On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Kuchař, Aleš; Šácha, Petr; Eichinger, Roland; Jacobi, Ch.; Pišoft, Petr; Rieder, Harald E.

doi:10.5194/wcd-2020-21

Cited by 6 publications

(18 citation statements)

References 51 publications

(70 reference statements)

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“…Code and data availability. All processed data files for this study are provided via Mendeley Data (Kuchar, 2020b), and all codes to reproduce our figures are provided via GitHub (Kuchar, 2020a). The authors would like to thank all colleagues involved in the CMAM-sd model simulation (obtained from http://climate-modelling.canada.ca/climatemodeldata/cmam/ output/CMAM/CMAM30-SD/index.shtml, last access: 25 September 2020) (Canadian Centre for Climate Modelling and Analysis, 2020); reanalyses: MERRA-2 (obtained from http://disc.…”

Section: Discussionmentioning

confidence: 99%

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Kuchař

Šácha

Eichinger

et al. 2020

Weather Clim. Dynam.

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Abstract. When orographic gravity waves (OGWs) break, they dissipate their momentum and energy and thereby influence the thermal and dynamical structure of the atmosphere. This OGW forcing mainly takes place in the middle atmosphere. It is zonally asymmetric and strongly intermittent. So-called “OGW hotspot regions” have been shown to exert a large impact on the total wave forcing, in particular in the lower stratosphere (LS). Motivated by this we investigate the asymmetrical distribution of the three-dimensional OGW drag (OGWD) for selected hotspot regions in the specified dynamics simulation of the chemistry-climate model CMAM (Canadian Middle Atmosphere Model) for the period 1979–2010. As an evaluation, we first compare zonal mean OGW fluxes and GW drag (GWD) of the model simulation with observations and reanalyses in the Northern Hemisphere. We find an overestimation of GW momentum fluxes and GWD in the model's LS, presumably attributable to the GW parameterizations which are tuned to correctly represent the dynamics of the Southern Hemisphere. In the following, we define three hotspot regions which are of particular interest for OGW studies, namely the Himalayas, the Rocky Mountains and East Asia. The GW drags in these hotspot regions emerge as strongly intermittent, a result that can also quantitatively be corroborated with observational studies. Moreover, a peak-detection algorithm is applied to capture the intermittent and zonally asymmetric character of OGWs breaking in the LS and to assess composites for the three hotspot regions. This shows that LS peak OGW events can have opposing effects on the upper stratosphere and mesosphere depending on the hotspot region. Our analysis constitutes a new method for studying the intermittency of OGWs, thereby facilitating a new possibility to assess the effect of particular OGW hotspot regions on middle atmospheric dynamics.

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Section: Discussionmentioning

confidence: 99%

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Kuchař

Šácha

Eichinger

et al. 2020

Weather Clim. Dynam.

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“…Due to the inhomogeneous data distribution, while these spatial clusters represent both large and small scales well, they contain highly uneven numbers of measurements, with a spread of 3 orders of magnitude in population (compared to 5 orders of magnitude using a regular 3° grid). While suitable for mapping, this may introduce spurious intercluster variations in the statistics we compute, namely, the median and Gini's coefficient of concentration G (used previously for GW studies in, e.g., Hindley et al, 2019; Kuchar et al, 2020; Plougonven et al, 2012; Wright et al, 2013). Means were also calculated for all clusters and showed spatially consistent results but with spike values in some clusters due to outliers.…”

Section: Methodsmentioning

confidence: 99%

Multidecadal Measurements of UTLS Gravity Waves Derived From Commercial Flight Data

Banyard

2020

JGR Atmospheres

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Gravity waves (GWs) are key drivers of atmospheric dynamics, with major impacts on climate and weather processes. However, they are challenging to measure in observational data, and as a result no large-area multidecadal GW time series yet exist. This has prevented us from quantifying the interactions between GWs and long-timescale climate processes. Here, we exploit temperatures measured by commercial aircraft since 1994 as part of the In-Service Aircraft for a Global Observing System (IAGOS) atmospheric chemistry research program to produce a novel 26-year time series of upper troposphere/lower stratosphere (UTLS) GW measurements across most of the Northern Hemisphere. We analyze 90,342 flight hours (76.2 million flight kilometers) of data, typically at a temporal resolution of seconds and with high temperature precision. We show that GW activity in the Northern Hemisphere UTLS is consistently strongest north of and above the upper tropospheric jet. We also show that GW sources not typically observed in stratospheric data but assumed in model schemes, such as the Rocky Mountains, are visible at these altitudes, suggesting that wave momentum from these sources is deposited specifically between ∼200 and 50 hPa. Our data show no significant impact of the Quasi-Biennial Oscillation, the Northern Annular Mode, or climate change. However, we do see strong evidence of links with the El Niño-Southern Oscillation, which modulates the measured GW signal by ∼25%, and weak evidence of links with the 11-year solar cycle. These results have important implications for atmospheric process modeling and for understanding large-scale climate teleconnections. Plain Language Summary We use 26 years of temperature measurements, made by commercial aircraft flying routine passenger and freight routes, to measure and understand small-scale atmospheric waves ("gravity waves"). These waves play many vital roles in the atmosphere, and they are critically important to understanding and predicting weather and climate. However, due to their small size, they are extremely difficult to study at typical flight altitudes using any other method. Our data provide the longest large-area record of gravity waves from any dataset, with 76 million flight kilometers of measurements made since 1994. We see strong evidence that El Niño affects the behavior of these small waves over northern Europe and central Asia, many thousands of kilometers away from the Pacific Ocean. We also see weak evidence that the waves may be affected by the 11-year cycle of solar intensity. Our results provide a unique window on the interactions between small-scale atmospheric behavior and long-time scale climate dynamical processes and have important implications both for improving atmospheric models and for understanding long-distance climate teleconnections.

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“…This corresponds to the peak magnitude of the drag during the respective strong OGWD event. As shown in Figure 8 of Kuchar et al (2020), the peak is already preceeded by a few days of significant OGWD anomalies in the region of the hotspot. Therefore, at lag = 0 we can see a response that has already been evolving over a few days prior to lag = 0 under an increasing OGWD forcing overlapping with an imprint of the "hotspot preconditioning."…”

Section: Resultsmentioning

confidence: 92%

“…The selected hotspots are the Rocky Mountains (RM, 235-257.5°E and 27.5-52°N; note that this hotspot was referred to as Western America in Kuchar et al, 2020), the Himalayas (HI, 70-102.5°E and 20-40°N) and Eastern Asia (EA,. These are computed using the peak-detection algorithm described in Kuchar et al (2020). This algorithm identifies peaks (local maxima of negative drag) of OGWD that exceed immediate neighbors separated by more than 20 days with amplitudes beyond a normalized threshold.…”

Section: Methodsmentioning

confidence: 99%

“…All processed data files for this study are provided via Mendeley Data Kuchar (2020), and all codes to reproduce our figures are provided via GitHub (Kuchar, 2021) (Jucker, 2018), cartopy (Met Office, 2010-2015, matplotlib (Hunter, 2007), numpy (Oliphant, 2006), pandas (McKinney, 2010, seaborn (Waskom et al, 2016), scipy (Virtanen et al, 2020), xarray (Hoyer et al, 2016), and Scientific color maps (Crameri, 2020).…”

Section: Data Availability Statementmentioning

confidence: 99%

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Diverse Dynamical Response to Orographic Gravity Wave Drag Hotspots—A Zonal Mean Perspective

Šácha

Kuchař

Eichinger

et al. 2021

Geophysical Research Letters

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In the extratropical atmosphere, Rossby waves (RWs) and internal gravity waves (GWs) propagating from the troposphere mediate a coupling with the middle atmosphere by influencing the dynamics therein. In state‐of‐the‐art chemistry‐climate models (CCMs), RW effects are well resolved while the majority of GW effects have to be parameterized. Here, we analyze orographic GW (OGW) interaction with resolved dynamics in a comprehensive CCM on daily time scales. For this, we apply a recently developed method of strong OGW drag event composites for three pronounced northern hemisphere OGW hotspots. We show that strong OGW drag events are associated with anomalous resolved wave propagation in the stratosphere. Causal links are inferred from previously published work and are supported by the anomalies in zonal circulation and wave activity tendencies. The nature of these anomalies varies depending on the hotspot region, which underlines the parameterized OGW‐resolved dynamics interaction being a two‐way process.

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On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Cited by 6 publications

References 51 publications

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

On the intermittency of orographic gravity wave hotspots and its importance for middle atmosphere dynamics

Multidecadal Measurements of UTLS Gravity Waves Derived From Commercial Flight Data

Diverse Dynamical Response to Orographic Gravity Wave Drag Hotspots—A Zonal Mean Perspective

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