Brant Liebmann

Brant Liebmann

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47
Publications
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Publications

Publications (47)
Article
Southeast Brazil (SE Brazil) is the most densely populated region in Brazil. Previous studies have shown evidence of positive trends in average precipitation and extreme events in a few locations, suggesting the increase in rainfall-related hazards with potential impacts to urbanized areas of SE Brazil. This study provides a comprehensive analysis...
Technical Report
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This chapter provides the climate analysis for the BLM Wyoming Basin Rapid Ecoregional Assessment. It describes the current climate of the Wyoming Basin, the range of potential climate change for the Wyoming Basin, and the reasonably foreseeable climate futures for ecosystems as they are understood now. The “reasonably foreseeable” concept is model...
Article
Full-text available
In eastern East Africa (the southern Ethiopia, eastern Kenya and southern Somalia region), poor boreal spring (long wet season) rains in 1999, 2000, 2004, 2007, 2008, 2009, and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision...
Article
This article evaluates the ability of the Coordinated Regional Downscaling Experiment (CORDEX) regional climate models (RCMs) in simulating monthly rainfall variation during the austral summer half year (October to March) over southern Africa, the timing of the rainy season and the relative frequencies of rainfall events of varying intensities. The...
Article
Full-text available
In southern Ethiopia, Eastern Kenya, and southern Somalia, poor boreal spring rains in 1999, 2000, 2004, 2007, 2008, 2009, and 2011 contributed to severe food insecurity and high levels of malnutrition. Predicting rainfall deficits in this region on seasonal and decadal time frames can help decision makers implement disaster risk reduction measures...
Article
Full-text available
We have observed that the dry-season length (DSL) has increased over southern Amazonia since 1979, primarily owing to a delay of its ending dates (dry-season end, DSE), and is accompanied by a prolonged fire season. A poleward shift of the subtropical jet over South America and an increase of local convective inhibition energy in austral winter (Ju...
Article
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Two new Global Forecast System (Environmental Modeling Center 2003) version 2 (GFS) were used to examine the question of whether SSTs caused the poor 2012 March-May eastern East African rains and increased the frequency of dry events over the past decade. The results indicate that non-ENSO SST variations substantially increased the risk of a dry ev...
Article
Full-text available
Intraseasonal (IS) variability in South America is analyzed during the cold season using 10–90 day bandpass filtered OLR anomalies (FOLR). IS variability explains a large percentage of variance with maximum values over Paraguay, northeastern Argentina, and southern Brazil. The leading pattern of FOLR, as isolated from an EOF analysis, (Cold Season...
Article
This paper discusses uncertainties in model projections of summer drying in the Euro-Mediterranean region related to errors and uncertainties in the simulation of the summer NAO (SNAO). The SNAO is the leading mode of summer SLP variability in the North Atlantic/European sector and modulates precipitation not only in the vicinity of the SLP dipole...
Article
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The South American monsoon system (SAMS) is the most important climatic feature in South America and is characterized by pronounced seasonality in precipitation during the austral summer. This study compares several statistical properties of daily gridded precipitation from different data (1998–2008): 1) Physical Sciences Division (PSD), Earth Syst...
Article
Climate models predict substantial summer precipitation reductions in Europe and the Mediterranean region in the twenty-first century, but the extent to which these models correctly represent the mechanisms of summertime precipitation in this region is uncertain. Here an analysis is conducted to compare the observed and simulated impacts of the dom...
Article
Climate simulations for the XXIst century project pronounced precipitation decreases in the entire Mediterranean region, particularly in summer. This projected summer drying is quite consistent across models, which makes this projection particularly reliable, but only in terms of model signal-to-noise. Overall, however, there is little observationa...
Article
Full-text available
The South American monsoon system (SAMS) is the most important climatic feature in South America and is characterized by pronounced seasonality in precipitation. This study uses the National Centers for Environmental Prediction Climate Forecast System, reforecasts version 2 (CFSRv2), to investigate the skill of probabilistic forecasts of onset and...
Article
Full-text available
This paper reviews recent progress made in our understanding of the functioning and variability of the South American Monsoon System (SAMS) on time scales varying from synoptic to long-term variability and climate change. The SAMS contains one of the most prominent summertime climate patterns in South America, featuring a strong seasonal variabilit...
Article
The South American Monsoon System (SAMS) is the most important climatic feature in South America and affects millions of people. SAMS is characterized by pronounced seasonality in rainfall, circulation and moisture transport. The South Atlantic convergence zone (SACZ) is a component of SAMS and plays significant role for the variability of precipit...
Article
Full-text available
Annual global surface temperature and global land surface temperature trends are calculated for all possible periods of the historical record between 1850 and 2009. Two-dimensional parameter diagrams show the critical influence of the choice of start and end years on the calculated trend and associated temperature changes and suggest time scales re...
Article
Analysis of twenty-first century projections indicate substantial drying over the American Southwest and the potential for ``Dust Bowl'' conditions to be the norm by the middle of century. Closer examination of monthly precipitation data from the CMIP3 models indicates that the annual cycle is actually amplified over the North American Monsoon (NAM...
Article
Full-text available
IntraseasonalandinterannualvariabilityofextremewetanddryanomaliesoversoutheasternBrazilandthe western subtropical South Atlantic Ocean are investigated. Precipitation data are obtained from the Global Precipitation Climatology Project (GPCP) in pentads during 23 austral summers (December-February 1979/ 80-2001/02). Extreme wet (dry) events are defi...
Article
Full-text available
Convectively coupled Kelvin waves over the South American continent are examined through the use of temporal and spatial filtering of reanalysis, satellite, and gridded rainfall data. They are most prominent from November to April, the season analyzed herein. The following two types of events are isolated: those that result from preexisting Kelvin...
Article
Full-text available
Daily precipitation data from three stations in subtropical Argentina are used to describe intraseasonal variability (20–90 days) during the austral summer. This variability is compared locally and regionally with that present in outgoing longwave radiation (OLR) data, in order to evaluate the performance of this variable as a proxy for convection...
Article
Onset and end of the wet season are examined using daily rainfall observations obtained from gauges. At most grid points, composite and interannual variations of onset and end are well-defined, although among individual stations that make up a grid average, variability is large. The wet season rain rate is a combination of the rainy day average, wh...
Article
Full-text available
The objective of this work is to provide a detailed description of the onset of the South American Monsoon based on precipitation observations available over tropical and subtropical South America. The analysis was also performed using outgoing longwave radiation (OLR) data in order to assess the ability of this particular dataset to reproduce the...
Article
Atmospheric Kelvin waves are prominent disturbances within the eastern tropical Pacific. Convectively coupled Kelvin waves modulate a substantial portion of the rainfall within the ITCZ. The convective envelopes of these waves move eastward at between 15-18 m/s on average, and are composed primarily of westward propagating features within them. Man...
Article
Atmospheric Kelvin waves are shown to be important disturbances within Amazonia and the ITCZ over the Pacific and Atlantic. These disturbances propagate eastward at around 15 m/s and have a substantial impact on deep convection, as measured by rain gauges and satellite irradiance. During warm ENSO events, Kelvin wave activity is enhanced in the Pac...
Article
A gridded dataset of historical daily precipitation for South America is now available. The data are combined in a simple manner into daily 1° and 2.5° gridded fields for the period 1940-2003. The fields provided are daily precipitation totals and station counts. The counts give the number of stations that are included in each grid point for each d...
Article
Full-text available
The most severe drought in tropical South America during the 20 th century occurred in 1926. This extreme El Nino year is further documented anecdotally, in an update of the river stage observations at Manaus, and in annual rainfall records. The annual rainfall anomaly is an east-west dipole over tropical South America, with drought to the west ove...
Article
Full-text available
1] Seasonal rainfall prediction, while useful for some planning, does not have the temporal resolution required for many applications. Information regarding sub-seasonal variations in rainfall is often needed for water management and agriculture sector decisions. Daily station observations are used to characterize rainfall frequency and intensity a...
Article
Full-text available
The characteristics of intensity, geographical location, and persistence of the South Atlantic convergence zone (SACZ) during the austral summer are investigated. Intensity and spatial features of the SACZ are identified by performing a factor analysis of structural properties of outgoing longwave radiation (OLR) data. The first two leading factors...
Article
Full-text available
¶An examination is made of the relationships between circulation and convection over South America as related to strong cooling in southern and southeastern Brazil during austral wintertime. Correlations between sub monthly (2–30 days) near-surface air temperature in southeastern Brazil reveal the preferred path of a quasi-stationary Rossby wave im...
Article
Full-text available
Interannual variability of seasonal rainfall in the Brazilian Amazon basin is examined in context of its relationship to sea surface temperatures in the tropical Pacific and Atlantic Oceans. Linear correlations reveal strong relationships, but rainfall patterns are of regional scale. Areas of rainfall exhibiting strong relationships with SST are co...
Article
Full-text available
The climatology and interannual variability of heavy, or "extreme," precipitation events are studied, using station data from the state of Sao Paulo, Brazil. An extreme event is defined at each station when daily rainfall exceeds a certain percent of its seasonal or annual mean. It is found that these events occur mainly from November to March and...
Article
In subtropical Argentina, Paraguay and southern Brazil, precipitation is most abundant during summer but its interannual variability is large. At this time a zone of low-level convergence, upper-level divergence, and intense convection is developed to the north of this area. This feature is known as the South Atlantic convergence zone (SACZ) and se...
Article
We propose a mechanism that may contribute to observed near-2-day variability in cloudiness observed over the equatorial Pacific Ocean during active phases of the Madden-Julian oscillation (MJO). Our hypothesis is motivated by the following already-established results: 1) Embedded within the MJO are eastward-propagating ‘superclusters’ (Nakazawa, 1...
Article
Any discussion of intraseasonal and interannual variability in the atmosphere must presume a reliable assessment of the observed variability. In spite of continued improvements in observing systems, quality control techniques, and data analysis schemes, however, and also because of them, this assessment remains difficult in the tropics.In this pape...
Article
We examine the persistence of outgoing longwave radiation (OLR) anomalies in the tropics on many different time scales during 1974-86. We calculate "one-lag autocorrelations' by constructing nonoverlapping 1-, 15-, and 60-day averages and calculating the correlation at every grid point between every time average and the following average for the en...
Article
The annual variation of the diurnal cycle of outgoing longwave radiation (OLR) is examined. Our results are based on the climatological amplitude and phase of the first diurnal harmonic for each month. The diurnal harmonic was extracted from a composite daily cycle from several polar orbiting satellites that flew in different years with ten differe...
Article
Outgoing longwave radiation (OLR) derived from narrow band AVHRR measurements from the NOAA operational satellite series is compared with OLR measured by satellites in the Earth Radiation Budget Experiment. Although a slight nonlinearity in the comparison is found over the ocean region, the standard deviation of the data is within 2 percent. It is...
Article
The work presented is a correlative study of the interaction between large-scale tropical convection and midlatitude wind anomalies, and the tropical wind field on subseasonal time scales. Outgoing longwave radiation (OLR) is used as a proxy for convection. Correlations are calculated from six years of 5-day averaged data for the December-February...
Article
Eight Northern Hemisphere winters of five- and ten-day average midlatitude 500 mb heights and tropical outgoing IR are used in a correlative study of tropical-midlatitude interaction. The seasonal cycle and interannual variability are removed so that only intraseasonal variability remains. Results indicate that energy predominantly propagates from...
Article
Interannual variability of outgoing IR in the tropical Pacific Ocean is studied using measurements derived from the NOAA scanning radiometer. In addition to the usual mean maps, seasonal anomaly maps are constructed from June, July, August 1974-December 1977, January, February 1978. These IR anomalies are closely related to changes in convective cl...
Article
We first estimate the vertically integrated atmospheric diabatic heating rate from two different analyses from the FGGE year. Then we obtain a dynamically consistent 3-d divergent circulation of each of the analyses from the vorticity and mass budgets by using an iterative procedure developed by Sardeshmukh (1992). The dynamically consistent diverg...
Article
Full-text available
Considerable attention has recently focused on low-frequency variability of precipitation over southeastern South America (Nogués-Paegle et al., 2002 and Barros et al., 2002). The temporal and spatial variability of the South American low-level jet east of the Andes (SALLJ) is still not well-understood, in part because the available limited upper-a...

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