data during the special observation period (SOP‐1) of January 10, to February 9, 1979. The first is the westward moving diurnal mode, with the zonal wave number (m) 5 (f = −1, m = 5), and the second is an eastward moving diurnal mode, with the zonal wave number 3 (f = 1, m = 3), where f is the frequency in day−1. These modes are closely related to wave number 4 of the topography at low latitudes and have clear peaks in the space‐time power spectra in the sea level pressure field. A maximum value of 0.2 mbar is the same with both modes, as expected from theory, while maximum values of the background diurnal (f = −1, m = 1) and semidiurnal (f = −2, m = 2) migrating modes are 0.6 and 1.2 mbar, respectively. These nonmigrating modes are essentially the same ones that Tokioka and Yagai [1987] reported in their analysis of general circulation model (GCM) simulation in January. By comparing FGGE IIIb data analysis and the Meteorological Research Institute (MRI) GCM‐I simulation, diurnal (f = −1, m = 1) and semidiurnal (f = −2, m = 2) modes are simulated well in the sea level pressure field and relatively well at the lower troposphere in the geopotential field. The simulated nonmigrating modes have horizontal structures similar to those observed in the sea level pressure field, which are the most reliable data and are based on a large enough number of observations to detect these modes. In the geopotential field, horizontal structure of the nonmigrating modes is identified in the troposphere at low latitudes by simulation and observation. The wind data is also analyzed, but the correspondence between the simulation and observation is found only at the lowest level of the (f = −1, m = 5) mode.

A study of oceanic surface heat fluxes in the Greenland, Norwegian, and Barents Seas

This study examines oceanic surface heat fluxes in the Norwegian, Greenland, and Barents seas using the gridded Navy Fleet Numerical Oceanography Central surface analysis and the First GARP Global Experiment (FGGE) IIc cloudiness data bases. Monthly and annual means of net and turbulent heat fluxes are computed for the FGGE year 1979. The FGGE IIb data base consisting of individual observations provides particularly good data coverage in this region for a comparison with the gridded Navy winds and air temperatures. The standard errors of estimate between the Navy and FGGE IIb winds and air temperatures are 3.6 m/s and 2.5°C, respectively. The computations for the latent and sensible heat fluxes are based on bulk formulas with the same constant heat exchange coefficient of 1.5×10−3. The results show extremely strong wintertime heat fluxes in the northern Greenland Sea and especially in the Barents Sea in contrast to previous studies. The highest monthly average net fluxes are well over 400 W m−2 in these two regions in January and February 1979. The estimated uncertainty for the higher heat fluxes based on the comparison between the FGGE IIb and the Navy data sets is about ±30%.

Meridional heat transport by the atmosphere and the ocean: analysis of FGGE data

The annual mean meridional heat transport by the atmosphere is evaluated by using FGGE (First GARP Global Experiment) level IIIb data. The transport by the atmosphere-ocean system is estimated using satellite radiation observations from the Nimbus 7 ERB (Earth Radiation Budget) experiment. The annual mean transport by the ocean is obtained as the difference between the two values. The latitudinal distribution of transport by the total system exhibits good symmetry between the two hemispheres, with maximum poleward transport of 5.9 × 1015 W around 35° latitude N and S. Atmospheric and oceanic contributions to the transport exhibit large differences between the two hemispheres. In particular, in the subtropics of the northern hemisphere, the ocean carries more heat poleward than in the same latitude of the southern hemisphere. The poleward transport by the ocean at20°–30°N evaluated in this study is about 3 × 1015 W, which is smaller by 0.5–1 × 1015 W than that found by Carissimo et al. but larger by 1–2 × 1015 W than recent estimates based on surface heat balance. The difference between the results of this study and Carissimo et al. comes from differences in estimates of the heat and moisture transport by mid-latitude atmospheric transient eddies.

Relationships between available potential energy, kinetic energy, and extratropical cyclone activity within East Coast cyclogenetic regions

Interrelationships between the available potential energy and kinetic energy associated with extratropical cyclones are examined for portions of the First GARP Global Experiment (FGGE) year. The study is confined to the cyclogenetically active regions encompassing the eastern coasts of Asia and North America. Calculations of vertically integrated available potential energy (APE) and kinetic energy (KE) are done for an active winter storm period (February 14–28, 1979) and a relatively inactive summer period (July 1–15, 1979) using gridded isentropic data produced from the FGGE Level IIIa set of global analyses. During both the winter and summer study periods, good agreement is indicated between cyclone tracks and the spatial distributions of time mean and standard deviations of vertically integrated APE and KE. Energy distributions composited for rapidly strengthening and weakening storms show the patterns of available potential energy and kinetic energy which are associated with cyclones in these stages of development. The rapidly intensifying storms are accompanied by strong gradients in APE equatorward of the surface cyclone with maximum KE to the south and southwest of the storm center. Smaller values of kinetic energy and weaker gradients of available potential energy accompany the rapidly decaying storms. An examination of twice daily distributions of APE and KE for 29 individual cyclones reveals that a similar temporal evolution of vertically integrated energy patterns accompanies storms in these east coast regions. An example of this evolution is presented in conjunction with a case analysis of the February 1979 Presidents' Day cyclone along the east coast of North America.

Spectral Energetics of the Canadian Climate Centre General Circulation Model

Abstract The available potential energy–kinetic energy budget of the Canadian Climate Centre general circulation model for the months of January. April, July and October is presented in terms of the two-dimensional wave-number. Five years of model results are compared to calculations based on observations taken during the First GARP Global Experiment (FGGE). Qualitatively, the simulated budget is realistic but a few of the magnitudes of the energies and conversions between them are not well simulated, arising in part from an excess of zonal available potential energy and zonal kinetic energy caused by the model's polar regions being too cold.

Large‐Scale Circulation Departures Related to Wet Episodes In North‐East Brazil

AbstractThis study examines the large‐scale tropical environment of north‐east Brazil during its 1979 rainy season. Data were primarily from the First GARP Global Experiment (FGGE). Results show that in the mean NE Brazil is south of the intertropical trough zone (ITZ) and north‐west of the South Atlantic high. This pattern results in a westward low‐level flow over the region. Immediately over NE Brazil, middle‐level subsidence and low‐level moisture divergence dominate, producing a mean local environment which is unfavourable for precipitation. During wet episodes cloudiness departures show a more active ITZ over the equatorial Atlantic. Strong sea level pressure departures are found in the vicinity of the subtropical highs indicating short period fluctuations in the Hadley cell. Locally, weaker middle‐level subsidence and weaker moisture divergence during wet episodes allow for increased convection.

Results of extensive integrations with simple NWP models over the tropics during FGGE

In this note, we present a summary of results from a total of some 980 forecast experiments made with two simple high-resolution regional models. The models are based on the principles of conservation of absolute vorticity (a streamfunction barotropic model) and of potential vorticity (the shallow water equations with bottom topography). These regional forecast models are applied to a number of different domains (winter monsoon, central Pacific Ocean during Northern winter, Central America, Eastern Atlantic and South America, West African Monsoon, Indian summer monsoon and summer monsoon over Southeast Asia). The data sets for these experiments are those derived from the First GARP Global experiment (FGGE), the Asian Monsoon experiment (MONEX) and the West African monsoon experiment (WAMEX). Statistical evaluation includes a comparison of the root mean square vector wind error with the corresponding persistence errors. The results of this study show that these models have a varied skill over different domains. The single-level primitive equation model over West Africa, South America and the Atlantic Ocean during northern summer shows a skill beyond the persistance for a range of 4 days of integration. The performance of the single-level primitive model appears quite promising over these regions. These long series of experiments with the single-level primitive equation model were carried out with the choice of the mean free surface height of 2 km with a maximum height of the orography of 1 km. A further effort at the optimization of the single level model was explored. Here, a parameter space consisting of the free surface height and the maximum height of the orography was explored in order to assess the skill of the vector wind error. Marked improvement in skill was noted over a domain centred over China from an optimization of these parameters. DOI: 10.1111/j.1600-0870.1987.tb00296.x

Lagrangian time scales connected with clouds and precipitation

An attempt is made to estimate Lagrangian time scales connected with clouds in the atmosphere. Three‐dimensional wind and relative humidity obtained from the First GARP Global Experiment (FGGE) data set are used to compute three‐dimensional trajectories with accompanying clouds. From the meteorological history of the trajectories, estimates are made of the average time from the release of a trajectory until the first cloud passage and the average time between first and second cloud passage. Geographical and seasonal variations of these parameters are calculated and discussed. Since the “clouds” parameterized from the FGGE data are limited to those connected with the large‐scale flow in the atmosphere, a substantial bias in our estimates is introduced. This implies that the estimates are more representative for major cloud systems, often connected with precipitation, than for clouds in general.

Data sensitivities of sea ice drift and ocean stress in North Atlantic high latitudes

Experiments with a limited‐area objective analysis are used to determine the effects of various data sources on surface stress and sea ice drift in North Atlantic high latitudes during a 7‐day period of the First GARP Global Experiment (FGGE). The objectively analyzed fields provide the input to a planetary boundary layer model, which provides the surface wind stresses for the forcing of a dynamic‐thermodynamic sea ice model. Different combinations of drifting buoy, surface marine, and satellite sounder data are deleted from the FGGE level IIB data input. On individual days the stresses are found to differ by as much as 50–100% and the ice drift speeds by as much as 10–15 km d−1 when buoy reports are deleted from the observing network. Seven‐day mean differences of the ice drift speeds are 3–5 km d−1 in some regions. The deviations from the “complete data” results are larger when both buoy/marine and satellite data are deleted than when only one type is deleted. While the high‐latitude sensitivities to satellite data are generally smaller than to buoy/marine data in the period considered here, large differences in ocean surface stress occasionally result from subtle effects of satellite data on the static stability of the near‐surface region. The results also show how data sensitivities can be exaggerated by the imposition of data rejection criteria in experiments utilizing consistent sets of guess fields and input data. The ice velocities obtained from the various experiments are compared with the available buoy displacements and with changes in the ice edge deduced from the Navy/NOAA weekly ice analyses.

Forecast Experiments with the NASA/GLA Stratospheric/Tropospheric Data Assimilation System

For the first time, a four-dimensional stratospheric/tropospheric data assimilation system with a top analysis level at 0.4 mb has been developed and used to produce physically consistent gridded analyses for the stratosphere as well as the troposphere for a period during the First GARP Global Experiment (FGGE) and Limb Infrared Monitor of the Stratosphere (LIMS) (November 1978-May 1979). The system consists of a two-dimensional optimum interpolation analysis with 18 mandatory pressure levels and a 19-level fourth order stratospheric/tropospheric general circulation model with a horizontal resolution of 4 (latitude) by 5 deg (longitude) and a top at 0.3 mb. The system allows the utilization of stratospheric data including LIMS, Tiros-N retrievals, rocketsondes and vertical temperature profile radiometer soundings in addition to the other FGGE level 2b data. These data are analyzed every six hours. In order to examine the quality of the analyzed data, forecast experiments starting from different analyses are performed for the period of the stratospheric sudden warming of late February 1979. The results indicate that by employing the present four-dimensional assimilation approach, the medium-range forecast skill for this event is improved.

Eddy kinetic energy distribution in the Southern Ocean from altimetry and FGGE drifting buoys

The eddy kinetic energy distribution in the Southern Ocean has been estimated from Seasat altimeter data available on repetitive orbits during 24 days in September–October 1978 and from 192 free‐drifting buoy trajectories obtained during the First GARP Global Experiment (FGGE) from November 1978 to the first months of 1980. A good spatial coherence is found between the results of these two independent methods in the Southern Ocean from 30°S to 65°S. The distribution shows strong, eddy kinetic activity near the western boundaries (Argentine Basin, Mozambique Plateau, Tasman Sea, etc.) and near topographic features (ridges and continental shelves: Drake Passage, Crozet and Kerguelen plateaus, Macquarie Rise, etc.). At first the ratio between both estimates was found to be very high, with kinetic energy distribution from FGGE drifters being 3 times larger than from the altimeter. After an investigation of the effect of the wind on eddy kinetic energy estimates from drifting buoys it seems that the wind cannot be the main reason for such a large discrepancy. Next, the eddy kinetic energy distribution from drifters was recomputed and processed through a band‐pass filter, in the range 1/6 to 1/24 cycles per day, in order to achieve a better match to the temporal scales explored by Seasat altimeter measurements. Although there still remain some differences between the two distributions, comparable values for mean eddy kinetic energy estimates over the whole Southern Ocean are then found. The remaining differences might be attributed to various sources, one of them being the nonsimultaneity of the two data bases.

Global Water Vapor Flux and Maintenance during FGGE

Abstract The relative humidity, temperature and wind fields generated by the First Global GARP Experiment (FGGE) III-b analysis of the Geophysical Fluid Dynamics Laboratory (GFDL) are used to examine the global precipitable water distribution, and the water vapor transport and maintenance for two extreme seasons of atmospheric circulation, i.e., December–February and June–August 1979. It has been observed that the major water vapor content exists in tropical areas, especially over three regions: equatorial Africa, the northern part of South America, and equatorial western Pacific in December-February; equatorial Africa, Central America and the northern part of South America, and monsoon areas in June-August. The water vapor transport was analyzed to explore how the high water vapor content of these areas is maintained by the large-scale atmospheric circulation. It is concluded that 1) the nondivergent stationary mode describes most of the atmospheric water vapor transport; 2) the stationary divergent mode...