National Meteorological Center Analyses Research Articles

Rayleigh lidar observations of temperature over Tsukuba: winter thermal structure and comparison studies

Routine lidar observations are in progress at the National Institute for Environmental Studies (NIES), Tsukuba, Japan (36°N, 140°E), providing vertical profiles of ozone and temperature in the stratosphere and lower mesosphere. The present study focuses the winter thermal structure over Tsukuba and validation/comparison of the lidar derived temperature profiles. Atmospheric temperatures for the altitude region 30–75 km are determined from the neutral density profiles. 33 temperature observations recorded during the winter months of 1995 and 1996 are used in the study. Winter thermal structure is characterized with its variability with an observed stratopause temperature of about 260 K. Although evidence of minor stratospheric warming is seen on some days, there appears to be no direct linkage with major mid winter warmings at the poles. Temperature profiles show evidence of mesospheric temperature inversion layers. For the purpose of validation/comparison of the lidar temperature profiles, other datasets based on rocketsondes, National Meteorological Center (NMC) analyses, Solar Mesosphere Explorer (SME) spacecraft measurements, and CIRA 86 have been used. Encouraging agreements between the lidar and rocket profiles are evident, which confirms the potential of lidar technique for deriving the absolute temperatures in the atmosphere. Climatological comparisons also reveal satisfactory agreement between the lidar and other datasets.

Estimating the Gross Moist Stability of the Tropical Atmosphere*

Recent theoretical studies have indicated that large-scale circulation in deep convective regions evolves subject to an overall static stability—termed the gross moist stability—that takes into account both dry static stability and moist convective effects. The gross moist stability has been explicitly defined for a continuously stratified atmosphere under convective quasi-equilibrium constraints. A subsidiary quantity—the gross moisture stratification—measures the overall effectiveness in producing precipitation subject to these quasi-equilibrium constraints. These definitions are relevant in regions that experience deep convection sufficiently often; criteria based on climatological precipitation and maximum level of convection are used to define a domain of applicability. In this paper, 10-yr monthly mean rawinsonde data, and European Centre for Medium-Range Weather Forecasts (ECMWF) and National Meteorological Center (NMC) analyses are used to estimate the magnitude and horizontal distribution of these two quantities in the Tropics within the domain of applicability. The gross moist stability is found to be positive but much smaller than typical dry static stability values. Its magnitude varies modestly from 200 to 800 J kg−1 and exhibits relatively little dependence on sea surface temperature (SST). These values correspond, for instance, to a phase speed change from 8 to 16 m s−1 for the Madden–Julian oscillation. The gross moisture stratification is larger and exhibits strong dependence on SST, varying from 1500 to 3500 J kg−1 between cold and warm SST regions. A high degree of cancellation between effects of increasing low-level moisture and maximum level of convection, respectively, tends to keep the gross moist stability values relatively constant. Differences among the ECMWF and NMC analysis products and the rawinsonde data affect the estimate, but there is qualitative agreement. It is encouraging that reasonably robust estimates of a small, positive gross moist stability (as the difference between larger dry static stability and gross moisture stratification quantities) can be obtained. This helps justify use of small, constant moist phase speeds in some simple models of tropical circulation, although it also points out inconsistencies in how such models neglect variations in the height of convection.

The Impact of Ocean Initial Conditions on ENSO Forecasting with a Coupled Model

Abstract A coupled atmosphere–ocean GCM (general circulation model) has been developed for climate predictions on seasonal to interannual timescales. The atmosphere model is a global spectral GCM T30L18 and the ocean model is global on a 1° grid. Initial conditions for the atmosphere were obtained from National Meteorological Center (now known as the National Centers for Environmental Prediction) analyses, while those for the ocean came from three ocean data assimilation (DA) systems. One system is a four-dimensional DA scheme that uses conventional SST observations and vertical temperature profiles inserted into the ocean model and is forced from winds from an operational analysis. The other two initialization schemes are based on the coupled model, both nudging the surface temperature toward observed SSTs and one nudging surface winds from an operational analysis. All three systems were run from 1979 to 1988, saving the state of the ocean every month, thus initial conditions may be obtained for any mont...

The effect of planetary waves on the total ozone zonal deviations in the presence of a persistent blocking anticyclone system

Strong planetary wave activity enhanced by the external forcing of a persisting anticyclone system can cause large total ozone zonal deviations. In January 1992 such a situation was observed with a high‐pressure system and associated low total ozone concentrations situated over Northern Europe. In this article, measurements from the total ozone mapping spectrometer (TOMS) are analyzed with a simple model based on the linearized stationary ozone continuity equation. It is shown that in such a meteorological situation, vertical advection of ozone caused by the wavenumber‐one quasi‐stationary planetary wave is the most important monthly mean transport mechanism. This is different from the climatological situation, where horizontal and vertical advection are almost equally important and where wavenumbers two and three contribute more to the total ozone zonal deviations. The dominance of vertical motions, which are in phase throughout the lower and middle stratosphere, also explains the high correlations found between temperatures at 50 hPa from National Meteorological Center analyses and total ozone. Under these special meteorological conditions, the high planetary wave activity is responsible for total ozone columns with about 60 Dobson units less ozone over the anticyclonic region than under normal conditions.

Large-Scale Atmospheric Moisture Cycling As Evaluated from NMC Global Analysis and Forecast Products

Abstract The broadscale aspects of the annual cycle of monthly mean global water vapor flux, flux divergence, evaporation, and precipitation derived from the National Meteorological Center (NMC) global analysis and forecast products were examined with two objectives in mind: 1) a critical evaluation of the usefulness of recent NMC products for descriptive and diagnostic studies of the global hydrological cycle and in the process and 2) to provide additional information on the behavior of the annual cycle of selected hydrological parameters over the globe in general and over the United States in particular. The 2-year period August 1991–July 1993, was chosen for study. The global-scale characteristics of the NMC vertically integrated vapor flux fields are described in terms of the rotational and divergent components of the stationary and transient parts of the vapor flux field. Values of the zonally averaged meridional vapor flux derived from the NMC analyses are broadly similar to those presented by Peixo...

Northern Hemisphere 500-hPa Trough Merger and Fracture: A Climatology and Case Study

Abstract The results of an objective climatology of 500hPa trough merger (defined as the amalgamation of two initially separate vorticity maxima) and trough fracture (defined as the splitting of a single vorticity center into two separate vorticity centers) are presented for the Northern Hemisphere. The data source is the gridded National Meteorological Center (NMC; now the National Centers for Environmental Prediction) analyses available on CD-ROM on the NMC operational octagonal grid (381-km resolution at 60°N) for the period September 1957 to May 1989. A total of 2152 (3053) merger (fracture) events are identified. Merger and fracture events tend to occur preferentially in the band of middle-latitude westerlies. Merger events exhibit a tendency to avoid major mountainous regions and show a somewhat higher frequency of occurrence downstream of these regions. Fracture events cluster somewhat over eastern ocean basins, the southwestern United States, and northwestern Africa while also avoiding major mount...

TRACE A trajectory intercomparison: 1. Effects of different input analyses

We address the problem of air mass trajectory uncertainty through an intercomparison of trajectories computed from operational meteorological analyses from the region and time period of the NASA/GTE/TRACE A experiment. This paper examines the trajectory uncertainty that results from the input meteorological analyses. We first compare the National Meteorological Center (NMC) and European Centre for Medium‐Range Forecasts (ECMWF) meteorological analyses to an independent set of observations, the dropsondes released from the NASA DC‐8 over the South Atlantic during TRACE A. We also compare the gridded wind and temperature fields with selected rawinsonde data that entered the analyses. These comparisons show that the ECMWF fields are marginally better than the ones from NMC, particularly in the tropical regions of the southern hemisphere. The NMC analyses are marginally better in the midlatitude westerlies in some cases. In general, slightly more confidence can be placed in trajectories computed with ECMWF data over the TRACE A region, based on our comparisons of the analyses with observations. Second, we compute 5‐day back trajectories with three different models from a grid of points over the South Atlantic and adjacent portions of South America and Africa as well as on the track of TRACE A flight 15 over the South Atlantic. When using the Goddard Space Flight Center isentropic model, horizontal separations of greater than 1000 km occur for about 50% of the points when trajectories run with the ECMWF and NMC analyses are compared. Greater sensitivity to the input analysis differences is noted when trajectories are computed with the FSU kinematic model (separations exceed 1000 km for 75% of the points). The problem of meteorological uncertainty should be addressed with two approaches. There are large differences between both sets of analyses and the TRACE A soundings; this is also likely to be the case in other remote regions. Therefore we recommend that a test set of trajectories be computed with both sets of input data to quantify the uncertainty due to analysis differences. In addition, clusters of trajectories about the points of interest should be run to assess the uncertainty due to wind shear. These recommendations are applicable to any region of the globe with sparse observations. The companion paper [Fuelberg et al., this issue, part 2] addresses uncertainties due to trajectory technique.

Summer hemisphere differences in temperature and transport in the lower stratosphere

Lower stratospheric temperatures during southern hemisphere summer are found to be warmer than at the same latitude poleward of the equator during northern hemisphere summer. Coincident with such warmer temperatures is a stronger residual circulation as calculated from radiative heating rates computed using as input observations from the Upper Atmospheric Research Satellite (UARS). Such a summertime asymmetry in extratropical downwelling in the lower stratosphere does not appear in the residual circulation calculated via the downward control technique based on National Meteorological Center (NMC) analyses. Computing the residual circulation with the downward control technique using Eliassen‐Palm flux divergences based on assimilated winds and temperatures does yield the above noted summertime hemispheric asymmetry in downward extratropical mass transport, although not as pronounced as with the radiative calculation. It is proposed that smaller‐scale zonal forces due to gravity waves, absent in the NMC downward control calculation, may be important for driving the southern hemisphere summer circulation in the lower stratosphere.

ON THE RELATIONSHIP BETWEEN EURASIAN SNOW COVER AND THE ASIAN SUMMER MONSOON

ABSTRACT In this paper, we document the possible linkage between Eurasian snow cover and the Asian summer monsoon by analysing the National Oceanic and Atmospheric Administmtion snow data and the atmospheric circulation fields from the National Meteorological Center analyses. Using updated data, we confirm the inverse relationship between the Eurasian snow cover and Indian monsoon rainfall reported in previous studies. We find that the relationship becomes stronger in the partial correlation calculations excluding the El Niiio years. It is found by comparing years of more snow cover with years of less snow cover that the atmosphere is colder over land and warmer over the oceans during the winter seasons with more snow. During the summer following the winter with more snow cover, the lower atmosphere is colder over the Asian continent, especially north of India. Associated with these temperature changes, a weaker Asian monsoon circulation appears. KEY WORDS: Eurasian snow cover; Asian monsoon; atmospheric circulation; interannual variability

Comparison of U.K. Meteorological Office and U.S. National Meteorological Center stratospheric analyses during northern and southern winter

Meteorological data from the United Kingdom Meteorological Office (UKMO), produced using a data assimilation system, and the U.S. National Meteorological Center (NMC), produced using an objective analysis procedure, are compared for dynamically active periods during the Arctic and Antarctic winters of 1992. The differences seen during these periods are generally similar to those seen during other winter periods. Both UKMO and NMC analyses capture the large‐scale evolution of the stratospheric circulation during northern hemisphere (NH) and southern hemisphere (SH) winters. Stronger vertical and horizontal temperature gradients develop in the UKMO than in the NMC data during stratospheric warmings; comparison with satellite measurements with better vertical resolution suggests that the stronger vertical temperature gradients are more realistic. The NH polar vortex is slightly stronger in the UKMO analyses than in the NMC in the middle and upper stratosphere, and midstratospheric temperatures are slightly lower. The SH polar vortex as represented in the UKMO analyses is stronger and colder in the midstratosphere than its representation in the NMC analyses. The UKMO analyses on occasion exhibit some difficulties in representing cross‐polar flow or changes in curvature of the wind field at very high latitudes. In addition to the above study of two wintertime periods, a more detailed comparison of lower‐stratospheric temperatures is done for all Arctic and Antarctic winter periods since the launch of the Upper Atmosphere Research Satellite. In the NH lower stratosphere during winter, NMC temperatures are consistently lower than UKMO temperatures and closer to radiosonde temperatures than are UKMO temperatures. Conversely, in the SH lower stratosphere during winter, UKMO temperatures are typically lower than NMC and are closer to radiosonde temperature observations.

Evolution of two oceanic extratropical cyclones as observed with the special sensor microwave/imager and the Geosat and ERS 1 altimeters

The evolution of two marine cyclones across the North Atlantic and the North Pacific Oceans is followed with a combination of sequential passive and active microwave data. The special sensor microwave/imager (SSM/I) provides estimates of atmospheric parameters: integrated water vapor, precipitation, and ocean surface wind speed. The Geosat and ERS 1 altimeter data are used to derive sea state parameters along the satellite tracks: the significant wave height and the ocean surface wind speed. The SSM/I integrated water vapor gradients are used to locate and follow the evolution of the atmospheric fronts. In regions of precipitation, often located behind the atmospheric fronts, the SSM/I surface wind speed cannot be derived, while the Geosat and ERS 1 altimeter wind speed yields estimates of wind speed gradients across the fronts. It is shown that the combination of SSM/I and satellite altimeters permits additional observations of surface fronts with higher resolution both in space and time than those given in the National Meteorological Center analyses.

Lidar measurements of stratospheric temperature during STOIC

Measurements of stratospheric temperature and density were acquired by the NASA/GSFC lidar during the Stratospheric Ozone Intercomparison Campaign (STOIC) experiment at the Jet Propulsion Laboratory Table Mountain Facility (TMF) (34.4°N, 117.7°W) in July and August 1989. Lidar temperatures, obtained on 21 nights preceding and during this experiment, are compared with temperatures derived by radiosondes, datasondes, Stratospheric Aerosol and Gas Experiment (SAGE II) satellite experiment, and National Meteorological Center (NMC) analyses. Radiosondes were flown from the TMF site as well as from San Nicholas Island (33.2°N, 119.5°W) located about 225 km southwest of TMF. Datasondes were deployed from Super‐Loki rockets also launched at San Nicholas Island. SAGE II satellite temperature measurements were made within 1000 km of the Table Mountain site. NMC temperature analyses derived from the NOAA satellite measurements were interpolated to coincide in space and time with the lidar measurements. The lidar temperatures, which were derived for altitudes between 30 and 65 km, were within 2–3 K of the temperatures measured by the other sensors in the altitude range 30–45 km. Between 30 and 35 km, lidar temperatures were about 2 K cooler than those obtained from the datasondes and the NMC analyses but were about 1–2 K warmer than those obtained from the radiosonde. These differences may be due to the time difference between the measurements as well as possible nonnegligible aerosol scattering near 30 km. Near and above the stratopause the temperature differences increased to 3–8 K. Lidar temperature profiles also show small‐scale variations possibly caused by wave activity.

Comparison of Tropospheric Temperature Derived from the Microwave Sounding Unit and the National Meteorological Center Analysis

Abstract The Microwave Sounding Units (MSU) aboard the NOAA series of polar-orbiting satellites (TIROS-N to NOAA-12) have provided stable and precise measurements of vertically integrated atmospheric temperature since December 1978. Comparisons are made between the MSU channel measurements and temperatures derived from the global data assimilation system (GDAS) at the National Meteorological Center (NMC) for the period 1979–1990. The largest correlations occur at high to midlatitudes, where the troposphere exhibits large monthly anomaly fields, and where radiosondes provide ample coverage for the GDAS. Intermonthly differences from each dataset had global correlations above 0.97. However, poor correlations with MSU were noted over areas of high terrain and tropical landmasses. These poorer correlations can be attributed to temporal changes and data limitations in the GDAS analysis. Comparisons between the GDAS and MSU temperature anomaly fields indicate that frequent model changes mask the climate signal ...

Potential Vorticity on Isentropic Surfaces: Climatology and Diagnostics

Abstract A 25-year dataset of potential vorticity on the 315-K isentropic surface is built from the National Meteorological Center (NMC) final analysis archive. Potential vorticity is calculated from the nonlinear gradient wind balance using temperature and geopotential fields, since the wind field is not available in the early part of the archive. The validity of this calculation is assessed by comparing the results with potential vorticity obtained directly from European Centre for Medium-Range Weather Forecasts (ECMWF) analyzed winds. The error due to the nonlinear balance approximation turns out to be smaller than the difference between ECMWF and NMC analysis. The possibility of studying diabatic forcing as a residual of the equation of potential vorticity conservation is examined. The average potential vorticity forcing found in this way is consistent with the authors knowledge of the mean diabatic heating. The amplitude of the residual decreases through the analysis period, reflecting the improvemen...

Angular momentum exchange among the solid Earth, atmosphere, and oceans: A case study of the 1982–1983 El Niño event

The 1982–1983 El Nino/Southern Oscillation (ENSO) event was accompanied by the largest interannual variation in the Earth's rotation rate on record. In this study we demonstrate that atmospheric forcing was the dominant cause for this rotational anomaly, with atmospheric angular momentum (AAM) integrated from 1000 to 1 mbar (troposphere plus stratosphere) accounting for up to 92% of the interannual variance in the length of day (LOD). Winds between 100 and 1 mbar contributed nearly 20% of the variance explained, indicating that the stratosphere can play a significant role in the Earth's angular momentum budget on interannual time scales. Examination of LOD, AAM, and Southern Oscillation Index (SOI) data for a 15‐year span surrounding the 1982–1983 event suggests that the strong rotational response resulted from constructive interference between the low‐frequency (∼4–6 year) and quasi‐biennial (∼2–3 year) components of the ENSO phenomenon, as well as the stratospheric Quasi‐Biennial Oscillation (QBO). Sources of the remaining LOD discrepancy (∼55 and 64 μs rms residual for the European Centre for Medium‐Range Forecasting (EC) and U.S. National Meteorological Center (NMC) analyses) are explored; noise and systematic errors in the AAM data are estimated to contribute 18 and 33 μs, respectively, leaving a residual (rms) of 40 (52) μs unaccounted for by the EC (NMC) analysis. Oceanic angular momentum contributions (both moment of inertia changes associated with baroclinic waves and motion terms) are shown to be candidates in closing the interannual axial angular momentum budget.

An Algorithm for Forecasting Mountain Wave–Related Turbulence in the Stratosphere

A global mountain wave parameterization for prediction of wave-related displacements and turbulence is described. The parameterization is used with input from National Meteorological Center (NMC) analyses of wind and temperature to examine small-scale disturbances encountered by the National Aeronautics and Space Administration high-altitude ER-2 during the Second Airborne Arctic Stratosphere Experiment (AASE-II). The magnitude and location of observed large wave events are well reproduced. A strong correlation is suggested between patches of moderate turbulence encountered by the ER-2 and locations where breaking mountain waves are predicted by the parameterization. These facts suggest that useful forecasts of global mountain wave activity, including wave-related clear-air turbulence, can be made quickly and inexpensively using our mountain wave parameterization with input from current numerical forecast models.

Mean meridional transport of energy in the earthatmosphere system using NMC global analyses and ERBE radiation data

Recently processed data from the Earth Radiation Budget Experiment (ERBE) provides an incentive to continue investigations addressing the energy transport of the earth-atmosphere system. Within this study, we compare the top-of atmosphere ERBE net radiation measurements and derived energy transports thereof with computed transports derived from the daily global analyses of the National Meteorological Center (NMC). The period of study is for the year March 1985–February 1986, and the results are divided into the annual and seasonal averages. The basic result is that most features depicted in the calculation of meridional energy transports within the atmosphere are physically realistic. Mean motions dominate in the tropics, with contributions by both the Hadley and Ferrel Cells evident. Comparisons between these ERBE/NMC results and published results of similar studies aid the evaluation process. The greatest differences are found in the tropics, where the mean transports derived from NMC analyses are somewhat smaller than expected due to a weak Hadley Cell circulation. DOI: 10.1034/j.1600-0870.1994.t01-2-00001.x

Interannual Variation of Summertime Stationary Eddies

Abstract An effort is made to explore the interannual variation of stationary eddies for the past 13 summers (1979–1991). Equatorial λ − t diagrams of sea surface temperature (SST), outgoing longwave radiation (OLR), the potential function of OLR (χOLR), and velocity potential (χ) derived from National Meteorological Center (NMC) analyses reveal the existence of a coherent and pronounced interannual variation, particularly over the Pacific. Performing regular empirical orthogonal function (EOF) analyses of eddy streamfunction and velocity potential departures from their multiple-summer averages at 200 mb [ψE(200 mb)] and χE(200 mb)] and correlating the distributions between these two variables, it is possible to identify two interannual variation modes of summertime stationary eddies. The horizontal structure of these two interannual variation modes, which differs from the Pacific-North American (PNA) teleconnection pattern, resembles the Matsuno-Gill type of tropically trapped modes. It is inferred from ...

Observation Error Statistics forNOAA-10 Temperature and Height Retrievals

In 1988, the algorithm for retrieving temperature soundings from radiances measured by NOAA's polar-orbiting satellites was changed from a statistical to a “physical” retrieval system. Because of this change, the National Meteorological Center (NMC) wanted to update the satellite temperature error statistics used in the NMC analyses. The authors, therefore, updated the estimates of observational error variances, horizontal covariances, and vertical correlations for layer mean temperatures retrieved from NOAA-10 satellite radiance data. The temperature error statistics have also been used to estimate analogous error statistics for isobaric height. The computations used radiosonde data as a substitute for true temperatures. Each “matchup” in the dataset consisted of a satellite retrieval close in space and time to a radiosonde sounding. The matchups were stratified into clear, partly cloudy, and cloudy cases, depending on the amount of cloud contamination in the satellite radiance data. In each of the nine mandatory pressure layers considered, from 1000–850 to 50–100 mb, the clear and partly cloudy matchup cases have nearly equal temperature error variances, while the variances for cloudy cases are substantially larger. Vertical error correlations for all three stratifications are similar. Root-mean-square height errors computed from satellite temperature errors are comparable to those computed from radiosonde errors in the clear and partly cloudy matchup cases, but larger in cloudy cases.

Forecasting Northern Hemisphere 700-mb Geopotential Height Anomalies Using Empirical Normal Modes

Abstract Multivariate linear prediction based on single-lag inverse modeling is developed further and critically examined. The method is applied to the National Meteorological Center analyses of Northern Hemisphere 700-mb geopotential height anomalies, which have been filtered to eliminate periods shorter than 10 days. Empirically derived normal modes of the randomly forced linear system are usually correlated, even at zero lag, suggesting that combinations of modes should be used in predictions. Due to nonlinearities in the dynamics and the neglect of interactions with other pressure levels, the lag at which the analysis is performed is crucial; best predictions obtain when the autocovariances involved in the analysis are calculated at a lag comparable to the exponential decay times of the modes. Errors in prediction have a significant seasonal dependence, indicating that the annual cycle affects the higher-order statistics of the field. Optimized linear predictions using this method are useful for about...