Il-Ju Moon

On physical factors that controlled the massive green tide occurrence along the southern coast of the Shandong Peninsula in 2008: A numerical study using a particle‐tracking experiment

Received 22 August 2011; revised 15 October 2011; accepted 18 October 2011; published 23 December 2011. [1] A Lagrangian-particle-tracking experiment has been conducted using Regional Ocean Modeling System to determine physical factors that controlled the occurrence of the record-breaking massive green tide along the southern coast of the Shandong Peninsula (SP) in 2008. The numerical results reveal that the southerly wind in May is responsible for the offshore movement of the green tide from the Jiangsu Province and the easterly wind in June is responsible for its extension up to the coast of the SP. From the analysis of 30 year wind fields, it was also found that the wind patterns in 2008, which were very unique and rare, provided the most favorable conditions for the migration of the bloom to the SP. Through analyzing the pathway of particles, a recurrent upwelling region due to tides was found between the Jiangsu coast and the western Yellow Sea where the massive green tide bloomed. This area seems to provide nutrients for the green tide blooms. In particular, it is estimated that the nutrient supply in 2008 was large because the upwelling occurred during a spring tide. These results suggest that the massive green tide along the SP in 2008 occurred due to the combination of a recent rapid expansion of seaweed aquaculture, unique wind patterns, and nutrient supplies due to strong tidal forcing in blooming regions. This implies that the massive green tides in the SP could occur again as a very rare event if all conditions become favorable for the blooming and migration in the future. Citation: Lee, J. H., I.-C. Pang, I.-J. Moon, and J.-H. Ryu (2011), On physical factors that controlled the massive green tide occurrence along the southern coast of the Shandong Peninsula in 2008: A numerical study using a particle-tracking experiment, J. Geophys. Res., 116, C12036, doi:10.1029/2011JC007512.

Roles of interbasin frequency changes in the poleward shifts of the maximum intensity location of tropical cyclones

An observed poleward migration in the average latitude at which tropical cyclones (TCs) achieved their lifetime-maximum intensities (LMIs) was previously explained by changes in the mean meridional environments favorable to storm development linked to tropical expansion and anthropogenic warming. We show that the poleward migration is greatly influenced by basin-to-basin changes in TC frequency associated with multi-decadal variability, particularly for the Northern Hemisphere (NH). The contribution of the frequency changes to the poleward migration is comparable to that of the mean meridional environmental changes. A statistically significant global poleward trend can be identified simply from the frequency changes in each basin. An opposite trend exists in the frequency variations over the past 30 years between the North Atlantic and the eastern North Pacific where climatological mean latitudes of LMI are high (26.1°N) and low (16.5°N), respectively, which is the key factor in driving the frequency contribution. The strong roles of the interbasin frequency changes in the poleward migration also suggest that if the phase of multidecadal variability in the NH is reversed, as found in earlier TC records, the poleward trend could be changed to an opposite, equatorward, trend in the future.

Responses of coastal waters in the Yellow Sea to Typhoon Bolaven

ABSTRACT Kim, C.S., Lim, H.S., Jeong, J.Y., Shim, J.S., Moon, I.J., Oh, Y.J., You, H.Y., 2014. Response of Coastal Waters in Yellow Sea to Typhoon Bolaven. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 278–283, ISSN 0749-0208. In August 2012, Typhoon Bolaven (1215) passed through the East China Sea (ECS) and the Yellow Sea (YS), leading to severe coastal damages in Korea. This study investigated the responses of the coastal waters along the meridional direction of the YS and the ECS to Typhoon Bolaven. This included the causes of record-breaking high waves in the ECS, the possible danger of coincident peak surges and high tides, resonant coupling between the typhoon, tides and topography, and the impact of Bolaven-induced sea surface cooling on the intensity of Typhoon Tembin (1214). Analyses were conducted using observations from an ocean platform, buoys, and tidal stations, as well as a numerical model during the passage of Bolaven. Results revealed that the western coast of the Korean Peninsula fortunately avoided severe storm surge damages due to weak tidal action during the passage of Bolaven, although pure surge components were significantly high. However, we found that there was the possibility of resonant coupling between surges, tides and topography in the YS, which would contribute to further enhancement of the storm surge. Based on the wave simulations, it was revealed that a straight track and fast translation of Bolaven maximized the production of record-breaking high waves in the ECS.

Increasing the highest storm surge in Busan harbor

ABSTRACT Oh, S.M.; Moon, I.-J., and Kwon, S.J., 2016. Increasing the highest storm surge in Busan harbor, In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 760–764. Coconut Creek (Florida), ISSN 0749-0208. One of the most pronounced effects of climate change in coastal regions is sea level rise and storm surges. Busan in particular, the fifth largest container handling port in the world, has suffered from serious storm surges and experienced a remarkable mean sea level (MSL) rise. This study investigates a long-term variation of annual maximum surge height (AMSH) using sea level data observed in Busan over 53 years (1962∼2014). The decomposition of astronomical tides and surge components shows that the AMSH has increased 18 cm over 53 years (i.e., 3.5 mm/year), which is much larger than the MSL trend (2.5 mm/year) in Busan. This significant increase in AMSH is mostly explained by the increased intensity of landfall typhoons over the Korean peninsula (KP), which is associated with the increase of sea surface temperature and the decrease of vertical wind shear at mid-latitudes of the western North Pacific. In a projected future warming environment, the combination of an increasing MSL and AMSH will accelerate the occurrence of record-breaking extreme sea levels, which will be a potential threat in Busan harbor.

Connection between the genesis number of tropical cyclones over the western North Pacific and summer rainfall over Northeast Asia

Since a tropical cyclone (TC) usually accompanies a large amount of rainfall, it is estimated that average amounts of rainfall in summer increase in Northeast Asia (NA) when the genesis of TC in the western North Pacific (WNP) is frequent. However, the present study found a negative correlation between TC genesis number in summer over the WNP and the amount of summer rainfall over the mid-latitudes of NA from 1980 to 2009. The results of the analysis reveal that in a positive TC genesis phase (years in which TCs occur more frequently than on average), an anomalous cyclone forms over the WNP, which generates anomalous cold and dry northeasterly winds in the mid-latitudes of NA, resulting in reduction of rainfall. In comparison, in a negative TC genesis phase (years in which TCs occur less frequently than on average), a large anomalous anticyclone develops over the western Pacific, which generates anomalous warm and humid southwesterly winds, resulting in increase of rainfall in the same region. The comparisons of the TC tracks between the two phases also reveal that in both phases, the TC passage number is rather low in the mid-latitudes of NA regardless of TC activities over the WNP. This suggests that TC number does not greatly affect the total amount of summer rainfall in NA; instead, a large-scale atmospheric circulation forming favorable (unfavorable) rainfall conditions in the negative (positive) TC genesis phase controls the summer rainfall in that area.

Impact of typhoons on the Changjiang plume extension in the Yellow and East China Seas

It is well known that river discharges, winds, ocean currents, and tides are major dynamical factors that determine the distribution and extension of the Changjiang plume (CP) in the Yellow and East China Seas (YECS). Using observations and numerical experiments, this study demonstrates that, in addition to these factors, typhoons in the YECS also play a crucial role in the extension of the CP during the summer season. The hydrographic data observed at the Ieodo Ocean Research Station (IORS) and by a research vessel during the period of Typhoons Ewiniar (0603) and Dianmu (1004) showed that the typhoon-induced strong vertical mixing modified spatial distribution of the CP significantly, resulting in the delay of the CPs extension by as much as up to 20 days. A series of numerical experiments for Typhoon Dianmu also showed that the typhoon plays a blocking role for the extension of CP for up to 17 days through the vertical mixing process and the change of background winds. In particular, it is found that the delay due to Dianmu in 2010 contributed to the avoidance of potential mass mortality of marine life by preventing the low-salinity water from spreading to the aquaculture regions near Jeju Island.

Two climate factors in May that affect Korean rainfall in September

This study revealed a high positive correlation between rainfall in Korea during September and the trade wind (TW)/Arctic Oscillation (AO) index in May that combines two climate factors, low-level TWs and the AO. This correlation was identified on the basis of the difference in the 850 h Pa streamline analysis between the positive and negative phases selected using the combined TW/AO index. In May, the spatial pattern of the anomalous pressure systems is similar to that in the positive AO phase. These anomalous pressure systems continue in June to August (JJA) and September, but the overall spatial distribution shifts a little to the south. Particularly in September, a huge anomalous anticyclone centered over the southeast seas of Japan strengthens inmost of the western north Pacific region and supplies a large volume of warm and humid air to the region near Korea. This characteristic is confirmed by the facts that during the positive TW/AO phase, the subtropical western north Pacific high (SWNPH) is more developed to the north and that the continuous positioning of the upper troposphere jet over Korea from May to September strengthens the anomalous upward flow, bringing warm and humid air to all layers. These factors contribute to increasing September rainfall in Korea during the positive TW/AO phase. Because the SWNPH develops more to the north in the positive phase, tropical cyclones tend to make landfall in Korea frequently, which also plays a positive role in increasing September rainfall in Korea. The above features are also reflected by the differences in average rainfall between the six years that had the highest May Niño 3.4 indices (El Niño phase) and the six years that had the lowest May Niño 3.4 indices (La Niña phase).

Statistical-dynamical typhoon intensity predictions in the western North Pacific using track pattern clustering and ocean coupling predictors

AbstractA statistical–dynamical model for predicting tropical cyclone (TC) intensity has been developed using a track-pattern clustering (TPC) method and ocean-coupled potential predictors. Based o...

Reply to Comment on ‘Roles of interbasin frequency changes in the poleward shifts of maximum intensity location of tropical cyclones’

Recently a pronounced global poleward shift in the latitude at which the maximum intensities of tropical cyclones (TC) occur has been identified. Moon et al (2015 Environ. Res. Lett. 10 104004) reported that the poleward migration is significantly influenced by changes in interbasin frequency. These frequency changes are a larger contributor to the poleward shift than the intrabasin migration component. The strong role of interbasin frequency changes in the poleward migration also suggest that the poleward trend could be changed to an opposite equatorward trend in the future due to multi-decadal variability that significantly impacts Northern Hemisphere TC frequency. In the accompanying comment, Kossin et al (2016 Environ. Res. Lett. 11 068001) questioned the novelty and robustness of our results by raising issues associated with subsampling, contributions from some basins to poleward migration, and data dependency. Here, we explain the originality and importance of our main findings, which are different from those of Kossin et al (2014 Nature 509 349–52) and reaffirm that our conclusions are maintained regardless of the issues that were raised.