Observational indications of downward-propagating gravity waves in middle atmosphere lidar data

Kaifler, Natalie; Kaifler, Bernd; Ehard, Benedikt; Gisinger, Sonja; Dörnbrack, Andreas; Rapp, Markus; Kivi, Rigel; Kozlovsky, Alexander; Lester, M.; Liley, Ben

doi:10.1016/j.jastp.2017.03.003

Cited by 42 publications

(59 citation statements)

References 30 publications

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“…The upward propagating waves are obviously predominant throughout year, which accounts for about 91% of all the IGWs. The downward propagating IGWs relatively increase in December–March with a maximum rate of 21% in December, which is consistent with the previous studies (N. Kaifler et al, ; Yoshiki & Sato, ). The significant portion of the downward propagating waves in austral winter in the Antarctic was also reported (Moffat‐Griffin et al, ; Zink & Vincent, ).…”

Section: Discussionsupporting

confidence: 92%

A Statistical Study of Inertia Gravity Waves in the Lower Stratosphere Over the Arctic Region Based on Radiosonde Observations

et al. 2018

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Relative to many investigations of inertial gravity waves (IGWs) in the Antarctic, IGW activity in the Arctic region was paid less attention to. We use radiosonde observations at the Ny‐Alesund station (78.9°N, 11.9°E) from April 2012 to June 2016 to study the IGW characteristics in the lower stratosphere over the Arctic. The observation reveals a prevailing eastward zonal background wind below 20 km and an obvious annual cycle of the background temperature from the troposphere to the lower stratosphere, which is different from the results in the middle and low latitudes. By combining Lomb‐Scargle spectrum and hodograph technique, case study demonstrates that the lower stratospheric IGWs exhibit a feature of freely propagating waves. Statistical analysis indicates that the IGWs have dominant horizontal (vertical) wavelength of 50–1,050 km (1–4 km) and ratio (1–2.5) of the intrinsic to inertia frequencies. Wave energy exhibits an annual oscillation with the maximum in winter and the minimum in summer. In winter, the downward propagating waves increase to about 20% due to polar stratospheric vortex. Because of the lower atmospheric filtering, the IGWs display a dominant direction of westward propagation, thus have a mean vertical flux of −0.647 mPa for the zonal momentum, which indicates that the IGWs can put a westward drag on the atmospheric wind field over the Arctic as they break and dissipate. All the vertical wavenumber spectra have spectral slopes from −2.23 to −2.99 close to the universal spectrum index of −3.

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Section: Discussionsupporting

confidence: 92%

A Statistical Study of Inertia Gravity Waves in the Lower Stratosphere Over the Arctic Region Based on Radiosonde Observations

et al. 2018

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“…8). The portable lidar systems as well as the data analysis procedure used during the three campaigns have been described in detail in Kaifler et al (2015Kaifler et al ( , 2017. In short, Rayleigh lidar measurements yield relative density profiles at altitudes where pure molecular scatter accounts for the signal, i.e., from above the stratospheric aerosol layer.…”

Section: Comparison Of Metop E P Values With Ecmwf Model Data and Gromentioning

confidence: 99%

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

2018

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Abstract. Temperature profiles based on radio occultation (RO) measurements with the operational European METOP satellites are used to derive monthly mean global distributions of stratospheric (20-40 km) gravity wave (GW) potential energy densities (E P ) for the period July 2014-December 2016. In order to test whether the sampling and data quality of this data set is sufficient for scientific analysis, we investigate to what degree the METOP observations agree quantitatively with ECMWF operational analysis (IFS data) and reanalysis (ERA-Interim) data. A systematic comparison between corresponding monthly mean temperature fields determined for a latitude-longitude-altitude grid of 5 • by 10 • by 1 km is carried out. This yields very low systematic differences between RO and model data below 30 km (i.e., median temperature differences is between −0.2 and +0.3 K), which increases with height to yield median differences of +1.0 K at 34 km and +2.2 K at 40 km. Comparing E P values for three selected locations at which also ground-based lidar measurements are available yields excellent agreement between RO and IFS data below 35 km. ERA-Interim underestimates E P under conditions of strong local mountain wave forcing over northern Scandinavia which is apparently not resolved by the model. Above 35 km, RO values are consistently much larger than model values, which is likely caused by the model sponge layer, which damps small-scale fluctuations above ∼ 32 km altitude. Another reason is the wellknown significant increase of noise in RO measurements above 35 km. The comparison between RO and lidar data reveals very good qualitative agreement in terms of the seasonal variation of E P , but RO values are consistently smaller than lidar values by about a factor of 2. This discrepancy is likely caused by the very different sampling characteristics of RO and lidar observations. Direct comparison of the global data set of RO and model E P fields shows large correlation coefficients (0.4-1.0) with a general degradation with increasing altitude. Concerning absolute differences between observed and modeled E P values, the median difference is relatively small at all altitudes (but increasing with altitude) with an exception between 20 and 25 km, where the median difference between RO and model data is increased and the corresponding variability is also found to be very large. The reason for this is identified as an artifact of the E P algorithm: this erroneously interprets the pronounced climatological feature of the tropical tropopause inversion layer (TTIL) as GW activity, hence yielding very large E P values in this area and also large differences between model and observations. This is because the RO data show a more pronounced TTIL than IFS and ERA-Interim. We suggest a correction for this effect based on an estimate of this "artificial" E P using monthly mean zonal mean temperature profiles. This correction may be recommended for application to data sets that can only be analyzed using a vertical background determination me...

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“…Primary sources of GWs in the troposphere and lower stratosphere are wind flow over topography, shallow and deep convection, wind shears, jet streams, and geostrophic/spontaneous adjustment processes (Fritts & Alexander, ; Plougonven & Zhang, ). Higher up in the atmosphere, local flow accelerations accompanying momentum transport, wave‐wave interactions, and others constitute secondary sources of GWs (e.g., Eliassen & Palm, ; Heale et al, ; Kaifler et al, ; Vadas et al, ). For topographically forced waves, linear theory predicts that the height of the obstacle, the thermal stratification, and the strength of the flow determine the magnitude of the energy and momentum transported by these waves (Gill, ).…”

Section: Introductionmentioning

confidence: 99%

Does Strong Tropospheric Forcing Cause Large‐Amplitude Mesospheric Gravity Waves? A DEEPWAVE Case Study

et al. 2017

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On 4 July 2014, during the Deep Propagating Gravity Wave Experiment (DEEPWAVE), strong low‐level horizontal winds of up to 35 m s−1 over the Southern Alps, New Zealand, caused the excitation of gravity waves having the largest vertical energy fluxes of the whole campaign (38 W m−2). At the same time, large‐amplitude mesospheric gravity waves were detected by the Temperature Lidar for Middle Atmospheric Research (TELMA) located at Lauder (45.0°S, 169.7°E), New Zealand. The coincidence of these two events leads to the question of whether the mesospheric gravity waves were generated by the strong tropospheric forcing. To answer this, an extensive data set is analyzed, comprising TELMA, in situ aircraft measurements, radiosondes, wind lidar measurements aboard the DLR Falcon as well as Rayleigh lidar and advanced mesospheric temperature mapper measurements aboard the National Science Foundation/National Center for Atmospheric Research Gulfstream V. These measurements are further complemented by limited area simulations using a numerical weather prediction model. This unique data set confirms that strong tropospheric forcing can cause large‐amplitude gravity waves in the mesosphere, and that three essential ingredients are required to achieve this: first, nearly linear propagation across the tropopause; second, leakage through the stratospheric wind minimum; and third, amplification in the polar night jet. Stationary gravity waves were detected in all atmospheric layers up to the mesosphere with horizontal wavelengths between 20 and 100 km. The complete coverage of our data set from troposphere to mesosphere proved to be valuable to identify the processes involved in deep gravity wave propagation.

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Observational indications of downward-propagating gravity waves in middle atmosphere lidar data

Cited by 42 publications

References 30 publications

A Statistical Study of Inertia Gravity Waves in the Lower Stratosphere Over the Arctic Region Based on Radiosonde Observations

A Statistical Study of Inertia Gravity Waves in the Lower Stratosphere Over the Arctic Region Based on Radiosonde Observations

An intercomparison of stratospheric gravity wave potential energy densities from METOP GPS radio occultation measurements and ECMWF model data

Does Strong Tropospheric Forcing Cause Large‐Amplitude Mesospheric Gravity Waves? A DEEPWAVE Case Study

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