Summertime Wave Research Articles

Impact of interannually varying background circulation on summertime wave patterns and tropical cyclone tracks in the western North Pacific

This study analyzed summertime wave patterns in the western North Pacific by separating them into those during El Nino (EN) and La Nina (LN) years for 1979–2015. The background flow revealed that in the EN years, the subtropical high was weaker and the East Asian summer monsoon trough was deeper and extended farther southeastward. The composite results indicated that in the EN years, tropical cyclone (TC) tracks were more solid and stably associated with wave pattern propagation routes because the circulation anomalies were significantly stronger. However, in the LN years, when the wave patterns were weak under the shorter and less organized monsoon trough due to the enhanced subtropical high, the TC tracks and cyclonic anomalies were irregular and sporadic. Further background flow analyses indicated that the EN circulation favored the development of the monsoon trough and east–west expansion and contraction of the subtropical ridge, whereas the stronger subtropical ridge dominated most western North Pacific areas in the LN years. Therefore, the monsoon trough was weaker in the LN years and induced recurving TCs to take more scattered routes near Taiwan and China’s east coast. Therefore, Taiwan experienced more rainfall during recurving TC periods in the LN years than in the EN years. For the straight-moving TCs passing through Taiwan, rainfall was concentrated over southern Taiwan in the EN years but more evenly distributed in the LN years. Thus, background flow changes strongly affect wave patterns and TCs.

Interannual Variability of the Intraseasonal Oscillation and Its Impact on the Summertime Wave Patterns and Tropical Cyclones over the Western North Pacific

AbstractIn this study, intraseasonal oscillations (ISOs) and submonthly wave patterns were separated into maximal variance (MaxV) and minimal variance (MinV) years on the basis of ISO variance from July to October. The mean-state 850-hPa streamfunction for submonthly cases indicated that, in the MinV years, tropical cyclones (TCs) formed near areas southeast of those in the MaxV years. ISOs propagated northward in the MaxV years, whereas a weaker westward-propagating tendency was observed in the MinV years. Track analysis of the centers of the submonthly cyclonic anomalies suggested that the background flow dictated the propagation routes of the easterly cyclonic anomalies in the MaxV years. However, the propagation routes of the westerly cyclonic anomalies were barely affected by the background flow. Further analysis of the ISO mean flow patterns showed that in the MaxV years, the propagation routes of the westerly cyclonic anomalies were more likely controlled by the anomalous easterly flow generated by the ISO westerly cyclonic anomalies. Moreover, rainfall was heavier in Taiwan in the MaxV years because the background flow in the MinV years caused the submonthly cyclonic anomaly tracks to shift away from Taiwan. Therefore, low-frequency large-scale circulations can affect smaller-scale phenomena and local weather.

Quasi-Periodic Behavior of the Pacific–Japan Pattern Affecting Propagation Routes of Summertime Wave Patterns and the Associated Tropical Cyclone Tracks over the Western North Pacific

Abstract This study introduces a modified Pacific–Japan (PJ) index that exhibits a substantial periodicity of 5–16 days in the East Asian summer monsoon region. The quasi-periodic fluctuations of the PJ index can indicate changes in the large-scale circulation systems. In the PJ high phase, the wave pattern propagates northwestward from the western North Pacific tropics to an area near northern Luzon and is then forced to move westward because of a stationary, anomalous high pressure system over southern Japan. The tropical cyclones (TCs) associated with the anomalous low pressure systems tend to follow a straight-moving propagation route through the northern South China Sea. The anomalous cyclonic flow causes heavy rainfall in eastern Taiwan. However, in the PJ low phase, the wave pattern and TCs follow a recurving propagation route toward higher latitudes. The circulation pattern typically brings heavy rainfall to northern Taiwan in the PJ low phase. Therefore, wave patterns under the influence of the quasi-periodic fluctuations of the PJ pattern affect rainfall because of the changing propagation routes of the wave patterns, as well as the TC tracks.

Future Projection of Ocean Wave Climate: Analysis of SST Impacts on Wave Climate Changes in the Western North Pacific

AbstractChanges in ocean surface waves elicit a variety of impacts on coastal environments. To assess the future changes in the ocean surface wave climate, several future projections of global wave climate have been simulated in previous studies. However, previously there has been little discussion about the causes behind changes in the future wave climate and the differences between projections. The objective of this study is to estimate the future changes in mean wave climate and the sensitivity of the wave climate to sea surface temperature (SST) conditions in an effort to understand the mechanism behind the wave climate changes by specifically looking at spatial SST variation. A series of wave climate projections forced by surface winds from the MRI-AGCM3.2 were conducted based on SST ensemble experiments. The results yield future changes in annual mean wave height that are within about ±0.3 m. The future changes in summertime wave height in the western North Pacific (WNP), which are influenced by tropical cyclone changes, are highly sensitive to SST conditions. To generalize the result, the wave climate change and SST relation found by this study was compared with multimodel wave ensemble products from the Coordinated Ocean Wave Climate Project (COWCLIP). The spatial variation of SST in the tropical Pacific Ocean is a major factor in the wave climate changes for the WNP during summer.

Summertime wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 62:71-78 (2014) - DOI: https://doi.org/10.3354/cr01260 Summertime wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan Teruhisa Shimada* Graduate School of Science, Tohoku University, Aramaki Aza Aoba 6-3, Aoba-ku, Sendai, Miyagi 980-8578, Japan *Corresponding author: shimada@ocean.caos.tohoku.ac.jp ABSTRACT: Wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan in June–August is investigated using in situ measurements and reanalysis data. The coastal wave height is dominated by the persistent easterly winds induced by the developed Okhotsk high. These winds, which can induce cool summers in northern Japan, favor wave development toward the coast of northern Japan. The wave variability is enhanced along the coast of northern Tohoku by the strong local winds occurring in the lee of Cape Erimo. The results for variability of wave height along the Pacific and Okhotsk Sea coasts of northern Japan are supported by composite analysis of reanalysis wave data. When the Okhotsk high develops and the resulting easterly winds are dominant, the wave height increases near the coast of and to the east of northern Japan. Wave height also increases in the Japan Sea and along the southern coast of Japan, whereas wave height decreases in the Okhotsk Sea. These wave height variations reflect the distinct wind fields associated with the developed Okhotsk high. Trends in wave height are examined using the in situ measurements available for over 20 yr. Only the decreasing trends in the south of northern Japan in August are statistically significant. KEY WORDS: Wave climate · Okhotsk high · Northern Japan · Significant wave height · Cool summer · Yamase Full text in pdf format PreviousCite this article as: Shimada T (2014) Summertime wave height variability along the Pacific and Okhotsk Sea coasts of northern Japan. Clim Res 62:71-78. https://doi.org/10.3354/cr01260 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 62, No. 1. Online publication date: December 02, 2014 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2014 Inter-Research.

FUTURE PROJECTION OF OCEAN WAVE CLIMATE CHANGE USING MULTI-SST ENSEMBLE EXPERIMENTS

Long term changes in ocean waves elicit a variety of impacts on a coastal environment. In order to assess the future changes in ocean wave climate, future projections of global wave climates have been carried out by previous studies. However, previously there has been little discussion about the causes behind changes in future wave climate and the differences between projections. The objective of this study is to estimate the future changes in mean wave climate and the sensitivity of the wave climate to Sea Surface Temperature (SST) conditions, in an effort to understand the mechanism behind the wave climate changes by specifically looking at spatial SST variation. A series of wave climate projections forced by surface winds from the MRI-AGCM3.2H were conducted based on SST ensemble experiments. The results show future changes in seasonal mean wave heights that are within about ± 0.4 m depending on the region and season. The future changes in summertime wave heights in the Western North Pacific (WNP) are highly sensitive to SST conditions that are influenced by tropical cyclone changes. The spatial variation of SST in the tropical Pacific Ocean is a major factor in the wave climate changes for the WNP during summer.

The 5‐day wave in the Arctic and Antarctic mesosphere and lower thermosphere

The 5‐day planetary wave in the polar mesosphere and lower thermosphere has been investigated using meteor radars at Esrange (68°N, 21°E) in the Arctic and Rothera (68°S, 68°W) in the Antarctic. The measurements span the 9‐year interval from October 1999 to December 2008 and the 4‐year interval from February 2005 to December 2008, respectively. The height range covered is approximately 80–100 km. Horizontal wind variance within a wave period range of 4–7 days is used as a proxy for the activity of the 5‐day wave. Strong wave activity is seen in winter and late summer. However, there is a high degree of interannual variability, and in some individual years wave activity is almost absent. The data are used to construct a representative climatology for the Arctic and Antarctic. The seasonal cycle of the 5‐day wave is found to be very similar in both polar regions. Wave activity in winter is present across the entire height range observed. Wintertime wave variance can reach about 65 m2/s2. The wave is largely absent around the equinoxes. Wave activity is also very strong in late summer, reaching about 75 m2/s2, but occurs only for 1–2 months and is confined to heights above about 90 km and excluded from the stronger westward winds at lower heights. Summertime wave activity peaks at a height of about 95 km and decays rapidly above and below that height. During this summer maximum, the wave cannot have ascended to the mesosphere and lower thermosphere from below and so must have been generated in situ and/or ducted across the equator from the winter hemisphere. The seasonal cycle of the 5‐day wave is remarkably similar to that observed for the 2‐day wave at these latitudes.

The two-day wave in the Antarctic and Arctic mesosphere and lower thermosphere

Abstract. There have been comparatively few studies reported of the 2-day planetary wave in the middle atmosphere at polar latitudes. Here we report on a study made using high-latitude meteor radars at Rothera in the Antarctic (68° S, 68° W) and Esrange in Arctic Sweden (68° N, 21° E). Observations from 2005–2008 are used for Rothera and from 1999–2008 for Esrange. Measurements were made of horizontal winds at heights of 80–100 km. The radar data revealed distinct summertime and wintertime 2-day waves. The Antarctic summertime wave occurs with significant amplitudes in January – February at heights between about 88–100 km. Horizontal wind monthly variances associated with the wave exceed 160 m2 s−2 and the zonal component has larger amplitudes than the meridional. In contrast, the Arctic summertime wave occurs for a longer duration, June–August and has meridional amplitudes larger than the zonal amplitudes. The Arctic summertime wave is weaker than that in the Antarctic and maximum monthly variances are typically 60 m2 s−2. In both hemispheres the summertime wave reaches largest amplitudes in the strongly sheared eastward zonal flow above the zero-wind line and is largely absent in the westward flow below. The observed differences in the summertime wave are probably due to the differences in the background zonal winds in the two hemispheres. The Antarctic and Arctic wintertime 2-day waves have very similar behaviour. The Antarctic wave has significant amplitudes in May–August and the Arctic wave in November–February. Both are evident across the full height range observed.

Summer-time nocturnal wave characteristics in mesospheric OH and O2 airglow emissions

Abstract The mesospheric temperature mapper (MTM) measurements on mesospheric OH (6, 2) and O2 (0, 1) band emissions from Maui, Hawaii during July, 2002 show significant day-to-day variability. The nocturnal variability reveals prominent wave signatures with a periodicity ranging from 6 to 13 h. For better characterization of the nocturnal wave in the data, a Krassovsky’s η (∼|η|e iφ) analysis was carried out. Deduced Krassovsky parameters show significant variability, with ranges of |η| ∼ 1.7–3.9 for the OH data and ∼4.3–13 for the O2 data. The phase values of Krassovsky parameters exhibit larger variability, with variations from approximately −91° to +23° for the OH data and −45° to −10° for the O2 data. Comparison of these values with existing observations and models show large deviations from model values and relatively better agreements with the observed values reported by other investigators. The deduced vertical wavelength from |η| and φ indicates that our data is mostly dominated by upward propagating waves with occasional high values ≥100 km, implying possible evanescent waves.

The wintertime two-day wave in the polar stratosphere, mesosphere and lower thermosphere

Abstract. Recent observations of the polar mesosphere have revealed that waves with periods near two days reach significant amplitudes in both summer and winter. This is in striking contrast to mid-latitude observations where two-day waves maximise in summer only. Here, we use data from a meteor radar at Esrange (68° N, 21° E) in the Arctic and data from the MLS instrument aboard the EOS Aura satellite to investigate the wintertime polar two-day wave in the stratosphere, mesosphere and lower thermosphere. The radar data reveal that mesospheric two-day wave activity measured by horizontal-wind variance has a semi-annual cycle with maxima in winter and summer and equinoctial minima. The MLS data reveal that the summertime wave in the mesosphere is dominated by a westward-travelling zonal wavenumber three wave with significant westward wavenumber four present. It reaches largest amplitudes at mid-latitudes in the southern hemisphere. In the winter polar mesosphere, however, the wave appears to be an eastward-travelling zonal wavenumber two, which is not seen during the summer. At the latitude of Esrange, the eastward-two wave reaches maximum amplitudes near the stratopause and appears related to similar waves previously observed in the polar stratosphere. We conclude that the wintertime polar two-day wave is the mesospheric manifestation of an eastward-propagating, zonal-wavenumber-two wave originating in the stratosphere, maximising at the stratopause and likely to be generated by instabilities in the polar night jet.

Analyses of Year-to-Year Variation and Trend for Wave Climatic Parameters along the Coasts of Japan Using Long-Term Measurement Data

Wave measurement data acquired over more than two decades along the coasts of Japan and the Pacific coast of USA are analyzed from three points of view (1) year-to-year variation, (2) jumps and (3) trends for wintertime- and summertime-meanvalues of significant wave height and period. Main findings are as follows:(1) the winter of 1998, containing the severest El-Nino period, gives the highest mean wave height along the western Pacific coast of Japan and the Pacific coast of USA.(2) a seesaw-like variation with a two-year period of season-separated meanwave heights along the Pacific coast of Japan may be observed and (3) one jump and an increasing trend in summer-time mean wave period data may be observed along the coasts of Japan.

Wave Flow Simulations Over Arctic Leads

We investigate the flow over Arctic leads using a mesoscale numerical model, typical of both summer and winter, under idealised conditions. We find that Arctic leads may be the source of standing atmospheric internal gravity waves during both seasons. The summertime wave may be compared with the wave generated by a small ridge, though with the phase reversed. The mechanism for exciting the wave is found to be the internal boundary layer developing due to horizontal variations in surface temperature and roughness length. During the more exploratory wintertime simulations, with substantial temperature difference between the lead and the ice surface, we find that secondary circulations and intermittent wave-breaking may occur. The effects of the lead appear far downstream.