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The Impact of Orography and Latent Heating on the Location of the Tropical Easterly Jet  [PDF]
Samrat Rao,J. Srinivasan
Physics , 2013,
Abstract: The Tropical Easterly Jet (TEJ) is a prominent atmospheric circulation feature observed during the Asian Summer Monsoon. It is generally assumed that Tibet is an essential ingredient in determining the location of the TEJ. However studies have also suggested the importance of latent heating in determining the jet location. The relative importance of Tibetan orography and latent heating is explored through simulations with a general circulation model. The simulation of TEJ by the Community Atmosphere Model, version 3.1 (CAM-3.1) has been discussed in detail. Although the simulated TEJ replicated many observed features of the jet, the jet maximum was located too far to the west when compared to observation. The precipitation in the control simulation was high to the west of India and this caused the TEJ to shift westwards by approximately the same amount. Orography was found to have minimal impact on the simulated TEJ hence indicating that latent heating is the crucial parameter. The primacy of latent heating in determining the jet location was confirmed by additional simulations where the simulated precipitation was brought closer to observations. This made the TEJ to also shift to the correct position.
The Wavenumber-Frequency Characteristics of the Tropical Waves in an Aqua-Planet GCM
WANG Zaizhi,MAO Jiangyu,WU Guoxiong,
WANG Zaizhi
,MAO Jiangyu,WU Guoxiong

大气科学进展 , 2008,
Abstract: Based on the aqua-planet experiments, the wavenumber-frequency characteristics of tropical waves and their influcing factors in SST distribution and the convective parameterization scheme are investigated using the spectral atmospheric general circulation model (SAMIL). Space-time spectral analysis is used to obtain the variance of convectively coupled tropical waves. In the Control experiment with maximum SST located at the equator the simulated tropical-wave behaviors are in agreement with those in observations and theoretical solutions. When the maximum SST is located at 5°N, the symmetric and antisymmetric waves are much weaker than those in the control experiment, suggesting that tropical wave activities are very sensitive to the SST distributions. Importantly, the variance maximum of Madden-Julian oscillation (MJO) is found to occur around 5°N, which suggests that the development of the MJO depends largely on the latitude of maximum SST. Furthermore, the seasonal variations of MJO may be mainly caused by the seasonal variations of the maximum SST. The experiment results with two different cumulus schemes--the Manabe moist convective adjustment and Zhang-McFarlane (ZM) convective scheme, were also compared to examine the impacts of convective parameterization. Weakened variances of each individual tropical wave when the ZM scheme is used suggest that the ZM scheme is not favorable for the tropical wave activities. However, the wave characteristics are different when the ZM scheme is used in different models, which may imply that the simulated basic state is important to the meridional distributions of the waves. The MJO signals suggest that the parameterization scheme may have great influence on the strength, but have less direct impact on the MJO distribution. The frequency of the tropical waves may be associated with the moisture control of convection and the large-scale condensation scheme used in the model.
Impact of convective downdrafts on model simulations: results from aqua-planet integrations
S. Sahany ,R. S. Nanjundiah
Annales Geophysicae (ANGEO) , 2008,
Abstract: The role of convective scale downdrafts has been examined, using the NCAR-CAM3.0 aqua-planet configuration. We find that, convective downdrafts make the atmosphere more unstable thus increasing the convective available potential energy (CAPE) of the atmosphere. It is noticed that, although the rate of CAPE consumption increases with the incorporation of downdrafts, the generation of CAPE increases with a higher rate. Also, it is noted that there is a reduction in the deep convective rainfall, with the inclusion of downdrafts, which is primarily due to the re-evaporation of precipitation within the downdrafts. There is a large increase in the low cloud fraction and the shortwave cloud forcing with the inclusion of convective scale downdrafts in the cumulus scheme, which along with the evaporation within the downdraft causes cooling in the troposphere. This is in contrast to previous studies on the impact of downdrafts using single column models. In Zhang and McFarlane (1995), using a single column model, it was shown that with the increase in the strength of the downdrafts, there was a reduction in CAPE. In the present study, using an aqua-planet framework, it is shown that CAPE is actually found to increase when the downdrafts are incorporated into the cumulus scheme, as compared to the case when there are no downdrafts. The rate of CAPE consumption which, is the same as the rate of stabilization of the atmosphere, is found to increase, but the mean CAPE as such is higher compared to the case when there are no downdrafts.
Performance of the HOMME dynamical core in the aqua-planet configuration of NCAR CAM4: equatorial waves
S. K. Mishra, M. A. Taylor, R. D. Nair, H. M. Tufo,J. J. Tribbia
Annales Geophysicae (ANGEO) , 2011,
Abstract: A new atmospheric dynamical core, named the High Order Method Modeling Environment (HOMME), has been recently included in the NCAR-Community Climate System Model version 4 (CCSM4). It is a petascale capable high-order element-based conservative dynamical core developed on a cubed-sphere grid. We have examined the model simulations with HOMME using the aqua-planet mode of CAM4 (atmospheric component of CCSM4) and evaluated its performance in simulating the equatorial waves, considered a crucial element of climate variability. For this we compared the results with two other established models in CAM4 framework, which are the finite-volume (FV) and Eulerian spectral (EUL) dynamical cores. Although the gross features seem to be comparable, important differences have been found among the three dynamical cores. The phase speed of Kelvin waves in HOMME is faster and more satisfactory than those in FV and EUL. The higher phase speed is attributed to an increased large-scale precipitation in the upper troposphere and a more top-heavy heating structure. The variance of the n=1 equatorial Rossby waves is underestimated by all three of them, but comparatively HOMME simulations are more reasonable. For the n=0 eastward inertio-gravity waves, the variances are weak and phase speeds are too slow, scaled to shallow equivalent depths. However, the variance in HOMME is relatively more compared to the two other dynamical cores. The mixed Rossby-gravity waves are feeble in all the three cases. In summary, model simulations using HOMME are reasonably good, with some improvement relative to FV and EUL in capturing some of the important characteristics associated with equatorial waves.
The Lick-Carnegie Exoplanet Survey: A 3.1 M_Earth Planet in the Habitable Zone of the Nearby M3V Star Gliese 581  [PDF]
Steven S. Vogt,R. Paul Butler,Eugenio J. Rivera,Nader Haghighipour,Gregory W. Henry,Michael H. Williamson
Physics , 2010, DOI: 10.1088/0004-637X/723/1/954
Abstract: We present 11 years of HIRES precision radial velocities (RV) of the nearby M3V star Gliese 581, combining our data set of 122 precision RVs with an existing published 4.3-year set of 119 HARPS precision RVs. The velocity set now indicates 6 companions in Keplerian motion around this star. Differential photometry indicates a likely stellar rotation period of ~94 days and reveals no significant periodic variability at any of the Keplerian periods, supporting planetary orbital motion as the cause of all the radial velocity variations. The combined data set strongly confirms the 5.37-day, 12.9-day, 3.15-day, and 67-day planets previously announced by Bonfils et al. (2005), Udry et al. (2007), and Mayor et al (2009). The observations also indicate a 5th planet in the system, GJ 581f, a minimum-mass 7.0 M_Earth planet orbiting in a 0.758 AU orbit of period 433 days and a 6th planet, GJ 581g, a minimum-mass 3.1 M_Earth planet orbiting at 0.146 AU with a period of 36.6 days. The estimated equilibrium temperature of GJ 581g is 228 K, placing it squarely in the middle of the habitable zone of the star and offering a very compelling case for a potentially habitable planet around a very nearby star. That a system harboring a potentially habitable planet has been found this nearby, and this soon in the relatively early history of precision RV surveys, indicates that eta_Earth, the fraction of stars with potentially habitable planets, is likely to be substantial. This detection, coupled with statistics of the incompleteness of present-day precision RV surveys for volume-limited samples of stars in the immediate solar neighborhood suggests that eta_Earth could well be on the order of a few tens of percent. If the local stellar neighborhood is a representative sample of the galaxy as a whole, our Milky Way could be teeming with potentially habitable planets.
Sensitivity of African easterly waves to boundary layer conditions
A. Lenouo,F. Mkankam Kamga
Annales Geophysicae (ANGEO) , 2008,
Abstract: A linearized version of the quasi-geostrophic model (QGM) with an explicit Ekman layer and observed static stability parameter and profile of the African easterly jet (AEJ), is used to study the instability properties of the environment of the West African wave disturbances. It is found that the growth rate, the propagation velocity and the structure of the African easterly waves (AEW) can be well simulated. Two different lower boundary conditions are applied. One assumes a lack of vertical gradient of perturbation stream function and the other assumes zero wind perturbation at the surface. The first case gives more realistic results since in the absence of horizontal diffusion, growth rate, phase speed and period have values of 0.5 day 1, 10.83 m s 1 and 3.1 day, respectively. The zero wind perturbation at the surface case leads to values of these parameters that are 50 percent lower. The analysis of the sensitivity to diffusion shows that the magnitude of the growth rate decreases with this parameter. Modelled total relative vorticity has its low level maximum around 900 hPa under no-slip, and 700 hPa under free slip condition.
Climatic study on the summer tropical easterly jet at 200 hPa

Lu Jingxi,Ding Yihui,

大气科学进展 , 1989,
Abstract: The low latitude easterlies at 200 hPa in summer (May-October) is analysed climatically during the 13-year period from 1968 to 1980, with a special emphasis on the relationship between the anomalous tropical easterly jet stream over South Asia and the low latitude atmospheric circulation, and also the summer monsoon precipitation in India. The compositing analysis shows that the tropical easterly jet stream over South Asia has five anomalous patterns at 200 hPa i.e. the western pattern, middle pattern, eastern pattern, two-branch pattern and multi-core pattern. Evidence has shown that the precipitaion in India anomalously increased during the anomalous period of the western pattern and the middle pattern, but reverse case is true in the eastern pattern. Some different anomalies of the precipitation in different area of India were found during the other two anomalous pattern.
O espetáculo do crescimento, de William Easterly
Paula Passanezi
Revista Ibero-Americana de Estratégia , 2007, DOI: 10.5585/riae.v4i1.84
Abstract: William Easterly, renomado consultor do Banco Mundial, com coragem e objetividade exp e a verdadeira face do fracasso de inúmeras medidas adotadas (e defendidas) por importantes organismos internacionais que, por muitos anos, vêm trabalhando em prol de um único objetivo: promover um crescimento sustentado e real para as economias que vivem em condi es precárias.
Aerosol distribution around Svalbard during intense easterly winds  [PDF]
A. D?rnbrack,I. S. Stachlewska,C. Ritter,R. Neuber
Atmospheric Chemistry and Physics Discussions , 2009,
Abstract: This paper reports on backscatter and depolarization measurements by an airborne lidar in the Arctic during the ASTAR 2004 campaign. A unique weather situation facilitated the observation of the aerosol concentration under strongly forced atmospheric conditions. The vigorous easterly winds distorted the flow past Svalbard in such a way that unique mesoscale features were visible in the remote-sensing observations. Mesoscale numerical modelling was applied to identify the sources of the aerosol plumes and to explain the observed patterns.
Planet migration  [PDF]
Edward W. Thommes,Jack J. Lissauer
Physics , 2002,
Abstract: A planetary system may undergo significant radial rearrangement during the early part of its lifetime. Planet migration can come about through interaction with the surrounding planetesimal disk and the gas disk--while the latter is still present--as well as through planet-planet interactions. We review the major proposed migration mechanisms in the context of the planet formation process, in our Solar System as well as in others.
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