Momentum budget of low level westerly jet during monsoon onset

In this paper a diagnostic study is carried Out to the source and sink terms for the formation and acceleration/deceleration of low level westerly Jet during monsoon onset. For this purpose momentum budget technique is used. The budget equation is derived in the (x.y.p.t) system. The area is confined to a small box the boundaries over the central Arabian Sea the westerly flow prominent during the onset of monsoon. Each tem in the budget equation is calculated separately. FGG E III b. 1200 UTC data set is used for the analysis. The Coriolis force term is found to be sink term rather than a source tern Tram. Transient north-south term is prominent source terms when time averaged momentum budget is considered. When the time averaged momentum budget for each pressure slab is considered. it is concluded that, north-south force terms are prominent source terms of momentum for all slabs and large .cumulus type convection may contribute to frictional dissipation of momentum for the upper pressure slabs. Frictional force is the main sink term when one examines the momentum budget for each day and the source term are varying day-by-day. On the average, the jet is accelerated during the period. It is also found that the net momentum tendency is small and oscillatory in nature. it is also found that at Minicoy. rainfall is inversely related to momentum tendency and whenever westerly jet is strong (weak) the rainfall is less (more). Distribution of U-momentum is also found to be oscillatory ill nature.

Approach to the 4/3 law for turbulent pipe and channel flows examined through a reformulated scale-by-scale energy budget

In this study, we propose a scale-by-scale (SBS) energy budget equation for flows with homogeneity in at least one direction. This SBS budget represents a modified form of the equation first proposed by Danaila et al. (J. Fluid Mech., vol. 430, 2001, pp. 87–109) for the channel centreline – the primary difference is that, here, we consider the role of pressure along with the errors associated with the isotropic approximations of the interscale divergence and Laplacian of the squared velocity increment. The term encompassing the effects of mean shear is also characterised such that the present analysis can be extended straightforwardly to locations away from the centreline. We show, based on a detailed analysis of previously published channel flow direct numerical simulations and pipe flow experiments near the centreline, how several terms in the present SBS budget equation (including the third-order velocity structure function) behave with increasing Reynolds number. The behaviour of these terms is shown to imply a rate of emergence and subsequent growth of the 4/3 law scale subrange at the channel centreline and pipe axis. The analysis also suggests that the peak magnitude of the third-order velocity structure function occurs at a scale that is fixed in proportion to the Taylor microscale at sufficiently high Reynolds number.

Oceanic Response to Tropical Cyclone Gonu (2007) in the Gulf of Oman and the Northern Arabian Sea: Estimating Depth of the Mixed Layer Using Satellite SST and Climatological Data

The category 5-equivalent tropical Cyclone Gonu (2007) was the strongest cyclone to enter the northern Arabian Sea and Gulf of Oman. The impact of this cyclone on the sea surface temperature (SST) cooling and deepening of the mixed layer was investigated herein using an optimally interpolated (OI) cloud-free sea surface temperature (SST) dataset, climatological profiles of water temperature, and data from Argo profilers. SST data showed a maximum cooling of 1.7–6.5 °C during 1–7 June 2007 over the study area, which is similar to that of slow- to medium-moving cyclones in previous studies. The oceanic heat budget equation with the assumptions of the dominant turbulent mixing effect was used to establish relationships between SST and mixed layer depth (MLD) for regions that were directly affected by cyclone-induced turbulent mixing. The relationships were applied to the SST maps from satellite to obtain maps of MLD for 1–7 June, when Gonu was over the study area. Comparing with the measured MLD from Argo data showed that this approach estimated the MLDs with an average error of 15%, which is an acceptable amount considering the convenience of this approach in estimating MLD and the simplifications applied in the heat budget equation. Some inconsistencies in calculating MLD were attributed to use of climatological temperature profiles that may not have appropriately represented the pre-cyclone conditions due to pre-existing cold/warm core eddies. Estimation of the diapycnal diffusion that quantified the turbulent mixing across the water column showed consistent temporal and spatial variations with the calculated MLDs.

Reduced misclosure of global sea-level budget with updated Tongji-Grace2018 solution

The global sea-level budget is studied using the Gravity Recovery and Climate Experiment (GRACE) solutions, Satellite Altimetry and Argo observations based on the updated budget equation. When the global ocean mass change is estimated with the updated Tongji-Grace2018 solution, the misclosure of the global sea-level budget can be reduced by 0.11–0.22 mm/year compared to four other recent solutions (i.e. CSR RL06, GFZ RL06, JPL RL06 and ITSG-Grace2018) over the period January 2005 to December 2016. When the same missing months as the GRACE solution are deleted from altimetry and Argo data, the misclosure will be reduced by 0.06 mm/year. Once retained the GRACE C20 term, the linear trends of Tongji-Grace2018 and ITSG-Grace2018 solutions are 2.60 ± 0.16 and 2.54 ± 0.16 mm/year, closer to 2.60 ± 0.14 mm/year from Altimetry–Argo than the three RL06 official solutions. Therefore, the Tongji-Grace2018 solution can reduce the misclosure between altimetry, Argo and GRACE data, regardless of whether the C20 term is replaced or not, since the low-degree spherical harmonic coefficients of the Tongji-Grace2018 solution can capture more ocean signals, which are confirmed by the statistical results of the time series of global mean ocean mass change derived from five GRACE solutions with the spherical harmonic coefficients truncated to different degrees and orders.

The Turbulent Flow over the BARC Rectangular Cylinder: A DNS Study

A direct numerical simulation (DNS) of the incompressible flow around a rectangular cylinder with chord-to-thickness ratio 5:1 (also known as the BARC benchmark) is presented. The work replicates the first DNS of this kind recently presented by Cimarelli et al. (J Wind Eng Ind Aerodyn 174:39–495, 2018), and intends to contribute to a solid numerical benchmark, albeit at a relatively low value of the Reynolds number. The study differentiates from previous work by using an in-house finite-differences solver instead of the finite-volumes toolbox OpenFOAM, and by employing finer spatial discretization and longer temporal average. The main features of the flow are described, and quantitative differences with the existing results are highlighted. The complete set of terms appearing in the budget equation for the components of the Reynolds stress tensor is provided for the first time. The different regions of the flow where production, redistribution and dissipation of each component take place are identified, and the anisotropic and inhomogeneous nature of the flow is discussed. Such information is valuable for the verification and fine-tuning of turbulence models in this complex separating and reattaching flow.

A Budget-Based Turbulence Length Scale Diagnostic

<p>The most frequently used boundary-layer turbulence parameterization in numerical weather prediction (NWP) models are turbulence kinetic energy (TKE) based schemes. However, these parameterizations suffer from a potential weakness, namely the strong dependence on an ad-hoc quantity, the so-called turbulence length scale. The physical interpretation of the turbulence length scale is difficult and hence it cannot be directly related to measurements or large eddy simulation (LES) data. Consequently, formulations for the turbulence length scale in basically all TKE schemes are based on simplified assumptions and are model-dependent. A good reference for the independent evaluation of the turbulence length scale expression for NWP modeling is missing. We propose a new turbulence length scale diagnostic which can be used in the gray zone of turbulence without modifying the  underlying TKE turbulence scheme. The new diagnostic is based on the TKE budget: The core idea is to encapsulate the sum of the molecular dissipation  and the cross-scale TKE transfer into an effective dissipation, and associate it with the new turbulence length scale. This effective dissipation can then be calculated as a residuum in the TKE budget equation (for horizontal sub-domains of different sizes) using LES data. Estimation of the scale dependence of the diagnosed turbulence length scale using this novel method is presented for several idealized cases.</p>

Estimation of potential groundwater recharge by a drywell in sandy clay soil

ABSTRACT We estimated the potential groundwater recharge (Rpot) of a drywell that receives, temporarily stores, and infiltrates direct surface runoff from a contribution area (180.5 m2) comprising a roof and a cemented floor. The Rpot for traditional rainwater management and for similar contribution area but covered with grass was also estimated for comparison. Our methodology involved the use of water budget equation, monitoring of rainfall and soil water content up to 1.92 m depth, estimation of drywell overflow using the modified Puls model, and determination of actual evapotranspiration using water stress coefficient in 2017 and 2018. Results revealed that the Rpot for drywell was 83.3% of the precipitated volume, 2.22 times higher than that of the grass-covered area (37.6%) given the increased area for evapotranspiration in the latter. In turn, the traditional urban drainage system did not demonstrate potential of groundwater recharge. Therefore, the drywell contributes significantly to groundwater recharge apart from serving as local flood control.

Future Changes in the Tropical Cyclone Intensity and Frequency over the Western North Pacific Based on 20-km HiRAM and MRI Models

The future changes in the tropical cyclone (TC) intensity and frequency over the western North Pacific (WNP) under global warming remain uncertain. In this study, we investigated such changes using 20-km resolution HiRAM and MRI models, which can realistically simulate the TC activity in the present climate. We found that the mean intensity of TCs in the future (2075−2099) would increase by approximately 15%, along with an eastward shift of TC genesis location in response to the El-Niño like warming. However, the lifetime of future TCs would be shortened because the TCs tend to have more poleward genesis locations and move faster due to a stronger steering flow related to the strengthened WNP subtropical high in a warmer climate. In other words, the enhancement of TC intensity in future is not attributable to the duration of TC lifetime.To understand the processes responsible for the change in TC intensity in a warmer climate, we applied the budget equation of synoptic-scale eddy kinetic energy along the TC tracks in model simulations. The diagnostic results suggested that both the upper level baroclinic energy conversion (CE) and lower-level barotropical energy conversion (CK) contribute to the intensified TCs under global warming. The increased CE results from the enhancement of TC-related perturbations of temperature and vertical velocity over the subtropical WNP, whereas the increased CK mainly comes from synoptic-scale eddies interacting with enhanced zonal-wind convergence associated with seasonal mean and intraseasonal flows over Southeast China and the northwestern sector of WNP.

Factors Regulating the Multidecadal Changes in MJO Amplitude over the Twentieth Century

This study examined multidecadal changes in the amplitude of the boreal-winter Madden–Julian oscillation (MJO) over the twentieth century using two century-long reanalysis datasets (20CR and ERA-20C). Both revealed reasonable MJO variability compared to other state-of-the-art reanalysis datasets. We detected pronounced multidecadal variations along with an increasing trend in MJO amplitude during the period 1900–2009 in both datasets, although this linear trend was less significant in the reconstructed MJO index proposed by Oliver and Thompson. The two twentieth-century reanalysis datasets and the Oliver–Thompson MJO index consistently showed the intensified amplitude of MJO precipitation and circulation in the later decades (1970–99) compared to the earlier decades (1920–49). The most significant enhancement of MJO precipitation in the later decades appeared over the western Pacific warm pool. To understand the mechanisms controlling the changes in western Pacific MJO precipitation amplitude over the twentieth century, we diagnosed the moisture budget equation. The enhanced MJO precipitation variability in the later decades mainly came from increased moisture associated with a strengthened low-level convergence anomaly working on background mean moisture []. Further diagnosis showed that the effect of anomalous circulation (∇ ⋅ V′) change on the MJO precipitation amplitude change over the twentieth century was about an order larger than that of mean moisture () change, different from the mechanisms (i.e., increased gradient of ) responsible for the intensified MJO precipitation amplitude under future warmer climate. The enhanced MJO circulation anomalies during 1970–99 may be caused by an enhanced diabatic heating anomaly, offset partly by the increased mean static stability.

Computing the Water Budget Components for Lakes by Using Meteorological Data

Lake Mariout located between the longitudes of 29° 49′ and 29° 56′E and latitudes of 31° 04′ and 31° 08′N in Egypt. It is situated on the southern side of Alexandria City, Egypt. The land surrounding the lake is occupied by agriculture field, population zones and fish farms. This makes the lake to serve as a sink to drain different kinds of drainage waters from surrounding catchment areas of Alexandria City. The water of Lake Mariout is pumped to the Mediterranean Sea through El-Max pump station. The water budget was computed by measuring or estimating all of the lake’s water gains and losses. Applying the hydrology budget balance for lakes takes the interaction between the inflow and the outflow water from lakes into account. It is very useful for conservation and better management of water resources. All water budget components of the lake are estimated. Groundwater amount is the most difficult component to be measured or estimated in the water budget equation. Most of the previous studies assumed that the residual of water budget to be the groundwater flow to the lake. The results show that the lake Mariout receives approximately 8.95 m3/d from the main drains which represents the major part of the inflow water to lake. The discharge of El-max pump station is also one of the largest components of the outflow water (102 m3/s), while the water loss by evaporation represents 3.2% of the outflow water from the lake. Moreover, the water gain by rainfall 0.38% of the inflow water. The Groundwater flow to/out the lake was estimated as a residual of the water budget equation. It represents 1.2% of the total inputs for the lake water budget. The result shows that the lake is under severe environmental pressure. One of that is the groundwater comes from catchments areas which may be affect the configuration and operating system management of El-Max pump station by the time running.