Tropical cyclone Genesis Potential Parameter (GPP) and it’s application over the north Indian Sea

bl 'kks/k i= esa mRrjh fgUn egklkxj esa m".kdfVca/kh; pØokr ds cuus ds foHko izkpy ¼th- ih- ih-½ dk fo’ys"k.k fd;k x;k gSA dksVy }kjk fodflr ¼2009½ pØokr cuus ds foHko izkpy dk vkdyu pkj ifjofrZrkvksa ds vk/kkj ij fd;k x;k gS tks bl izdkj gS % 850 gSDVkikLdy ij Hkzfeyrk] e/; {kksHkeaMyh; lkisf{kd vknzZrk] e/; {kksHkeaMyh; vfLFkjrk vkSj ml LFkku ds lHkh fxzM IokbaVksa ij m/okZ/kj iou vi:i.kA bu fLFkfr;ksa esa fxzM IokbaV ij th-ih-ih- ij ;g fopkj fd;k x;k fd lHkh ifjorhZ Hkzfeyrk] e/; {kksHkeaMyh; lkisf{kd vknzZrk] e/; {kksHkeaMyh; fLFkjrk vkSj m/okZ/kj iou vi:i.k 'kwU; ls cM+k gS vkSj ;g ekuk x;k gS fd tc buesa ls dksbZ Hkh ifjorhZ 'kwU; ls de ;k cjkcj gks rks og 'kwU; gh ekuk tk,xkA ;wjksih; e/;kof/k ekSle iwokZuqeku dsUnz ¼b-lh-,e-MCY;w-,Q-½ fun’kZ vk¡dM+ksa dk mi;ksx djrs gq, bu ifjofrZrkvksa dk vkdyu fd;k x;k gSaA b- lh- ,e- MCY;w- ,Q- fun’kZ dh lwpukvksa ¼http://www.imd.gov.in/section/nhac/dynamic/analysis.htm ij miyC/k½ dk okLrfod le; dk mi;ksx djrs gq, lkr fnuksa rd ds fy, tsusfll izkpy ds iwokZuqeku Hkh rS;kj fd, x,A ml {ks= esa th-ih-ih- ds mPprj ekuksa ls ml LFkku ds tsfufll ds mPprj foHko dk irk pyk gSA ml LFkku ij th-ih-ih- ds eku 30 ds cjkcj vFkok vf/kd gksus dh fLFkfr esa pØokr mRifRr ds fy, mPp foHko {ks= ik;k x;k gSA izkpy ds fo’ys"k.k vkSj 2010 esa pØokrh fo{kksHkksa ds nkSjku budh izHkko’khyrk ls mRrjh fgUn egklkxj esa pØokr mRifÙk ds fy, iwokZuqeku lwpd flaxuy ¼4&5 fnu igys½ ds :i esa vkSj fodkl dh vkjafHkd voLFkkvksa esa fodflr vkSj xSj&fodflr iz.kkfy;ksa ds rzhohdj.k ds fy, foHko dk fu/kkZj.k gsrq budh mi;ksfxrk dh iqf"V gqbZ gSA An analysis of tropical cyclone genesis potential parameter (GPP) for the North Indian Sea is carried out. The genesis potential parameter developed by Kotal et al. (2009) is computed based on the product of four variables, namely: vorticity at 850 hPa, middle tropospheric relative humidity, middle tropospheric instability and the inverse of vertical wind shear at all grid points over the area. The GPP at a grid point is considered under the conditions that all the variables vorticity, middle tropospheric relative humidity, middle tropospheric instability and the vertical wind shear are greater than zero and it is taken as zero when any one of these variables is less or equal to zero. The variables are computed using the European Centre for Medium Range Weather Forecast (ECMWF) model data. Forecast of the genesis parameter up to seven days is also generated on real time using the ECMWF model output (available at http://www.imd.gov.in/section/nhac/dynamic/Analysis.htm). Higher value of the GPP over a region indicates higher potential of genesis over the region. Region with GPP value equal or greater than 30 is found to be high potential zone for cyclogenesis. The analysis of the parameter and its effectiveness during cyclonic disturbances in 2010 affirm its usefulness as a predictive signal (4-5 days in advance) for cyclogenesis over the North Indian Sea and for determining potential for intensification of developing and non-developing systems at the early stages of development.

The Performance of ECMWF sub-seasonal forecasts to predict the Rainy Season Onset Dates in Vietnam

The onset of the rainy season is an important date for the mostly rain-fed agricultural practices in Vietnam. Sub-seasonal to seasonal (S2S) ensemble hindcasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) are used to evaluate the predictability of the rainy season onset dates (RSODs) over five climatic sub-regions of Vietnam. The results show that the ECMWF model reproduces well the observed inter-annual variability of RSODs, with a high correlation ranging from 0.60 to 0.99 over all sub-regions at all lead times (up to 40 days) using five different RSOD definitions. For increasing lead times, forecasted RSODs tend to be earlier than the observed ones. Positive skill score values for almost all cases examined in all sub-regions indicate that the model outperforms the observed climatology in predicting the RSOD at sub-seasonal lead times (~28–35 days). However, the model is overall more skilful at shorter lead times. The choice of the RSOD criterion should be considered because it can significantly influence the model performance. The result of analysing the highest skill score for each sub-region at each lead time shows that criteria with higher 5-day rainfall thresholds tend to be more suitable for the forecasts at long lead times. However, the values of mean absolute error are approximately the same as the absolute values of the mean error, indicating that the prediction could be improved by a simple bias correction. The present study shows a large potential to use S2S forecasts to provide meaningful predictions of RSODs for farmers.

Correction of wind bias for the lidar on board Aeolus using telescope temperatures

The European Space Agency (ESA) Earth Explorer satellite Aeolus provides continuous profiles of the horizontal line-of-sight wind component globally from space. It was successfully launched in August 2018 with the goal to improve numerical weather prediction (NWP). Aeolus data have already been successfully assimilated into several NWP models and have already helped to significantly improve the quality of weather forecasts. To achieve this major milestone the identification and correction of several systematic error sources were necessary. One of them is related to small fluctuations of the temperatures across the 1.5 m diameter primary mirror of the telescope which cause varying wind biases along the orbit of up to 8 m s−1. This paper presents a detailed overview of the influence of the telescope temperature variations on the Aeolus wind products and describes the approach to correct for this systematic error source in the operational near-real-time (NRT) processing. It was shown that the telescope temperature variations along the orbit are due to changes in the top-of-atmosphere reflected shortwave and outgoing longwave radiation of the Earth and the related response of the telescope's thermal control system. To correct for this effect ECMWF model-equivalent winds are used as a reference to describe the wind bias in a multiple linear regression model as a function of various temperature sensors located on the primary telescope mirror. This correction scheme has been in operational use at ECMWF since April 2020 and is capable of reducing a large part of the telescope-induced wind bias. In cases where the influence of the temperature variations is particularly strong it was shown that the bias correction can improve the orbital bias variation by up to 53 %. Moreover, it was demonstrated that the approach of using ECMWF model-equivalent winds is justified by the fact that the global bias of model u-component winds with respect to radiosondes is smaller than 0.3 m s−1. Furthermore, this paper presents the alternative of using Aeolus ground return winds which serve as a zero-wind reference in the multiple linear regression model. The results show that the approach based on ground return winds only performs 10.8 % worse than the ECMWF model-based approach and thus has a good potential for future applications for upcoming reprocessing campaigns or even in the NRT processing of Aeolus wind products.

Predictable Patterns and Their Corresponding Signal Sources of Midsummer Surface Air Temperature Over Eastern China in the ECMWF S2S Forecasts

The maximum signal-to-noise empirical orthogonal function (MSN EOF) method is used to evaluate the midsummer 2-m air temperature (T2m) over Eastern China of subseasonal to seasonal scale forecast data in ECMWF model, and investigate the underlying mechanisms between temperature modes and predictable sources. The first predictable pattern mainly presents the dipole mode of positive value in the south and negative value in the north. The model captures the signal of the transition from preceding El Niño to La Niña and accompanying tropical Indian Ocean warm surface temperature. In the summer of transforming years, the West Pacific Subtropical High is stronger and westward, meanwhile the southwest monsoon strengthens, which are the main direct influence factors of the high pressure in the south and the more precipitation in the north. Compared with observations, although the model captures the relationship between the temperature mode and the previous sea surface temperature signal, it obscures the mediating role of the Western Pacific Subtropical High. The second predictable pattern is the warmer characteristic of the Yangtze River valley (YRV), and North Atlantic Oscillation which the atmospheric internal variability is the main signal. The wave train propagating from northwestern Russia to Northeast Asia is the main cause of the abnormal high pressure over YRV. The third mode is mainly the temperature trend item, and the spatial characteristics of observation and model are quite different. ECMWF model shows high forecasting skills in the three modes, and presents high (low) surface pressure in areas with high (lower) temperatures, reduced (increased) precipitation and increased (reduced) solar radiation, which proving the model simulates the potential mechanism of circulation anomalies affecting surface air temperature commendably.

A forecasting approach of tropical cyclone genesis based on thresholds of multi-physical parameters and its verification using ECMWF model data

While considerable studies have proved that the track and intensity forecasts of tropical cyclone (TC) relied heavily on output from numerical weather prediction (NWP) model, few researches investigated how well NWP models forecast TC genesis in the western North Pacific (WNP) basin. In order to understand the characteristics of TC genesis forecast in WNP basin by NWP models, this study derives a set of criteria to identify the formation of TC using historical data and verifies it based on ECMWF model data between 2013 and 2015. The results show that the percentile values adopted as the criteria thresholds have a significant impact on the performance of algorithm based on the criteria. A reasonable adjustment of threshold in a specific interval can effectively improve the TC genesis prediction. For example, in the WNP basin the forecast results are most sensitive to small changes in the relative vorticity on the 850 hPa level. The results of forecast test of the optimal threshold combination scheme indicate that the turning point of performance lies between 24 and 48 hours with regard to the hit rate in the 12-72 hours prior to the formation of TC. For lead time less than 24 hours, the hit rate was basically maintained at a high level above 0.7 with a small decrease. After that, the performance drops sharply before stabilizing beyond 48 hours. In addition, the performance of the TC genesis prediction in ECMWF model varies significantly from year to year and also in different WNP regions. It performs better to the east of the Philippines than over the South China Sea (SCS). On the other hand, high false alarm (FA) rates are found in the central parts of the SCS up to the waters around the Philippines and the central part of the WNP. The significant discrepancy in ECMWF’s performance can also be observed between different basins. Within the 24 hours before the genesis of a TC, the forecasts for the WNP basin verify better than those for the Atlantic basin.

Dynamical mechanisms linking Indian monsoon precipitation and the circumglobal teleconnection

The circumglobal teleconnection (CGT) is an important mode of circulation variability, with an influence across many parts of the northern hemisphere. Here, we examine the excitation mechanisms of the CGT in the ECMWF seasonal forecast model, and the relationship between the Indian summer monsoon (ISM), the CGT and the extratropical northern hemisphere circulation. Results from relaxation experiments, in which the model is corrected to reanalysis in specific regions, suggest that errors over northwest Europe are more important in inhibiting the model skill at representing the CGT, in addition to northern hemisphere skill more widely, than west-central Asia and the ISM region, although the link between ISM precipitation and the extratropical circulation is weak in all experiments. Thermal forcing experiments in the ECMWF model, in which a heating is applied over India, suggest that the ISM does force an extratropical Rossby wave train, with upper tropospheric anticyclonic anomalies over east Asia, the North Pacific and North America associated with increased ISM heating. However, this eastward-propagating branch of the wave train does not project into Europe, and the response there occurs largely through westward-propagating Rossby waves. Results from barotropic model experiments show a response that is highly consistent with the seasonal forecast model, with similar eastward- and westward-propagating Rossby waves. This westward-propagating response is shown to be important in the downstream reinforcement of the wave train between Asia and North America.

Correction of wind bias for the lidar on-board Aeolus using telescope temperatures

The European Space Agency satellite Aeolus provides continuous profiles of the horizontal line-of-sight wind component at a global scale. It was successfully launched into space in August 2018 with the goal to improve numerical weather prediction (NWP). Aeolus data has already been successfully assimilated into several NWP models and has already helped to significantly improve the quality of weather forecasts. To achieve this major milestone the identification and correction of several systematic error sources was necessary. One of them is related to small temperatures fluctuations across the 1.5 m diameter primary mirror of the telescope which cause varying wind biases along the orbit of up to 8 m/s. This paper presents a detailed overview of the influence of the telescope temperature variations on the Aeolus wind products and describes the approach to correct for this systematic error source in the operational near-real-time (NRT) processing. It was shown that the telescope temperature variations along the orbit are due to changes of the top-of-atmosphere short- and long-wave radiation of the Earth and the response of the telescope’s thermal control system to that. To correct for this effect ECMWF model-equivalent winds are used as bias reference to describe the wind bias in a multiple linear regression model as a function of various temperature sensors located on the primary telescope mirror. This correction scheme has been in operational use at ECMWF since April 2020 and is capable of reducing a large part of the telescope-induced wind bias. In cases where the influence of the temperature variations is particularly strong it was shown that the bias correction can improve the orbital bias variation by up to 53 %. Moreover, it was demonstrated that the approach of using ECMWF model-equivalent winds is justified by the fact that the global bias of models u-component winds w.r.t to radiosondes is smaller than 0.3 m/s. However, this paper also presents the alternative of using Aeolus ground return winds which serve as zero wind reference in the multiple linear regression model. The results show that the approach based on ground return winds only performs 10.8 % worse than the ECMWF model-based approach and thus has good potential for future applications for upcoming reprocessing campaigns or even in the NRT processing of Aeolus wind products.

The full-spectrum correlated-k method to accelerate radiative transfer in NWP models

<div data-editor="4ssjd" data-offset-key="7gnbn5cf-0-0"> <div><span>Radiative transfer is frequently cited as the slowest part of an atmospheric model; while perhaps a little unfair (radiation accounting for only 3.5% of the cost of ECMWF's highest resolution operational model), there is no shortage of ideas in the literature for speeding up radiation schemes. In this talk I will describe a flexible tool "ecCKD" for generating gas optics models using the correlated k-distribution (CKD) method, and in particular explore the potential to use the "full-spectrum correlated-k" (FSCK) method in NWP. Via the use of one band for the entire thermal infrared and one for the entire near-infrared, FSCK enables the number of pseudo-monochromatic spectral intervals to be drastically reduced, from over 100 in each of the shortwave and longwave spectra (in the current operational gas optics scheme at ECMWF) to around 25, with a corresponding factor-of-4 speed-up in the radiation scheme. Training against 50 line-by-line test profiles and 34 greenhouse gas scenarios ensures that the resultings gas-optics models are accurate for the full range of terrestrial conditions, plus climate conditions from the last glacial maximum up to 8x pre-industrial CO2 concentrations. Care must be taken to ensure there are sufficient spectral intervals to represent the spectrum of cloud absorption and scattering, as well as surface albedo variations. The reduced number of spectral intervals leads to increased noise in the stochastic McICA solver, but recent optimizations of the Tripleclouds solver make it as fast as McICA but free from stochastic noise. Finally, the new gas optics scheme is demonstrated online in forecasts by the ECMWF model.</span></div> </div><div data-editor="4ssjd" data-offset-key="1kp4kee7-0-0"> <div> </div> </div>

Pannonian Basin Nocturnal Boundary Layer and Fog Formation: Role of Topography

Under high-pressure systems, the nocturnal atmospheric boundary layer in the Pannonian Basin is influenced by gravity flows generated at the mountain ranges and along the valleys, determining the variability of wind and temperature at a local scale and the presence of fog. The mechanisms at the mountain foothills are explored at Zagreb Airport using data from a sodar and high-resolution WRF-ARW numerical simulations, allowing identification of how the downslope flows from the nearby Medvednica mountain range condition the temperature inversion and the visibility at night and early morning. These flows may progress tens of kilometres away from the mountain ranges, merging with valley flows and converging in the central areas of the basin. The ECMWF model outputs allow us to explore the mesoscale structures generated in form of low-level jets, how they interact when they meet, and what is the effect of the synoptic pressure field over eastern Europe, to illustrate the formation of a basin-wide cold air pool and the generation of fog in winter.