the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 08 Mar 2023
Distinct role of intraseasonal and interannual sea surface temperature anomaly in the rapid intensification onset of Typhoon Megi (2010)
Abstract. This study aims to explain the rapid intensification (RI) onset of Typhoon Megi from a new perspective of the intraseasonal and interannual sea surface temperature anomaly (SSTA) effect. Simulation result indicates that the warmer intraseasonal SSTA along tropical cyclone (TC) track seems to be more conducive to the early occurrence of TC RI onset than the interannual SSTA for Megi. For the experiment with intraseasonal SSTA (SST-intraseasonal), it has cooler averaged SST in TC inner-core, outer-core, and external environment than the experiment with interannual SSTA (SST-interannual). Cooler TC outer-core and environmental SST provide more midlevel radial inflow, resulting in a strong TC lower-level warm core in SST-intraseasonal. For SST-interannual, the stronger upper-level VWS related to the warmer environmental SST strongly tilts TC structure, delaying the time of RI onset. Conceptual model of Megi RI onset proposed that, when TC lower-level warm core gradually weakens and TC upper-level alignment is basically completed, TC RI onset occurs. Our results underscore the effect of intraseasonal SSTA on Megi RI onset, and provide a new perspective for improving the prediction of TC RI onset.
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Interactive discussion
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RC1: 'Comment on egusphere-2023-61', Anonymous Referee #1, 16 Mar 2023
Review comments on “Distinct role of intraseasonal and interannual sea surface temperature anomaly in the rapid intensification onset of Typhoon Megi (2010)” by Shao et al.
General comments:
In this study, the authors attempted to explain the rapid intensification (RI) onset of Typhoon Megi from a new perspective of the intraseasonal and interannual sea surface temperature anomaly (SSTA) effect. By adding either intraseasonal and interannual SSTA, they found a different RI onset timing. Overall, there are many misconceptions in the manuscript. This is not a convincing result and should be rejected at the current version. The specific points are listed as follows:
- Methodologically, the experiments are conducted by adding either intraseasonal and interannual SSTA. as pointed in the text, the RI onset timing is highly sensitive to the relative distributions of SSTA and the TC track. Namely, the results are highly sensitive to the simulated tracks. For this particular case, there is only a single run for each experiment. Indeed, there are some uncertainties in terms of track forecasting. If there are some spreads in the tracks, the result would be invalid. Moreover, in this particular case, the track across the positive difference of SSTA between intraseasonal and interannual scales. If there is a TC case moves into the negative SSTA as shown in Fig. 1(f), should we get the opposite results? Hence, we don’t agree the claim that “provide a new perspective for improving the prediction of TC RI onset”. Of course, to remedy the uncertainties, the ensemble simulations are necessary to make a solid conclusion.
- Meanwhile, for the influence of different SSTA distributions, we guess that the SSTA likely affects the surface heat flexes. Namely, different SSTA contrast in either East-West or North-south direction should modulate the asymmetric distribution of surface heat fluxes and thus the PBL enthalpy. This asymmetry will affect the evolution of asymmetric convection as triggered by the VWS. This aspect is should be discussed.
- When citing two ventilation pathways to examine the influences of VWS, the potential temperature (𝜃) is used. This is a mistake and misleads to a misconception. In the previous literatures, the equivalent potential temperature (𝜃e) or enthalpy is applied to examine the thermodynamical process. As such, in this study, the role of moisture is completely neglected, which should play an important role in modulating the efficiency.
- As pointed out in L375: “ the hypothes is put forward is that relatively high lower-level VWS in SST-intraseasonal is beneficial to TC Megi RI onset.” Furthermore, given the schematic diagram, it is speculated these factors play crucial roles in RI. If it is true, there should be salient differences in terms of the profiles and magnitudes of VWS in both experiments. However, as shown in Fig. 8, we cannot find the significant differences in both upper and lower level VWS. Initially, the atmospheric variables (and thus initial VWS) are identical in both cases, one crucial issue is what processes lead to such discrepancies of sequential VWS? In other words, how do the different scales of SSTA (i.e., interannual and intraseasonal) affect the evolution of VWS?
- In the potential temperature budget section, it is argued that a significant magnitude of warm-core is a potential signal of RI. In other words, the result indicates that a strong TC lower-level warm core and TC upper-level alignment should be considered as the indicators of TC Megi RI onset. Generally, the magnitude of warm-core is closely corelated with the Vmax. Is there any time-lead relationship between warm-core and Vmax? Some literatures pointed out the upper-level warm core is a signal of RI or major hurricane. For the establishment of upper-level warm-core, it is well realized that the inflow forced by the outflow jet channel rather than the upper VWS is a crucial factor.
- There are too many misconceptions in the text. For instance, as pointed out in L362-363: “We demonstrate that the cooler outer-core SST and stronger lower-level VWS by cooler environmental SST brings more angular momentum input, resulting in more condensation warming in TC inner-core”. What is the relation between angular momentum input and condensation warming?
Citation: https://doi.org/10.5194/egusphere-2023-61-RC1
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-61', Anonymous Referee #1, 16 Mar 2023
Review comments on “Distinct role of intraseasonal and interannual sea surface temperature anomaly in the rapid intensification onset of Typhoon Megi (2010)” by Shao et al.
General comments:
In this study, the authors attempted to explain the rapid intensification (RI) onset of Typhoon Megi from a new perspective of the intraseasonal and interannual sea surface temperature anomaly (SSTA) effect. By adding either intraseasonal and interannual SSTA, they found a different RI onset timing. Overall, there are many misconceptions in the manuscript. This is not a convincing result and should be rejected at the current version. The specific points are listed as follows:
- Methodologically, the experiments are conducted by adding either intraseasonal and interannual SSTA. as pointed in the text, the RI onset timing is highly sensitive to the relative distributions of SSTA and the TC track. Namely, the results are highly sensitive to the simulated tracks. For this particular case, there is only a single run for each experiment. Indeed, there are some uncertainties in terms of track forecasting. If there are some spreads in the tracks, the result would be invalid. Moreover, in this particular case, the track across the positive difference of SSTA between intraseasonal and interannual scales. If there is a TC case moves into the negative SSTA as shown in Fig. 1(f), should we get the opposite results? Hence, we don’t agree the claim that “provide a new perspective for improving the prediction of TC RI onset”. Of course, to remedy the uncertainties, the ensemble simulations are necessary to make a solid conclusion.
- Meanwhile, for the influence of different SSTA distributions, we guess that the SSTA likely affects the surface heat flexes. Namely, different SSTA contrast in either East-West or North-south direction should modulate the asymmetric distribution of surface heat fluxes and thus the PBL enthalpy. This asymmetry will affect the evolution of asymmetric convection as triggered by the VWS. This aspect is should be discussed.
- When citing two ventilation pathways to examine the influences of VWS, the potential temperature (𝜃) is used. This is a mistake and misleads to a misconception. In the previous literatures, the equivalent potential temperature (𝜃e) or enthalpy is applied to examine the thermodynamical process. As such, in this study, the role of moisture is completely neglected, which should play an important role in modulating the efficiency.
- As pointed out in L375: “ the hypothes is put forward is that relatively high lower-level VWS in SST-intraseasonal is beneficial to TC Megi RI onset.” Furthermore, given the schematic diagram, it is speculated these factors play crucial roles in RI. If it is true, there should be salient differences in terms of the profiles and magnitudes of VWS in both experiments. However, as shown in Fig. 8, we cannot find the significant differences in both upper and lower level VWS. Initially, the atmospheric variables (and thus initial VWS) are identical in both cases, one crucial issue is what processes lead to such discrepancies of sequential VWS? In other words, how do the different scales of SSTA (i.e., interannual and intraseasonal) affect the evolution of VWS?
- In the potential temperature budget section, it is argued that a significant magnitude of warm-core is a potential signal of RI. In other words, the result indicates that a strong TC lower-level warm core and TC upper-level alignment should be considered as the indicators of TC Megi RI onset. Generally, the magnitude of warm-core is closely corelated with the Vmax. Is there any time-lead relationship between warm-core and Vmax? Some literatures pointed out the upper-level warm core is a signal of RI or major hurricane. For the establishment of upper-level warm-core, it is well realized that the inflow forced by the outflow jet channel rather than the upper VWS is a crucial factor.
- There are too many misconceptions in the text. For instance, as pointed out in L362-363: “We demonstrate that the cooler outer-core SST and stronger lower-level VWS by cooler environmental SST brings more angular momentum input, resulting in more condensation warming in TC inner-core”. What is the relation between angular momentum input and condensation warming?
Citation: https://doi.org/10.5194/egusphere-2023-61-RC1
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