James Pfaendtner

An assimilated dataset for Earth science applications

The Data Assimilation Office at NASAs Goddard Space Flight Center is currently producing a multiyear gridded global atmospheric dataset for use in climate research, including tropospheric chemistry applications. The data, which are being made available to the scientific community, are well suited for climate research since they are produced by a fixed assimilation system designed to minimize the spinup in the hydrological cycle. By using a nonvarying system, the variability due to algorithm change is eliminated and geophysical variability can be more confidently isolated. The analysis incorporates rawinsonde reports, satellite retrievals of geopotential thickness, cloud-motion winds, and aircraft, ship, and rocketsonde reports. At the lower boundary, the assimilating atmospheric general circulation model is constrained by the observed sea surface temperature and soil moisture derived from observed surface air temperature and precipitation fields. The available output data include all prognostic variables...

Aspects of the Hydrological Cycle of the Ocean-Atmosphere System

Abstract The balance equations for atmospheric water vapor and freshwater in the oceans are used to illustrate that evaporation and precipitation represent the major linkage between the atmospheric and oceanic branches of the global hydrological cycle. Attempts are also made to establish the hydrological cycle of the coupled ocean-atmosphere system using water vapor flux divergence, precipitation, and interoceanic freshwater transport estimates from previous studies as well as computational results with more recent data. This hydrological cycle works as follows: the atmospheric water vapor converged to the Pacific results in an excess of precipitation and a freshwater transport across the Bering Strait and the Arctic Sea to the Atlantic. The atmospheric water vapor is then diverged out of the latter ocean due to an excess of evaporation there.

Inclusion of Special Sensor Microwave/imager (SSM/I) Total Precipitable Water Estimates into the GEOS-1 Data Assimilation System

Abstract At this time, most current data assimilation systems use dewpoint depression data, converted to an appropriate moisture variable (relative humidity or mixing ratio), provided by rawinsondes as the lone source of moisture information. Because of the poor spatial and temporal characteristics of this data, additional moisture data are necessary to better resolve the global moisture field. This study investigates the impact of using the Special Sensor Microwave/Imager (SSM/I) total precipitable water (TPW) estimates as an additional source of moisture information. One forecast and four data assimilation experiments were performed to determine the impact of assimilating SSM/I TPW estimates into the NASA/Goddard Earth Observing System (version 1 ) Data Assimilation System (GEOS-1 DAS). It is shown that assimilation of SSM/I TPW estimates improves the precipitation pattern in the Tropics. In addition, a known dry bias in the GEOS-1 DAS was reduced by over 50% and observation minus first guess (O − F) er...

Low-Frequency Variations in the Atmospheric Branch of the Global Hydrological Cycle

Abstract According to the atmospheric water balance equation, the divergence of the water vapor flux is responsible for the exchange of water vapor between its source and sink regions. Because the water vapor flux divergence is primarily determined by the divergent circulation, time variations of the global hydrological cycle reflect the pronounced low-frequency modes of the global divergent circulation, that is, the annual and intraseasonal (30–60 day) modes. The annual variation of the hydrological cycle is illustrated in terms of hemispheric-mean hydrological variables for the Northern and Southern Hemispheres, while the intraseasonal variations of the global hydrological cycle are illustrated with mean values over two hemispheres that form an east-west partition of the globe. This partition is defined by the 60°E–120°W great circle and was chosen so that the mean precipitation difference and the divergent water vapor transport between the two hemispheres was maximized. Two years (1979–80) of daily pre...

On the Atmospheric Branch of the Hydrological Cycle

Abstract Recently, HIRS2/MSU data have been used at the Goddard Laboratory for Atmospheres(GLA) to generate global precipitation estimates. A synergistic mix of the GLA precipitation, together with the global wind and moisture fields produced by the Global Data Assimilation System of the European Centre for Medium-Range Weather Forecasts, was employed to delineate the atmospheric branch of the hydrological cycle during the 1978/79 Northern Hemisphere winter and the 1979 Northern Hemisphere summer. The transport of water vapor from source to sink regions was illustrated geographically by a combination of the divergent component of water vapor transport and precipitation.

The 12-24-day mode of global precipitation

Abstract Global precipitation estimates derived from satellite data at the Goddard Laboratory for Atmospheres for 1979–80 were used to explore time variations in global precipitation. Time series of the area-averaged precipitation [P] over the Asian-Australian (AA) monsoon (60°E–12°W), and the extra-AA monsoon (120°W–60°E) hemispheres were used in describing the variations. A distinct seesawlike intraseasonal variation of precipitation between these two hemispheres emerges from the two time series. Two intraseasonal (30–60 and 12–24 day) modes stand our in die spectral analysis of the two [P] time series. The 30–60 day mode is well known, while the 12–24-day mode is identified here for the first time. Using data generated by the Global Data Assimilation System of the National Meteorological Center, an effort was made to investigate the characteristics of the 12–24-day mode of global precipitation via potential functions for the 200-mb wind, water vapour transport, and precipitation. It is found that the 1...

Variability of the global precipitable water with a timescale of 90–150 days

A 90-150 day signal is identified in the global precipitable water field generated by the Global Data Assimilation Systems (GDAS) of the Goddard Laboratory for Atmospheres (GLA), National Meteorological Center, and European Centre for Medium-Range Weather Forecasts. The finding of this intraseasonal signal in global precipitable water is significant for two reasons : (1) it suggests that there is 90-150 day intraseasonal variability in the atmospheric branch of the global hydrological cycle and (2) it provides a useful parameter to test the sensitivity of the GDAS-generated hydrological data. This newly identified intraseasonal signal in the global precipitable water was verified with Special Sensor Microwave/Imager precipitable water data over oceans and station-mixing ratio data over the continental United States. Based upon some simple statistical analyses and global and regional composite charts, it was found that the 90-150 day low-frequency oscillations contained in different GDAS data sets are more coherent with each other in regions with good data coverage but are poorly correlated over the data-sparse areas. Furthermore, the GLA GDAS provides the most realistic representation of this intraseasonal global precipitable water signal.

The Effect of Horizontal Resolution on Systematic Errors of the GLA Forecast Model

Abstract Systematic prediction errors of the Goddard Laboratory for Atmospheres (GLA) forecast system are reduced when the higher-resolution (2° × 2.5°) model version is used. Based on a budget analysis of the 200-mb eddy streamfunction, the improvement of stationary eddy forecasting is seen to be caused by the following mechanism: By increasing the horizontal spatial resolution of the forecast model, atmospheric diabatic heating over the three tropical continents is changed in a way that intensifies the planetary-scale divergent circulations associated with the three pairs of divergent-convergent centers over these continents. The intensified divergent circulation results in an enhancement of vorticity sources in the Northern Hemisphere. The additional vorticity is advected eastward by a stationary wave train along 30°N, thereby reducing systematic errors in the lower-resolution (4° × 5°) GLA forecast model.

A complementary depiction of the interannual variation of atmospheric circulation associated with ENSO events: Research note

Abstract A simple diagnostic scheme, which combines a low‐pass temporal filter (with an 18‐month cutoff time) with a regular empirical orthogonal function (EOF) analysis, is used to delineate the synchronous evolution of El Nino‐Southern Oscillation‐related (ENSO‐related) modes in various variables of the ocean‐atmosphere system. Based on the causal relation chain of diabatic heating, divergent circulation and rotational flow, the diagnostic scheme extracts ENSO modes from the following data sources: the Pacific sea surface temperature (SST), the past 14‐years (1979–1992) of data generated by the Global Data Assimilation System of the National Meteorological Center, and a 10‐year (1979–1988) general circulation model climate simulation made at the Goddard Laboratory for Atmospheres. The analysis reveals the following: (a) the eigencoefficient time series of the first eigenmodes of selected filtered variables, which explain about 40–50% of their total variance, synchronize with the filtered SST averaged ov...

The vertical structure of diabatic heating associated with the Madden‐Julian oscillation simulated by the Goddard Laboratory for Atmospheres climate model

Previous studies have shown that numerical simulations of the Madden-Julian oscillation (MJO) are very sensitive to the vertical distribution of diabatic heating. Since atmospheric diabatic heating is generally difficult to estimate, the vertical diabatic heating profile associated with the MJO is not well known. Judged by its propagation properties and spatial structure, the MJO is reasonably well simulated by the nine-layer Goddard Laboratory for Atmospheres (GLA) general circulation model. Although only a simulation the model MJO may provide an indication of the vertical diabatic heating profile associated with the real oscillation. The diabatic heating structure of the model MJO is illustrated with composite charts made for those times when this low-frequency mode reaches its maximum and minimum amplitudes. These composite charts compare the vertically integrated diabatic heating with potential functions, the vertical distribution of diabatic heating with the east-west mass flux function in the tropics, and the vertical profiles of diabatic heating at the centers of maximum and minimum MJO amplitude. Three interesting features of the model MJOs diabatic heating are revealed: (1) the maximum heating rate of this low-frequency mode is located over the Asian monsoon region and its amplitude is about a half of the maximum value of the seasonal mean heating rate in this region, (2) the vertical diabatic heating rate profile has a maximum at 500 mbar and resembles the seasonal mean total heating profile, and (3) the total diabatic heating is for the most part composed of the latent heat released by cumulus convection.