scholarly journals Variations of Kelvin waves around the TTL region during the stratospheric sudden warming events in the Northern Hemisphere winter

2016 ◽  
Vol 34 (3) ◽  
pp. 331-345 ◽  
Author(s):  
Yue Jia ◽  
Shao Dong Zhang ◽  
Fan Yi ◽  
Chun Ming Huang ◽  
Kai Ming Huang ◽  
...  
Keyword(s):  
Zonal Wind ◽  
Reanalysis Data ◽  
Wave Activity ◽  
Equatorial Region ◽  
Kelvin Waves ◽  
Composite Analysis ◽  
Kelvin Wave ◽  
Stratospheric Sudden Warming ◽  
Tropical Tropopause ◽  
Hemisphere Winter

Abstract. Spatial and temporal variabilities of Kelvin waves during stratospheric sudden warming (SSW) events are investigated by the ERA-Interim reanalysis data, and the results are validated by the COSMIC temperature data. A case study on an exceptionally large SSW event in 2009, and a composite analysis comprising 18 events from 1980 to 2013 are presented. During SSW events, the average temperature increases by 20 K in the polar stratosphere, while the temperature in the tropical stratosphere decreases by about 4 K. Kelvin wave with wave numbers 1 and 2, and periods 10–20 days, clearly appear around the tropical tropopause layer (TTL) during SSWs. The Kelvin wave activity shows obvious coupling with the convection localized in the India Ocean and western Pacific (Indo-Pacific) region. Detailed analysis suggests that the enhanced meridional circulation driven by the extratropical planetary wave forcing during SSW events leads to tropical upwelling, which further produces temperature decrease in the tropical stratosphere. The tropical upwelling and cooling consequently result in enhancement of convection in the equatorial region, which excites the strong Kelvin wave activity. In addition, we investigated the Kelvin wave acceleration to the eastward zonal wind anomalies in the equatorial stratosphere during SSW events. The composite analysis shows that the proportion of Kelvin wave contribution ranges from 5 to 35 % during SSWs, much larger than in the non-SSW mid-winters (less than 5 % in the stratosphere). However, the Kelvin wave alone is insufficient to drive the equatorial eastward zonal wind anomalies during the SSW events, which suggests that the effects of other types of equatorial waves may not be neglected.

scholarly journals Long-term behavior of the Kelvin waves revealed by CHAMP/GPS RO measurements and their effects on the tropopause structure

2006 ◽  
Vol 24 (5) ◽  
pp. 1355-1366 ◽  
Author(s):  
M. Venkat Ratnam ◽  
T. Tsuda ◽  
T. Kozu ◽  
S. Mori
Keyword(s):  
Wave Activity ◽  
Kelvin Waves ◽  
Tropopause Height ◽  
Kelvin Wave ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause ◽  
Hemisphere Winter ◽  
Biennial Oscillation ◽  
Northern Hemisphere Winter

Abstract. The vertical and temporal variations of Kelvin waves and the associated effects on the tropical tropopause were studied using long-term (from May 2001 to October 2005) CHAMP/GPS (CHAllenging Mini satellite Payload/Global Positioning System) radio occultation (RO) measurements. The periods of these waves were found to be varying in between 10 and 15 days, with vertical wavelengths 5–8 km. These variations clearly show eastward phase propagation in the time-longitude section and eastward phase tilts with height in altitude-longitude, displaying the characteristics of Kelvin waves. The peak variance in the temperature is found over the Indian Ocean and into the western Pacific within the broad region of the equator. Kelvin wave amplitudes were found significantly enhanced in the eastward shear of the quasi-biennial oscillation (QBO) and are confined in and around the tropopause during westward phase of QBO, where it extends between 17 and 25 km during the eastward phase of QBO and is damped away above, consistent with earlier reported results. The amplitudes are increasing during the months of Northern Hemisphere winter and sometimes they are highly sporadic in nature. Seasonal and inter-annual variations in the Kelvin wave amplitudes near the tropical tropopause coincide exactly with the tropopause height and temperature, with a sharp tropopause during maximum Kelvin wave activity. A clear annual oscillation, along with a month-to-month coincidence is evident most of the time in both the tropopause height and Kelvin wave activity, with maximum and minimum Kelvin wave amplitudes during the Northern Hemisphere winter and summer, respectively. In addition, a signature of quasi-biennial oscillation (QBO) in the tropopause structure is also seen in long-term tropopause variations, although the amplitudes are less when compared to the annual oscillation. In the westward phase of QBO (during strong Kelvin wave activity) at 20km (in 2001–2002 winter and 2003–2004 winter), the tropopause height was slightly larger with a sharp tropopause and low temperature. The process behind these observed features has been discussed.

scholarly journals Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements

2017 ◽  
Vol 17 (2) ◽  
pp. 793-806 ◽  
Author(s):  
Barbara Scherllin-Pirscher ◽  
William J. Randel ◽  
Joowan Kim
Keyword(s):  
Large Scale ◽  
Deep Convection ◽  
Wave Activity ◽  
Kelvin Waves ◽  
Temperature Variability ◽  
Stationary Waves ◽  
Kelvin Wave ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause ◽  
Tropopause Region

Abstract. Tropical temperature variability over 10–30 km and associated Kelvin-wave activity are investigated using GPS radio occultation (RO) data from January 2002 to December 2014. RO data are a powerful tool for quantifying tropical temperature oscillations with short vertical wavelengths due to their high vertical resolution and high accuracy and precision. Gridded temperatures from GPS RO show the strongest variability in the tropical tropopause region (on average 3 K2). Large-scale zonal variability is dominated by transient sub-seasonal waves (2 K2), and about half of sub-seasonal variance is explained by eastward-traveling Kelvin waves with periods of 4 to 30 days (1 K2). Quasi-stationary waves associated with the annual cycle and interannual variability contribute about a third (1 K2) to total resolved zonal variance. Sub-seasonal waves, including Kelvin waves, are highly transient in time. Above 20 km, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO) in stratospheric zonal winds, with enhanced wave activity during the westerly shear phase of the QBO. In the tropical tropopause region, however, peaks of Kelvin-wave activity are irregularly distributed in time. Several peaks coincide with maxima of zonal variance in tropospheric deep convection, but other episodes are not evidently related. Further investigations of convective forcing and atmospheric background conditions are needed to better understand variability near the tropopause.

scholarly journals Tropical temperature variability and Kelvin wave activity in the UTLS from GPS RO measurements

2016 ◽  
Author(s):  
Barbara Scherllin-Pirscher ◽  
William J. Randel ◽  
Joowan Kim
Keyword(s):  
High Frequency ◽  
Large Scale ◽  
Wave Activity ◽  
Kelvin Waves ◽  
Temperature Variability ◽  
Kelvin Wave ◽  
Quasi Biennial Oscillation ◽  
Tropical Tropopause ◽  
Tropopause Region ◽  
High Frequency Waves

Abstract. Tropical temperature variability over 10–30 km and associated Kelvin wave activity is investigated using GPS radio occultation (RO) data from January 2002 to December 2014. RO data are a powerful tool to quantify tropical temperature oscillations with short vertical wavelengths due to their high vertical resolution and high accuracy and precision. Gridded temperatures from GPS RO show strongest variability in the tropical tropopause region (on average 3 K2). Large-scale zonal variability is dominated by transient high-frequency waves (2 K2) and about half of high-frequency variance is explained by eastward traveling Kelvin waves with periods of 7 to 30 days (1 K2). Quasi-stationary waves associated with the annual cycle and inter-annual variability contribute about a third (1 K2) to total resolved zonal variance. High-frequency waves, including Kelvin waves, are highly transient in time. Above 20 km, Kelvin waves are strongly modulated by the quasi-biennial oscillation (QBO) in stratospheric zonal winds, with enhanced wave activity during the westerly shear phase of the QBO. In the tropical tropopause region, however, peaks of Kelvin wave activity are irregularly distributed in time. Several peaks coincide with maxima of zonal variance in tropospheric deep convection, but other episodes are not evidently related. Further investigations of convective forcing and atmospheric background conditions are needed to better understand variability near the tropopause.

scholarly journals Vertically Propagating Kelvin Waves and Tropical Tropopause Variability

2008 ◽  
Vol 65 (6) ◽  
pp. 1817-1837 ◽  
Author(s):  
Jung-Hee Ryu ◽  
Sukyoung Lee ◽  
Seok-Woo Son
Keyword(s):  
Tropical Pacific ◽  
Wave Action ◽  
Kelvin Waves ◽  
Western Pacific ◽  
Tropopause Height ◽  
Kelvin Wave ◽  
Western Tropical Pacific ◽  
Tropical Tropopause ◽  
Vertically Propagating ◽  
The Western Pacific

Abstract The relationship between local convection, vertically propagating Kelvin waves, and tropical tropopause height variability is examined. This study utilizes both simulations of a global primitive-equation model and global observational datasets. Regression analysis with the data shows that convection over the western tropical Pacific is followed by warming in the upper troposphere (UT) and cooling in lower stratosphere (LS) over most longitudes, which results in a lifting of the tropical tropopause. The model results reveal that these UT–LS temperature anomalies are closely associated with vertically propagating Kelvin waves, indicating that these Kelvin waves drive tropical tropopause undulations at intraseasonal time scales. The model simulations further show that regardless of the longitudinal position of the imposed heating, the UT–LS Kelvin wave reaches its maximum amplitude over the western Pacific. This result, together with an analysis based on wave action conservation, is used to contend that the Kelvin wave amplification over the western Pacific should be attributed to the zonal variation of background zonal wind field, rather than to the proximity of the heating. The wave action conservation law is also used to offer an explanation as to why the vertically propagating Kelvin waves play the central role in driving tropical tropopause height undulations. The zonal and vertical modulation of the Kelvin waves by the background flow may help explain the origin of the very cold air over the western tropical Pacific, which is known to cause freeze-drying of tropospheric air en route to the stratosphere.

scholarly journals Ultrafast Kelvin waves in the MLT airglow and wind, and their interaction with the atmospheric tides

2018 ◽  
Vol 36 (1) ◽  
pp. 231-241 ◽  
Author(s):  
Fabio Egito ◽  
Ricardo Arlen Buriti ◽  
Amauri Fragoso Medeiros ◽  
Hisao Takahashi
Keyword(s):  
Middle Atmosphere ◽  
Rotational Temperature ◽  
Meridional Wind ◽  
Equatorial Region ◽  
Kelvin Waves ◽  
Atmospheric Composition ◽  
Atmospheric Tides ◽  
Kelvin Wave ◽  
Composition And Structure ◽  
Integrated Intensities

Abstract. Airglow and wind measurements from the Brazilian equatorial region were used to investigate the presence and the effects of the 3–4-day ultrafast Kelvin waves in the MLT. The airglow integrated intensities of the OI557.7 nm, O2b(0-1) and OH(6-2) emissions, as well as the OH rotational temperature, were measured by a multichannel photometer, and the zonal and meridional wind components between 80 and 100 km were obtained from a meteor radar. Both instruments are installed in the Brazilian equatorial region at São João do Cariri (7.4∘ S, 36.5∘ W). Data from 2005 were used in this study. The 3–4-day oscillations appear intermittently throughout the year in the airglow. They were identified in January, March, July, August and October–November observations. The amplitudes induced by the waves in the airglow range from 26 to 40 % in the OI557.7 nm, 17 to 43 % in the O2b(0-1) and 15 to 20 % in the OH(6-2) emissions. In the OH rotational temperature, the amplitudes were from 4 to 6 K. Common 3–4-day oscillations between airglow and neutral wind compatible with ultrafast Kelvin waves were observed in March, August and October–November. In these cases, the amplitudes in the zonal wind were found to be between 22 and 28 m s−1 and the vertical wavelength ranges from 44 to 62 km. Evidence of the nonlinear interaction between the ultrafast Kelvin wave and diurnal tide was observed. Keywords. Atmospheric composition and structure (airglow and aurora) – meteorology and atmospheric dynamics (middle atmosphere dynamics; waves and tides)

scholarly journals Correlation between equatorial Kelvin waves and the occurrence of extremely thin ice clouds at the tropical tropopause

2008 ◽  
Vol 8 (14) ◽  
pp. 4019-4026 ◽  
Author(s):  
F. Immler ◽  
K. Krüger ◽  
M. Fujiwara ◽  
G. Verver ◽  
M. Rex ◽  
...  
Keyword(s):  
Kelvin Waves ◽  
Clear Correlation ◽  
Temperature Structure ◽  
Kelvin Wave ◽  
Ice Clouds ◽  
Tropical Tropopause Layer ◽  
Tropical Tropopause ◽  
Water Vapour Concentration ◽  
Vapour Concentration ◽  
The Tropics

Abstract. A number of field-campaigns in the tropics have been conducted in recent years with two different LIDAR systems at Paramaribo (5.8° N, 55.2° W), Suriname. The lidars detect particles in the atmosphere with high vertical and temporal resolution and are capable of detecting extremely thin cloud layers which frequently occur in the tropical tropopause layer (TTL). Radiosonde as well as operational ECMWF analysis showed that equatorial Kelvin waves propagated in the TTL and greatly modulated its temperature structure. We found a clear correlation between the temperature anomalies introduced by these waves and the occurrence of thin cirrus in the TTL. In particular we found that extremely thin ice clouds form regularly where cold anomalies shift the tropopause to high altitudes. These findings suggest an influence of Kelvin wave activity on the dehydration in the TTL and thus on the global stratospheric water vapour concentration.

scholarly journals Rapid Transitions in Zonal Wind Around the Tropical Tropopause and their Relation to the Amplified Equatorial Kelvin Waves

SOLA ◽  
2007 ◽  
Vol 3 ◽  
pp. 13-16 ◽  
Author(s):  
Noriyuki Nishi ◽  
Junko Suzuki ◽  
Atsushi Hamada ◽  
Masato Shiotani
Keyword(s):  
Zonal Wind ◽  
Kelvin Waves ◽  
Tropical Tropopause

Linking Equatorial African precipitation to Kelvin wave processes in the CP4-Africa convection-permitting regional climate simulation

2021 ◽  
Author(s):  
Godwin Ayesiga ◽  
Christopher Holloway ◽  
Charles Williams ◽  
Gui-Ying Yang ◽  
Rachel Stratton ◽  
...  
Keyword(s):  
Observational Studies ◽  
Model Simulation ◽  
Wave Activity ◽  
Kelvin Waves ◽  
Specific Humidity ◽  
Climate Simulation ◽  
Kelvin Wave ◽  
Low Level ◽  
Equatorial Africa ◽  
Precipitation Anomalies

<p>Synoptic timescale forecasts over Equatorial Africa are important for averting weather-and climate-related disasters and the resulting agricultural losses. Observational studies have shown that rainfall anomalies often propagate eastward across Equatorial Africa, and that there is a linkage between synoptic-scale eastward-propagating precipitation and Convectively Coupled Kelvin Waves (CCKWs) over this region. We explore the mechanisms in which CCKWs modulate the propagation of precipitation from West to East over Equatorial Africa. We examine the first Africa-wide climate simulation from a convection permitting model (CP4A) along with its global driving-model simulation (G25) and evaluate both against observations (TRMM) and ERA-Interim (ERA-I), with a focus on precipitation and Kelvin wave activity.</p><p>Lagged composites show that both simulations capture the eastward propagating precipitation signal seen in observational studies, though G25 has a weaker signal. Composite analysis on high-amplitude Kelvin waves further shows that both simulations capture the connection between the eastward propagating precipitation anomalies and Kelvin waves. In comparison to TRMM, however, the precipitation signal is weaker in G25, while CP4A is more realistic. As the Kelvin wave activity is also well represented in both simulations when compared to ERA-I, the weak precipitation signal in G25 may be partly associated with the weak coupling between the precipitation and Kelvin waves. We show that CCKWs modulate the eastward propagation of convection and precipitation across Equatorial Africa through at least two related physical processes. Firstly, an enhancement of the low-level westerlies leads to increased low-level convergence; secondly, westerly moisture flux anomalies amplify lower-to-mid-tropospheric specific humidity. Results show that both CP4A and G25 generally simulate the key horizontal features of CCKWs, with anomalous low-level westerlies in phase with positive precipitation anomalies. However, both models show a weakness in capturing the vertical profile of anomalous specific humidity, and the zonal-vertical circulation is too weak in G25 and incoherent in CP4A compared to ERA-I.</p><p>In both ERA-I and the simulations, Kelvin wave-induced convergence and the westward tilt with height of anomalous zonal winds and specific humidity tends to weaken to the east of the East African highlands. It appears that these highlands impede the coherent eastward propagation of the wave-precipitation coupled structure.</p>

scholarly journals Morphology of the Wavenumber 1 and Wavenumber 2 Stratospheric Kelvin Waves Using the Long-Term Era-Interim Reanalysis Dataset

Atmosphere ◽  
2020 ◽  
Vol 11 (4) ◽  
pp. 421
Author(s):  
Chen-Jeih Pan ◽  
Shih-Sian Yang ◽  
Uma Das ◽  
Wei-Sheng Chen
Keyword(s):  
Temporal Variations ◽  
Equatorial Region ◽  
Kelvin Waves ◽  
Full Time ◽  
Kelvin Wave ◽  
Reanalysis Dataset ◽  
Quasi Biennial Oscillation ◽  
Cycle Variation ◽  
The Waves

The atmospheric Kelvin wave has been widely studied due to its importance in atmospheric dynamics. Since a long-term climatological study is absent in the literature, we have employed the two-dimensional fast Fourier transform (2D-FFT) method for the 40-year long-term reanalysis of the dataset, ERA-Interim, to investigate the properties of Kelvin waves with wavenumbers 1 (E1) and 2 (E2) at 6–24 days wave periods over the equatorial region of ±10° latitude between a 15 and 45 km altitude during the period 1979–2019. The spatio-temporal variations of the E1 and E2 wave amplitudes were compared to the information of stratospheric quasi-biennial oscillation (QBO), and the wave amplitudes were found to have an inter-QBO cycle variation that was related to sea surface temperature and convections, as well as an intra-QBO cycle variation that was caused by interactions between the waves and stratospheric mean flows. Also, the E1 waves with 6–10 day periods and the E2 waves with 6 days period were observed to penetrate the westerly regime of QBO, which has a thickness less than the vertical wavelengths of those waves, and the waves could further propagate upward to higher altitudes. In a case study of the period 2006–2013, the wave amplitudes showed a good correlation with the Niño 3.4 index, outgoing longwave radiation (OLR), and precipitation during 2006–2013, though this was not the case for the full time series. The present paper is the first report on the 40-year climatology of Kelvin waves, and the morphology of Kelvin waves will help us diagnose the anomalies of wave activity and QBO in the future.

scholarly journals Correlation between equatorial Kelvin waves and the occurrence of extremely thin ice clouds at the tropical tropopause

2008 ◽  
Vol 8 (1) ◽  
pp. 2849-2862 ◽  
Author(s):  
F. Immler ◽  
K. Krüger ◽  
M. Fujiwara ◽  
G. Verver ◽  
M. Rex ◽  
...  
Keyword(s):  
Kelvin Waves ◽  
Clear Correlation ◽  
Kelvin Wave ◽  
Ice Clouds ◽  
Tropical Tropopause Layer ◽  
Temperature Anomalies ◽  
Tropical Tropopause ◽  
Water Vapour Concentration ◽  
Cold Point ◽  
The Tropics

Abstract. A number of field-campaigns in the tropics have been conducted in the recent years with two different LIDAR systems at Paramaribo in Suriname (5.8° N, 55.2° W). The lidars detect particles in the atmosphere with high vertical and temporal resolution and are capable of detecting extremely thin cloud layers which frequently occur in the tropical tropopause layer (TTL). Radiosonde as well as operational ECMWF analysis show that temperature anomalies caused by equatorial Kelvin waves propagate downward, well below the cold point tropopause (CPT). We find a clear correlation between the temperature anomalies introduced by these waves and the occurrence of thin cirrus in the TTL. In particular we found that extremely thin ice clouds form regularly where cold anomalies shift the tropopause to high altitudes. This finding suggests an influence of Kelvin wave activity on the dehydration in the TTL and thus on the global stratospheric water vapour concentration.

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