Showing papers by "Eugenia Kalnay published in 2003"

Impact of urbanization and land-use change on climate

Abstract: The most important anthropogenic influences on climate are the emission of greenhouse gases1 and changes in land use, such as urbanization and agriculture2. But it has been difficult to separate these two influences because both tend to increase the daily mean surface temperature3,4. The impact of urbanization has been estimated by comparing observations in cities with those in surrounding rural areas, but the results differ significantly depending on whether population data5 or satellite measurements of night light6,7,8 are used to classify urban and rural areas7,8. Here we use the difference between trends in observed surface temperatures in the continental United States and the corresponding trends in a reconstruction of surface temperatures determined from a reanalysis of global weather over the past 50 years, which is insensitive to surface observations, to estimate the impact of land-use changes on surface warming. Our results suggest that half of the observed decrease in diurnal temperature range is due to urban and other land-use changes. Moreover, our estimate of 0.27 °C mean surface warming per century due to land-use changes is at least twice as high as previous estimates based on urbanization alone7,8.

AIRS/AMSU/HSB on the Aqua mission: design, science objectives, data products, and processing systems

Abstract: The Atmospheric Infrared Sounder (AIRS), the Advanced Microwave Sounding Unit (AMSU), and the Humidity Sounder for Brazil (HSB) form an integrated cross-track scanning temperature and humidity sounding system on the Aqua satellite of the Earth Observing System (EOS). AIRS is an infrared spectrometer/radiometer that covers the 3.7-15.4-/spl mu/m spectral range with 2378 spectral channels. AMSU is a 15-channel microwave radiometer operating between 23 and 89 GHz. HSB is a four-channel microwave radiometer that makes measurements between 150 and 190 GHz. In addition to supporting the National Aeronautics and Space Administration's interest in process study and climate research, AIRS is the first hyperspectral infrared radiometer designed to support the operational requirements for medium-range weather forecasting of the National Ocean and Atmospheric Administration's National Centers for Environmental Prediction (NCEP) and other numerical weather forecasting centers. AIRS, together with the AMSU and HSB microwave radiometers, will achieve global retrieval accuracy of better than 1 K in the lower troposphere under clear and partly cloudy conditions. This paper presents an overview of the science objectives, AIRS/AMSU/HSB data products, retrieval algorithms, and the ground-data processing concepts. The EOS Aqua was launched on May 4, 2002 from Vandenberg AFB, CA, into a 705-km-high, sun-synchronous orbit. Based on the excellent radiometric and spectral performance demonstrated by AIRS during prelaunch testing, which has by now been verified during on-orbit testing, we expect the assimilation of AIRS data into the numerical weather forecast to result in significant forecast range and reliability improvements.

Use of the breeding technique to estimate the structure of the analysis "errors of the day"

Abstract: A 3D-variational data assimilation scheme for a quasi-geostrophic channel model (Morss, 1998) is used to study the structure of the background error and its relation- ship to the corresponding bred vectors. The "true" evolution of the model atmosphere is defined by an integration of the model and "rawinsonde observations" are simulated by ran- domly perturbing the true state at fixed locations. Case studies using different observational densities are considered to compare the evolution of the Bred Vectors to the spatial structure of the background error. In addition, the bred vector dimension (BV-dimension), defined by Patil et al. (2001) is applied to the bred vectors. It is found that after 3-5 days the bred vectors develop well organized structures which are very similar for the two dif- ferent norms (enstrophy and streamfunction) considered in this paper. When 10 surrogate bred vectors (corresponding to different days from that of the background error) are used to describe the local patterns of the background error, the ex- plained variance is quite high, about 85-88%, indicating that the statistical average properties of the bred vectors represent well those of the background error. However, a subspace of 10 bred vectors corresponding to the time of the background error increased the percentage of explained variance to 96- 98%, with the largest percentage when the background errors are large. These results suggest that a statistical basis of bred vectors collected over time can be used to create an effective constant background error covariance for data assimilation with 3D- Var. Including the "errors of the day" through the use of bred vectors corresponding to the background forecast time can bring an additional significant improvement.

Bred Vectors of the Zebiak–Cane Model and Their Potential Application to ENSO Predictions

Abstract: The breeding method is used to obtain the bred vectors (BV) of the Zebiak–Cane (ZC) atmosphere–ocean coupled model. Bred vectors represent a nonlinear, finite-time extension of the leading local Lyapunov vectors of the ZC model. The spatial structure and growth rate of bred vectors are strongly related to the background ENSO evolution of the ZC model. It is equally probable for the BVs to have a positive or negative sign (defined using the Nino-3 index of the BV), though often there is a sign change just before or after an El Nino event. The growth rate (and therefore the spatial coherence) of the BVs peaks several months prior to and after an El Nino event and it is nearly neutral at the mature stage. Potential applications of bred vectors for ENSO predictions are explored in the context of data assimilation and ensemble forecasting under a perfect model scenario. It is shown that when bred vectors are removed from random initial error fields, forecast errors can be reduced by up to 30%. This su...

Changes in Global Monsoon Circulations Since 1950

Abstract: We examined changes in several independent intensity indices of four major tropical monsoonal circulations for the period 1950-1998. These intensity indices included observed land surface precipitation and observed ocean surface pressure in the monsoon regions as well as upper- level divergence calculated at several standard levels from the NCAR/NCEP reanalysis. These values were averaged seasonally over appropriate regions of southeastern Asian, western Africa, eastern Africa and the Australia/Maritime continent and adjacent ocean areas. As a consistency check we also examined two secondary indices: mean sea level pressure trends and low level convergence both from the NCEP reanalysis. We find that in each of the four regions examined, a consistent picture emerges indicating signi- ficantly diminished monsoonal circulations over the period of record, evidence of diminished spatial maxima in the global hydrological cycle since 1950. Trends since 1979, the period of strongest reported surface warming, do not indicate any change in monsoon circulations. When strong ENSO years are removed from each of the time series the trends still show a general, significant reduc- tion of monsoon intensity indicating that ENSO variability is not the direct cause for the observed weakening. Most previously reported model simulations of the effects of rising CO2 show an increase in monsoonal activity with rising global surface temperature. We find no support in these data for an increasing hydrological cycle or increasing extremes as hypothesized by greenhouse warming scenarios.

Statistics of locally coupled ocean and atmosphere intraseasonal anomalies in Reanalysis and AMIP data

Abstract: We apply a simple dynamical rule to determine the dominant forcing direction in locally coupled ocean- atmosphere anomalies in the National Centers for Environ- mental Prediction/National Center for Atmospheric Research (NCEP/ NCAR) reanalysis data. The rule takes into account the phase relationship between the low-level vorticity anoma- lies and the Sea Surface Temperature (SST) anomalies. Anal- ysis of the frequency of persistent coupled anomalies for five-day average data shows that, in general, the ocean tends to force the atmosphere in the tropics while the atmosphere tends to force the ocean in the extratropics. The results agree well with those obtained independently using lagged correla- tions between atmospheric and oceanic variables, suggesting that the dynamical rule is generally valid. A similar procedure carried out using data from the NCEP global model run with prescribed SST (in which the cou- pling is one-way, with the ocean always forcing the atmo- sphere) produces fewer coupled anomalies in the extratrop- ics. They indicate, not surprisingly, an increase in ocean- driving anomalies in the model. In addition, and very impor- tantly, there is a strong reduction of persistent atmosphere- driving anomalies, indicating that the one-way interaction of the ocean in the model run may provide a spurious negative feedback that damps atmospheric anomalies faster than ob- served.

Corrigendum: Impact of urbanization and land-use change on climate

Abstract: Nature 423, 528–531 (2003). When calculating areal averages, which involve weighting gridded data with the cosine of the latitude of half-degree grid boxes, we divided the sum by the total number of grids but omitted to divide the sum also by the average cosine latitude of the domain, which is 0.786. This error affects only the area-averaged values, not the maps or the station values, or the relative differences between station and reanalysis values.

The USWRP Workshop on the Weather Research Needs of the Private Sector

Abstract: Private sector meteorology is a rapidly growing enterprise. It has been estimated that the provision of weather information has, by some estimates, a global market totaling in the billions of dollars. Further, the decisions based on such information could easily total trillions of dollars in the U.S. economy alone. The private sector clearly plays an important, and growing, role at the interface of weather research and the weather information needs of society. To date, little information has been paid to the connections of the meteorological research community and the scientific needs of the private sector. Thus, the time is ripe to stimulate a more active dialogue between what is generally considered the “basic” research community of physical and social scientists and those individuals and businesses that provide weather information to myriad customers across the U.S. economy. In December 2000, the U.S. Weather Research Program (supported by NSF, NOAA, NASA, and the U.S. Navy) sponsored a worksh...

Local Low Dimensionality and Relation to Effects Of Targeted Weather Observations

Abstract: A statistic, the BV (bred vector) dimension, is introduced to measure the effective local finite‐time dimensionality of a spatiotemporally chaotic system It is shown that the Earth’s atmosphere often has low BV‐dimension The implications for improving weather forecasting through data assimilation and targeted observations are discussed