Search Results

You are looking at 1 - 10 of 13 items for :

  • U.S. CLIVAR Drought x
  • All content x
Clear All
Matías Méndez and Víctor Magaña

analysis of prolonged drought in Mexico should focus on Northern Hemisphere (NH) summer rains. During this season, trade winds and easterly waves produce moisture flux from the Americas warm pools into continental Mesoamerica (i.e., the geographical area that extends from central Mexico down through Central America) ( Mestas-Nuñez et al. 2002 ; Wu et al. 2009 ). In the northern part of Mexico subsidence persists most of the year. It is only when easterly waves (EW) or tropical cyclones (TC) force

Full access
Scott J. Weaver, Siegfried Schubert, and Hailan Wang

28°C isotherm, suggesting that the model response is to generate precipitation anomalies where the area of warmest SST is perturbed. Given that the idealized SST patterns and in particular a warm Pacific and cold Atlantic appears important in generating a regional SLP anomaly that can strengthen the GPLLJ and central U.S. precipitation it is of interest to analyze the regional moisture flux response. Figure 13 shows the column-integrated (1000–200 hPa) moisture fluxes (arrows) and their

Full access
Renu Joseph and Ning Zeng

–Southern Oscillation (ENSO) on vegetation and the carbon cycle ( Zeng et al. 2005 ; Qian et al. 2008 ). The model consists of the global version of the atmospheric model Quasi-equilibrium Tropical Circulation Model (QTCM) ( Neelin and Zeng 2000 ; Zeng et al. 2000 ), which simulates a reasonable seasonal climate compared to observations in the tropics and midlatitudes. The QTCM is coupled to the simple-land model ( Zeng et al. 2000 ), and a slab mixed layer ocean model with Q-flux to represent the effects of

Full access
Kingtse C. Mo, Jae-Kyung E. Schemm, and Soo-Hyun Yoo

were extracted. For the GFS runs, the vertically integrated moisture flux (qflux) and flux divergence D ( Q ) were derived from cross products (qu and qv) at all levels. The GFS is used as an example to describe the procedures used to calculate the frequency of drought occurrence and anomalies. We pooled P from nine experiments together to form a time series of 36 × 12 × 9 months. The total SSTAs averaged over the nine experiments are zero. To determine the impact of SSTAs on drought, we

Full access
Bradfield Lyon

land to be negatively correlated is well known ( Madden and Williams 1978 ; Huang and van den Dool 1993 ; Trenberth and Shea 2005 ; Déry and Wood 2005 , and many others). The physical linkage is via the surface energy budget with below-average precipitation typically associated with reduced soil moisture and increased insolation with both favoring an increase in the surface sensible heat flux and therefore higher surface air temperature. The full picture is somewhat more nuanced, as it is the

Full access
Alfredo Ruiz-Barradas and Sumant Nigam

, the models used, the SST forcing, and an overview of the results. The hierarchy of interactions that give rise to precipitation variability within a model, that is, local land surface–atmosphere versus remote SST–moisture fluxes, plays a crucial role in the simulation of regional summer hydroclimate variability. Regional hydroclimate over the central United States strongly depends on the moisture transport from the Gulf of Mexico via the Great Plains low-level jet, particularly in the summer

Full access
Alfredo Ruiz-Barradas and Sumant Nigam

-Barradas and Nigam 2005 , 2006 ). Simulations of the twentieth-century climate based on some models from international research centers, which are part of the CMIP3 multimodel dataset ( Meehl et al. 2007 ), revealed difficulties in two aspects of their simulations: the observed distribution of climatological summer precipitation and the observed link between precipitation variability and moisture flux convergence over the central United States ( Ruiz-Barradas and Nigam 2006 ). While it is likely that at

Full access
Rachel R. McCrary and David A. Randall

precipitation, the annual cycle of evapotranspiration averaged over the Great Plains region experiences large seasonal variations ( Fig. 1b ). Minimum evapotranspiration rates occur in fall and winter when both water and energy availability (measured here as the shortwave radiative flux) at the surface are limited ( Figs. 1a,c ). Evapotranspiration rates then increase in spring and summer when both water and energy at the surface increase. Throughout the entire seasonal cycle, both CM2.0 and HadCM3

Full access
Kerry H. Cook and Edward K. Vizy

Pacific coast of moisture to form the MSD intraseasonal variation. At the same time, the strengthening of the jet enhances moisture flux divergence to the east, which leads to a midsummer rainfall minimum over the Caribbean ( Muñoz et al. 2008 ). On interannual time scales, the CLLJ strength and Caribbean rainfall rates are anticorrelated. Although CLLJ wind speeds are similar in boreal summer and boreal winter, there is a distinct difference in the large-scale context of the jet in these seasons. One

Full access
Yochanan Kushnir, Richard Seager, Mingfang Ting, Naomi Naik, and Jennifer Nakamura

(cooling) of the tropical atmosphere; this causes the maximum in the westerlies to move equatorward (poleward) of its mean position and change the pattern of baroclinic eddy momentum flux convergence in the upper troposphere, thus affecting the mean meridional circulation (MMC). The result is a zonally and hemispherically symmetric anomalous ascent (decent) in the midlatitudes, which in the Northern Hemisphere enhances (suppresses) precipitation in the latitude band of 25°–45°N. In winter, the

Full access