Interactions between waves and mean flows play a crucial role in understanding the long-term aspects of atmospheric and oceanographic modelling. Indeed, our ability to predict climate change hinges on our ability to model waves accurately. This book gives a modern account of the nonlinear interactions between waves and mean flows, such as shear flows and vortices. A detailed account of the theory of linear dispersive waves in moving media is followed by a thorough introduction to classical wave-mean interaction theory. The author then extends the scope of the classical theory and lifts its restriction to zonally symmetric mean flows. It can be used as a fundamental reference, a course text, or by geophysicists and physicists needing a first introduction. This second edition includes brand new material, including a section on Langmuir circulations and the Craik–Leibovich instability. The author has also added exercises to aid students' learning.

Waves and Mean Flows

The DEEPWAVE (deep-propagating wave experiment) campaign was designed for an airborne and ground-based exploration of gravity waves from their tropospheric sources up to their dissipation at high altitudes It was performed in and around New Zealand from 24 May till 27 July 2014, being the first comprehensive field campaign of this kind A variety of airborne instruments was deployed onboard the research aircraft NSF/NCAR Gulfstream V (GV) and the DLR Falcon Additionally, ground-based measurements were conducted at different sites across the southern island of New Zealand, including the DLR Rayleigh lidar located at Lauder (4504 S, 16968 E)

We focus on the intensive observing period (IOP) 10 on the 4 July 2014, when strong WSW winds of about 40 m/s at 700 hPa provided intense forcing conditions for mountain waves At tropopause level, the horizontal wind exceeded 50 m/s and favored the vertical propagation of gravity waves into the stratosphere The DLR Rayleigh Lidar measured temperature fluctuations with peak-to-peak amplitudes of about 20 K in the mesosphere (60 km to 80 km MSL) over a period of more than 10 hours Two research flights were conducted by the DLR Falcon (Falcon Flight 04 and 05) during this period with straight transects (Mt Aspiring 2a) over New Zealand´s Alps at three different flight-levels around the tropopause (approx 11 km MSL) These research flights were coordinated with the GV (Research Flight 16) where the largest mountain wave amplitudes at flight-level (approx 13 km MSL) were measured during DEEPWAVE Additionally a first analysis of Falcon's in-situ flight-level data revealed amplitudes in the vertical wind larger than 4 m/s at all altitudes in the vicinity of the highest peaks of the Southern Alps

Here, we present a comprehensive picture of the gravity wave characteristics and propagation properties during this interesting gravity wave event We use the airborne observations combined with a comprehensive set of ground-based measurements consisting of 13 radiosoundings (15 hourly interval) together with the DLR Rayleigh lidar To cover the altitude range from the troposphere to the mesosphere, high-resolution (1 hourly) ECMWF analyses and forecasts are used to estimate the propagation conditions of the excited mountain waves The goal of our investigation is to find out whether the large amplitude mesospheric gravity waves are caused by the strong tropospheric forcing

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

The Earth's thermosphere and ionosphere (TI) are characterized by perpetual variability as integral parts of the atmosphere system, with intermittent disturbances from solar and geomagnetic forcing. This review examines how the TI variability is affected by processes originating from the lower atmosphere and implications for quantifying and forecasting the TI. This aspect of the TI variability has been increasingly appreciated in recent years from both observational and numerical studies, especially during the last extended solar minimum. This review focuses on the role of atmospheric waves, including tides, planetary waves, gravity waves, and acoustic waves, which become increasingly significant as they propagate from their source region to the upper atmosphere. Recent studies have led to better understanding of how these waves directly or indirectly affect TI wind, temperature, and compositional structures; the circulation pattern; neutral and ion species transport; and ionospheric wind dynamo. The variability of these waves on daily to interannual scales has been found to significantly impact the TI variability. Several outstanding questions and challenges have been highlighted: (i) large, seemingly stochastic, day-to-day variability of tides in the TI; (ii) control of model error in the TI region by the lower atmosphere; and (iii) the increasing importance of processes with shorter spatial and temporal scales at higher altitudes. Addressing these challenges requires model capabilities to assimilate observations of both lower and upper atmosphere and higher model resolution to capture complex interactions among processes over a broad range of scales and extended altitudes.

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Variability and predictability of the space environment as related to lower atmosphere forcing

We analyze the results of the gravity wave (GW)-resolving, high-resolution Kühlungsborn Mechanistic general Circulation Model in July at McMurdo Station (166.69∘E and 77.84∘S), where strong downslope eastward winds create strong mountain wave (MW) events. These MWs have horizontal wavelengths of λH ≃ 230 km, propagate to z ∼ 40–60 km, and can have upward phases in time if the eastward wind accelerates in time. Additionally, inertia-GWs (IGWs) with λH ∼ 500–800 km and ground-based periods of τr ∼ 5–6 hr are generated in the troposphere from unbalanced, large-scale flow. The density-scaled GW amplitudes are ∼10 times smaller at z ∼ 80–100 km than at z < 50 km because of severe wave dissipation. “Fishbone” structures are seen at z ∼ 30–60 km with upward (downward) phases in time below (above) the “knee” at zknee. We horizontally filter the perturbations to isolate the GWs in a fishbone structure for a particular MW event. We find that these GWs have strikingly similar parameters below and above zknee = 46 km, with ground-based horizontal phase speeds of cH ∼ 40–60 m/s, τr ∼ 9–10 hr, λH ∼ 1,600–2,050 km, vertical wavelengths of λz ∼ 18–25 km, and azimuths of Υ = 145∘ –151∘ east of north. We show that these are secondary GWs excited by a body force at zknee created by MW dissipation approximately 400 km northwest of McMurdo 2.5 hr earlier and that the secondary GW scales and propagation directions are consistent with this force. Importantly, we show that most of the GWs at z> 70 km are secondary GWs not primary GWs from the troposphere.

Numerical Modeling of the Excitation, Propagation, and Dissipation of Primary and Secondary Gravity Waves during Wintertime at McMurdo Station in the Antarctic

We investigate the effects on the mesosphere and thermosphere from a strong mountain wave (MW) event over the wintertime Southern Andes using a gravity wave (GW)-resolving global circulation model. During this event, MWs break and attenuate at z ∼ 50–80 km, thereby creating local body forces that generate large-scale secondary GWs having concentric ring structure with horizontal wavelengths λH = 500–2,000 km, horizontal phase speeds cH = 70–100 m/s, and periods τr ∼ 3–10 hr. These secondary GWs dissipate in the upper mesosphere and thermosphere, thereby creating local body forces. These forces have horizontal sizes of 180–800 km, depending on the constructive/destructive interference between wave packets and the overall sizes of the wave packets. The largest body force is at z = 80–130 km, has an amplitude of ∼2,400 m/s/day, and is located ∼1,000 km east of the Southern Andes. This force excites mediumand large-scale “tertiary GWs” having concentric ring structure, with λH increasing with radius from the centers of the rings. Near the Southern Andes, these tertiary GWs have cH = 120–160 m/s, λH = 350–2,000 km, and τr ∼ 4–9 hr. Some of the larger-λH tertiary GWs propagate to the west coast of Africa with very large phase speeds of cH ≃ 420 m/s. The GW potential energy density increases exponentially at z ∼ 95–115 km, decreases at z ∼ 115–125 km where most of the secondary GWs dissipate, and increases again at z > 125 km from the tertiary GWs. Thus, strong MW events result in the generation of mediumto large-scale fast tertiary GWs in the mesosphere and thermosphere via this multistep vertical coupling mechanism.

Numerical Modeling of the Generation of Tertiary Gravity Waves in the Mesosphere and Thermosphere During Strong Mountain Wave Events Over the Southern Andes

The Deep Propagating Gravity Wave Experiment (DEEPWAVE) was designed to quantify gravity wave (GW) dynamics and effects from orographic and other sources to regions of dissipation at high altitudes. The core DEEPWAVE field phase took place from May through July 2014 using a comprehensive suite of airborne and ground-based instruments providing measurements from Earth’s surface to ∼100 km. Austral winter was chosen to observe deep GW propagation to high altitudes. DEEPWAVE was based on South Island, New Zealand, to provide access to the New Zealand and Tasmanian “hotspots” of GW activity and additional GW sources over the Southern Ocean and Tasman Sea. To observe GWs up to ∼100 km, DEEPWAVE utilized three new instruments built specifically for the National Science Foundation (NSF)/National Center for Atmospheric Research (NCAR) Gulfstream V (GV): a Rayleigh lidar, a sodium resonance lidar, and an advanced mesosphere temperature mapper. These measurements were supplemented by in situ probes, dropson...

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The deep propagating gravity wave experiment (deepwave): an airborne and ground-based exploration of gravity wave propagation and effects from their sources throughout the lower and middle atmosphere

Alison Rockwell

Papers

The deep propagating gravity wave experiment (deepwave): an airborne and ground-based exploration of gravity wave propagation and effects from their sources throughout the lower and middle atmosphere