Engineering topics

Lindzen, Richard S.

Publications and source records attributed to Lindzen, Richard S..

At least 19 records

NASA NTRS2002

Comments on "Tropical Convection and the Energy Balance at the Top of the Atmosphere"

Analyses of the Earth Radiation Budget Experiment (ERBE) data show that the effects of clouds on the solar and thermal infrared radiation in the tropical deep convective regions have a similar magnitude but opposite signs. This small difference in the effects of clouds on radiation led Hartmann et al. (2001) to conclude that the contrast in the net radiation at the top of the atmosphere between the convective and non-convective regions must also be small. However, we have found that the ERBE data do not generally show a small contrast in the radiation between the convective and non-convective regions, and the model used by Hartmann et al., therefore, seems unlikely to represent the real physical processes involving convection, radiation, and climate in an appropriate way.

Chou, Ming-Dah↗

NASA NTRS2001

Response to "The Iris Hypothesis: A Negative or Positive Cloud Feedback?"

Based on radiance measurements of Japan's Geostationary Meteorological Satellite, Lindzen et al. found that the high-level cloud cover averaged over the tropical western Pacific decreases with increasing sea surface temperature. They further found that the response of high-level clouds to the sea surface temperature had an effect of reducing the magnitude of climate change, which is referred as a negative climate feedback. Lin et al. reassessed the results found by Lindzen et al. by analyzing the radiation and clouds derived from the Tropical Rainfall Measuring Mission Clouds and the Earth's Radiant Energy System measurements. They found a weak positive feedback between high-level clouds and the surface temperature. We have found that the approach taken by Lin et al. to estimating the albedo and the outgoing longwave radiation is incorrect and that the inferred climate sensitivity is unreliable.

Chou, Ming-Dah↗

NASA NTRS2001

Response to Comment on "Does the Earth Have an Adaptive Infrared IRIS?"

Harrison's (2001) Comment on the Methodology in Lindzen et al (2001) has prompted re-examination of several aspects of study. Probably the most significant disagreement in our conclusions is due to our different approaches to minimizing the influence of long-time-scale variations in the variables A and T on the results. Given the strength of the annual cycle and the 20-month period covered by the data, we believe that removing monthly means is a better approach to minimizing the long-time-scale behavior of the data than removal of the linear trend, which might actually add spurious long- time- scale variability into the modified data. We have also indicated how our statistical methods of establishing statistical significance differ. More definitive conclusions may only possible after more data have been analyzed, but we feel that our results are robust enough to encourage further study of this phenomenon.

Bell, Thomas L.↗

NASA NTRS2001

Response to Comment on "Does the Earth Have an Adaptive Infrared Iris?"

In his comment on Lindzen et al., Harrison found that the amount of high-level clouds, A, and the sea-surface temperature beneath clouds, T, averaged over a large oceanic domain in the western Pacific have secular linear trends of opposite signs over a period of 20 months. He found that when the linear trends are subtracted from the data, the correlation between the residual A and T is much reduced. His estimates of the confidence levels for the correlation indicate, moreover, that this correlation is not statistically significant. The domain-averaged A and, to a lesser degree, T, have distinct intra-seasonal and seasonal variations. These variations are influenced by the large-scale wind and temperature distributions and by the seasonal variation of insolation. To separate the local effect from the effect of slowly changing large-scale conditions, rather than subtracting 20-month linear trends from the series, which has the potential to spuriously extrapolate intra-seasonal and seasonal variations to even longer time scales, we subtracted 30-day running means of A and T from each time series; in effect, the data were high-pass filtered. The number of points (days), N, is reduced by this process from the original value of 510 to 480.

Bell, Thomas L.↗

NASA NTRS2001

Response to "No Evidence for Iris"

Hartmann and Michelsen claimed that there was no evidence for the negative relation between the high-level clouds and the sea surface temperature as suggested by Lindzen et al. The assertion made by Hartmann and Michelsen that there is a need for clouds thousands of kilometers away from the equator to be connected to convection at the equator does not seem to have any validity. Nor does their suggestion that the causes of the observational relations shown in Lindzen et al. do not involve detrainment.

Chou, Ming-Dah↗

NASA NTRS2000

Does The Earth Have an Adaptive Infrared Iris?

Observations and analyses of water vapor and clouds in the tropics over the past decade suggest a different approach to radiative climate feedbacks: namely, that high clouds and high free-tropospheric relative humidity are largely tied to each other, and that the main feedback consists in changing the relative areas of cloudy/moist regions vis a vis clear/dry regions in response to the surface temperature of the cloudy/moist regions - as opposed to altering the humidity in either of the regions. This is an intrinsically 2-dimensional (horizontal and vertical) effect which does not readily enter simple 1-dimensional (vertical) radiative-convective schemes which emphasize average humidity, etc. Preliminary analyses of cloud data for the eastern part of the Western Pacific from the Japanese GMS-5(Geostationary Meteorological Satellite), are supportive of this suggestion - pointing to a 15% reduction in cloudy/moist area for a 1C increase of the sea surface temperature as measured by the cloud-weighted SST (sea surface temperature). The implication of this result is examined using a simple 2-dimensional radiative-convective model. The calculations show that such a change in the tropics would lead to a strong negative feedback in the global climate, with a feedback factor of about -1.7, which, if correct, would easily dominate the positive water vapor feedback found in current models. This new feedback mechanism, in effect, constitutes an adaptive infrared iris that opens and closes in order to control the OLR (outgoing longwave radiation) in response to changes in surface temperature in a manner similar to the way in which an eye's iris opens and closes in response to changing light levels. The climate sensitivity resulting from this thermostatic mechanism is consistent with the independent determination by Lindzen and Giannitisis (1998). Preliminary attempts to replicate observations with GCMs (General Circulation Models) suggest that models lack such a negative cloud/moist areal feedback.

Lindzen, Richard S.↗

NASA NTRS2000

High-Level Clouds and Relation to Sea Surface Temperature as Inferred from Japan's GMS Measurements

High-level clouds have a significant impact on the radiation energy budgets and, hence, the climate of the Earth. Convective cloud systems, which are controlled by large-scale thermal and dynamical conditions, propagate rapidly within days. At this time scale, changes of sea surface temperature (SST) are small. Radiances measured by Japan's Geostationary Meteorological Satellite (GMS) are used to study the relation between high-level clouds and SST in the tropical western and central Pacific (30 S-30 N; 130 E-170 W), where the ocean is warm and deep convection is intensive. Twenty months (January 1998 - August, 1999) of GMS data are used, which cover the second half of the strong 1997-1998 El Nino. Brightness temperature at the 11-micron channel is used to identify high-level clouds. The core of convection is identified based on the difference in the brightness temperatures of the 11- and 12-micron channels. Because of the rapid movement of clouds, there is little correlation between clouds six hours apart. When most of deep convection moves to regions of high SST, the domain averaged high-level cloud amount decreases. A +2C change of SST in cloudy regions results in a relative change of -30% in high-level cloud amount. This large change in cloud amount is due to clouds moving from cool regions to warm regions but not the change in SST itself. A reduction in high-level cloud amount in the equatorial region implies an expanded dry upper troposphere in the off-equatorial region, and the greenhouse warming of high clouds and water vapor is reduced through enhanced longwave cooling to space. The results are important for understanding the physical processes relating SST, convection, and water vapor in the tropics. They are also important for validating climate simulations using global general circulation models.

Chou, Ming-Dah↗

NASA NTRS1994

The effect of concentrated PV gradients on stationary waves

The author reexamines the Charney-Drazin problem with special attention to the concentration of potential vorticity gradient in the neighborhood of the tropopause. It is found that the degree of concentration has a profound effect on the response to stationary forcing, with greater concentration leading to greater response. Smoothing the concentration either analytically or numerically (by using coarser resolution) both lead to reduced responses, especially at higher wavenumbers. The results suggest a potentially important interaction between baroclinically unstable eddies and stationary waves. Insofar as the former act to mix potential vorticity in the troposphere while concentrating gradients at tropopause levels, they significantly condition the basic state for the latter.

Lindzen, Richard S.↗

NASA NTRS1994

The Eady problem for a basic state with zero PV gradient but beta does not equal 0

The classic Eady problem is modified to include beta does not equal 0, but with the basic distributions of temperature and zonal flow adjusted to preserve zero meridional gradients of basic-state potential vorticity in the fluid interior. Much of the mathematical simplicity of the classic problem is retained; however, the results differ in important ways. Specifically, the instability now has a long-wave cutoff in addition to the traditional short-wave cutoff. The former is associated with the fact that the phase speeds of the edge waves begin to differ so much as wavenumber is reduced that the two edge waves can no longer interact in order to form unstable modes. For the unstable modes, this manifests itself in that the steering level for unstable modes is always below the middle of the fluid and approaches the lower boundary near the long-wave cutoff. Relatedly, the amplitude of the unstable geopotential perturbations is larger at the upper boundary than at the lower boundary. Finally, below the long-wave cutoff, one of the neutral waves has a phase speed that becomes increasingly easterly as wavenumber decreases. This allows a resonant response to planetary-scale stationary forcing.

Lindzen, Richard S.↗

NASA NTRS1994

Gravitational tides on Jupiter. 3: Atmospheric response and mean flow acceleration

The gravitational tidal response at the visible cloud level of Jupiter is obtained as a function of static stability in the planetary interior. It is suggested that confirmation of the presence of static stability in the planetary interior could be achieved by observing tidal fields at cloud level. We also calculate the mean flow acceleration induced by tidal fields and suggest that, if the interior is even marginally statically stable, the tides may provide the momentum source maintaining the alternating zonal jets observed at the cloud level of the planet.

Ioannou, Petros J.↗

NASA NTRS1994

A PV view of the zonal mean distribution of temperature and wind in the extratropical troposphere

The dependence of the temperature and wind distribution of the zonal mean flow in the extratropical troposphere on the gradient of pontential vorticity along isentropes is examined. The extratropics here refer to the region outside the Hadley circulation. Of particular interest is whether the distribution of temperature and wind corresponding to a constant potential vorticity (PV) along isentropes resembles the observed, and the implications of PV homogenization along isentropes for the role of the tropics. With the assumption that PV is homogenized along isentropes, it is found that the temperature distribution in the extratropical troposphere may be determined by a linear, first-order partial differential equation. When the observed surface temperature distribution and tropical lapse rate are used as the boundary conditions, the solution of the equation is close to the observed temperature distribution except in the upper troposphere adjacent to the Hadley circulation, where the troposphere with no PV gradient is considerably colder. Consequently, the jet is also stronger. It is also found that the meridional distribution of the balanced zonal wind is very sensitive to the meridional distribution of the tropopause temperature. The result may suggest that the requirement of the global momentum balance has no practical role in determining the extratropical temperature distribution. The authors further investigated the sensitivity of the extratropical troposphere with constant PV along isentropes to changes in conditions at the tropical boundary (the edge of the Hadley circulation). It is found that the temperature and wind distributions in the extratropical troposphere are sensitive to the vertical distribution of PV at the tropical boundary. With a surface distribution of temperature that decreases linearly with latitude, the jet maximum occurs at the tropical boundary and moves with it. The overall pattern of wind distribution is not sensitive to the change of the position of the tropical boundary. Finally, the temperature and wind distributions of an extratropical troposphere with a finite PV gradient are calculated. It is found that the larger the isentropic PV gradient, the warmer the troposphere and the weaker the jet.

Sun, De-Zheng↗

NASA NTRS1993

Distribution of tropical tropospheric water vapor

Utilizing a conceptual model for tropical convection and observational data for water vapor, the maintenance of the vertical distribution of the tropical tropospheric water vapor is discussed. While deep convection induces large-scale subsidence that constrains the turbulent downgradient mixing to within the convective boundary layer and effectively dries the troposphere through downward advection, it also pumps hydrometeors into the upper troposphere, whose subsequent evaporation appears to be the major source of moisture for the large-scale subsiding motion. The development of upper-level clouds and precipitation from these clouds may also act to dry the outflow, thus explaining the low relative humidity near the tropopause. A one-dimensional model is developed to simulate the mean vertical structure of water vapor in the tropical troposphere. It is also shown that the horizontal variation of water vapor in the tropical troposphere above the trade-wind boundary layer can be explained by the variation of a moisture source that is proportional to the amount of upper-level clouds. Implications for the nature of water vapor feedback in global warming are discussed.

Sun, De-Zheng↗

NASA NTRS1993

Baroclinic neutrality and the tropopause

It is noted that the atmosphere has a baroclinically neutral state that permits strong temperature gradients at the ground. In this state, the concentrated potential vorticity gradient at the ground is separated from the concentrated potential vorticity gradient at the tropopause by a region where the potential vorticity gradient is zero. The resulting basic state is analogous to the basic state in the Eady problem. A minimum meridional wavenumber is established by the width of the subtropical jet, and neutrality is established by moving the tropopause to a sufficient height so that the total wavenumber corresponds to the short-wave cutoff in the Eady problem. The resulting height is approximately the observed tropopause height.

Lindzen, Richard S.↗

NASA NTRS1993

Gravitational tides in the outer planets. I - Implications of classical tidal theory. II - Interior calculations and estimation of the tidal dissipation factor

Classical tidal theory is applied to the atmospheres of the outer planets. The tidal geopotential due to satellites of the outer planets is discussed, and the solution of Laplace's tidal equation for Hough modes appropriate to tides on the outer planets is examined. The vertical structure of tidal modes is described, noting that only relatively high-order meridional mode numbers can propagate vertically with growing amplitude. Expected magnitudes for tides in the visible atmosphere of Jupiter are discussed. The classical theory is extended to planetary interiors taking the effects of spherically and self-gravity into account. The thermodynamic structure of Jupiter is described and the WKB theory of the vertical structure equation is presented. The regions for which inertial, gravity, and acoustic oscillations are possible are delineated. The case of a planet with a neutral interior is treated, discussing the various atmospheric boundary conditions and showing that the tidal response is small.

Ioannou, Petros J.↗

NASA NTRS1993

Water vapor feedback and the ice age snowline record

Average tropical sea surface temperatures during the last major glaciation may have been no more than about 1 C cooler than at present, while snow lines on high peaks may have descended 1 km, suggesting a drop in temperature of about 5 C in the mid-troposphere. This feature is likely to be characteristic, since the tropical atmosphere cannot sustain large horizontal temperature gradients. This implies that during the last glaciation the lapse rate in the lower half of the tropical troposphere was about 20 percent greater than at present. A reduction in the radiative cooling rate at these levels is required for such a reduction in static stability. A radiative-convective model with a physical parameterization for tropical convection is used to determine that only a significant increase in relative humidity in the middle and upper troposphere can cause the necessary increase in the lapse rate in the lower troposphere.

Sun, De-Zheng↗

NASA NTRS1993

Numerical experiments on consistent horizontal and vertical resolution for atmospheric models and observing systems

Simple numerical experiments are performed in order to determine the effects of inconsistent combinations of horizontal and vertical resolution in both atmospheric models and observing systems. In both cases, we find that inconsistent spatial resolution is associated with enhanced noise generation. A rather fine horizontal resolution in a satellite-data observing system seems to be excessive when combined with the usually available relatively coarse vertical resolution. Using horizontal filters of different strengths, adjusted in such a way as to render the effective horizontal resolution more consistent with vertical resolution for the observing system, may result in improvement of the analysis accuracy. The increase of vertical resolution for a satellite data observing system with better vertically resolved data, the results are different in that little or no horizontal filtering is needed to make spatial resolution more consistent for the system. The obtained experimental estimates of consistent vertical and effective horizontal resolution are in a general agreement with consistent resolution estimates previously derived theoretically by the authors.

Fox-Rabinovitz, Michael S.↗

NASA NTRS1993

On the establishment of stationary waves in the Northern Hemisphere winter

The establishment of stationary waves in the Northern Hemisphere winter is investigated using stationary and time-dependent linear primitive equation models. Confirming the results of Nigam and Lindzen, we find that small displacements of the subtropical jet can cause significant changes in the stationary-wave response. The time scale for stationary establishment is found to be on the order of 5 days, both in the troposphere and in the lower stratosphere. The exception is for a northward shift of the subtropical jet, in which case the establishment of the new stationary solution in the stratosphere occurs on a longer time scale, which is mainly determined by dissipation. Implications for low-frequency atmospheric variability and mid- and long-range weather forecasting are discussed.

Da Silva, Arlindo M.↗

NASA NTRS1992

Numerical experiments on consistent horizontal and vertical resolution for atmospheric models and observing systems

Simple numerical experiments are performed in order to determine the effects of inconsistent combinations of horizontal and vertical resolution in both atmospheric models and observing systems. In both cases, we find that inconsistent spatial resolution is associated with enhanced noise generation. A rather fine horizontal resolution in a satellite data observing system seems to be excessive when combined with the usually available relatively coarse vertical resolution. Using different strength horizontal filters, adjusted in such a way as to render the effective horizontal resolution more consistent with vertical resolution for the observing system, may result in improvement of the analysis accuracy. However, the increase of vertical resolution for a satellite data observing system is desirable. For the conventional data observing system with better vertically resolved data, the results are different in that little or no horizontal filtering is needed to make spatial resolution more consistent for the system. The obtained experimental estimates of consistent vertical and effective horizontal resolution are in a general agreement with consistent resolution estimates previously derived theoretically by the authors.

Fox-Rabinovitz, Michael S.↗