Institute of Geophysics, University of TehranJournal of the Earth and Space Physics2538-371X47220210723Verification of potential intensity relations for the northwest Indian Ocean tropical cyclones during 1990-2019Verification of potential intensity relations for the northwest Indian Ocean tropical cyclones during 1990-20193713868152110.22059/jesphys.2021.316954.1007279FANafisehPegahfarAssistant Professor, Atmospheric Science Center, Iranian National Institute for Oceanography and Atmospheric Science, Tehran, Iran0000-0003-4885-7428Journal Article20210115Prediction of tropical cyclone (TC) intensity has been considered in numerous research studies, due to TC destructive effects. Hence, various parameters were combined in potential intensity relations to show the maximum probable intensity that a TC can achieve. The relations of potential intensity are different, since each relation has been suggested based on various factors affecting TC intensity. In this research, the validity of five potential intensity relations, defined by other researchers for the other basins, was verified for all TCs formed over the northwest of the Indian Ocean from 1990 to 2019. In this duration, sixteen cyclonic storms, nine sever cyclonic storms, ten very sever cyclonic storms and ten extremely severe cyclonic storms occurred. In this research, two sets of data reported by India Meteorological Department (IMD) and reanalysis data from the fifth generation of the European Center for Medium Range Weather Forecast (ECMWF, ERA5) with the horizontal resolution of 0.25 degrees were used. The IMD data included position (latitude/longitude) of the TC’s eye and maximum wind speed. The reanalysis data consisted of meteorological parameters from sea level to the tropopause level, including relative and specific humidity, temperature, pressure, dew point temperature and horizontal wind vector. The first relation for the potential intensity is based on the difference between convective available potential energy values at the radius of maximum wind using saturated and unsaturated air mass. The second one considers the difference between saturated entropy at sea level and environmental value of entropy. The third relation consists of the ratio of difference between upper-level and lower-level temperature to the outflow temperature and also the discrepancy between saturated and unsaturated enthalpy. The fourth relation includs difference of saturated and unsaturated values of equivalent potential temperature at the radius of maximum wind. The last relation not only uses the ratio of temperature of inflow and outflow and discrepancy between surface and boundary layer entropy, but also emphasizs on surface temperature. The ratio of the enthalpy and drag coefficients is used in the all relations, while thermodynamic efficiency is included in some recent relations. The potential intensity values achieved using the empirical relations, were evaluated using the maximum wind speed reported by IMD. The comparison was done based on some statistical indexes and the Taylor diagrams. The statistical indices include (I) index of agreement (IOA), (II) standard deviation, (III) root mean square deviation and (IV) correlation coefficient. For the intensity of depression and deep depression states, the minimum value of IOA was achieved using the first relation, while the other relations produced the close values of around 0.7. For the CS-Category intensity, the first two relations produced the lowest IOA values. For the SCS- Category the last two relations did the best performance, while for VSCS- and ESCS-Categories, the second relation produced the most consistent results. The results from IOA showed that the fifth relation produced the highest agreement with the IMD data. This showed that the discrepancy between sea surface temperature and tropopause temperature and the difference between environmental entropy and inner-core entropy played the most important role in intensification for the first four categories of intensity. However, for the last two categories of intensity the discrepancy between the saturated entropy at surface and entropy of boundary layer produced IOA of 0.73 and 0.75, respectively. It is notable that the difference between saturated equivalent potential temperature and potential temperature of boundary layer, and also difference between temperature of inflow and outflow produced the same results for the beginning state. The other statistical indices were analyzed based on the Taylor diagram focusing on all considered tropical cyclones that were intensified to the various intensities. Conclusions demonstrated that the last and the second potential intensity relations produced the best performance in the all categories for the TCs formed over the northwest of the Indian Ocean during 2019-1990. Prediction of tropical cyclone (TC) intensity has been considered in numerous research studies, due to TC destructive effects. Hence, various parameters were combined in potential intensity relations to show the maximum probable intensity that a TC can achieve. The relations of potential intensity are different, since each relation has been suggested based on various factors affecting TC intensity. In this research, the validity of five potential intensity relations, defined by other researchers for the other basins, was verified for all TCs formed over the northwest of the Indian Ocean from 1990 to 2019. In this duration, sixteen cyclonic storms, nine sever cyclonic storms, ten very sever cyclonic storms and ten extremely severe cyclonic storms occurred. In this research, two sets of data reported by India Meteorological Department (IMD) and reanalysis data from the fifth generation of the European Center for Medium Range Weather Forecast (ECMWF, ERA5) with the horizontal resolution of 0.25 degrees were used. The IMD data included position (latitude/longitude) of the TC’s eye and maximum wind speed. The reanalysis data consisted of meteorological parameters from sea level to the tropopause level, including relative and specific humidity, temperature, pressure, dew point temperature and horizontal wind vector. The first relation for the potential intensity is based on the difference between convective available potential energy values at the radius of maximum wind using saturated and unsaturated air mass. The second one considers the difference between saturated entropy at sea level and environmental value of entropy. The third relation consists of the ratio of difference between upper-level and lower-level temperature to the outflow temperature and also the discrepancy between saturated and unsaturated enthalpy. The fourth relation includs difference of saturated and unsaturated values of equivalent potential temperature at the radius of maximum wind. The last relation not only uses the ratio of temperature of inflow and outflow and discrepancy between surface and boundary layer entropy, but also emphasizs on surface temperature. The ratio of the enthalpy and drag coefficients is used in the all relations, while thermodynamic efficiency is included in some recent relations. The potential intensity values achieved using the empirical relations, were evaluated using the maximum wind speed reported by IMD. The comparison was done based on some statistical indexes and the Taylor diagrams. The statistical indices include (I) index of agreement (IOA), (II) standard deviation, (III) root mean square deviation and (IV) correlation coefficient. For the intensity of depression and deep depression states, the minimum value of IOA was achieved using the first relation, while the other relations produced the close values of around 0.7. For the CS-Category intensity, the first two relations produced the lowest IOA values. For the SCS- Category the last two relations did the best performance, while for VSCS- and ESCS-Categories, the second relation produced the most consistent results. The results from IOA showed that the fifth relation produced the highest agreement with the IMD data. This showed that the discrepancy between sea surface temperature and tropopause temperature and the difference between environmental entropy and inner-core entropy played the most important role in intensification for the first four categories of intensity. However, for the last two categories of intensity the discrepancy between the saturated entropy at surface and entropy of boundary layer produced IOA of 0.73 and 0.75, respectively. It is notable that the difference between saturated equivalent potential temperature and potential temperature of boundary layer, and also difference between temperature of inflow and outflow produced the same results for the beginning state. The other statistical indices were analyzed based on the Taylor diagram focusing on all considered tropical cyclones that were intensified to the various intensities. Conclusions demonstrated that the last and the second potential intensity relations produced the best performance in the all categories for the TCs formed over the northwest of the Indian Ocean during 2019-1990. https://jesphys.ut.ac.ir/article_81521_78ba813b9fb41cc036e5a010d207187b.pdf