How anthropogenic climate change will affect hydroclimate in the arid regions of southwestern North America has implications for allocation water resources and course regional development. Here we show that there is a broad consensus among models this region dry 21st century transition to more should already be under way. If these are correct, levels aridity recent multiyear drought or Dust Bowl 1950s droughts become new climatology American Southwest within time frame years decades.

Inspired by paleoclimate evidence that much past climate change has been symmetric about the equator, causes of hemispherically variability in recent observational record are examined using National Centers for Environmental Prediction–National Center Atmospheric Research reanalysis dataset and numerical models. It was found dominant cause is El Niño–Southern Oscillation. During an Niño event Tropics warm at all longitudes subtropical jets both hemispheres strengthen on their equatorward...

Recent studies have pointed out the impact of stratosphere on troposphere by dynamic coupling. In present paper, observational evidence for an effect downward planetary wave reflection in Northern Hemisphere tropospheric waves is given combining statistical and dynamical diagnostics. A time-lagged singular value decomposition analysis applied to daily stratospheric height fields recomposed a single zonal wavenumber. geometry diagnostic propagation characteristics that separates index...

The patterns of precipitation anomalies forced by the El Niño–Southern Oscillation during northern hemisphere winter and spring are remarkably hemispherically symmetric and, in midlatitudes, have a prominent zonally component. Observations global variability moisture budget within atmospheric reanalyses examined to argue that component is caused interactions between transient eddies tropically-forced changes subtropical jets. During Niño events jets strengthen each shift equatorward. Changes...

Abstract The stratosphere contains ~17% of Earth’s atmospheric mass, but its existence was unknown until 1902. In the following decades our knowledge grew gradually as more observations were made. 1913 ozone layer, which protects life from harmful ultraviolet radiation, discovered. From and water vapor observations, a first basic idea stratospheric general circulation put forward. Since 1950s mesosphere has expanded rapidly, importance this region in climate system become clear. With several...

Abstract The Hadley circulation (HC) has widened in recent decades, and it widens as the climate warms simulations. But mechanisms responsible for widening remain unclear, simulations is generally smaller than observed. To identify HC model–observation discrepancies, this study analyzes how interannual variations of tropical-mean temperatures meridional temperature gradients influence width. Changes mean are part any global warming signal, whereas changes primarily associated with ENSO....

While the Atlantic Ocean is ventilated by high-latitude deep water formation and exhibits a pole-to-pole overturning circulation, Pacific does not. This asymmetric global pattern has persisted for past 2–3 million years, with evidence different ventilation modes in deeper past. In current climate, Atlantic-Pacific asymmetry occurs because more saline, enabling convection. To what extent salinity contrast between two basins dominated atmospheric processes (larger net evaporation over...

Abstract Wave and zonal mean features of the downward dynamic coupling between stratosphere troposphere are compared by applying a time-lagged singular value decomposition analysis to Northern Hemisphere height fields decomposed into its deviations. It is found that both wave components contribute interaction, with 1 (due reflection) dominating on short time scale (up 12 days) wave–mean-flow interaction) longer scale. further shown two processes dominate during different years, depending...

Abstract El Niño–Southern Oscillation (ENSO) related precipitation anomalies in North America are to changes the paths of storm systems across Pacific Ocean, with a more southern route into southwestern during Niños and northern Northwest La Niñas. Daily reanalysis data analyzed confirm these changes. Seasonal mean upper tropospheric eddy statistics show, for (La Niñas), pattern that is shifted southward (northward) compared climatology. Paths coherent phase propagation transient eddies wave...

Abstract The nature of downward wave coupling between the stratosphere and troposphere in both hemispheres is analyzed using 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40) dataset. Downward occurs when planetary waves reflected impact troposphere, it distinct from zonal-mean coupling, which results dissipation its subsequent on flow. Cross-spectral correlation analysis geometry diagnostics reveal that wave-1 presence a vertical reflecting surface...

Abstract Extreme large‐scale North American cold events are associated with strong undulations in the tropospheric jet stream which bring polar air southward over continent. Here we propose that these part of Circumglobal Teleconnection Pattern—a pair zonally oriented waves zonal wave number 5 quadrature each other. While Pacific/North pattern is first circumglobal pattern, extreme second pattern. The 300 hPa meridional wind and surface temperature anomalies packet similar to those strongest...

Abstract. Rossby wave-breaking events describe the last stage in life cycle of baroclinic atmospheric disturbances. These breaking can strongly influence large-scale circulation and are also related to weather extremes such as heat waves, blocking, extreme precipitation events. Nonetheless, a complete understanding synoptic-scale dynamics involved with is still absent. For example, it not clear how well theoretical experiments, which use specified initial perturbation single zonal wavenumber...

Abstract The distribution of near-surface and tropospheric temperature variability in midlatitudes is distinguishable from a Gaussian meteorological reanalysis data; consistent with this, warm extremes occur preferentially poleward the location cold extremes. To understand factors that drive this non-Gaussianity, dry general circulation model simple Lagrangian advection are used to investigate connections between dynamical processes occurrence extreme events near surface. non-Gaussianity...

The effects of an upper-stratospheric reflecting surface on the vertical structure stratospheric planetary waves are considered. A diagnostic basic-state wave propagation characteristics, which is particularly useful for determining existence and location turning surfaces meridional propagation, developed. used a more accurate indicator regions than index refraction because it diagnoses separately. tested series simple models, both steady state time dependent. It found that waveguide sets...

The effects of variations in jet width on the downstream growth baroclinic waves are studied, using a simple quasigeostrophic model with vertically varying basic state and variable channel width, as well simplified primitive equation that varies latitude height. This study is motivated by observations midwinter Pacific storm track weaker narrower during years when strong. linear models able to reproduce observed decrease spatial rate shear, if narrowing accounted for assuming it decreases...

The interannual variations in the Northern Hemisphere storm tracks during 1949–99 based on unassimilated radiosonde data are examined and compared to similarly derived quantities using NCEP–NCAR reanalysis at sonde times locations. This is done with motivation of determining extent which track real. Emphasis placed assessing previous findings, data, that both intensified from 1960s 1990s much intensification occurring early 1970s, Atlantic Pacific significantly correlated. Sonde suggest...

We examine the differences between observed stratospheric vertical wave reflection and absorption events, which differ in that wave‐induced deceleration remains confined to upper levels former. The two types of events signify winter dynamics, associated with different downward coupling troposphere. Using time‐lagged composites, we find main factor influencing event will occur is duration, time, upward pulse activity entering stratosphere from Short pulses accelerate flow at their trailing...

Abstract Downward wave coupling occurs when an upward-propagating planetary from the troposphere decelerates flow in upper stratosphere and forms a downward reflecting surface that redirects waves back to troposphere. To test this mechanism potential factors influencing coupling, three 145-yr sensitivity simulations with NCAR’s Community Earth System Model [CESM1(WACCM)], state-of-the-art high-top chemistry–climate model, are analyzed. The results show quasi-biennial oscillation (QBO) SST...

Abstract An abrupt transition from a merged jet regime to subtropical is analyzed using two-layer modified quasigeostrophic (QG) spherical model. Unlike the common version of QG models, this model includes advection zonal mean momentum by ageostrophic meridional circulation, allowing for relatively realistic balance in tropics and subtropics. The single inside Ferrel cell created merging eddy-driven jets, mainly thermally driven at Hadley edge. maintenance each type depends on dominant...

Abstract. Atmospheric jet streams are typically separated into primarily “eddy-driven” (or polar-front) jets and “thermally driven” subtropical) jets. Some regions also display “merged” jets, resulting from the (quasi-)collocation of eddy generation with subtropical jet. The different locations driving mechanisms these arise very underlying result in characteristics. Here, we link current understanding dynamical maintenance mechanisms, mostly arising conceptual or idealized models, to...

The atmospheric circulation is often decomposed into high- and low- frequency variability. For example, the low-frequency variability in North-Atlantic includes slowly varying weather regimes such as North Atlantic Oscillation, with timescales of weeks. high synoptic systems, which shape our daily fluctuations. interaction among these mediated by Rossby Wave Breaking (RWB) events, involve irreversible breaking dissipation baroclinic waves. To investigate this interaction, a simple RWB recipe...

A moist, idealized model is used to examine the driving influence of deep tropical convection on wintertime subtropical jet. The run with fixed zonally symmetric sea surface temperatures under perpetual solstice conditions. To focus strongest convective activity, daily data re-centered around longitude maximum convection. qualitative picture that emerges suggests in summer hemisphere drives an anomalous localized Hadley cell crosses into winter and a locally strengthened jet downstream via...

A method is presented which allows one to diagnose and analyze Rossby wave resonance along a circum-global midlatitude jet in the framework of inviscid linear barotropic model with beta-plane geometry. Zonally symmetric Gaussian-shaped jets varying amplitude width are specified as basic state. The system forced by pseudo-orography varies sinusoidally zonal direction, has very small meridional extent. Solutions obtained through straightforward numerical methods. strength diagnosed...