Atmospheric Jet Stream Research Articles

Increased light, moderate, and severe clear-air turbulence in response to climate change

Anthropogenic climate change is expected to strengthen the vertical wind shears at aircraft cruising altitudes within the atmospheric jet streams. Such a strengthening would increase the prevalence of the shear instabilities that generate clear-air turbulence. Climate modelling studies have indicated that the amount of moderate-or-greater clear-air turbulence on transatlantic flight routes in winter will increase significantly in future as the climate changes. However, the individual responses of light, moderate, and severe clear-air turbulence have not previously been studied, despite their importance for aircraft operations. Here, we use climate model simulations to analyse the transatlantic wintertime clear-air turbulence response to climate change in five aviation-relevant turbulence strength categories. We find that the probability distributions for an ensemble of 21 clear-air turbulence diagnostics generally gain probability in their right-hand tails when the atmospheric carbon dioxide concentration is doubled. By converting the diagnostics into eddy dissipation rates, we find that the ensembleaverage airspace volume containing light clear-air turbulence increases by 59% (with an intra-ensemble range of 43%–68%), light-to-moderate by 75% (39%–96%), moderate by 94% (37%–118%), moderate-to-severe by 127% (30%–170%), and severe by 149% (36%–188%). These results suggest that the prevalence of transatlantic wintertime clear-air turbulence will increase significantly in all aviation-relevant strength categories as the climate changes.

In the Warming Arctic Seas

In the Warming Arctic Seas

ATMOSPHERIC DYNAMICS OF TERRESTRIAL EXOPLANETS OVER A WIDE RANGE OF ORBITAL AND ATMOSPHERIC PARAMETERS

The recent discoveries of terrestrial exoplanets and super-Earths extending over a broad range of orbital and physical parameters suggest that these planets will span a wide range of climatic regimes. Characterization of the atmospheres of warm super-Earths has already begun and will be extended to smaller and more distant planets over the coming decade. The habitability of these worlds may be strongly affected by their three-dimensional atmospheric circulation regimes, since the global climate feedbacks that control the inner and outer edges of the habitable zone including transitions to Snowball-like states and runaway-greenhouse feedbacks depend on the equator-to-pole temperature differences, patterns of relative humidity, and other aspects of the dynamics. Here, using an idealized moist atmospheric general circulation model including a hydrological cycle, we study the dynamical principles governing the atmospheric dynamics on such planets. We show how the planetary rotation rate, stellar flux, atmospheric mass, surface gravity, optical thickness, and planetary radius affect the atmospheric circulation and temperature distribution on such planets. Our simulations demonstrate that equator-to-pole temperature differences, meridional heat transport rates, structure and strength of the winds, and the hydrological cycle vary strongly with these parameters, implying that the sensitivity of the planet to global climate feedbacks will depend significantly on the atmospheric circulation. We elucidate the possible climatic regimes and diagnose the mechanisms controlling the formation of atmospheric jet streams, Hadley and Ferrel cells, and latitudinal temperature differences. Finally, we discuss the implications for understanding how the atmospheric circulation influences the global climate.

Springtime ENSO phase evolution and its relation to rainfall in the continental U.S.

AbstractSpringtime El Niño–Southern Oscillation (ENSO) phase evolution and associated U.S. rainfall variability are explored by performing composite analysis of observational data. Although the tropical Pacific ENSO sea surface temperature anomalies are weaker and less coherent in boreal spring compared to those in winter, there are unique and significant patterns of U.S. rainfall anomalies frequently appearing during the onset and decay phases of ENSO. In early spring of a decaying El Niño, the atmospheric jet stream and associated storm track shift southward, causing more frequent wet conditions across the southern U.S. and dry conditions in a belt south and east of the Ohio River. In late spring of a developing El Niño, the synoptic activity over the U.S. reduces overall and the southwesterly low‐level winds that carry moist air from the Gulf of Mexico to the U.S. shift westward, causing a similar dipole of rainfall anomalies between the southern U.S. and the Ohio Valley.

Diagnosing the warming of the Northeastern U.S. Coastal Ocean in 2012: A linkage between the atmospheric jet stream variability and ocean response

The temperature in the coastal ocean off the northeastern U.S. during the first half of 2012 was anomalously warm, and this resulted in major impacts on the marine ecosystem and commercial fisheries. Understanding the spatiotemporal characteristics of the warming and its underlying dynamical processes is important for improving ecosystem management. Here, we show that the warming in the first half of 2012 was systematic from the Gulf of Maine to Cape Hatteras. Moreover, the warm anomalies extended through the water column, and the local temperature change of shelf water in the Middle Atlantic Bight was largely balanced by the atmospheric heat flux. The anomalous atmospheric jet stream position induced smaller heat loss from the ocean and caused a much slower cooling rate in late autumn and early winter of 2011–2012. Strong jet stream intraseasonal oscillations in the first half of 2012 systematically increased the warm anomalies over the continental shelf. Despite the importance of advection in prior northeastern U.S. continental shelf interannual temperature anomalies, our analyses show that much of the 2012 warming event was attributed to local warming from the atmosphere.

Diagnosing the warming of the Northeastern U.S. Coastal Ocean in 2012: A linkage between the atmospheric jet stream variability and ocean response

Diagnosing the warming of the Northeastern U.S. Coastal Ocean in 2012: A linkage between the atmospheric jet stream variability and ocean response

The Peruvian atmospheric jet stream: Synoptic mechanism and variability reasons

The most frequently observed (classic) scenario and two types of deviations from it are revealed using the data of the analysis of synoptic situations accompanying the formation of the Peruvian jet stream (JS). It is established that the movement of the Peruvian High (the eastern part of the South Pacific High divided into two high-pressure zones) is of the key importance for the formation of the Peruvian JS. Determined is the relationship between the formation of the Peruvian JS and the disruption of the circulation in the Hadley cell in the eastern Pacific. Derived is the dependence of the synoptic mechanism of the Peruvian JS formation in the years with two different types of El Nino, when the Peruvian High formation due to the weakening of the South Pacific High often causes the final anticyclone of the cyclonic series in the mid-latitudes of the Southern Hemisphere. The regression analysis demonstrated the existence of the complex nonlinear relationship between the Peruvian JS formation and the Madden-Julian Oscillation through the impact on the pressure field.

Enhanced warming over the global subtropical western boundary currents

Subtropical western boundary currents are warm, fast-flowing currents that form on the western side of ocean basins. They carry warm tropical water to the mid-latitudes and vent large amounts of heat and moisture to the atmosphere along their paths, affecting atmospheric jet streams and mid-latitude storms, as well as ocean carbon uptake1, 2, 3, 4. The possibility that these highly energetic currents might change under greenhouse-gas forcing has raised significant concerns5, 6, 7, but detecting such changes is challenging owing to limited observations. Here, using reconstructed sea surface temperature datasets and century-long ocean and atmosphere reanalysis products, we find that the post-1900 surface ocean warming rate over the path of these currents is two to three times faster than the global mean surface ocean warming rate. The accelerated warming is associated with a synchronous poleward shift and/or intensification of global subtropical western boundary currents in conjunction with a systematic change in winds over both hemispheres. This enhanced warming may reduce the ability of the oceans to absorb anthropogenic carbon dioxide over these regions. However, uncertainties in detection and attribution of these warming trends remain, pointing to a need for a long-term monitoring network of the global western boundary currents and their extensions.

Uncertainty generation in deterministic flows: Theory and application with an atmospheric jet stream model

How uncertainties are generated in deterministic geophysical fluid flows is an important but mostly overlooked subject in the atmospheric and oceanic research. In this study, it is shown that the generating mechanisms include local entropy generation (LEG) and cumulant information transfer, both of which are explicitly expressed with the aid of a theorem established herein. To a system the former is intrinsic, representing the evolutionary trend of a marginal entropy and bringing connections between the two physical notions namely uncertainty and instability. The latter results from the interaction between different locations through dynamic event synchronization, and appears only in the course of state evolution. Although in practice it is a notoriously difficult task to estimate entropy and entropy-related quantities for atmospheric and oceanic systems, which are in general of large dimensionality, estimation of the LEG can be accurately fulfilled with ensembles of limited size. If, furthermore, the processes of a system under consideration are quasi-ergodic and quasi-stationary, its LEG actually can be fairly satisfactorily estimated even without appealing to ensemble predictions. These assertions are illustrated and verified in an application with two simulated quasi-geostrophic jet streams with compact chaotic attractors, one global over the whole domain and another highly localized. The LEG study provides an objective way of rapid assessment for predictions, which is important in the practical fields such as adaptive sampling and adaptive modeling.

Windy clues to Saturn's spin

Saturn's rotation period has been a mystery. An estimate based on its meteorology comes with implications for our understanding of the planet's atmospheric jet streams and interior structure.

Atmospheric Control on the Thermohaline Circulation

Abstract In an attempt to elucidate the role of atmospheric and oceanic processes in setting a vigorous ocean overturning circulation in the North Atlantic but not in the North Pacific, a comparison of the observed atmospheric circulation and net surface freshwater fluxes over the North Atlantic and Pacific basins is conducted. It is proposed that the more erratic meridional displacements of the atmospheric jet stream over the North Atlantic sector is instrumental in maintaining high surface salinities in its subpolar gyre. In addition, it is suggested that the spatial pattern of the net freshwater flux at the sea surface favors higher subpolar Atlantic salinity, because the geographical line separating net precipitation from net evaporation is found well south of the time-mean gyre separation in the North Pacific, whereas the two lines tend to coincide in the North Atlantic. Numerical experiments with an idealized two-gyre system confirm that these differences impact the salinity budget of the subpolar gyre. Further analysis of a coupled climate model in which the Atlantic meridional overturning cell has been artificially weakened suggests that the more erratic jet fluctuations in the Atlantic and the shift of the zero [net evaporation minus precipitation (E − P)] line are likely explained by features independent of the state of the thermohaline circulation. It is thus proposed that the atmospheric circulation helps “locking” high surface salinities and an active coupling between upper and deep ocean layers in the North Atlantic rather than in the North Pacific basin.

Jet stream intraseasonal oscillations drive dominant ecosystem variations in Oregon's summertime coastal upwelling system

Summertime wind stress along the coast of the northwestern United States typically exhibits intraseasonal oscillations (ISOs) with periods from approximately 15 to 40 days, as well as fluctuations on the 2- to 6-day "weather-band" and 1-day diurnal time scales. Coastal upwelling of cool, nutrient-rich water is driven by extended periods of equatorward alongshore winds, and we show that the approximately 20-day ISOs in alongshore wind stress dominated the upwelling process during summer 2001 off Oregon. These wind stress ISOs resulted from north-south positional ISOs of the atmospheric jet stream (JS). Upper-ocean temperature, phytoplankton, and zooplankton varied principally on the approximately 20-day time scale as well, and these correlated with the ISOs in alongshore wind stress and JS position, even though there also were weather-band stress fluctuations of comparable magnitude. Such wind stress ISOs are typical along Oregon in the summer upwelling season, occurring in 10 of 12 years examined, including 2001. We present a previously unreported direct connection from the atmospheric JS to oceanic primary and secondary production on the intraseasonal time scale and show the leading importance of ISOs in driving this coastal upwelling ecosystem during a typical summer.

Dynamical Origin of Low-Frequency Variability in a Highly Nonlinear Midlatitude Coupled Model

Abstract A novel mechanism of decadal midlatitude coupled variability, which crucially depends on the nonlinear dynamics of both the atmosphere and the ocean, is presented. The coupled model studied involves quasigeostrophic atmospheric and oceanic components, which communicate with each other via a constant-depth oceanic mixed layer. A series of coupled and uncoupled experiments show that the decadal coupled mode is active across parameter ranges that allow the bimodality of the atmospheric zonal flow to coexist with oceanic turbulence. The latter is most intense in the regions of inertial recirculation (IR). Bimodality is associated with the existence of two distinct anomalously persistent zonal-flow modes, which are characterized by different latitudes of the atmospheric jet stream. The IR reorganizations caused by transitions of the atmosphere from its high- to low-latitude state and vice versa create sea surface temperature anomalies that tend to induce transition to the opposite atmospheric state. The decadal–interdecadal time scale of the resulting oscillation is set by the IR adjustment; the latter depends most sensitively on the oceanic bottom drag. The period T of the nonlinear oscillation is 7–25 yr for the range of parameters explored, with the most realistic parameter values yielding T ≈ 20 yr. Aside from this nonlinear oscillation, an interannual Rossby wave mode is present in all coupled experiments. This coupled mode depends neither on atmospheric bimodality, nor on ocean eddy dynamics; it is analogous to the mode found previously in a channel configuration. Its time scale in the model with a closed ocean basin is set by cross-basin wave propagation and equals 3–5 yr for a basin width comparable with the North Atlantic.

Vertical alignment of the Gulf Stream

A historical set of expendable bathythermograph (XBT) and Pegasus sections across the Gulf Stream in natural coordinates is examined to investigate the isopycnic structure of the current off Cape Hatteras. In isopycnic-natural coordinates, the axis of the Stream remains vertically aligned, in contrast to its well-known offshore tilting when plotted as a function of depth. These results are confirmed using the geostrophic velocities obtained from a synthetic temperature field for the Gulf Stream. We prove that a baroclinic current aligned with density cannot be aligned with depth, and vice versa, and we show that the density alignment of the Gulf Stream results from the distortion of the density field and has negligible dependence on the choice of reference level. The invariable character of intense geophysical jets is supported through analogous representations for the upper level atmospheric jet stream in isentropic coordinates. These show that the atmospheric jet, when plotted on to a section normal to the direction of its maximum velocity core, is vertically aligned with potential temperature.

A Study of the Interaction of the North Atlantic Oscillation with Ocean Circulation

Observed patterns of wind stress curl and air‐sea heat flux associated with the North Atlantic oscillation (NAO) are used to discuss the response of ocean gyres and thermohaline circulation to NAO forcing and their possible feedback on the NAO. The observations motivate, and are interpreted in the framework of, a simple mathematical model that couples Ekman layers, ocean gyres, and thermohaline circulation to the atmospheric jet stream. Meridional shifts in the zero wind stress curl line are invoked to drive anomalies in ocean gyres, and north‐south dipoles in air‐sea flux drive anomalous thermohaline circulation. Both gyres and thermohaline circulation play a role in modulating sea surface temperature anomalies and hence, through air‐sea interaction, the overlying jet stream. The model, which can be expressed in the form of a delayed oscillator with ocean gyres and/or thermohaline circulation providing the delay, identifies key nondimensional parameters that control whether the ocean responds passively to NAO forcing or actively couples. It suggests that both thermohaline circulation and ocean gyres can play a role in coupled interactions on decadal timescales.

Analysis of the 1993 midwestern flood using satellite and ground data

The 1993 summer flood event in the midwestern United States was one of the most devastating floods of modern times. Record amounts of rain fell throughout the midwest causing extensive damage. The precipitation events can be attributed to anomalies in atmospheric circulation patterns and jet stream flows. These factors coupled with the above normal soil moisture beginning in the end of May 1993 set the stage for a massive flood event with the advent of considerable precipitation. The authors attempt to relate this increased soil moisture to the afternoon minus morning surface temperature differences as observed by the high resolution infrared sounder (HIRS2) on the NOAA-11 and NOAA-12 satellites. It is seen using satellite data that increased rainfall decreases this diurnal surface temperature difference. This is related to the discharge values at gauging stations along the Mississippi River at McGregor, IA (upstream) and St. Louis, MO (downstream).

Jet Streaks in the Gulf Stream

Mesoscale alongstream speed changes of the Gulf Stream are diagnosed from an array of current meters at depths 400, 700, and 1000 m, near 688W, during the development of steep [ratio of ‘‘amplitude’’ to ‘‘wavelength’’ O(1)] meanders. Speed maxima (jet streaks) are generally found between trough and crest axes in steep meanders with local speed minima near the trough and crest axes. Speed changes along streamlines can be quite dramatic. Speed changes along the jet axis, between jet streaks and local minima in excess of 0.60, 0.40, and 0.35 m s 21, are observed at depth 400, 700, and 1000 m, respectively. This is in comparison with peak speeds in a frontal coordinates system mean of 1.22, 0.67, and 0.28 m s21, at depth 400, 700, and 1000 m, respectively, from a previous study. The presence of the jet streaks can be explained kinematically as a superposition of the Gulf Stream and barotropic vortices. The development of these jet streaks in relation to the developing steep meanders differs from the canonical picture of jet streak/baroclinic wave development in the atmospheric jet stream in that the jet streaks in the Gulf Stream are predominantly fixed in place with respect to meanders as they steepen.

El Niño rides again

Another weather‐disrupting El Niño may be brewing in the Pacific Ocean, according to ocean measurements taken by NASA instruments on two orbiting satellites. Sea‐surface height measurements taken by the radar altimeter on board the joint U.S.‐French TOPEX/Poseidon satellite and wind data collected by the NASA scatterometer on Japan's Advanced Earth Observing Satellite (ADEOS) have been used together for the first time to predict changing weather conditions in the tropical Pacific Ocean.El Niño occurs when steady westward blowing trade winds weaken and reverse direction, moving the mass of warm water near Australia eastward to the coast of South America. The displacement of the warm water mass alters the atmospheric jet stream and weather patterns around the world. The TOPEX/Poseidon satellite uses an altimeter to bounce radar signals off the ocean's surface to make precise measurements of the distance between the satellite and sea surface. Researchers then map the barely perceptible hills and valleys of the sea surface by combining these data with measurements pinpointing the satellite's exact location in space.

A macrophysical model of the holocene intertropical convergence and jetstream positions and rainfall for the Saharan region

Using a macrophysical model, it has been found possible to model the Late Pleistocene and Holocene history of glacial volume and mean temperature as a function of solar radiation seasonality and modulation of the solar radiation by volcanic aerosols (Bryson, 1988). From this model it has been possible to model the Indian monsoon with fair agreement with the field data (Bryson, 1989). The present paper represents an extension of this effort to the modeling of the position of the Intertropical Convergence in North Africa and the latitude of the atmospheric polar jetstream in the same longitudes.

Thermal convection in a rotating shear flow

The dynamics of thermal convection in a rotating shear flow was studied using a three-dimensional time-dependent numerical model of the flow. The model assumes a sheared zonal wind in the form of an atmospheric jet stream and considers convective motions imbedded in this flow. It was found that rotation plays a vital role in the dynamics. Without rotation, the convective motions extract energy and momentum from the mean zonal flow. With rotation, the convective motions feed the energy and momentum into the mean flow. The results show how the small-scale convection might influence the large-scale dynamics of rotating stars and planets.