A study of the seasonal migration of ITCZ and the quasi-periodic oscillations in a simple monsoon system using an energy balance model   总被引：1，自引：0，他引：1  

K. Alapati  S. Raman 《Meteorology and Atmospheric Physics》1989,41(4):191-211

Summary A zonally averaged global energy balance model with feedback mechanisms was constructed to simulate (i) the poleward limits of ITCZ over the continent and over the ocean and (ii) a simple monsoon system as a result of differential heating between the continent and the ocean. Three numerical experiments were performed with lower boundary as (1) global continent, (2) global ocean and (3) continent-ocean, with freezing latitudes near the poles. Over the continent, midlatitude deserts were found and the ITCZ migrates 25° north and south with seasons. Over a global swamp ocean results do not show migration of ITCZ with time but once the ocean currents are introduced the ITCZ migrates 5° north and south with seasons. It was found that the seasonal migration of ITCZ strongly depends on the meridional distribution of the surface temperature. It was also found that continent influences the location of the oceanic ITCZ. In the tropics northward progression of quasi-periodic oscillations called events are found during the pre- and post-monsoon periods with a period of 8 to 15 days. This result is consistent with the observed quasi-periodic oscillations in the tropical region. Northward propagation of the surface temperature perturbation appears to cause changes in the sensible heat flux which in turn causes perturbations in vertical velocity and latent heat flux fields.List of Symbols vertical average - ₀ zonal average - vertical mean of the zonal average - _0s zonal average at the surface - _0a zonal average at 500 mb level - latitude We now define the various symbols used in the model rate of atmospheric heating due to convective cloud formation (K/sec) - dp/dt (N/m²/sec) - density - potential temperature (K) - rate of rotation of the earth (rad/sec) - empirical constant - humidity mixing ratio - ^* saturated humidity mixing ratio - opacity of the atmosphere - ₁,₂ factors for downward and upward effective black body long wave radiation from the atmosphere - Stefan-Boltzmann constant - emissivity of the surface - _D subsurface temperature (K) - a specific volume - _0xs ,_0ys eastward and northward components of surface frictional stress - ^* vertical velocity at the top of the boundary layer (N/m²/sec) - P Thickness of the boundary layer (mb) - nondimensional function of pressure - P pressure - P _a pressure of the model atmosphere (N/m²) - P _s pressure at the surface (N/m²) - t time (sec) - U eastward wind speed (m/sec) - V northward wind speed (m/sec) - surface water availability - T absolute temperature (K) - heat addition due to water phase changes - g acceleration due to gravity (m²/sec) - a radius of the earth (m) - R gas constant for dry air (J/Kg/K) - C _p specific heat of air at constant pressure (J/Kg/K) - k R/C _p - L latent heat of condensation (J/Kg) - f coriolis parameter (rad/sec) - H _s H _0s ⁽¹⁾ +H _0s ⁽²⁾ +H _0s ⁽³⁾ +H _0s ⁽⁴⁾ +H _0s ⁽⁵⁾ (J/m²/Sec)=sum of the rates of vertical heat fluxes per unit surface area, directed toward the surface - H _a H _0a ⁽¹⁾ +H _0a ⁽²⁾ +H _0a ⁽³⁾ +H _0a ⁽⁴⁾ (J/m²/Sec)=sum of the rates of heat additions to the atmospheric column per unit horizontal area by all processes - H _0s ⁽¹⁾ ,H _0a ⁽¹⁾ heat flux due to short wave radiation - H _0s ⁽²⁾ ,H _0a ⁽²⁾ heat flux due to long wave radiation - H _0s ⁽³⁾ ,H _0a ⁽³⁾ heat flux due to small scale convection - H _0s ⁽⁴⁾ heat flux due to evaporation - H _0a ⁽⁴⁾ heat flux due to condensation - H _0s ⁽⁵⁾ heat flux due to subsurface conduction and convection - e ^* saturation vapor pressure - R solar constant (W/m²) - r _a albedo of the atmosphere - r _s albedo of the surface - b ₂ empirical constant (J/m²/sec) - c ₂ empirical constant (J/m²/sec) - e ₂ nondimensional empirical constant - f ₂ empirical constant (J/m₂/sec) - factor proportional to the conductive capacity of the surface medium - a _s constant used in Sellers model - b _s positive constant of proportionality used in the Sellers model (kg m²/J/sec²) - K _HT coefficient for eddy diffusivity of heat (m²/sec) - K _HE exchange coefficient for water vapor (m²/sec) - h depth of the water column (m) - z height (m) - V _0ws meridional component of surface current (m/sec) - n cloud amount - G _0,n long wave radiation form the atmosphere for cloud amount n (W/m²) - B ₀ long wave radiation from the surface (W/m²) - S _0,n short wave radiation from the atmosphere for cloud amount n (W/m²) - A _n albedo factor for a cloud amount n - R _f1 large scale rainfall (mm/day) - R _f2 small scale rainfall (mm/day) With 22 Figures  相似文献   

Structure of the marine atmospheric boundary layer during two cold air outbreaks of varying intensities: GALE 86     

Robert J. Wayland  Sethu Raman 《Boundary-Layer Meteorology》1994,71(1-2):43-66

Aircraft, surface, upper air and satellite measurements have been used to observe the evolution and growth of the convective Marine Atmospheric Boundary Layer (MABL) offshore of North Carolina in close proximity to the Gulf Stream, during the intense cold air outbreak of 28 January 1986 and the moderate event of 12 February 1986, as part of the Genesis of Atlantic Lows Experiment (GALE). Air mass modification processes, driven primarily by the ocean-atmosphere exchanges of surface turbulent sensible and latent heat fluxes, caused the overlying air mass to warm and moisten as it advected over the warmer waters of the eastern United States continental shelf. Maximum observed near-surface total heat fluxes were 1045 and 811 W·m^–2 over the core of the Gulf Stream, for 28 January and 12 February 1986, respectively. The observed changes in the overlying air mass occurred almost instantaneously as the ambient flow traversed different underlying SST conditions.The turbulent structure showed a buoyancy-dominated MABL below approximately 0.8z/h. However, shear was also observed to be an important production term above 0.8z/h and below 0.1z/h for the 28 January 1986 event. Dissipation of turbulent kinetic energy was the dominant destruction term in the budgets, but vertical transport of energy was a strong contributor below 0.5z/h, above which this term became a source of turbulent energy. Additionally, the normalized standard deviations of the horizontal velocity components showed a near-equal contribution to the turbulence, while the vertical velocity components displayed the characteristic mid-layer maximum profile observed for a convective, well-mixed boundary layer.  相似文献   

A study of mean boundary-layer structures over the Arabian Sea and the Bay of Bengal during active and break monsoon periods     

Teddy Holt  Sethu Raman 《Boundary-Layer Meteorology》1987,38(1-2):73-94

Observations from research ships which took part in the Indo-Soviet Monsoon Experiment of 1977 (MONSOON 77) and the International Monsoon Experiments (MONEX 79) over the central Arabian Sea and the north central Bay of Bengal were analyzed to study the mean wind and temperature structure of the monsoon boundary layer during active and break conditions. Mean profiles of wind speed and direction along with virtual potential temperature obtained by averaging data from several research ships during 1977 and 1979 indicate that onset conditions were associated with substantial increases in wind speed over the Arabian Sea and a shift to strong southwest flow. Monsoon onset was also characterized by near-neutral to slightly unstable temperature profiles in the lowest kilometer. Break conditions in 1977 in which the monsoon trough moved northward and substantial (5 mb) pressure rises were noted over the Arabian Sea show wind speeds typically decreasing from approximately 18 m s^–1 during active conditions to roughly 8 m s ^–1. Temperature profiles during break conditions are similar to those observed in pre-monsoon conditions in that the boundary layer is observed to be generally much more stable up to 900 mb. Above 900 mb, profiles of virtual potential temperature show little variation.Analysis of latent and sensible heat fluxes during June 1977 calculated by the bulk aerodynamic method indicates values of latent heat flux during active conditions to be roughly two to three times larger than those during break conditions. Sensible heat flux shows an increase from approximately 20 to 80 W m ^–1 during the onset of the monsoon. Surface fluxes of water vapor indicate the importance of water vapor transport over the ship observation region in the central Arabian Sea during active conditions. Onset of the monsoon over the Arabian Sea is accompanied by an increase in the surface moisture flux by a factor of about two. Time histories of precipitable water show decreases of approximately 15% from active to break periods.  相似文献   

Editorial     

U. C. Mohanty  Sethu Raman  D. V. Bhaskar Rao 《Natural Hazards》2007,42(2):253-255

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Surface layer turbulence spectra and dissipation rates during low winds in tropics     

Anil Kumar Yadav  Sethu Raman  Maithili Sharan 《Boundary-Layer Meteorology》1996,79(3):205-223

Spectral characteristics of surface layer turbulence in an urban atmosphere are investigated. The observations used for this purpose represent low wind conditions in the tropics. The normalized power spectral shapes exhibit the usual characteristics in the inertial subrange and obey Monin-Obukhov scaling. However, the low-frequency behaviours do not conform to the previous observed relations. For horizontal components, large energy is contained in the low frequencies in contrast to the vertical component where roll-off to zero frequency is faster.The turbulent kinetic energy dissipation rate estimated from the spectra using Kolmogorov's inertial subrange law is found to be isotropic unlike the velocity variances. The expressions for the dimensionless dissipation rate do not seem to work well in low winds in an urban atmosphere. For the data considered, the dissipation rate exhibits a power law relationship with the mean windspeed and the friction velocity.  相似文献   

HST UV measurements of wind structure and velocities in Local Group OB stars     

Raman K. Prinja  & Paul A. Crowther 《Monthly notices of the Royal Astronomical Society》1998,300(3):828-836

Archival HST FOS and GHRS data sets have been used to collect ultraviolet evidence for large- and small-scale stellar wind structure in extragalactic Local Group OB stars (i.e. SMC, LMC including R136, M31, M33 and NGC 6822). By comparison with previous studies of Galactic OB stars, wind activity is principally diagnosed in individual spectrograms via the presence of 'narrow absorption components' and saturated 'black' absorption troughs in the resonance line doublets. Their characteristics broadly suggest that these stars share the same physical mechanisms for perturbing the winds as those that act in Galactic stars. Both of these spectral indicators are also used to provide reliable measures of wind terminal velocities. These velocities are directly compared with previously published Galactic values, without reliance on model profile fitting. Relative to Galactic OB stars, the most discrepant terminal velocities (and wind line profiles) result from main-sequence early O-type stars in the SMC.  相似文献   

A note on disturbances in a certain type of visco-elastic solid deformed by a magnetic field     

Rukmini Raman Giri 《Pure and Applied Geophysics》1965,62(1):41-48

Summary The present note is an attempt to study the propagation of disturbances in a semiinfinite visco-elastic rod which is of three-parameter type, and which is subjected to a static magnetic field.  相似文献   

Numerical Simulation of the Sensitivity of Summer Monsoon Circulation and Rainfall over India to Land Surface Processes     

S. Raman  U. C. Mohanty  N. C. Reddy  K. Alapaty  R. V. Madala 《Pure and Applied Geophysics》1998,152(4):781-809

—The influence of soil moisture and vegetation variation on simulation of monsoon circulation and rainfall is investigated. For this purpose a simple land surface parameterization scheme is incorporated in a three-dimensional regional high resolution nested grid atmospheric model. Based on the land surface parameterization scheme, latent heat and sensible heat fluxes are explicitly estimated over the entire domain of the model. Two sensitivity studies are conducted; one with bare dry soil conditions (no latent heat flux from land surface) and the other with realistic representation of the land surface parameters such as soil moisture, vegetation cover and landuse patterns in the numerical simulation. The sensitivity of main monsoon features such as Somali jet, monsoon trough and tropical easterly jet to land surface processes are discussed.¶Results suggest the necessity of including a detailed land surface parameterization in the realistic short-range weather numerical predictions. An enhanced short-range prediction of hydrological cycle including precipitation was produced by the model, with land surface processes parameterized. This parameterization appears to simulate all the main circulation features associated with the summer monsoon in a realistic manner.  相似文献   

Macrobenthos relative to the oxygen minimum zone on the East Indian margin,Bay of Bengal          下载免费PDF全文

Akkur V. Raman  Rayaroth Damodaran  Lisa A. Levin  Thiruchitrambalam Ganesh  Yannamani K. V. Rao  Sateesh Nanduri  Rakhesh Madhusoodhanan 《Marine Ecology》2015,36(3):679-700

The Bay of Bengal remains one of the least studied of the world's oxygen minimum zones (OMZs). Here we offer a detailed investigation of the macrobenthos relative to oxygen minimum zone [OMZ – DO (dissolved oxygen), concentration <0.5 ml·1^?1] at 110 stations off the North East Indian margin (16⁰ and 20⁰ N) featuring coastal, shelf and slope settings (10–1004 m). Macrobenthos (>0.5 mm) composition, abundance and diversity were studied in relation to variations in depth, dissolved oxygen, sediment texture and organic carbon. Using multivariate procedures powered by SIMPROF analysis we identified distinct OMZ core sites (depth 150–280 m; DO 0.37 ml·1^?1) that exhibited dense populations of surface‐feeding polychaetes (mean 2188 ind. m^?2) represented by spionids and cossurids (96%). Molluscs and crustaceans were poorly represented except for ampeliscid amphipods. The lower OMZ sites (DO > 0.55 ml·l^?1) supported a different assemblage of polychaetes (cirratulids, amphinomids, eunicids, orbinids, paraonids), crustaceans and molluscs, albeit with low population densities (mean 343 ind. m^?2). Species richness [E(S₁₀₀)], diversity (Margalef d; H’) and evenness (J’) were lower and dominance was higher within the OMZ core region. Multiple regression analysis showed that a combination of sand, clay, organic carbon, and dissolved oxygen explained 62–78% of the observed variance in macrobenthos species richness and diversity: E(S₁₀₀) and H’. For polychaetes, clay and oxygen proved important. At low oxygen sites (DO <1 ml·l^?1), depth accounted for most variance. Residual analysis (after removing depth effects) revealed that dissolved oxygen and sediment organic matter influenced 50–62% of residual variation in E(S₁₀₀), H’ and d for total macrofauna. Of this, oxygen alone influenced up to ~50–62%. When only polychaetes were evaluated, oxygen and organic matter explained up to 58–63%. For low oxygen sites, organic matter alone had the explanatory power when dominance among polychaetes was considered. Overall, macrobenthic patterns in the Bay of Bengal were consistent with those reported for other upwelling margins. However, the compression of faunal gradients at shallower depths was most similar to the Chile/Peru margin, and different from the Arabian Sea, where the depth range of the OMZ is two times greater. The Bay of Bengal patterns may take on added significance as OMZs shoal globally.  相似文献   

Elevation,slope aspect and integrated nutrient management effects on crop productivity and soil quality in North-west Himalayas,India     

Birendra Nath Ghosh  Narinder Kumar Sharma  Nurnabi Meherul Alam  Raman Jeet Singh  Gopal Prasad Juyal 《山地科学学报》2014,11(5):1208-1217

On farm bio-resource recycling has been given greater emphasis with the introduction of conservation agriculture specifically withclimate change scenarios in the mid-hills of the north-west Himalaya region（NWHR）. Under this changing scenario, elevation, slope aspect and integrated nutrient management（INM） may affect significantly soil quality and crop productivity. A study was conducted during 2009-2010 to 2010-2011 at the Ashti watershed of NWHR in a rainfed condition to examine the influence of elevation, slope aspect and integrated nutrient management（INM） on soil resource and crop productivity. Two years of farm demonstration trials indicated that crop productivity and soil quality is significantly affected by elevation, slope aspect and INM. Results showed that wheat equivalent yield（WEY） of improved technology increased crop productivity by -20%-37% compared to the conventional system. Intercropping of maize with cowpea and soybean enhanced yield by another 8%-17%. North aspect and higher elevation increased crop productivity by 15%-25% compared to south aspect and low elevation（except paddy）. Intercropping of maize with cowpea and soybean enhanced yield by another 8%-15%. Irrespective of slope, elevation and cropping system, the WEY increased by -30% in this region due to INMtechnology. The influence of elevation, slope aspect and INM significantly affected soil resources（SQI） and soil carbon change（SCC）. SCC is significantly correlated with SQI for conventional（R2 = 0.65＊）, INM technology（R2 = 0.81＊） and for both technologies（R2 = 0.73＊）. It is recommended that at higher elevation.（except for paddy soils） with a north facing slope, INM is recommended for higher crop productivity; conservation of soil resources is recommended for the mid hills of NWHR; and single values of SCC are appropriate as a SQI for this region.  相似文献