Terms Of Energy Budget Research Articles

Evolution of withdrawal features of the southwest monsoon over India

ABSTRACTThe withdrawal features of the Indian summer monsoon (ISM) are investigated with the large‐scale circulations and significant terms of kinetic energy (KE), heat and moisture budget. The daily reanalysis datasets of National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) for the period of 1981–2005 are used. The results reveal that the strength of low‐level westerlies over the Arabian Sea, Indian landmass and Bay of Bengal decreases during the transition of withdrawal phase of the summer monsoon. On the other hand, the strength of upper level tropical easterly jet weakens from pre‐retreat to post‐retreat. The intensity and position of rising and sinking flow of vertical velocity shifted towards south from pre‐retreat to post‐retreat period. The diagnostic analysis indicates that the zones of Somali coast and southwest Bay of Bengal show stronger generation of KE during pre‐retreat period. Further, the flux convergence of heat observed over central Indian Ocean and the flux divergence of heat over east African region during post‐retreat period. The flux convergence of heat and moisture are stronger over the equatorial Indian Ocean during post‐retreat phase as compared to pre‐retreat. The convective activity and moisture flux convergence are stronger over the Indian Ocean during post‐retreat period, which is due to the movement of Inter Tropical Convergence Zone towards south during the transition from summer to winter monsoon over India. Thus, the dynamic and thermodynamic behaviour of monsoon has great impact on the transition during retreat phase of the ISM.

Impacts of Shallow Convection on MJO Simulation: A Moist Static Energy and Moisture Budget Analysis

Abstract The role of shallow convection in Madden–Julian oscillation (MJO) simulation is examined in terms of the moist static energy (MSE) and moisture budgets. Two experiments are carried out using the NCAR Community Atmosphere Model, version 3.0 (CAM3.0): a “CTL” run and an “NSC” run that is the same as the CTL except with shallow convection disabled below 700 hPa between 20°S and 20°N. Although the major features in the mean state of outgoing longwave radiation, 850-hPa winds, and vertical structure of specific humidity are reasonably reproduced in both simulations, moisture and clouds are more confined to the planetary boundary layer in the NSC run. While the CTL run gives a better simulation of the MJO life cycle when compared with the reanalysis data, the NSC shows a substantially weaker MJO signal. Both the reanalysis data and simulations show a recharge–discharge mechanism in the MSE evolution that is dominated by the moisture anomalies. However, in the NSC the development of MSE and moisture anomalies is weaker and confined to a shallow layer at the developing phases, which may prevent further development of deep convection. By conducting the budget analysis on both the MSE and moisture, it is found that the major biases in the NSC run are largely attributed to the vertical and horizontal advection. Without shallow convection, the lack of gradual deepening of upward motion during the developing stage of MJO prevents the lower troposphere above the boundary layer from being preconditioned for deep convection.

Meta-analyses of the effects of river flow on fish movement and activity

Estimating the timing and magnitude of fish movements relative to environmental factors can provide insight into why fishes behave as they do. To make broad-level inferences about fish movement in lotic environments, we conducted random-effects meta-analyses on the effects of river flow magnitude on (i) non-migratory movements, (ii) upstream migratory movements, (iii) downstream migratory movements, and (iv) fine-scale activity. We found a significant positive effect of river discharge on non-migratory movements ([Formula: see text] = 0.41 (mean) ± 0.07 (SE), Z = 6.06, p < 0.01, k (sample size) = 27); fishes made larger and (or) more frequent movements during periods of elevated discharge. Furthermore, non-salmonids were more affected by river flow than salmonids. River discharge also had a significant positive effect on the rate, frequency, and probability of upstream migratory movements ([Formula: see text] = 0.23 ± 0.10, Z = 2.24, p < 0.05, k = 8). However, the effect of discharge on the rate of downstream migratory movements ([Formula: see text] = –0.05 ± 0.15, Z = –0.35, p > 0.05, k = 5) and fine-scale activity ([Formula: see text] = 0.01 ± 0.11, Z = 0.08, p > 0.05, k = 5) were not significant. Heterogeneity of effect sizes was evident in all meta-analyses as well as inclusion and (or) publication bias. Collectively, our meta-analyses suggested that changes to a river’s flow regime can modulate non-migratory fish behaviour, the consequences of which need to be explored in terms of habitat use and energy budgets. However, more studies are needed to examine potential effect modifiers and improve sample sizes overall.

A Characterization of the Present-Day Arctic Atmosphere in CCSM4

Abstract Simulation of key features of the Arctic atmosphere in the Community Climate System Model, version 4 (CCSM4) is evaluated against observational and reanalysis datasets for the present-day (1981–2005). Surface air temperature, sea level pressure, cloud cover and phase, precipitation and evaporation, the atmospheric energy budget, and lower-tropospheric stability are evaluated. Simulated surface air temperatures are found to be slightly too cold when compared with the 40-yr ECMWF Re-Analysis (ERA-40). Spatial patterns and temporal variability are well simulated. Evaluation of the sea level pressure demonstrates some large biases, most noticeably an under simulation of the Beaufort High during spring and autumn. Monthly Arctic-wide biases of up to 13 mb are reported. Cloud cover is underpredicted for all but summer months, and cloud phase is demonstrated to be different from observations. Despite low cloud cover, simulated all-sky liquid water paths are too high, while ice water path was generally too low. Precipitation is found to be excessive over much of the Arctic compared to ERA-40 and the Global Precipitation Climatology Project (GPCP) estimates. With some exceptions, evaporation is well captured by CCSM4, resulting in P − E estimates that are too high. CCSM4 energy budget terms show promising agreement with estimates from several sources. The most noticeable exception to this is the top of the atmosphere (TOA) fluxes that are found to be too low while surface fluxes are found to be too high during summer months. Finally, the lower troposphere is found to be too stable when compared to ERA-40 during all times of year but particularly during spring and summer months.

Noah-GEM and Land Data Assimilation System (LDAS) based downscaling of global reanalysis surface fields: Evaluations using observations from a CarboEurope agricultural site

This study provides the first assessment of the Noah and Noah-GEM (photosynthesis-based Gas exchange Evapotranspiration Model) land surface model using observations from the Avignon, France CarboEurope agricultural site during 2006 and 2007. Noah and Noah-GEM are integrated within a Land Data Assimilation System (LDAS) framework. The LDAS fields of soil moisture, temperature field, and surface and subsurface water and energy budget terms are useful for meteorological model initial conditions, and agricultural applications. The models were integrated using 1km grid spacing with meteorological forcing from the Japanese global reanalysis (JRA). Consistent with results compiled over the US Southern Great Plains, the Noah and Noah-GEM based model performance was comparable for sorghum and wheat cropland. Both models had a relatively better performance during the low LAI plant growth stage however the performance deteriorated during peak green conditions and the bias between the observed and modeled latent heat flux was consistently higher by 100Wm−2. To further diagnose this bias, a series of experiments were undertaken by considering observed biweekly dynamic leaf area index (LAI), vegetation height, roughness length (z0), and albedo changes. These experiments were conducted using Noah-GEM because of similar results between Noah and Noah-GEM and also because Noah-GEM has an explicit C3 and C4 photosynthesis model. The results were compared with the default model run as well as in situ surface flux and soil moisture/temperature observations. Prescribing onsite characteristics led to modest improvements in the model fields, however the model still could not capture the peak growing heat flux values of sensible heat for both C3 and C4 plants. Additional experiments were undertaken to investigate the inconsistencies in model parameterization. These include experiments with a CO2-based transpiration and thermal roughness formulation in surface-layer physics; the surface coupling coefficient through the “Zilitinkevich constant”; effect of soil texture and model spin-up time. Based on the study results and the experiments, we conclude that a high resolution LDAS/Noah setup can be driven using global reanalysis fields producing reasonably good results when evaluated against point observations. The model performance was enhanced after using dynamic LAI and albedo feedback; however the key feature was the tuning of the model structure through coupling and modifying Vmax as a function of LAI. These results highlight the need for improvements in the turbulent surface layer and plant physiological modules, and model deficiencies cannot be overcome by onsite biophysical data alone.

An Energy Balance Snowmelt Model for Application at a Continental Alpine Site

The objectives of this study are to measure and evaluate the energy balance of a continental alpine snowpack during spring snowmelt conditions, to evaluate the performance of a point energy and mass balance model of a snow cover in alpine conditions. The investigation is conducted during the 1997 snowmelt season at Niwot Ridge in the Colorado Front Range. Further comparisons of the modeled results to the previously described measured results are made below the energy budget terms. The fluxes are corroborated using a point energy and mass balance model for a snowpack to determining snowpack energy exchanges, with minor differences found between flux magnitudes. This comparison suggests that the representation of internal snowpack energy and mass exchange processes is generally orrect.

Reynolds number effects on scale energy balance in wall turbulence

The scale energy budget utilizes a modified version of the classical Kolmogorov equation of wall turbulence to develop an evolution equation for the second order structure function [R. J. Hill, “Exact second-order structure-function relationships,” J. Fluid Mech. 468, 317 (2002)]. This methodology allows for the simultaneous characterization of the energy cascade and spatial fluxes in turbulent shear flows across the entire physical domain as well as the range of scales. The present study utilizes this methodology to characterize the effects of Reynolds number on the balance of energy fluxes in turbulent channel flows. Direct numerical simulation data in the range Reτ = 300–934 are compared to previously published results at Reτ = 180 [N. Marati, C. M. Casciola, and R. Piva, “Energy cascade and spatial fluxes in wall turbulence,” J. Fluid Mech. 521, 191 (2004)]. The present results show no Reynolds number effects in the terms of the scale energy budget in either the viscous sublayer or buffer regions of the channel. In the logarithmic layer, the transfer of energy across scales clearly varies with Reynolds number, while the production of turbulent kinetic energy is not dependent on Reynolds number. An envelope of inverse energy cascade is quantified in the buffer region within which energy is transferred from small to larger scales. This envelope is observed in the range 6 < y+ < 37, where all scales except the smallest scales display characteristics of an inverse energy cascade. The cross-over scale lc+, which indicates the transition between production dominated and scale transfer dominated regimes, increases with Reynolds number, implying a larger range of transfer dominated scales, before the dominant mechanism switches to production. At higher Reynolds numbers, two distinct regimes of lc+ as a function of wall-normal location are observed, which was not captured at Reτ = 180. The variations of lc+ match the trends of the shear scale, which is a representation of the mean shear in the flow. Thus, this study demonstrates the utility and importance of the use of higher Reynolds number data in order to accurately characterize and understand the energy dynamics of various scales across the entire boundary layer.

Analysis of the Arctic atmospheric energy budget in WRF: A comparison with reanalyses and satellite observations

[1] The Weather Research and Forecasting (WRF) model is used to dynamically downscale the regional climate of the Arctic, an area undergoing rapid climate changes. Because the WRF model is increasingly being run over larger spatial and temporal scales, an assessment of its ability to reconstruct basic properties of regional climates, such as terms in the energy budget, is crucial. Estimates of the Arctic energy budget from WRF are compared with estimates from reanalyses and satellite observations. The WRF model was run on a large pan-Arctic domain continuously from 2000 to 2008. Apart from a few systematic shortcomings, WRF sufficiently captures the Arctic energy budget. The major deficiency, with differences from reanalyses and satellite observations as large as 40 W m−2 in summer months, is in the shortwave radiative fluxes at both the surface and top of atmosphere (TOA). WRF's positive bias in upwelling shortwave radiation is due to a specified constant sea ice albedo of 0.8, which is too high during the summer. When sea ice albedo in WRF is allowed to vary in a more realistic manner in a test simulation, both surface and TOA energy budget components improve, while showing little impact on the atmospheric energy convergence and storage. A second, similar WRF simulation was performed but with gridded nudging enabled. When the large-scale circulation is constrained to the forcing data, the two energy budget terms that are most dependent on weather patterns, the convergence of atmospheric energy transport and the tendency of column-integrated energy, closely resemble their reanalysis counterparts.

Global Energy and Water Budgets in MERRA

Abstract Reanalyses, retrospectively analyzing observations over climatological time scales, represent a merger between satellite observations and models to provide globally continuous data and have improved over several generations. Balancing the earth’s global water and energy budgets has been a focus of research for more than two decades. Models tend to their own climate while remotely sensed observations have had varying degrees of uncertainty. This study evaluates the latest NASA reanalysis, the Modern Era Retrospective-Analysis for Research and Applications (MERRA), from a global water and energy cycles perspective, to place it in context of previous work and demonstrate the strengths and weaknesses. MERRA was configured to provide complete budgets in its output diagnostics, including the incremental analysis update (IAU), the term that represents the observations influence on the analyzed states, alongside the physical flux terms. Precipitation in reanalyses is typically sensitive to the observational analysis. For MERRA, the global mean precipitation bias and spatial variability are more comparable to merged satellite observations [the Global Precipitation and Climatology Project (GPCP) and Climate Prediction Center Merged Analysis of Precipitation (CMAP)] than previous generations of reanalyses. MERRA ocean evaporation also has a much lower value, which is comparable to independently derived estimate datasets. The global energy budget shows that MERRA cloud effects may be generally weak, leading to excess shortwave radiation reaching the ocean surface. Evaluating the MERRA time series of budget terms, a significant change occurs that does not appear to be represented in observations. In 1999, the global analysis increments of water vapor changes sign from negative to positive and primarily lead to more oceanic precipitation. This change is coincident with the beginning of Advanced Microwave Sounding Unit (AMSU) radiance assimilation. Previous and current reanalyses all exhibit some sensitivity to perturbations in the observation record, and this remains a significant research topic for reanalysis development. The effect of the changing observing system is evaluated for MERRA water and energy budget terms.

A sensitivity study to global desertification in cold and warm climates: results from the IPSL OAGCM model

Many simulations have been devoted to study the impact of global desertification on climate, but very few have quantified this impact in very different climate contexts. Here, the climatic impacts of large-scale global desertification in warm (2100 under the SRES A2 scenario forcing), modern and cold (Last Glacial Maximum, 21 thousand years ago) climates are assessed by using the IPSL OAGCM. For each climate, two simulations have been performed, one in which the continents are covered by modern vegetation, the other in which global vegetation is changed to desert i.e. bare soil. The comparison between desert and present vegetation worlds reveals that the prevailing signal in terms of surface energy budget is dominated by the reduction of upward latent heat transfer. Replacing the vegetation by bare soil has similar impacts on surface air temperature South of 20°N in all three climatic contexts, with a warming over tropical forests and a slight cooling over semi-arid and arid areas, and these temperature changes are of the same order of magnitude. North of 20°N, the difference between the temperatures simulated with present day vegetation and in a desert world is mainly due to the change in net radiation related to the modulation of the snow albedo by vegetation, which is obviously absent in the desert world simulations. The enhanced albedo in the desert world simulations induces a large temperature decrease, especially during summer in the cold and modern climatic contexts, whereas the largest difference occurs during winter in the warm climate. This temperature difference requires a larger heat transport to the northern high latitudes. Part of this heat transport increase is achieved through an intensification of the Atlantic Meridional Overturning Circulation. This intensification reduces the sea-ice extent and causes a warming over the North Atlantic and Arctic oceans in the warm climate context. In contrast, the large cooling North of 20°N in both the modern and cold climate contexts induces an increase in sea-ice extent.

DNS Scrutiny of the ζ-f Elliptic-Relaxation Eddy-Viscosity Model in Channel Flows with a Moving Wall

In this paper we present a Direct Numerical Simulations (DNS) of channel flow with stationary and moving walls. Three cases, Poiseuille-type with UW/Ub = 0.75, intermediate-type with UW/Ub = 1.215, and Couette-type with UW/Ub = 1.5 (UW and Ub are the wall and the bulk velocity), were compared with the pure Poiseuille UW/Ub = 0, at a bulk Reynolds number equal to 4,800 corresponding to Re\(_{\uptau} =288\). The DNS results were used to scrutinize the capabilities of ζ-f eddy viscosity model (based on the elliptic relaxation concept) in reproducing the near-wall turbulence in non conventional flows where the shear stress structures are strongly different with respect to the cases used for models calibration. The ζ-f model (also in its basic formulation) demonstrated to have good prospects to reproduce the main phenomenology of such class of flows due to its built-in capabilities to account separately for the different (and opposite) near wall effects on turbulence: the damping due to viscosity and pressure reflection. The results of the computations demonstrated that standard ζ-f model can reasonably reproduce the phenomenology of these flows in terms of velocity and turbulent kinetic energy profiles and budgets.

Turbulent kinetic energy balance measurements in the wake of a low-pressure turbine blade

The turbulent kinetic energy budget in the wake generated by a high lift, low-pressure two-dimensional blade cascade of the T106 profile was investigated experimentally using hot-wire anemometry. The purpose of this study is to examine the transport mechanism of the turbulent kinetic energy and provide validation data for turbulence modeling. Point measurements were conducted on a high spatial resolution, two-dimensional grid that allowed precise derivative calculations. Positioning of the probe was achieved using a high accuracy traversing mechanism. The turbulent kinetic energy (TKE) convection, production, viscous diffusion and turbulent diffusion were all obtained directly from experimental measurements. Dissipation and pressure diffusion were calculated indirectly using techniques presented and validated by previous investigators. Results for all terms of the turbulent kinetic energy budget are presented and discussed in detail in the present work.

An energy budget approach for evaluating the biocontrol potential of cotton aphid (Aphis gossypii) by the ladybeetle Propylaea japonica

AbstractBiological control of economically important crop pests is an important component of integrated pest management (IPM) strategies. Predator–prey energy relationships are critical to the success of biocontrol strategies; however, these relationships are often ignored in many IPM programs. In this study, the biocontrol potential of cotton aphid, Aphis gossypii (Glover) (Hemiptera: Aphididae), by the ladybeetle Propylaea japonica (Thunberg) (Coleoptera: Coccinellidae) was estimated in terms of energy budgets calculated at 27 ± 1 °C. The energy equivalent of prey subjects (aphids) consumed was estimated from bomb calorimetry and partitioned into the energy associated with ingestion, assimilation, respiration, reproduction, and waste for each developmental stage of the lady beetle. The average assimilation efficiencies for larval and adult ladybeetles were 88.2 and 91.1%, respectively, whereas net ecological efficiencies were 17.6% for larvae and 2.6% for adults. Similarly, assimilation efficiencies of cotton aphids were 71.5 and 74.4% for nymphs and adults, respectively. Based on energy budget calculations, approximately 520, 3‐day‐old aphids and 5 356, 3‐day‐old aphids were estimated to be consumed by the ladybeetle larval stage and the female adult stage, respectively. These estimates were similar to the actual number of aphids consumed by the ladybeetles, based on actual counts. The current data demonstrate that P. japonica is an important natural enemy of the cotton aphid, and that predator–prey energy relationships can play a critical role in biocontrol strategies and IPM programs.

A Multimodel Analysis for the Coordinated Enhanced Observing Period (CEOP)

Abstract A collection of eight operational global analyses over a 27-month period have been processed to common data structures to facilitate comparisons among the analyses and global observational datasets. The present study evaluated the global precipitation, outgoing longwave radiation (OLR) at the top of the atmosphere, and basin-scale precipitation over the United States. In addition, a multimodel ensemble was created from a linear average of the available data, as close to the analysis time as each system permitted. The results show that the monthly global precipitation and OLR from the multimodel ensemble compares generally better to the observations than any single analysis. Likewise, the daily precipitation from the ensemble exhibits better statistical comparison (in space and time) to gauge observations over the Mississippi River basin. However, the comparisons have seasonality, when the members of the ensemble exhibit generally more skill, during winter. There is notably higher skill of the summertime basin precipitation by the ensemble. Using the global precipitation and OLR, the sensitivity was tested to selectively choose the members with the best statistical comparisons to the reference data. Only small improvements in the statistics were found when comparing a selective ensemble to the full ensemble. Additionally, terms of the global energy budget were compared among the ensemble and to other estimates. The ensemble data and the variance of the ensemble should make a useful point of comparison for the development of model and assimilation components of global analyses.

Long-Term Study of Lake Evaporation and Evaluation of Seven Estimation Methods: Results from Dickie Lake, South-Central Ontario, Canada

Establishing satisfactory calculation methods of lake evaporation has been crucial for research and manage-ment of water resources and ecosystems. A 30 year dataset from Dickie Lake, south-central Ontario, Canada added to the limited long-term studies on lake evaporation. Evaporation during ice-free season was calcu-lated separately using seven evaporation methods, based on field meteorology, hydrology and lake water temperature data. Actual evaporation determined during a portion of a year was estimated using a lake en-ergy budget model, and the estimation was used as reference evaporation for evaluation of the seven methods. The deviation of method-induced evaporation from the reference evaporation was compared among the seven methods, and a performance rank was proposed based on the root mean squared deviation and coeffi-cient of efficiency. As for the whole ice-free season (roughly May to November), the water balance was the best method, followed by Makkink, DeBruin-Kejiman, Penman, Priestley-Taylor, Hamon, and Jensen-Haise methods. As for shorter duration (a week to a month), the DeBruin-Kejiman was the best method, followed by Penman, Priestley-Taylor, Makkink, Hamon, Jensen-Haise, and water balance method. Annual and sea-sonal changes of energy budget terms and the compensation function of lake heat storage in evaporation flux were also analyzed.

The Beijing Climate Center atmospheric general circulation model: description and its performance for the present-day climate

The Beijing Climate Center atmospheric general circulation model version 2.0.1 (BCC_AGCM2.0.1) is described and its performance in simulating the present-day climate is assessed. BCC_AGCM2.0.1 originates from the community atmospheric model version 3 (CAM3) developed by the National Center for Atmospheric Research (NCAR). The dynamics in BCC_AGCM2.0.1 is, however, substantially different from the Eulerian spectral formulation of the dynamical equations in CAM3, and several new physical parameterizations have replaced the corresponding original ones. The major modification of the model physics in BCC_AGCM2.0.1 includes a new convection scheme, a dry adiabatic adjustment scheme in which potential temperature is conserved, a modified scheme to calculate the sensible heat and moisture fluxes over the open ocean which takes into account the effect of ocean waves on the latent and sensible heat fluxes, and an empirical equation to compute the snow cover fraction. Specially, the new convection scheme in BCC_AGCM2.0.1, which is generated from the Zhang and McFarlane’s scheme but modified, is tested to have significant improvement in tropical maximum but also the subtropical minimum precipitation, and the modified scheme for turbulent fluxes are validated using EPIC2001 in situ observations and show a large improvement than its original scheme in CAM3. BCC_AGCM2.0.1 is forced by observed monthly varying sea surface temperatures and sea ice concentrations during 1949–2000. The model climatology is compiled for the period 1971–2000 and compared with the ERA-40 reanalysis products. The model performance is evaluated in terms of energy budgets, precipitation, sea level pressure, air temperature, geopotential height, and atmospheric circulation, as well as their seasonal variations. Results show that BCC_AGCM2.0.1 reproduces fairly well the present-day climate. The combined effect of the new dynamical core and the updated physical parameterizations in BCC_AGCM2.0.1 leads to an overall improvement, compared to the original CAM3.

An Observational Analysis and Evaluation of Land Surface Model Accuracy in the Nebraska Sand Hills

Abstract In this study, the influence of subsurface water on the energy budget components of three locations with heterogeneous land surfaces in the Nebraska Sand Hills are examined through observations and use of the Noah land surface model (LSM). Observations of the four primary components of the surface energy budget are compared for a wet interdunal meadow valley, a dry interdunal valley, and a dunal upland location. With similar atmospheric forcing at each site, it was determined that differences in the partitioning of the mean diurnal net radiation (Rnet) existed among the three locations due to the influence of varied soil moisture and vegetation through the year. At the wet valley, observations indicated that almost 65% of the mean daily peak Rnet was used for latent heating, due to the relatively higher soil moisture content resulting from an annual upward gradient of subsurface water and denser vegetation. In sharp contrast, the dunal upland site yielded only 21% of the mean daily peak Rnet going to latent heating, and a greater mean diurnal soil heat flux with typically drier soils and sparser vegetation than at the wet valley. The dry valley partition of the peak Rnet fell between the wet valley and dunal upland site, with approximately 50% going to sensible heating and 50% toward latent heating. In addition to the observational analysis, an uncoupled land surface model was forced with the observations from each site to simulate the energy budgets, with no tuning of the model’s fundamental equations and with little adjustment of the model parameters to improve results. While the model was able to reasonably simulate the mean diurnal and annual energy budget components at all locations, in most instances with root-mean-square errors within 20%–25% of the observed values, the lack of explicit treatment of subsurface water within the model limited predictability, particularly at the wet valley site. For instance, only 25% of the peak mean diurnal Rnet went toward latent heating in the model simulation of the wet valley, compared to 65% as estimated by observations. Model evaluation statistics are presented to document the land surface model’s ability to capture the annual and mean diurnal variations in the surface energy budget terms at the dry valley and dunal upland sites, but the absence of subsurface water results in large errors in the wet valley simulation. From these results, a case is made for the future inclusion of the explicit treatment of subsurface water within the Noah LSM to better approximate the prediction of the surface energy budget in such environments.

Energetics of Madden Julian Oscillations in the NCAR CAM3: A Composite View

This study further examines the simulation of the tropical Madden‐Julian oscillation (MJO) using the modified Zhang‐McFarlane convection scheme in the National Center for Atmospheric Research Community Atmospheric Model version 3 (CAM3). The results demonstrate that modifications to the Zhang‐McFarlane scheme lead to significantly enhanced MJO and much improvement of the MJO structures. However, the propagation speed is too fast compared to observations. The westward tilting structures of moisture flux convergence over the western Pacific warm pool are simulated very well by the modified CAM3 (CAM3m). The modified Zhang‐McFarlane convection scheme also improves the energetic structures of the MJOs. With the climatological mean of the energetics from the composite MJO removed, the energy budget terms show clear eastward propagation following MJO movement in the CAM3m and ECMWF reanalysis (ERA40). The results further support that the interaction between convection and large‐scale circulation is important in the maintenance and growth of the MJO through perturbation kinetic energy (PKE) conversion from perturbation available potential energy (PAPE) generated by the correlation of specific volume (α) and large‐scale heating (Q1). Too weak Q1 and PAPE generated through (α, Q1) is responsible for the weak MJO and intraseasonal variability simulated by the standard CAM3. Too strong climatology mean of the energetics in the CAM3m may be caused by too strong stationary intraseasonal variability. Moisture flux convergence is responsible for the changes of specific humidity in the CAM3m and CAM3 during the cycle of the MJO over the Indian and western Pacific Oceans. These results indicate that interaction between convection, moisture and convergence in the lower troposphere may be responsible for the MJO development over the Indian and western Pacific Ocean in both observations and simulations. The weak intraseasonal variability and MJO simulated by the original Zhang‐McFarlane deep convection scheme is attributed to the lack of coherent shallow convection ahead of deep convection in the MJO cycle.

Influence of Precipitation Assimilation on a Regional Climate Model’s Surface Water and Energy Budgets

Abstract Initialization of the moisture profiles has been used to overcome the imbalance between analysis schemes and prediction models that generates the so-called spinup problem seen in the hydrological fields. Here precipitation assimilation through moisture adjustment has been proposed as a technique to reduce this problem in regional climate simulations by adjusting the specific humidity according to 3-hourly North American Regional Reanalysis rain rates during two simulated years: 1988 and 1993. A control regional simulation provided the initial condition fields for both simulations. The precipitation assimilation simulation was then compared to the control regional climate simulation, reanalyses, and observations to determine whether assimilation of precipitation had a positive influence on modeled surface water and energy budget terms. In general, rainfall assimilation improved the regional model surface water and energy budget terms over the conterminous United States. Precipitation and runoff correlated better than the control and the global reanalysis fields to the regional reanalysis and available observations. Upward shortwave and downward short- and longwave radiation fluxes had regional seasonal cycles closer to the observed values than the control, and the near-surface temperature anomalies were also improved.

A Study of Mean Winter Circulation Characteristics and Energetics over Southeastern Asia

A mean climatology is studied to examine atmospheric circulation characteristics to assess the wintertime (December, January, February and March - DJFM) synoptic weather system affecting northern India. The main objective is to study the mean circulation and mean energetics distribution pertaining to the winter season, which are embedded with an eastward moving synoptic weather system in westerlies, called Western Disturbances (WDs). Forty years (1958–1997) of uninitialized daily re-analysis data of the National Center for Environmental Prediction - National Center for Atmospheric Research (NCEP- NCAR, henceafter NCEP), U.S. has been considered for this study. Winter circulations are considered over the domain 15°S–45°N and 30°E–120°E. This domain is considered particularly to illustrate the impact of wintertime synoptic weather system Western Disturbances (WDs), which travel towards the east over the western Himalayas during winter and yield an enormous amount of precipitation in the form of snow. Large-scale balances of kinetic energy, vorticity, angular momentum, heat and moisture budget terms are analyzed. The main findings of the study show that strong rising motion in the extratropical region brings a significant amount of precipitation over the region of study. Also, horizontal flux of kinetic energy converges in the tropical region and diverges over the extratropical region. It is seen that both the zonal and meridional component of kinetic energy contributes to the production of kinetic energy in the upper troposphere. Vorticity budget shows that wintertime circulation over the western Himalayas is characterized by a negative generation of vorticity. The relative and planetary vorticity advection contributes to the horizontal transport of vorticity. The moisture flux transported into the region shows that in the middle tropospheric levels moisture undergoes phase transformation due to turbulent exchange and hence releases latent heat.