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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Mars atmospheric dynamics as simulated by the NASA Ames General Circulation Model. II - Transient baroclinic eddies

A large set of experiments performed with the NASA Ames Mars General Circulation Model is analyzed to determine the properties, structure, and dynamics of the simulated transient baroclinic eddies. There is strong transient baroclinic eddy activity in the extratropics of the Northern Hemisphere during the northern autumn, winter, and spring seasons. The eddy activity remains strong for very large dust loadings, though it shifts northward. The eastward propagating eddies are characterized by zonal wavenumbers of 1-4 and periods of about 2-10 days. The properties of the GCM baroclinic eddies in the northern extratropics are compared in detail with analogous properties inferred from Viking Lander meteorology observations.

Barnes, Jeffrey R.↗
NASA NTRS2016

Detection of Northern Hemisphere Transient Baroclinic Eddies in REMS Pressure Data at Gale Crater Mars

Wintertime transient baroclinic eddies in the northern midlatitudes of Mars were identified in Viking Lander 2 (VL2, 48.3N, 134.0E) surface pressure data back in the early 1980s. Here we report the results of an analysis of REMS surface pressure data acquired by the Curiosity Rover in Gale Crater (4.5S, 137.4E) that suggests the meridional scale of these eddies is so large that the disturbances in the surface pressure fields they create extend across the equator and into the southern hemisphere. A power spectrum analysis of the seasonally detrended REMS pressure data from Ls=240-280 shows dominant periods of ~ 6 sols and ~2.2 sols (though with greatly reduced power) which are close the dominant periods of the transient eddies observed by VL2 at this season. Analysis of the surface pressure fields from the Ames Mars GCM for the same season also shows dominant periods at the grid points closest to VL2 and Gale Crater similar to those observed. In the model, the disturbances responsible for these oscillations are eastward traveling baroclinic eddies whose amplitudes are greatest at northern mid latitudes at this season, but whose meridional extent does indeed extend into the low latitudes of the southern hemisphere. REMS appears to be seeing the signature of these eddies, not only for this season but for the early fall and late winter seasons as well. While orbital images of the so called “flushing storms”, which more closely correspond to the shorter period waves, show dust-lifting frontal systems that cross the equator, REMS data - even though acquired at a longitude of comparatively weak storm activity - provide the first in-situ evidence that northern hemisphere transient eddies can be detected at the surface in low latitudes of the southern hemisphere.

REMS Data↗
NASA NTRS1986

Effects of eddy initial conditions on nonlinear forcing of planetary scale waves by amplifying baroclinic eddies

The previous study of Young and Villere concerning growth of planetary scale waves forced by wave-wave interactions of amplifying intermediate scale baroclinic eddies is extended to investigate effects of different eddy initial conditions. A global, spectral, primitive equation model is used for the calculations. For every set of eddy initial conditions considered, growth rates of planetary modes are considerably greater than growth rates computed from linear instability theory for a fixed zonally independent basic state. However, values of growth rates ranged over a factor of 3 depending on the particular set of eddy initial conditions used. Nonlinear forcing of planetary modes via wave-wave coupling becomes more important than baroclinic growth on the basic state at small values of the intermediate-scale modal amplitudes. The relative importance of direct transfer of kinetic energy from intermediate scales of motion to a planetary mode, compared to baroclinic conversion of available potential energy to kinetic energy within that planetary mode, depends on the individual case. In all cases, however, the transfer of either kinetic or available potential energy to the planetary modes was accomplished principally by wave-wave transfer from intermediate scale eddies, rather than from the zonally averaged state. The zonal wavenumber 2 planetary mode was prominent in all solutions, even in those for which eddy initial conditions were such that a different planetary mode was selectively forced at the start. General characteristics of the structural evolution of the planetary wave components of total heat and momentum flux, and modal structures themselves, were relatively insensitive to variations in eddy initial conditions, even though quantitative details varied from case to case.

Young, Richard E.↗
NASA NTRS2016

Detection of Northern Hemisphere Transient Baroclinic Eddies at Gale Crater Mars

The Rover Environmental Monitoring Station (REMS) on the Mars Science Laboratory’s (MSL) Curiosity rover has been operating in Gale Crater Mars (4.5°S, 137.4°E) for over 2 Mars years. Analysis of its pressure data, which have a precision of approximately 0.2 Pa (see Haberle et al., 2014; Harri et al., 2014), reveal temporal oscillations in its seasonally de-trended daily averaged pressures at some seasons with 2-5 Pa amplitudes that have periods similar to those observed at the Viking Lander 2 (VL-2) site (48.3°N, 134.0°E) several decades ago. As illustrated in Fig 1 there are clear peaks in the variance at a frequency f approximately 0.45 and 0.06 per sol for the fall season of Mars Year (MY) 31, and at f approximately 0.15 and 0.06 per sol for MY 32. These frequencies correspond to periods of 2.2, 6.7, and 16.7 sols, and are very similar to those observed at VL-2 (Fig 2, and see Barnes, 1980). Since orbital imaging data show dust frontal systems associated with eastward traveling baroclinic eddies that occasionally cross the equator (Wang et al., 2003), these findings suggest that MSL may be seeing their signature in its pressure data. To make this case we show that (a) the spectral peaks in the MSL are not only similar to those at VL-2, they have the same seasonal variation, (b) at least for some seasons the peaks are statistically significant and not likely due to random noise in the data, and (c) Global Circulation Model (GCM) results from the Ames GCM support this interpretation.

The Rover Environmental Monitoring Station (REMS)↗
NASA NTRS1985

Nonlinear forcing of planetary scale waves by amplifying unstable baroclinic eddies generated in the troposphere

The present investigation is mainly concerned with isolating the effects of wave-wave coupling on the growth of planetary-scale baroclinic modes of zonal wavenumber 1-3. It is shown that a global distribution of amplifying intermediate-scale baroclinic modes can cause rapid growth of planetary-scale modes. The growth rates of the planetary modes are found to be comparable to the growth rates of the most unstable baroclinic modes during the first 5-10 days. Thereafter the planetary waves continue to grow (albeit at a slower rate and not necessarily monotonically), and do not exhibit a decay phase as pronounced as that which is characteristic of the intermediate-scale modes.

Young, R. E.↗
NASA NTRS1986

Influence of transient baroclinic eddies on planetary-scale waves

Low-order models with a mean zonal flow forced by zonally symmetric heating and one planetary-scale wave forced by topography have multiple flow equilibria. Two stable equilibria are characterized by strong zonal flow with low wave amplitude (high index circulation) and weak zonal flow with a high wave amplitude (low index circulation) fixed in phase with the topography. These two states presumably represent normal zonal circulation and a blocking configuration, respectively. When a shorter, baroclinically unstable wave is dded to this low-order model, the planetary-scale wave no longer stays in stable equilibrium states. Instead, the long wave remains in weather regimes or preferred regions in phase space. These regimes are, in general, different from the equilibria of the model with the planetary-scale wave only. Thus, the short unstable wave adds some randomness to planetary-scale circulation and changes its position with respect to the planetary-scale topography. The Reinhold and Pierrehumbert model is further explored here by adding a long-wave in the thermal forcing and exploring wider parameter space. When the symmetric thermal forcing is weak so that the short wave is stable, the planetary scale wave is fixed in amplitude and phase by the asymmetric forcing. However, when the symmetric forcing is increased to an unstable level, the planetary-scale wave becomes less organized. With asymmetric thermal forcing only (i.e., no topography) the long-wave is randomly distributed through phase space. Thermal forcing seems to be less effective in organizing weather regimes than topographic forcing.

Branscome, L. E.↗
NASA NTRS2020

Midlatitude Cloud Systems

In contrast to the tropics and subtropics, the middle latitudes are characterised by large meridional temperature gradients, created as a consequence of differential radiative heating between high and low latitudes. These meridional temperature gradients often concentrate in relatively narrow baroclinic zones that become unstable to wave-like perturbations called baroclinic eddies, or more commonly baroclinic storms or midlatitude cyclones. Baroclinic storms constitute the primary source of poleward energy transport at midlatitudes, which is accomplished through contrasting transports of warm air masses poleward (warm fronts) and cold air masses equatorward (cold fronts). Baroclinic storms also flux momentum into midlatitude regions, driving a region of enhanced westerly winds from the surface to the upper troposphere called the eddy-driven jet stream.

Midlatitude clouds↗
NASA NTRS1986

Thermal balance of the atmospheres of Jupiter and Uranus

Two-dimensional, radiative-convective-dynamical models of the visible atmospheres of Jupiter and Uranus are presented. Zonally-averaged temperatures and heat fluxes are calculated numerically as functions of pressure and latitude. In addition to radiative heat fluxes, the dynamical heat flux due to large-scale baroclinic eddies is included and is parametrized using a mixing length theory which gives heat fluxes similar to those of Stone. The results for Jupiter indicate that the internal heat flow is non-uniform in latitude and nearly balances the net radiative flux leaving the atmosphere. The thermal emission is found to be uniform in latitude in agreement with Pioneer and Voyager observations. Baroclinic eddies are calculated to transport only a small amount of the meridional heat flow necessary to account for the uniformity of thermal emission with latitude. The bulk of the meridional heat transfer is found to occur very deep in the stable interior of Jupiter as originally proposed by Ingersoll and Porco. The relative importance of baroclinic eddies vs. internal heat flow in the thermal balance of Uranus depends on the ratio of emitted thermal power to absorbed solar power. The thermal balance of Uranus is compared to that of Jupiter for different values of this ratio.

Friedson, A. J.↗
NASA NTRS1990

Parameterization of eddy sensible heat transports in a zonally averaged dynamic model of the atmosphere

A Charney-Branscome based parameterization has been tested as a way of representing the eddy sensible heat transports missing in a zonally averaged dynamic model (ZADM) of the atmosphere. The ZADM used is a zonally averaged version of a general circulation model (GCM). The parameterized transports in the ZADM are gaged against the corresponding fluxes explicitly simulated in the GCM, using the same zonally averaged boundary conditions in both models. The Charney-Branscome approach neglects stationary eddies and transient barotropic disturbances and relies on a set of simplifying assumptions, including the linear appoximation, to describe growing transient baroclinic eddies. Nevertheless, fairly satisfactory results are obtained when the parameterization is performed interactively with the model. Compared with noninteractive tests, a very efficient restoring feedback effect between the modeled zonal-mean climate and the parameterized meridional eddy transport is identified.

Genthon, Christophe↗
NASA NTRS1979

Atmospheric lapse rate regimes and their parameterization

Lapse rates, moist adiabatic lapse rates and the critical lapse rate for baroclinic adjustment are calculated and compared for the mean annual, January and July states in the Northern Hemisphere. The small seasonal changes in hemispheric mean lapse rates can be attributed to counteracting seasonal changes in the strength of moist convection and baroclinic eddies. A major conclusion is that the vertical temperature structure may be well approximated by a radiative-convective equilibrium model with two critical lapse rates, viz. the moist adiabatic lapse rate and the critical lapse rate for baroclinic adjustment.

Stone, P. H.↗
NASA NTRS2021

The Influence of Direct Radiative Forcing Versus Indirect Sea Surface Temperature Warming on Southern Hemisphere Subtropical Anticyclones Under Global Warming

Southern hemisphere subtropical anticyclones are projected to change in a warmer climate during both austral summer and winter. A recent study of CMIP 5 & 6 projections found a combination of local diabatic heating changes and static-stability-induced changes in baroclinic eddy growth as the dominant drivers. Yet the underlying mechanisms forcing these changes still remain uninvestigated. This study aims to enhance our mechanistic understanding of what drives these Southern Hemisphere anticyclones changes during both seasons. Using an AGCM, we decompose the response to CO2-induced warming into two components: (1) the fast atmospheric response to direct CO2 radiative forcing, and (2) the slow atmospheric response due to indirect sea surface temperature warming. Additionally, we isolate the influence of tropical diabatic heating with AGCM added heating experiments. As a complement to our numerical AGCM experiments, we analyze the Atmospheric and Cloud Feedback Model Intercomparison Project experiments. Results from sensitivity experiments show that slow subtropical sea surface temperature warming primarily forces the projected changes in subtropical anticyclones through baroclinicity change. Fast CO2 atmospheric radiative forcing on the other hand plays a secondary role, with the most notable exception being the South Atlantic subtropical anticyclone in austral winter, where it opposes the forcing by sea surface temperature changes resulting in a muted net response. Lastly, we find that tropical diabatic heating changes only significantly influence Southern Hemisphere subtropical anticyclone changes through tropospheric wind shear changes during austral winter.

Subtropical anticyclone↗
NASA NTRS1986

Current Scientific Issues in Large Scale Atmospheric Dynamics

Topics in large scale atmospheric dynamics are discussed. Aspects of atmospheric blocking, the influence of transient baroclinic eddies on planetary-scale waves, cyclogenesis, the effects of orography on planetary scale flow, small scale frontal structure, and simulations of gravity waves in frontal zones are discussed.

Miller, T. L.↗
NASA NTRS1986

The Martian climate and energy balance models with CO2/H2O atmospheres

The analysis begins with a seasonal energy balance model (EBM) for Mars. This is used to compute surface temperature versus x = sin(latitude) and time over the seasonal cycle. The core model also computes the evolving boundaries of the CO2 icecaps, net sublimational/condensation rates, and the resulting seasonal pressure wave. Model results are compared with surface temperature and pressure history data at Viking lander sites, indicating fairly good agreement when meridional heat transport is represented by a thermal diffusion coefficient D approx. 0.015 W/sq. m/K. Condensational wind distributions are also computed. An analytic model of Martian wind circulation is then proposed, as an extension of the EMB, which incorporates vertical wind profiles containing an x-dependent function evaluated by substitution in the equation defining the diffusion coefficient. This leads to a parameterization of D(x) and of the meridional circulation which recovers the high surface winds predicted by dynamic Mars atmosphere models (approx. 10 m/sec). Peak diffusion coefficients, D approx. 0.6 w/sq m/K, are found over strong Hadley zones - some 40 times larger than those of high-latitude baroclinic eddies. When the wind parameterization is used to find streamline patterns over Martian seasons, the resulting picture shows overturning hemispheric Hadley cells crossing the equator during solstices, and attaining peak intensities during the south summer dust storm season, while condensational winds are most important near the polar caps.

Hoffert, M. I.↗
NASA NTRS1987

Seasonal meridional energy balance and thermal structure of the atmosphere of Uranus - A radiative-convective-dynamical model

A model is presented for the thermodynamics of the seasonal meridional energy balance and thermal structure of the Uranian atmosphere. The model considers radiation and small-scale convection, and dynamical heat fluxes due to large-scale baroclinic eddies. Phase oscillations with a period of 0.5 Uranian year are discerned in the total internal power and global enthalpy storage. The variations in the identity of the main transport agent with the magnitude of the internal heat source are discussed. It is shown that meridional heat transport in the atmosphere is sufficient to lower seasonal horizontal temperature contrasts below those predicted with radiative-convection models.

Friedson, James↗
NASA NTRS1990

Waves and instability in the atmosphere of Mars: NASA planetary atmospheres program

A broad range of phenomena were addressed by the study including the following: (1) polar warming; (2) forced stationary waves; (3) gravity waves; (4) transient baroclinic eddies; and (5) radiative-dynamical instabilities. A variety of numerical models have been employed in these studies, as well as analytical approaches. Some of the most significant results from this work are very briefly summarized.

Barnes, Jeffrey R.↗
NASA NTRS1974

The meridional variation of the eddy heat fluxes by baroclinic waves and their parameterization

The meridional and vertical eddy fluxes of sensible heat produced by small-amplitude growing baroclinic waves are calculated using solutions to the two-level model with horizontal shear in the mean flow. The results show that the fluxes are primarily dependent on the local baroclinicity, i.e., the local value of the isentropic slopes in the mean state. Where the slope exceeds the critical value, the transports are poleward and upward; where the slope is less than the critical value, the transports are equatorward and downward. These results are used to improve an earlier parameterization of the tropospheric eddy fluxes of sensible heat based on Eady's model. Comparisons with observations show that the improved parameterization reproduces the observed magnitude and sign of the eddy fluxes and their vertical variations and seasonal changes, but the maximum in the poleward flux is too near the equator.

Stone, P. H.↗
NASA NTRS1982

Short-term fluctuations in the eddy heat flux and baroclinic stability of the atmosphere

National Meteorological Center data from midlatitudes for three Januaries is used in calculating time series of the zonal mean meridional eddy heat flux and the zonal mean baroclinic stability, as measured by the difference between the zonal wind shear and the critical value of the shear in two-level models. Time-lagged correlations between the two series reveal a highly significant negative correlation for short time lags, peaking at approximately -0.4 when the stability parameter lags one half day behind the eddy flux. They also reveal that strongly unstable conditions are not followed by significant increases in the eddy flux. These results are seen as indicating that the synoptic variations of the zonal mean eddy flux are not closely related to the degree of baroclinic instability of the zonal mean flow. The autocorrelation of the eddy flux is then compared with those expected for autoregressive processes. A Bayesian information criterion suggests that the behavior is represented best by a damped oscillation, with a damping time of 0.8 day and a period of five days.

Stone, P. H.↗