Numerical prediction of the Orissa super cyclone (1999) : Sensitivity to the parameterisation of convection, boundary layer and explicit moisture processes

& ih- ,l- ;w- @ ,u- lh- ,- vkj- ,e- ,e- 5 dk mi;ksx djds mM+hlk esa 1999 esa vk, egkpØokr dh xfrfof/k;ksa vkSj mldh rhozrk ds la[;kRed iwokZuqeku dk bl 'kks/k&i= esa v/;;u fd;k x;k gSA laogu] xzgh; ifjlhek Lrj vkSj fuf’pr ueh Ldheksa dh izkpyhdj.k ;kstukvksa dh Hkwfedk dk v/;;u djus ds fy, laosnu’khyrk iz;ksx fd, x, gSaA caxky dh [kkM+h esa 90] 30 vkSj 10 fd-eh- {kSfrt varjkyksa ds rhu ikjLifjd iz{ks=ksa ¼Mksesu½ dk irk yxkus ds fy, bl ekWMy dh ifjdYiuk dh xbZ gSA ,d va’k ds varjky ij miyC/k gq, ,u- lh- bZ- ih- ,Q- ,u- ,y- vk¡dM+ksa dk mi;ksx djds izkjafHkd {ks=ksa vkSj fHkUu le; ds ifjlhek ifjorhZ rFkk 12 ?kaVs ds varjky ij leqnz lrg rkieku miyC/k djk, x, gSaA laogu] xzgh; ifjlhek Lrj vkSj fuf’pr ueh izfØ;kvksa ds laca/k esa pØokr ds ekxZ dk iwokZuqeku vkSj mldh rhozrk dh laosnu’khyrk dk v/;;u djus ds fy, rhu iz;ksx fd, x, gSaA blls izkIr gq, ifj.kkeksa ls pØokr ds ekxZ ds iwokZuqeku esa laoguh; izfØ;kvksa dh egRoiw.kZ Hkwfedk dk irk pyk gS rFkk dSu&fÝ’k 2 Ldhe ls pØokr ds ekxZ dk lcls lVhd <ax ls irk yxk;k tk ldk gSA blds vykok ;g irk pyrk gS fd xzgh; ifjlhek Lrj izfØ;k,¡ esyj&;eknk Ldhe ds lg;ksx ls lcls izpaMre pØokr dh rhozrk dks Kkr dj ldrh gSaA fuf’pr ueh izfØ;k,¡ pØokr dh xfr dks fu;af=r djrh gSa tks Hkhrjh iz{ks= ¼Mksesu½ ds 10 fd-eh- ds lw{e foHksnu ds QyLo:Ik laHko gks ldrk gSA dSu&fÝz’k 2 vkSj esyj&;eknk dh la;qDr pj.kc) ;kstuk ls pØokr ds ekxZ vkSj mldh rhozrk ds laca/kksa dks csgrj <ax ls izfr:fir fd;k x;k gSA fdlh ,dek= iz;ksx dh rqyuk esa lHkh feystqys iz;ksxksa ls pØokr ds ekxZ vkSj mldh rhozrk dk csgrj vkdyu fd;k tk ldk gSA izfr:fir pØokr esa ,diw.kZ fodflr pØokr ds] m".k ØksM] dsanz vkSj dsanz&fHkfRr tSls lHkh y{k.k ik, x, gSaA ekWMy ls izfr:fir o"kkZ forj.k vkSj rhozrk izs{k.kksa ds vuq:Ik ikbZ xbZ gSA Numerical prediction of the movement and intensification of the Orissa Super Cyclone (1999) is studied using PSU/NCAR MM5. Sensitivity experiments were made to study the role of the parameterisation schemes of convection, planetary boundary layer and explicit moisture schemes. The model is designed to have three interactive domains with 90, 30 and 10 km horizontal resolutions covering the Bay of Bengal region. The initial fields and time varying boundary variables and sea surface temperatures at 12 hour interval are provided from NCEP FNL data available at 1° resolution. Three groups of experiments were performed to study the sensitivity of the cyclone track prediction and intensification to the schemes of convection, planetary boundary layer and explicit moisture processes. The results indicate that convective processes play an important role in the cyclone track prediction and the scheme of Kain-Fritsch 2 produces the best track and the planetary boundary layer processes control the intensification with the scheme of Mellor-Yamada producing the strongest cyclone. The explicit moisture processes modulate the movement of the cyclone, which may be due to the fine resolution of the 10 km for the innermost domain. The mixed-phase scheme in combination with Kain-Fritsch 2 and Mellor-Yamada produce the best simulation in terms of the track as well as intensification. The ensemble mean of all the conducted experiments estimate the track positions and intensification better than any individual experiment. The simulated cyclone shows all the characteristics of a mature cyclone, with warm core, formation of the eye and eye wall. The model simulated rainfall distribution and intensity have good agreement with the observations.

Model development in practice: A comprehensive update to the boundary layer schemes in HARMONIE-AROME cycle 40

The parameterised description of subgrid-scale processes in the clear and cloudy boundary layer has a strong impact on the performance skill in any Numerical Weather Prediction (NWP) or climate model and is still a prime source of uncertainty. Yet, improvement of this parameterised description is hard because operational models are highly optimised and contain numerous compensating errors. Therefore, improvement of a single parameterised aspect of the boundary layer often results in an overall deterioration of the model as a whole. In this paper we will describe a comprehensive integral revision of three parameterisation schemes in the HARMONIE-AROME model that together parameterise the boundary layer processes: the cloud scheme, the turbulence scheme, and the shallow cumulus convection scheme. One of the major motivations for this revision is the poor representation of low clouds in the current model cycle. The new revised parametric descriptions provide not only an improved prediction of low clouds but also of precipitation. Both improvements can be related to a stronger accumulation of moisture under the atmospheric inversion. The three improved parameterisation schemes are included in a recent update of the HARMONIE-AROME configuration, but its description and the insights in the underlying physical processes are of more general interest as the schemes are based on commonly applied frameworks. Moreover, this work offers an interesting look behind the scenes of how parameterisation development requires an integral approach and a delicate balance between physical realism and pragmatism.

Topoclimate Mapping Using Landsat ETM+ Thermal Data: Wolin Island, Poland

Variations in climatic pattern due to boundary layer processes at the topoclimatic scale are critical for ecosystems and human activity, including agriculture, fruit harvesting, and animal husbandry. Here, a new method for topoclimate mapping based on land surface temperature (LST) computed from the brightness temperature of Landsat ETM+ thermal bands (band6) is presented. The study was conducted in a coastal lowland area with glacial landforms (Wolin Island). The method presented is universal for various areas, and is based on freely available remote sensing data. The topoclimatic typology obtained was compared to the classical one based on meteorological data. It was proven to show a good sensitivity to changes in topoclimatic conditions (demonstrated by changes in LST distribution) even in flat, agricultural areas with only small variations in topography. The technique will hopefully prove to be a convenient and relatively fast tool that can improve the topoclimatic classification of other regions. It could be applied by local authorities and farmer associations for optimizing agricultural production.

Assessing a planetary boundary layer scheme by using the GABLS1 experiment in a single-column version of the global model developed based on potential vorticity

&lt;p&gt;Determining the accuracy of a hydrostatic weather forecast model in representing atmospheric phenomena is a complex process involving various considerations and test cases. This study delineates an objective assessment of a planetary boundary layer scheme based on turbulent kinetic energy in a single-column version of the innovative atmospheric general circulation model developed at the University of Tehran, which is called UTGAM. Single-column models provide simple frameworks to investigate the fidelity of the simulated physical processes in the atmospheric models. Dependable parameterization of the boundary layer processes has significant impacts on weather forecasts. Specifically, an ongoing issue for the operational hydrostatic models is their deficiencies in the accurate representation of the unresolved processes in stably stratified conditions.&lt;/p&gt;&lt;p&gt;We have utilized the first GABLS intercomparison experiment set up as a simple tool to evaluate the diffusion scheme in the UTGAM. Two different sigma-theta and sigma-pressure single-column grid staggering combined with 33 and 14 vertical levels below 3 km height have been used for the low- and high-resolution simulations. The GABLS1 Large Eddy Simulation (LES) results have been used as a benchmark for comparison. The diffusion scheme explored here is the same as the one in the ECHAM model which has been adapted for use in the UTGAM.&lt;/p&gt;&lt;p&gt;Results depict subtle nuances between the sigma-theta and sigma-pressure coordinates in intercomparison between the low and high vertical resolutions separately, which are more apparent in the lower vertical resolution. Nevertheless, it seems that the diffusion processes have been simulated a bit more accurately in the high-resolution sigma-pressure vertical coordinate. The boundary layer scheme in the UTGAM analogous with most of the operational models in the GABLS1 intercomparison experiment overestimate the diffusion coefficients of momentum and heat. The wind profile with height depicts maxima that are higher than the corresponding LES profile. It is inferred that the scheme mixed momentum over a deeper layer than the LES, but the simulated wind profile is better compared to the other operational models in GABLS1. Considering the vertical profiles of potential temperature revealed that the amount of heat mixing is not suitable in this experiment and causes a negative bias in the lower part of the simulated boundary layer. The simulated amounts of surface friction velocity have proved significant differences with the LES results in all separate experiments. However, the latter large amounts seem unlikely to have a detrimental effect on forecast scores in the operational model. Moreover, the sensitivity of the scheme to the lowest full-level has been partially explored. Decreasing the lowest full-level height concurrent with increasing the vertical resolution exerts a modest influence on the simulation of the boundary layer processes. All the results confirm notable improvements by increasing the vertical resolution in both sigma-theta and sigma-pressure coordinates.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Keywords:&lt;/strong&gt; Simulation, GABLS1, stable boundary layer, vertical coordinate, diffusion coefficients, UTGAM&lt;/p&gt;

Contrasting the role of regional and remote circulation in driving the Asian monsoon in HadGEM3-GA7

&lt;p&gt;Monsoon biases are long-standing and an important problem to solve because nearly half of the world&amp;#8217;s population is affected by monsoon precipitation and circulation. The effect of local and remote circulation biases on Asian monsoon biases is studied with dynamical nudging using the latest version of the atmospheric component of the HadGEM3 model. Constraining the large-scale circulation substantially reduces oceanic biases in precipitation and circulation, particularly over the extra-tropics. Tropical wet biases may become even stronger because of unconstrained convection. By contrast, model biases over land are less sensitive to nudging due to the prominent role of local planetary boundary layer processes in modulating the low-level circulation. Nudging reduces the seasonal excess (deficit) precipitation over India in winter (summer) by reducing the local cyclonic (anti-cyclonic) biases. Constraining the circulation outside Asia demonstrates that the wet (dry) biases are mostly remotely (locally) controlled in winter (summer) over India. The monsoon biases over China show small changes with nudging, suggesting they are more thermodynamically driven. Monsoon variability is improved over India but not over China in nudged simulations. Despite the remaining errors in nudged simulations, our study suggests that nudging serves as a useful tool to disentangle the contribution of regional and remote circulation in generating the monsoon responses.&lt;/p&gt;