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Kunihiko Kodera - One of the best experts on this subject based on the ideXlab platform.

  • dynamics and predictability of downward propagating stratospheric Planetary Waves observed in march 2007
    Journal of the Atmospheric Sciences, 2017
    Co-Authors: Hitoshi Mukougawa, Shunsuke Noguchi, Yuhji Kuroda, Ryo Mizuta, Kunihiko Kodera
    Abstract:

    AbstractThe predictability of a downward propagating event of stratospheric Planetary Waves observed in early March 2007 is examined by conducting ensemble forecasts using an AGCM. It is determined that the predictable period of this event is about 7 days. Regression analysis using all members of an ensemble forecast also reveals that the downward propagation is significantly related to an amplifying quasi-stationary Planetary-scale anomaly with barotropic structure in polar regions of the upper stratosphere. Moreover, the anomaly is 90° out of phase with the ensemble mean field. Hence, the upper stratospheric anomaly determines the subsequent vertical propagating direction of incoming Planetary Waves from the troposphere by changing their vertical phase tilt, which depends on its polarity. Furthermore, the regressed anomaly is found to have similar horizontal structure to the pattern of greatest spread among members of the predicted upper-stratospheric height field, and the spread growth rate reaches a m...

  • Influence of the vertical and zonal propagation of stratospheric Planetary Waves on tropospheric blockings
    Journal of Geophysical Research: Atmospheres, 2013
    Co-Authors: Kunihiko Kodera, Hitoshi Mukougawa, Aki Fujii
    Abstract:

    [1] Case studies are used to elucidate the relationship between stratospheric Planetary wave reflection and blocking formation in the troposphere. The enhanced upward propagation of a Planetary-scale wave packet from the Eurasian sector, involving a Euro-Atlantic blocking, leads to a stratospheric sudden warming (SSW). Following the weakening of the stratospheric westerly jet due to polar warming, the stratospheric Planetary wave packet then propagates downward over the American sector, inducing a ridge over the North Pacific as well as a trough over eastern Canada in the upper troposphere. The ridge promotes the formation of a Pacific blocking. This result explains why Pacific blockings tend to form after SSW, and why they are associated with suppressed upward propagation of Planetary Waves.

  • Tropospheric impact of reflected Planetary Waves from the stratosphere
    Geophysical Research Letters, 2008
    Co-Authors: Kunihiko Kodera, Hitoshi Mukougawa, Shingo Itoh
    Abstract:

    [1] A reflection of stratospheric Planetary Waves and its impact on the troposphere during a stratospheric sudden warming of March 2007 are investigated. Zonal propagation and reflection of the Planetary Waves is clearly seen in the longitude-height sections of the eddy geopotential height and the vertical and zonal component of the three-dimensional wave activity flux. A wave packet propagating upward and eastward from Eurasian continent was reflected by a negative wind shear in the upper stratospheric westerly jet caused by stratospheric warming. Waves then propagated downward to the American-Atlantic sector of the troposphere, which led to the formation of a deep trough over the Atlantic and brought cold weather to the northeastern part of the American continent.

  • Role of Planetary Waves in the stratosphere‐troposphere coupled variability in the northern hemisphere winter
    Geophysical Research Letters, 1999
    Co-Authors: Yuhji Kuroda, Kunihiko Kodera
    Abstract:

    The role of Planetary Waves in stratosphere-troposphere coupled variability is investigated using an extended singular value decomposition analysis of zonal-mean zonal wind and the vertical component of the Eliassen-Palm (E-P) flux for the winters from 1979/80 to 1995/96. The results suggest a close relationship between anomalies of zonal-mean zonal wind and the convergence zone of E-P flux, which together shift poleward and downward from the stratosphere to the troposphere as time advances. Following enhanced vertical propagation of Waves into the stratosphere, the Arctic Oscillation (AO) pattern is seen in the 500 hPa geopotential height field in association with an increased poleward propagation of tropospheric Waves.

  • role of Planetary Waves in the stratosphere troposphere coupled variability in the northern hemisphere winter
    Geophysical Research Letters, 1999
    Co-Authors: Yuhji Kuroda, Kunihiko Kodera
    Abstract:

    The role of Planetary Waves in stratosphere-troposphere coupled variability is investigated using an extended singular value decomposition analysis of zonal-mean zonal wind and the vertical component of the Eliassen-Palm (E-P) flux for the winters from 1979/80 to 1995/96. The results suggest a close relationship between anomalies of zonal-mean zonal wind and the convergence zone of E-P flux, which together shift poleward and downward from the stratosphere to the troposphere as time advances. Following enhanced vertical propagation of Waves into the stratosphere, the Arctic Oscillation (AO) pattern is seen in the 500 hPa geopotential height field in association with an increased poleward propagation of tropospheric Waves.

D Pancheva - One of the best experts on this subject based on the ideXlab platform.

  • Planetary Waves observed by timed saber in coupling the stratosphere mesosphere lower thermosphere during the winter of 2003 2004 part 2 altitude and latitude Planetary wave structure
    Journal of Atmospheric and Solar-Terrestrial Physics, 2009
    Co-Authors: Plamen Mukhtarov, B. Andonov, D Pancheva, N J Mitchell, J M Forbes
    Abstract:

    Abstract Part 2 of the present paper is focused on the Planetary wave coupling from the stratosphere to the lower thermosphere (30–120 km) during the Arctic winter of 2003/2004. The Planetary Waves seen in the TIMED/SABER temperature data in the latitudinal range 50°N–50°S are studied in detail. The altitude and latitude structures of the Planetary wave (stationary and travelling) clearly indicate that the stratosphere and mesosphere (30–90 km) are coupled by direct vertical propagation of the Planetary Waves, while the lower thermosphere (above 90–95 km altitude) is only partly connected with the lower levels probably indirectly through in-situ generation of disturbances by the dissipation and breaking of gravity Waves filtered by lower atmospheric Planetary Waves. A peculiar feature of the thermal regime in the lower thermosphere is that it is dominated by zonally symmetric Planetary Waves.

  • Planetary Waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004
    Journal of Geophysical Research, 2008
    Co-Authors: Anne K. Smith, Plamen Mukhtarov, B. Andonov, D Pancheva, N J Mitchell, E G Merzlyakov, W Singer, W K Hocking, C E Meek
    Abstract:

    [1] The vertical coupling of the stratosphere-mesosphere system through quasi-stationary and traveling Planetary Waves during the major sudden stratospheric warming (SSW) in the Arctic winter of 2003/2004 has been studied using three types of data. The UK Met Office (UKMO) assimilated data set was used to examine the features of the global-scale Planetary disturbances present in the winter stratosphere of the Northern Hemisphere. Sounding the Atmosphere using Broadband Emission Radiometry (SABER) satellite measurements were used as well for extracting the stationary Planetary Waves in the zonal and meridional winds of the stratosphere and mesosphere. Radar measurements at eight stations, four of them situated at high latitudes (63–69N) and the other four at midlatitudes (52–55N) were used to determine Planetary Waves in the mesosphere-lower thermosphere (MLT). The basic results show that prior to the SSW, the stratospheremesosphere system was dominated by an upward and westward propagating � 16-day wave detected simultaneously in the UKMO and MLT zonal and meridional wind data. After the onset of the SSW, longer-period (� 22–24 days) oscillations were observed in the zonal and meridional MLT winds. These likely include the upward propagation of stationary Planetary Waves from below and in situ generation of disturbances by the dissipation and breaking of gravity Waves filtered by stratospheric winds. Citation: Pancheva, D., et al. (2008), Planetary Waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003/2004, J. Geophys. Res., 113, D12105, doi:10.1029/2007JD009011.

  • Planetary Waves and variability of the semidiurnal tide in the mesosphere and lower thermosphere over esrange 68 n 21 e during winter
    Journal of Geophysical Research, 2004
    Co-Authors: D Pancheva, N J Mitchell
    Abstract:

    [1] The main features of the Planetary Waves and the variability of the semidiurnal tide with Planetary wave periods observed by meteor radar over Esrange (68°N, 21 °E) have been investigated. The interval of 39 months covering continuous measurements from October 1999 to December 2002 has been examined. The Planetary Waves most frequently observed by meteor radar measurements in the mesosphere and lower thermosphere (80-100 km) over Esrange are: 5-, 8- to 10-, 16-, and 23-day Waves (the quasi-2-day wave is excluded in this study). They are strongly amplified in the winter. Some differences between high- and middle-latitude Planetary Waves notwithstanding, the 5-, 10-, and 16-day Waves are most probably related to the well-known normal mode. There are some reasons to believe that the vertically upward propagating 23-day wave could be generated by solar forcing. The variability of the semidiurnal tide with periods of Planetary Waves has been thoroughly studied as well. It is found that in the winter when the Planetary Waves are significantly amplified, a very strong periodic variability of the semidiurnal tide is observed as well. This result indicates that the most probable mechanism responsible for the periodic tidal variability during winter is in situ nonlinear coupling between tides and Planetary Waves. Two winter periods have been examined (1999/2000 and 2001/2002) in order to find strong evidence supporting this suggestion. The validity of the frequency, phase, and vertical wavenumber (wavelength) relationship between the prime (the Planetary wave and semidiurnal tide) and secondary Waves has been established. The novel aspect of this work is that we show for the first time that the calculated vertical structures (vertical wavelengths) of the sum and difference secondary Waves, which have very close periods, are actually very different.

  • Planetary Waves and midlatitude sporadic e layers strong experimental evidence for a close relationship
    Journal of Geophysical Research, 2002
    Co-Authors: C Haldoupis, D Pancheva
    Abstract:

    [1] A large-amplitude, 7-day period westward propagating S = 1 Planetary wave has been reported from ground radar and satellite wind measurements in the mesosphere lower thermosphere (MLT) during the second half of August and well into September 1993. Following recent suggestions that Planetary Waves might play a role in the formation of midlatitude sporadic E layers (Es), we have obtained and analyzed, for the period from August 1 to September 30, 1993, the sporadic E critical frequency (foEs) time series from eight midlatitude ionosonde stations covering a large longitudinal zone from ∼58°E to 157°W. The analysis revealed that all eight station foEs data showed a strong 7-day periodicity, occurring concurrently with the 7-day Planetary wave reported elsewhere. Using independent methods for the analysis of the foEs time series, we computed identical estimates for the propagation direction, zonal wave number, and phase velocity of the 7-day wave, which are in agreement with those reported from radar and satellite neutral wind MLT measurements. The present findings provide the first direct evidence, proving that Planetary Waves play an important role in the physics of midlatitude sporadic E region layers. In addition, our results include an important implication, that the Es parameters measured routinely and rather reliably with a dense global network of digital ionosondes, as well as the enormous ionogram databases existing in World Data Centers, may be used as an alternative means of studying large-scale neutral atmospheric dynamics in the MLT region.

Anne K. Smith - One of the best experts on this subject based on the ideXlab platform.

  • MIDDLE ATMOSPHERE | Planetary Waves
    Encyclopedia of Atmospheric Sciences, 2015
    Co-Authors: Anne K. Smith, J. Perlwitz
    Abstract:

    Planetary Waves are vertically propagating disturbances that are identified by large-scale variations in the pressure, temperature, winds, and composition. Much of the large-scale longitude variability in the middle atmosphere is due to Planetary Waves. They can be stationary or travel in longitude with periods of a few days to a few weeks. Planetary Waves interact with other Waves and with the background atmosphere. Large-amplitude Waves can contribute to rapid changes in wind and temperature. Planetary Waves also play a role in the impact of stratospheric changes on the troposphere.

  • Planetary Waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003 2004
    Journal of Geophysical Research, 2008
    Co-Authors: Anne K. Smith, Plamen Mukhtarov, B. Andonov, D Pancheva, N J Mitchell, E G Merzlyakov, W Singer, W K Hocking, C E Meek
    Abstract:

    [1] The vertical coupling of the stratosphere-mesosphere system through quasi-stationary and traveling Planetary Waves during the major sudden stratospheric warming (SSW) in the Arctic winter of 2003/2004 has been studied using three types of data. The UK Met Office (UKMO) assimilated data set was used to examine the features of the global-scale Planetary disturbances present in the winter stratosphere of the Northern Hemisphere. Sounding the Atmosphere using Broadband Emission Radiometry (SABER) satellite measurements were used as well for extracting the stationary Planetary Waves in the zonal and meridional winds of the stratosphere and mesosphere. Radar measurements at eight stations, four of them situated at high latitudes (63–69N) and the other four at midlatitudes (52–55N) were used to determine Planetary Waves in the mesosphere-lower thermosphere (MLT). The basic results show that prior to the SSW, the stratospheremesosphere system was dominated by an upward and westward propagating � 16-day wave detected simultaneously in the UKMO and MLT zonal and meridional wind data. After the onset of the SSW, longer-period (� 22–24 days) oscillations were observed in the zonal and meridional MLT winds. These likely include the upward propagation of stationary Planetary Waves from below and in situ generation of disturbances by the dissipation and breaking of gravity Waves filtered by stratospheric winds. Citation: Pancheva, D., et al. (2008), Planetary Waves in coupling the stratosphere and mesosphere during the major stratospheric warming in 2003/2004, J. Geophys. Res., 113, D12105, doi:10.1029/2007JD009011.

  • The Origin of Stationary Planetary Waves in the Upper Mesosphere
    Journal of the Atmospheric Sciences, 2003
    Co-Authors: Anne K. Smith
    Abstract:

    Abstract Satellite observations indicate that quasi-stationary Planetary Waves often exist to at least 100 km in the winter mesosphere. Waves are also seen in the summer upper mesosphere. A three-dimensional numerical model was used to simulate these Waves and to diagnose the physical processes involved. The Waves simulated in the model closely resemble observed Waves. Several model runs that isolate specific processes are used to determine the relative importance of two forcing mechanisms. In the model, Planetary Waves that propagate from below are significantly damped at the altitude where gravity wave drag becomes large (about 75 km in the winter midlatitudes) or below if a reversal in the mean wind is encountered. Momentum forcing associated with breaking gravity Waves that have been filtered by Planetary-scale wind variations below acts to generate Planetary Waves in the middle and upper mesosphere. The amplitude from in situ forcing by gravity wave breaking exceeds the amplitude from the upward-prop...

  • Stationary Planetary Waves in Upper Mesospheric Winds
    Journal of the Atmospheric Sciences, 1997
    Co-Authors: Anne K. Smith
    Abstract:

    Abstract Quasi-stationary Planetary-scale longitudinal variations are found in the upper mesospheric winds measured during winter by the HRDI satellite instrument. These are negatively correlated with eddy winds in the stratosphere. Two different mechanisms are proposed to explain the mesospheric perturbation winds and their anticorrelation with stratospheric winds: 1) Planetary Waves propagate through the stratosphere and into the mesosphere, with a phase shift of one-half cycle and 2) mesospheric perturbations are forced in situ by gravity Waves whose spectrum has longitudinal asymmetries due to filtering by Planetary Waves in the stratosphere. The first mechanism is more consistent with the observations during Southern Hemisphere late winter (August) and also may explain the observations during Northern Hemisphere early winter (December). The second mechanism gives a more consistent explanation for the Northern Hemisphere late winter observations, as previously shown by the author. The hemispheric diff...

Yuhji Kuroda - One of the best experts on this subject based on the ideXlab platform.

  • dynamics and predictability of downward propagating stratospheric Planetary Waves observed in march 2007
    Journal of the Atmospheric Sciences, 2017
    Co-Authors: Hitoshi Mukougawa, Shunsuke Noguchi, Yuhji Kuroda, Ryo Mizuta, Kunihiko Kodera
    Abstract:

    AbstractThe predictability of a downward propagating event of stratospheric Planetary Waves observed in early March 2007 is examined by conducting ensemble forecasts using an AGCM. It is determined that the predictable period of this event is about 7 days. Regression analysis using all members of an ensemble forecast also reveals that the downward propagation is significantly related to an amplifying quasi-stationary Planetary-scale anomaly with barotropic structure in polar regions of the upper stratosphere. Moreover, the anomaly is 90° out of phase with the ensemble mean field. Hence, the upper stratospheric anomaly determines the subsequent vertical propagating direction of incoming Planetary Waves from the troposphere by changing their vertical phase tilt, which depends on its polarity. Furthermore, the regressed anomaly is found to have similar horizontal structure to the pattern of greatest spread among members of the predicted upper-stratospheric height field, and the spread growth rate reaches a m...

  • Role of Planetary Waves in the stratosphere‐troposphere coupled variability in the northern hemisphere winter
    Geophysical Research Letters, 1999
    Co-Authors: Yuhji Kuroda, Kunihiko Kodera
    Abstract:

    The role of Planetary Waves in stratosphere-troposphere coupled variability is investigated using an extended singular value decomposition analysis of zonal-mean zonal wind and the vertical component of the Eliassen-Palm (E-P) flux for the winters from 1979/80 to 1995/96. The results suggest a close relationship between anomalies of zonal-mean zonal wind and the convergence zone of E-P flux, which together shift poleward and downward from the stratosphere to the troposphere as time advances. Following enhanced vertical propagation of Waves into the stratosphere, the Arctic Oscillation (AO) pattern is seen in the 500 hPa geopotential height field in association with an increased poleward propagation of tropospheric Waves.

  • role of Planetary Waves in the stratosphere troposphere coupled variability in the northern hemisphere winter
    Geophysical Research Letters, 1999
    Co-Authors: Yuhji Kuroda, Kunihiko Kodera
    Abstract:

    The role of Planetary Waves in stratosphere-troposphere coupled variability is investigated using an extended singular value decomposition analysis of zonal-mean zonal wind and the vertical component of the Eliassen-Palm (E-P) flux for the winters from 1979/80 to 1995/96. The results suggest a close relationship between anomalies of zonal-mean zonal wind and the convergence zone of E-P flux, which together shift poleward and downward from the stratosphere to the troposphere as time advances. Following enhanced vertical propagation of Waves into the stratosphere, the Arctic Oscillation (AO) pattern is seen in the 500 hPa geopotential height field in association with an increased poleward propagation of tropospheric Waves.

Ian Simmonds - One of the best experts on this subject based on the ideXlab platform.