Showing papers in "Bulletin of the American Meteorological Society in 2006"

North american regional reanalysis

Abstract: In 1997, during the late stages of production of NCEP–NCAR Global Reanalysis (GR), exploration of a regional reanalysis project was suggested by the GR project's Advisory Committee, “particularly if the RDAS [Regional Data Assimilation System] is significantly better than the global reanalysis at capturing the regional hydrological cycle, the diurnal cycle and other important features of weather and climate variability.” Following a 6-yr development and production effort, NCEP's North American Regional Reanalysis (NARR) project was completed in 2004, and data are now available to the scientific community. Along with the use of the NCEP Eta model and its Data Assimilation System (at 32-km–45-layer resolution with 3-hourly output), the hallmarks of the NARR are the incorporation of hourly assimilation of precipitation, which leverages a comprehensive precipitation analysis effort, the use of a recent version of the Noah land surface model, and the use of numerous other datasets that are additional or improv...

Where are the most intense thunderstorms on earth

Abstract: The instruments on the Tropical Rainfall Measuring Mission (TRMM) satellite have been observing storms as well as rainfall since December 1997. This paper shows the results of a systematic search through seven full years of the TRMM database to find indicators of uncommonly intense storms. These include strong (> 40 dBZ) radar echoes extending to great heights, high lightning flash rates, and very low brightness temperatures at 37 and 85 GHz. These are used as proxy variables, indicating powerful convective updrafts. The main physical principles supporting this assertion involve the effects of such updrafts in producing and lofting large ice particles high into the storm, where TRMM's radar easily detects them near storm top. TRMM's passive microwave radiometer detects the large integrated ice water path as very low brightness temperatures, while high lightning flash rates are a physically related but instrumentally independent indicator. The geographical locations of these very intense convective storms ...

African Monsoon Multidisciplinary Analysis: An International Research Project and Field Campaign

Abstract: African Monsoon Multidisciplinary Analysis (AMMA) is an international project to improve our knowledge and understanding of the West African monsoon (WAM) and its variability with an emphasis on daily-to-interannual time scales. AMMA is motivated by an interest in fundamental scientific issues and by the societal need for improved prediction of the WAM and its impacts on West African nations. Recognizing the societal need to develop strategies that reduce the socioeconomic impacts of the variability of the WAM, AMMA will facilitate the multidisciplinary research required to provide improved predictions of the WAM and its impacts. This will be achieved and coordinated through the following five international working groups: i) West African monsoon and global climate, ii) water cycle, iii) surface–atmosphere feedbacks, iv) prediction of climate impacts, and v) high-impact weather prediction and predictability. AMMA promotes the international coordination of ongoing activities, basic research, and a...

GSWP-2 Multimodel Analysis and Implications for Our Perception of the Land Surface

Abstract: Quantification of sources and sinks of carbon at global and regional scales requires not only a good description of the land sources and sinks of carbon, but also of the synoptic and mesoscale meteorology. An experiment was performed in Les Landes, southwest France, during May–June 2005, to determine the variability in concentration gradients and fluxes of CO2 The CarboEurope Regional Experiment Strategy (CERES; see also http://carboregional.mediasfrance.org/index) aimed to produce aggregated estimates of the carbon balance of a region that can be meaningfully compared to those obtained from the smallest downscaled information of atmospheric measurements and continental-scale inversions. We deployed several aircraft to sample the CO2 concentration and fluxes over the whole area, while fixed stations observed the fluxes and concentrations at high accuracy. Several (mesoscale) meteorological modeling tools were used to plan the experiment and flight patterns. Results show that at regional scale the relation...

AIRS: Improving Weather Forecasting and Providing New Data on Greenhouse Gases.

Abstract: This paper discusses the performance of AIRS and examines how it is meeting its operational and research objectives based on the experience of more than 2 yr with AIRS data. We describe the science background and the performance of AIRS in terms of the accuracy and stability of its observed spectral radiances. We examine the validation of the retrieved temperature and water vapor profiles against collocated operational radiosondes, and then we assess the impact thereof on numerical weather forecasting of the assimilation of the AIRS spectra and the retrieved temperature. We close the paper with a discussion on the retrieval of several minor tropospheric constituents from AIRS spectra.

A Statistical Deterministic Approach to Hurricane Risk Assessment

Abstract: Hurricanes are lethal and costly phenomena, and it is therefore of great importance to assess the long-term risk they pose to society. Among the greatest threats are those associated with high winds and related phenomena, such as storm surges. Here we assess the probability that hurricane winds will affect any given point in space by combining an estimate of the probability that a hurricane will pass within some given radius of the point in question with an estimate of the spatial probability density of storm winds. To assess the probability that storms will pass close enough to a point of interest to affect it, we apply two largely independent techniques for generating large numbers of synthetic hurricane tracks. The first treats each track as a Markov chain, using statistics derived from observed hurricane-track data. The second technique begins by generating a large class of synthetic, time-varying wind fields at 850 and 250 hPa whose variance, covariance, and monthly means match NCEP–NCAR reanalysis d...

Feasibility of a 100-Year Reanalysis Using Only Surface Pressure Data

Abstract: Climate variability and global change studies are increasingly focused on understanding and predicting regional changes of daily weather statistics. Assessing the evidence for such variations over the last 100 yr requires a daily tropospheric circulation dataset. The only dataset available for the early twentieth century consists of error-ridden hand-drawn analyses of the mean sea level pressure field over the Northern Hemisphere. Modern data assimilation systems have the potential to improve upon these maps, but prior to 1948, few digitized upper-air sounding observations are available for such a “reanalysis.” We investigate the possibility that the additional number of newly recovered surface pressure observations is sufficient to generate useful weather maps of the lower-tropospheric extratropical circulation back to 1890 over the Northern Hemisphere, and back to 1930 over the Southern Hemisphere. Surprisingly, we find that by using an advanced data assimilation system based on an ensemble Kalman filte...

The Dvorak Tropical Cyclone Intensity Estimation Technique: A Satellite-Based Method that Has Endured for over 30 Years

Abstract: The history of meteorology has taught us that weather analysis and prediction usually advances by a series of small, progressive studies. Occasionally, however, a special body of work can accelerate this process. When that work pertains to high-impact weather events that can affect large populations, it is especially notable. In this paper we review the contributions by Vernon F. Dvorak, whose innovations using satellite observations of cloud patterns fundamentally enhanced the ability to monitor tropical cyclones on a global scale. We discuss how his original technique has progressed, and the ways in which new spaceborne instruments are being employed to complement Dvorak's original visions.

The south american low-level jet experiment

Abstract: Moisture is transported in South America westward from the tropical Atlantic Ocean to the Amazon basin, and then southward toward the extratropics. A regional intensification of this circulation to the east of the Andes Mountains is called the South American low-level jet (SALLJ), with the strongest winds found over eastern Bolivia. SALLJ is present all year and channels moisture to the La Plata basin, which is analogous to the better-known Amazon basin in terms of its biological and habitat diversity, and far exceeds the latter in its economic importance to southern and central South America in terms of hydroelectricity and food production. The relatively small SALLJ spatial scale (compared with the density of the available sounding network) has a limited understanding of and modeling capability for any variations in the SALLJ intensity and structure as well as its possible relationship to downstream rainfall. The SALLJ Experiment (SALLJEX), aimed at describing many aspects of SALLJ, was carried...

What Do Networks Have to Do with Climate

Abstract: The study of networks has recently exploded into a major research tool in many areas of science. The discovery of “small world” and scale-free networks has led to many new insights about the collective behavior of a large number of interacting agents and complex systems. Here we introduce the basic ideas behind networks, as well as some initial applications of networks to the climate system. Our results suggest that the climate system exhibits aspects of small-world networks as well as scale-free networks, with supernodes corresponding to major teleconnection patterns. This result suggests that the organization of teleconnections may play a role in the stability of the climate system. In addition, preliminary work suggests that temporal changes in the network's architecture may be used to identify signatures of global change. These and other applications suggest that networks provide a new tool for investigating and reconstructing climate dynamics from both models and observations.

African Climate Change: Taking the Shorter Route

Abstract: Numerous factors are associated with poverty and underdevelopment in Africa, including climate variability. Rainfall, and climate more generally, are implicated directly in the United Nations “Millennium Development Goals” to eradicate extreme poverty and hunger, and reduce child mortality and incidence of diseases such as malaria by the target date of 2015. But, Africa is not currently on target to meet these goals. We pose a number of questions from a climate science perspective aimed at understanding this background: Is there a common origin to factors that currently constrain climate science? Why is it that in a continent where human activity is so closely linked to interannual rainfall variability has climate science received little of the benefit that saw commercialization driving meteorology in the developed world? What might be suggested as an effective way for the continent to approach future climate variability and change? We make the case that a route to addressing the challenges of climate change in Africa rests with the improved management of climate variability. We start by discussing the constraints on climate science and how they might be overcome. We explain why the optimal management of activities directly influenced by interannual climate variability (which include the development of scientific capacity) has the potential to serve as a forerunner to engagement in the wider issue of climate change. We show this both from the perspective of the climate system and the institutions that engage with climate issues. We end with a thought experiment that tests the benefits of linking climate variability and climate change in the setting of smallholder farmers in Limpopo Province, South Africa.

A test bed for new seasonal hydrologic forecasting approaches in the western united states

Abstract: An experimental forecast system based on modern hydrologic models facilitates the evaluation of data assimilation methods, ensemble climate forecasts, and dissemination of visual nowcast and forecast products in ways not possible with current operational methods.

Improving Global Analysis and Forecasting with AIRS

Abstract: AMERICAN METEOROLOGICAL SOCIETY | 891 AFFILIATIONS : LE MARSHALL, JUNG, DERBER, TREADON, LORD, GOLDBERG, WOLF, LIU, JOINER, WOOLLEN, TODLING, VAN DELST, AND TAHARA—NASA, NOAA, and U.S. Department of Defense Joint Center for Satellite Data Assimilation, Camp Springs, Maryland; CHAHINE—NASA Jet Propulsion Laboratory, Pasadena, California CORRESPONDING AUTHOR: John Le Marshall, Joint Center for Satellite Data Assimilation, NOAA Science Center, 5200 Auth Road, Camp Springs, MD 20746 E-mail: John.Lemarshall@noaa.gov

REFORECASTS An Important Dataset for Improving Weather Predictions

Abstract: A “reforecast” (retrospective forecast) dataset has been developed. This dataset is comprised of a 15-member ensemble run out to a 2-week lead. Forecasts have been run every day from 0000 UTC initial conditions from 1979 to the present. The model is a 1998 version of the National Centers for Environmental Prediction's (NCEP's) Global Forecast System (GFS) at T62 resolution. The 15 initial conditions consist of a reanalysis and seven pairs of bred modes. This dataset facilitates a number of applications that were heretofore impossible. Model errors can be diagnosed from the past forecasts and corrected, thereby dramatically increasing the forecast skill. For example, calibrated precipitation forecasts over the United States based on the 1998 reforecast model are more skillful than precipitation forecasts from the 2002 higher-resolution version of the NCEP GFS. Other applications are also demonstrated, such as the diagnosis of the bias for model development and an identification of the most predictable patt...

Detailed Simulations of Atmospheric Flow and Dispersion in Downtown Manhattan: An Application of Five Computational Fluid Dynamics Models

Abstract: Computational fluid dynamics (CFD) model simulations of urban boundary layers have improved in speed and accuracy so that they are useful in assisting in planning emergency response activities related to releases of chemical or biological agents into the atmosphere in large cities such as New York, New York. In this paper, five CFD models [CFD-Urban, Finite Element Flow (FEFLO), Finite Element Model in 3D and Massively-Parallel version (FEM3MP), FLACS, and FLUENT–Environmental Protection Agency (FLUENT-EPA)] have been applied to the same 3D building data and geographic domain in Manhattan, using approximately the same wind input conditions. Wind flow observations are available from the Madison Square Garden 2005 (MSG05) field experiment. Plots of the CFD models' simulations and the observations of near-surface wind fields lead to the qualitative conclusion that the models generally agree with each other and with field observations over most parts of the computational domain, within typical atmosp...

The Intensity Forecasting Experiment: A NOAA Multiyear Field Program for Improving Tropical Cyclone Intensity Forecasts

Abstract: In 2005, NOAA's Hurricane Research Division (HRD), part of the Atlantic Oceanographic and Meteorological Laboratory, began a multiyear experiment called the Intensity Forecasting Experiment (IFEX). By emphasizing a partnership among NOAA's HRD, Environmental Modeling Center (EMC), National Hurricane Center (NHC), Aircraft Operations Center (AOC), and National Environmental Satellite Data Information Service (NESDIS), IFEX represents a new approach for conducting hurricane field program operations. IFEX is intended to improve the prediction of tropical cyclone (TC) intensity change by 1) collecting observations that span the TC life cycle in a variety of environments; 2) developing and refining measurement technologies that provide improved real-time monitoring of TC intensity, structure, and environment; and 3) improving the understanding of the physical processes important in intensity change for a TC at all stages of its life cycle. This paper presents a summary of the accomplishments of IFEX d...

Seasonal to Decadal Prediction of Southern African Climate and Its Links with Variability of the Atlantic Ocean

Abstract: A review of the interannual to interdecadal variability of the southern African region and its links with the Atlantic is given. Emphasis is placed on modes such as the Benguela Nĩno that develop within the Atlantic and may have some predictability. Seasonal forecasting and climate prediction efforts within the region are discussed. Most southern African countries rely on a combination of products obtained overseas and simple statistical methods. GCM based forecasts and statistical downscaling of their outputs are used operationally in South Africa and also applied to some neighboring countries. A review of these downscaling efforts and their various applications is given. Research is also taking place into the predictability of quantities such as the onset of the rainy season (which appears to be associated with anomalous South Atlantic anticyclonic ridging) and dry spell frequencies within it. These parameters are often more useful to farmers in the region than forecasting above- or belowaverage seasona...

The NPOESS VIIRS Day/Night Visible Sensor

Abstract: The National Polar-orbiting Operational Environmental Satellite System (NPOESS) will feature the Visible-Infrared Imager-Radiometer Suite (VIIRS), a 22-channel imager that will contribute to nearly half of the NPOESS environmental data records. Included on VIIRS will be the Day/Night band (DNB), a visible channel designed to image the Earth and its atmosphere in all conditions ranging from bright solar illumination, to nocturnal lunar illumination, and negligible external illumination. Drawing heritage from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS) instruments orbiting since the late 1960s, the DNB will be used to detect clouds at night, understand patterns of urban development based on the emissions of cities, monitor fires, and image scenes of snow and ice at the surface of the Earth. Thanks to significant engineering improvements, the DNB will produce superior capabilities to the OLS for a number of new applications.

Hurricane Isabel (2003): New Insights into the Physics of Intense Storms. Part I. Mean Vortex Structure and Maximum Intensity Estimates

Abstract: This study is an observational analysis of the inner-core structure, sea surface temperature, outflow layer, and atmospheric boundary layer of an intense tropical cyclone whose intensity and structure is consistent with recent numerical and theoretical predictions of superintense storms. The findings suggest new scientific challenges for the current understanding of hurricanes. Unprecedented observations of the category-5 Hurricane Isabel (2003) were collected during 12–14 September. This two-part article reports novel dynamic and thermodynamic aspects of the inner-core structure of Isabel on 13 September that were made possible by analysis of these data. Here, a composite of the axisymmetric structure of the inner core and environment of Isabel is estimated using global positioning system dropwindsondes and in situ aircraft data. In Part II, an extreme wind speed observation on the same day is discussed in the context of this work. The axisymmetric data composite suggests a reservoir of high-ent...

Retrieval of Latent Heating from TRMM Measurements

Abstract: Precipitation, in driving the global hydrological cycle, strongly influences the behavior of the Earth's weather and climate systems and is central to their variability. Two-thirds of the global rainfall occurs over the Tropics, which leads to its profound effect on the general circulation of the atmosphere. This is because its energetic equivalent, latent heating (LH), is the tropical convective heat engine's primary fuel source as originally emphasized by Riehl and Malkus (1958). At low latitudes, LH stemming from extended bands of rainfall modulates large-scale zonal and meridional circulations and their consequent mass overturnings (e.g., Hartmann et al. 1984; Hack and Schubert 1990). Also, LH is the principal energy source in the creation, growth, vertical structure, and propagation of long-lived tropical waves (e.g., Puri 1987; Lau and Chan 1988). Moreover, the distinct vertical distribution properties of convective and stratiform LH profiles help influence climatic outcomes via their tight control on large-scale circulations (Lau and Peng 1987; Nakazawa 1988; Sui and Lau 1988; Emanuel et al. 1994; Yanai et al. 2000; Sumi and Nakazawa 2002; Schumacher et al. 2004). The purpose of this paper is to describe how LH profiles are being derived from satellite precipitation rate retrievals, focusing on those being made with Tropical Rainfall Measuring Mission (TRMM) satellite measurements.

Recent Trends in Cloudiness over the United States: A Tale of Monitoring Inadequacies.

Abstract: Automated Surface Observation Systems (ASOS) were widely introduced to replace manned weather stations around the mid-1990s over North America and other parts of the world. While laser beam ceilometers of the ASOS in North America measure overhead clouds within the lower 3.6 km of the atmosphere, they do not contain cloud-type and opacity information and are not comparable with previous cloud records. However, a network of 124 U.S. military weather stations with continuous human observations provides useful information of total cloud cover over the contiguous United States, thus lessening the disruption caused by the ASOS. Analyses of the military cloud data suggest an increasing trend (∼1.4% of the sky cover per decade) in U.S. total cloud cover from 1976 to 2004, with increases over most of the country except the Northwest, although large uncertainties exist because of sparse spatial sampling. Thus, inadequacies exist in surface observations of global cloud amounts and types, especially over th...

THE HURRICANE RAINBAND AND INTENSITY CHANGE EXPERIMENT Observations and Modeling of Hurricanes Katrina, Ophelia, and Rita

Abstract: The Hurricane Rainband and Intensity Change Experiment (RAINEX) used three P3 aircraft aided by high-resolution numerical modeling and satellite communications to investigate the 2005 Hurricanes Katrina, Ophelia, and Rita. The aim was to increase the understanding of tropical cyclone intensity change by interactions between a tropical cyclone's inner core and rainbands. All three aircraft had dual-Doppler radars, with the Electra Doppler Radar (ELDORA) on board the Naval Research Laboratory's P3 aircraft, providing particularly detailed Doppler radar data. Numerical model forecasts helped plan the aircraft missions, and innovative communications and data transfer in real time allowed the flights to be coordinated from a ground-based operations center. The P3 aircraft released approximately 600 dropsondes in locations targeted for optimal coordination with the Doppler radar data, as guided by the operations center. The storms were observed in all stages of development, from tropical depression to category ...

Research Needs and Directions of Regional Climate Modeling Using WRF and CCSM

Abstract: In final form 12 September 2006 ©2006 American Meteorological Society limate varies across a wide range of temporal and spatial scales. Yet, climate modeling has long been approached using global models that can resolve only the broader scales of atmospheric processes and their interactions with land, ocean, and sea ice. Clearly, large-scale climate determines the environment for mesoscale and microscale processes that govern the weather and local climate, but, likewise, processes that occur at the regional scale may have significant impacts on the large-scale circulation. Resolving such scale interactions will lead to a muchimproved understanding of how climate both influences and is influenced by human activities. Since October 2003, the National Center for Atmospheric Research (NCAR) has supported an effort to develop regional climate modeling capability using the Weather Research and Forecasting (WRF) model (see information online at www.wrfmodel.org/index.php) and the Community Climate System Model (CCSM) (information online at www. ccsm.ucar.edu/models). The goal is to develop a next-generation community Regional Climate Model (RCM) that can address both downscaling and upscaling issues in climate modeling. Downscaling is the process of deriving regional climate information based on large-scale climate conditions. Both dynamical and statistical downscaling methods have been used to produce regional climate change scenarios; however, their resolution and physical fidelity are considered inadequate. Hence, the global change community has expressed a strong demand for improved regional climate information to explore the implications of adaptation and mitigation and assess climate change impacts (see information online at www.climatescience. gov/events/workshop2002/). Upscaling encapsulates the aggregate effects of small-scale physical and dynamical processes on Research Needs and Directions of Regional Climate Modeling Using WRF and CCSM

Land Surface Microwave Emissivities over the Globe for a Decade

Abstract: Microwave land surface emissivities have been calculated over the globe for ∼10 yr between 19 and 85 GHz at 53° incidence angle for both orthogonal polarizations, using satellite observations from the Special Sensor Microwave Imager (SSM/I). Ancillary data (IR satellite observations and meteorological reanalysis) help remove the contribution from the atmosphere, clouds, and rain from the measured satellite signal and separate surface temperature from emissivity variations. The method to calculate the emissivity is general and can be applied to other sensors. The monthly mean emissivities are available for the community, with a 0.25° × 0.25° spatial resolution. The emissivities are sensitive to variations of the vegetation density, the soil moisture, the presence of standing water at the surface, or the snow behavior, and can help characterize the land surface properties. These emissivities (not illustrated in this paper) also allow for improved atmospheric retrieval over land and can help evaluat...

Hurricanes and Global Warming— Potential Linkages and Consequences

Abstract: he potential relationships between tropical cyclones and global climate change are scientifically and socially complex, with great implications for society The exceptional nature of the 2005 North Atlantic hurricane season alone provides great incentives for better understanding the full range of interactions and causes and effects thereof The 2005 season saw the largest number (27) of named storms (sustained winds over 17 m s–1) and the largest number (14) of hurricanes (sustained winds over 33 m s–1), and it was the only year with three category 5 storms (maximum sustained winds over 67 m s–1) Also recorded was the most intense storm on record (Wilma, minimum pressure 882 hPa), the most intense storm ever in the Gulf of Mexico (Rita, 897 hPa), and the most costly storm on record (Katrina; some estimates put the cost of Katrina at as high as $200 billion; see information online at wwwrmscom/Publications/ KatrinaReport_LessonsandImplicationspdf) (Please see wwwncdcnoaagov/oa/climate/research/2005/ hurricanes05html for additional details) The climate is in the process of a rapid warming, caused in part by human activities, including emission of greenhouse gases (GHGs) and aerosols, and changes in land use (Houghton et al 2001; Karl and Trenberth 2003) These climate changes may well be changing the properties of tropical cyclones, yet the potential relationships between climate change and tropical cyclones and the consequences for humans have been downplayed or dismissed by a number of recent articles, testimonies, and press releases (eg, Michaels et al 2005;1 Pielke et al 2005; Mayfield 2005) For example, the recent article with the allencompassing title “Hurricanes and global warming” by Pielke et al (2005) raises several important points, yet it is incomplete and misleading because it 1) omits any mention of several of the most important aspects of the potential relationships between hurricanes and global warming, including rainfall, sea level, and storm surge; 2) leaves the impression that there is no significant connection between recent climate change caused by human activities and hurricane characteristics and impacts; and 3) does not take full account of the significance of recently identified trends and variations in tropical storms in causing impacts as compared to increasing societal vulnerability In a similar vein, public statements and testimonies by prominent hurricane forecasters have denied or minimized important connections between global warming and tropical cyclones, attributing interannual variations in tropical cyclones only to natural variability (eg, Mayfield 2005) It is true that society’s vulnerability to hurricane damage is increasing rapidly, predominantly because of the rise in population and property values near

NOMADS A Climate and Weather Model Archive at the National Oceanic and Atmospheric Administration

Abstract: An online archive of real-time and historical weather and climate model output and observationaldata is now available from the National Oceanic and Atmospheric Administration (NOAA). This archive, known asthe NOAA National Operational Model Archive and Distribution System (NOMADS), was jointly initiated in 2001 by the National Climatic Data Center (NCDC), the National Centers for Environmental Prediction (NCEP), and the Geophysical Fluid Dynamics Laboratory (GFDL). At present, NOMADS provides access to realtime and historical 1) numerical weather prediction (NWP) model input and output, 2) GFDL's Coupled Global Climate Models (CGCM) output, 3) global and regional reanalysis from NCEP and the National Center for Atmospheric Research (NCAR), and 4) limited surface, upper-air, and satellite observational datasets from NCDC and NOAA's National Ocean Data Center (NODC) and Earth System Research Laboratory [formerly the Forecast System Laboratory (FSL)]. NOMADS is but one of many similar data services ...

The name 2004 field campaign and modeling strategy

Abstract: The North American Monsoon Experiment (NAME) is an internationally coordinated process study aimed at determining the sources and limits of predictability of warm-season precipitation over North America. The scientific objectives of NAME are to promote a better understanding and more realistic simulation of warm-season convective processes in complex terrain, intraseasonal variability of the monsoon, and the response of the warm-season atmospheric circulation and precipitation patterns to slowly varying, potentially predictable surface boundary conditions. During the summer of 2004, the NAME community implemented an international (United States, Mexico, Central America), multiagency (NOAA, NASA, NSF, USDA) field experiment called NAME 2004. This article presents early results from the NAME 2004 campaign and describes how the NAME modeling community will leverage the NAME 2004 data to accelerate improvements in warm-season precipitation forecasts for North America.

Probing Finescale Dynamics and Microphysics of Clouds with Helicopter-Borne Measurements

Abstract: Helicopter-based measurements provide an opportunity for probing the finescale dynamics and microphysics of clouds simultaneously in space and time. Due to the low true air speed compared with research aircraft, a helicopter allows for measurements with much higher spatial resolution. To circumvent the influence of the helicopter downwash the autonomous measurement payload Airborne Cloud Turbulence Observation System (ACTOS) is carried as an external cargo 140 m below the helicopter. ACTOS allows for collocated measurements of the dynamical and cloud microphysical parameters with a spatial resolution of better than 10 cm. The interaction between turbulence and cloud microphysical processes is demonstrated using the following two cloud cases from recent helicopter measurements: i) a cumulus cloud with a low degree of turbulence and without strong vertical dynamics, and, in contrast, ii) an actively growing cloud with increased turbulence and stronger updrafts. The turbulence and microphysical measurements ...

Daily Precipitation Grids for South America

Abstract: e are pleased to see the development of new daily precipitation databases, such as that of Liebmann and Allured (2005, hereafter LA2005) Precipitation information at daily resolution is vital for many applied research topics in climatology, ecology, and hydrology The development of a new database for South America is particularly welcome, because this important region has received limited attention with regard to precipitation databases (Cook et al 2003) Still, we are troubled that daily precipitation continues to be gridded using approaches that filter out important spatial and probabilistic information The new database produced by LA2005 as well as the Climate Prediction Center’s Unified Raingauge Dataset (URD; Higgins et al 2000) for the contiguous United States use spatial operators that smooth spatial patterns of precipitation and drastically alter the daily precipitation probability distribution Below, we i) discuss the essential problems with filtered daily precipitation products, ii) illustrate these problems by using an example from the midwestern United States, and iii) present solutions that overcome many of these problems As noted in their section on “Quality of gridded data,” LA2005 acknowledge some of the problems with the spatial averaging of daily precipitation What LA2005 refer to as “singularities” or “noise,” however, is what many scientists refer to as an important climatological or hydrological event Knowing more about the spatial distribution and historical probabilities of these events is essential to understanding their causes and impacts By using averages of daily precipitation data within grid circles (LA2005) or the Cressman spatial filter (Higgins et al 2000), much of the information that is important at the daily time scale has been removed Smoothed daily precipitation is perhaps more useful for modeling applications, but a high-resolution gridded product that has realistic spatial and probabilistic information can be smoothed and transferred to a model grid of any size To illustrate the problems with the simple averaging and smoothing of daily precipitation data, we have applied the methods of LA2005 to data from south-central Indiana (a grid point centered on 39°N, 86°W; precipitation observations from the US Daily Historical Climate Network) When daily precipitation data are averaged or smoothed, a grid point that has precipitation occurring at any nearby precipitation will have a precipitation value As a result, precipitation frequency is vastly altered by the averaging process For the south-central Indiana example, precipitation station observations produce frequencies that range from 24% to 35% (ie, precipitation occurs on 24%–35% of the days), depending on season and location A 1° grid point with simple averaging of nearby precipitation produces precipitation frequencies of around 45%–52% Larger grids are even worse, due to more stations being averaged When using simple averaging, a 25° grid point in south-central Indiana produces precipitation frequencies of 57%–66% Due to the damping nature of the spatial averaging process, the entire precipitation probability distribution is shifted toward more frequent, smaller precipitation events As a result, extreme precipitation events (such as those associated with 10or 50-year return periods) are vastly smaller when data are gridded using averaging The following two approaches are available to remedy the problems of excessively smoothed daily precipitation grids: i) simulation-based approaches and ii) unconventional spatial interpolation methods An example of a simulation-based approach is a stochastic weather generator, as used in the VEMAP2 database (Kittel et al 2004) The advantage of a simulation-based approach is that the precipitation probability distribution is preserved; however, the simulation does reduce the utility of the database as a historical record (actual daily precipitation events

The CarboEurope regional experiment strategy

Abstract: Models and observational strategies of carbon exchange need to take into account synoptic and mesoscale transport for correct interpretation of the relation between surface fluxes and atmospheric concentration gradients.