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Soumaya Belmecheri, Flurin Babst, Amy R. Hudson, Julio Betancourt, and Valerie Trouet

), resulting in the broad-scale die-off of millions of trees and record wildfires ( Asner et al. 2016 ). The drought also threatened California’s economy and human welfare through diminished hydroelectric power generation and water shortages for both urban and agriculture consumers ( Bartos and Chester 2015 ). In each of these cases, the extreme weather was associated with anomalous and persistent ridging and troughing of the Northern Hemisphere jet stream (NHJ) over North America ( Jensen 2015 ; Yang et

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Mark R. Jury

distinguishing factor; the SW trough has cool-north positive shear ( Kahana et al. 2002 ), while the AEW has warm-north negative shear. Naturally, intertropical convergence between the Hadley cells reaches a northern limit during summer [July–September (JAS)], so moisture can be fed into AEW despite their limited equatorward extent. The SW trough relies on upper kinematic forcing by the subtropical westerly jet stream ( Saaroni et al. 1998 ; Kahana et al. 2004 ; Ziv et al. 2005 ; Tsvieli and Zangvil 2005

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Mark R. Jury

4 , and O 3 were analyzed up to 500 hPa, and the diurnal cycle of MERRA-2 hourly PBL height, near-surface wind speed, and 3-hourly CMORPH rainfall was calculated. Vertical cross-sections of the MERRA-2 meridional circulation and wind vorticity were analyzed for key features, such as the equatorial trough and subtropical jet. The daily time series were ranked, and MERRA-2 near-surface winds were analyzed for the peak episode of 24–26 December 2010, when NO 2 and other trace gas concentrations

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Falko K. Fye, David W. Stahle, and Edward R. Cook

mechanisms of SST forcing of atmospheric circulation. The process of thermal forcing the atmospheric circulation by tropical oceans involves heating of the atmosphere, instability, convective precipitation, latent heat release, and divergent flow in the upper troposphere. The poleward component of this divergent flow is often manifested as the subtropical jet stream and may transfer significant quantities of momentum and moisture into the extratropics. The extratropical response to this influx of energy

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Mark R. Jury and América R. Gaviria Pabón

vectors and upper jet contours and (c) west–east axis (7°–13°S) zonal vectors; vertical motion is exaggerated 50-fold. (d) MODIS AOD 0.550 μ m and southern Amazon index (outlined box). (e) Seasonal aerosol profiles from CALIPSO 0.532- μ m extinction over the southern Amazon index area, with dry season shaded. Table 1. Dataset acronyms and details. MERRA-2 is based on global data assimilation by NASA that provides gridded fields of atmospheric variables, aerosols, and trace gases, coupled with the

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Mark R. Jury

cyclonic circulation near Puerto Rico and a 40 m s −1 westerly jet streak over Venezuela. The upper wave was asymmetrical: 200-mb streamlines were confluent to the west and diffluent to the east of the trough axis on 64°W. Low-level 700-mb southerly flow over the eastern Antilles was fed by tropical Atlantic easterlies. CAPE exceeded 1600 J kg −1 east of the Antilles, where stronger surface winds were noted (cf. Figure 1e ). The surface weather chart for 0000 UTC 25 December 2013 ( Figure 4c ) shows

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Ana M. B. Nunes and John O. Roads

features such as the South American low-level jet (SALLJ), which is characterized by an increase of the horizontal wind speed at lower-troposphere levels along the eastern part of the Andes. Transport of moisture from the Amazon region toward the southern part of South America, and moisture carried out from the Amazon basin, often condenses and precipitates in the region of the SALLJ convergence, producing explosive mesoscale convective complexes downstream of the low-level jet core, with a maximum of

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Sultan Hameed, Henry H. Norwood, Michael Flanagan, Steven Feldstein, and Chien-hsiung Yang

years when the average AIPD index is high, and 2) what is the physical relationship between the Niño-3 index and the Asian bird fallouts? In addressing the first question, research was conducted into the possible relationship between storms associated with large fallouts of Asian birds and the location of the jet stream in the upper troposphere. This effort was motivated by the theoretical relationship between the track taken by storms and the largest values of the local atmospheric refractive index

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Jacqueline J. Shinker

Comrie 1997 ). 3.2. Spatial and temporal patterns of precipitation 3.2.1. Broadscale patterns The broadscale patterns in the annual cycle of precipitation ( Movie 2a ) reflect the large-scale trade-off between Pacific Ocean (winter) and Gulf of Mexico (summer) moisture sources and precipitation-generating mechanisms ( Shinker et al. 2006 ). The winter-dominated precipitation regions are influenced by the Aleutian low in the North Pacific Ocean and the southward shift of the polar jet stream, which

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Richard Seager, Nathan Lis, Jamie Feldman, Mingfang Ting, A. Park Williams, Jennifer Nakamura, Haibo Liu, and Naomi Henderson

a west–east aridity gradient. During summer, there is strong southerly flow as part of the Great Plains low-level jet (LLJ) from the Gulf of Mexico into the Great Plains, as previously noted by Higgins et al. (1999) . This brings moist air into the plains and creates the potential for precipitation. Although the moisture convergence is more widespread in winter than in summer, summer precipitation is generally greater in the plains due to the higher evapotranspiration and recycling ( Seager et

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