The January 2022 Hunga Tonga–Hunga Ha’apai eruption was one of the most explosive volcanic events of the modern era, producing a vertical plume that peaked more than 50 km above the Earth. The ...initial explosion and subsequent plume triggered atmospheric waves that propagated around the world multiple times. A global-scale wave response of this magnitude from a single source has not previously been observed. Here we show the details of this response, using a comprehensive set of satellite and ground-based observations to quantify it from surface to ionosphere. A broad spectrum of waves was triggered by the initial explosion, including Lamb waves propagating at phase speeds of 318.2 ± 6 m s^(−1) at surface level and between 308 ± 5 to 319 ± 4 m s^(−1) in the stratosphere, and gravity waves propagating at 238 ± 3 to 269 ± 3 m s^(−1) in the stratosphere. Gravity waves at sub-ionospheric heights have not previously been observed propagating at this speed or over the whole Earth from a single source. Latent heat release from the plume remained the most significant individual gravity wave source worldwide for more than 12 h, producing circular wavefronts visible across the Pacific basin in satellite observations. A single source dominating such a large region is also unique in the observational record. The Hunga Tonga eruption represents a key natural experiment in how the atmosphere responds to a sudden point-source-driven state change, which will be of use for improving weather and climate models.
Tropical convective systems are major sources of atmospheric gravity waves (GWs). These waves are a key driver of global atmospheric circulation, especially in the middle and upper atmosphere. ...Tropical cyclones (TCs) such as hurricanes and typhoons are particularly dramatic examples of such systems, and are therefore potentially significant individual sources of GWs. To investigate this effect, GW observations from three satellite limb sounders in the vicinity of TCs are produced and analysed. By statistically combining 15 years of GW observations from 1,379 individual TCs represented in the International Best Track Archive for Climate Stewardship, it is shown that TCs are associated with a 15% increase of GW amplitudes over background and a 25% increase in measured momentum fluxes, primarily during the period immediately before the TC. It is further shown that this additional contribution is small relative to other GW‐generating processes, and thus that individual TCs do not have a large quantitative effect on the dynamics of the middle and upper atmosphere as a whole. Thus, it is concluded that accurate modelling of TC‐generated short vertical wavelength GWs need not be a development priority for the next generation of weather and climate models. The results also demonstrate that stronger GW activity is associated with TCs that will later develop into hurricane‐intensity storms than is observed for those that will not, and thus that better space‐based monitoring of stratospheric GW activity could be a useful tool to help improve the forecasting of strong hurricane events in the presence of obscuring tropospheric cloud.
Three satellite limb sounders are used to assess the generation of gravity waves by tropical cyclones. Increased wave activity is seen, but the overall contribution to global‐scale gravity wave driving is small. Notably enhanced gravity wave activity is seen during hurricane development.
Gravity waves play a critical role in transporting energy and momentum between the troposphere, stratosphere, and mesosphere. Satellite measurements provide a powerful tool to investigate these waves ...across the globe. However, many present methods cannot yield reliable estimates of wave momentum fluxes or the directions of these fluxes. Here we present a new method which addresses this problem by combining observations from Atmospheric Infrared Sounder (AIRS) and Microwave Limb Sounder (MLS) in three dimensions. The method allows direct estimation of horizontal and vertical wavelengths as well as wave amplitude. This in turn allows estimation of both wave momentum flux and the full 3‐D direction of propagation, crucially including the horizontal direction. The method thus allows separation of the data into, for example, eastward and westward momentum fluxes, allowing estimation of the net atmospheric forcing due to these waves. We illustrate this method with a proof‐of‐concept study over the Andes, arguably the largest source of gravity waves in the world. We further critically assess the advantages and disadvantages of our method. Our study highlights the importance of the difference between net and absolute measures of momentum flux.
Key Points
We present a new method of detecting gravity waves in 3‐D from satellite data
This method allows the computation of net momentum fluxes, i.e., after directional cancelation
Our observational filter lies in the highest‐momentum flux part of the spectrum
Atmospheric reanalyses are data-assimilating weather models
which are widely used as proxies for the true state of the atmosphere in the
recent past. This is particularly the case for the ...stratosphere, where
historical observations are sparse. But how realistic are these stratospheric
reanalyses? Here, we resample stratospheric temperature data from six modern
reanalyses (CFSR, ERA-5, ERA-Interim, JRA-55, JRA-55C and MERRA-2) to produce
synthetic satellite observations, which we directly compare to retrieved
satellite temperatures from COSMIC, HIRDLS and SABER and to brightness
temperatures from AIRS for the 10-year period of 2003–2012. We explicitly
sample standard public-release products in order to best assess their
suitability for typical usage. We find that all-time all-latitude
correlations between limb sounder observations and synthetic observations
from full-input reanalyses are 0.97–0.99 at 30 km in altitude, falling to
0.84–0.94 at 50 km. The highest correlations are seen at high latitudes and
the lowest in the sub-tropics, but root-mean-square (RMS) differences are
highest (10 K or greater) in high-latitude winter. At all latitudes,
differences increase with increasing height. High-altitude differences become
especially large during disrupted periods such as the post-sudden
stratospheric warming recovery phase, in which zonal-mean differences can be as
high as 18 K among different datasets. We further show that, for the
current generation of reanalysis products, a full-3-D sampling approach (i.e.
one which takes full account of the instrument measuring volume) is always
required to produce realistic synthetic AIRS observations, but is almost
never required to produce realistic synthetic HIRDLS observations. For
synthetic SABER and COSMIC observations full-3-D sampling is required in
equatorial regions and regions of high gravity-wave activity but not
otherwise. Finally, we use cluster analyses to show that full-input
reanalyses (those which assimilate the full suite of observations, i.e.
excluding JRA-55C) are more tightly correlated with each other than with
observations, even observations which they assimilate. This may suggest that
these reanalyses are over-tuned to match their comparators. If so, this could
have significant implications for future reanalysis development.
Gravity waves (GWs) transport momentum and energy in the atmosphere, exerting a profound influence on the global circulation. Accurately measuring them is thus vital both for understanding the ...atmosphere and for developing the next generation of weather forecasting and climate prediction models. However, it has proven very difficult to measure the full set of GW parameters from satellite measurements, which are the only suitable observations with global coverage. This is particularly critical at latitudes close to 60° S, where climate models significantly under-represent wave momentum fluxes. Here, we present a novel fully 3-D method for detecting and characterising GWs in the stratosphere. This method is based around a 3-D Stockwell transform, and can be applied retrospectively to existing observed data. This is the first scientific use of this spectral analysis technique. We apply our method to high-resolution 3-D atmospheric temperature data from AIRS/Aqua over the altitude range 20–60 km. Our method allows us to determine a wide range of parameters for each wave detected. These include amplitude, propagation direction, horizontal/vertical wavelength, height/direction-resolved momentum fluxes (MFs), and phase and group velocity vectors. The latter three have not previously been measured from an individual satellite instrument. We demonstrate this method over the region around the Southern Andes and Antarctic Peninsula, the largest known sources of GW MFs near the 60° S belt. Our analyses reveal the presence of strongly intermittent highly directionally focused GWs with very high momentum fluxes (∼ 80–100 mPa or more at 30 km altitude). These waves are closely associated with the mountains rather than the open ocean of the Drake Passage. Measured fluxes are directed orthogonal to both mountain ranges, consistent with an orographic source mechanism, and are largest in winter. Further, our measurements of wave group velocity vectors show clear observational evidence that these waves are strongly focused into the polar night wind jet, and thus may contribute significantly to the missing momentum at these latitudes. These results demonstrate the capabilities of our new method, which provides a powerful tool for delivering the observations required for the next generation of weather and climate models.
We conducted simulations with a 4‐km resolution for Hurricane Joaquin in 2015 using the weather research and forecast (WRF) model. The model data are used to study stratospheric gravity waves (GWs) ...generated by the hurricane and how they correlate with hurricane intensity. The simulation results show spiral GWs propagating upward and anticlockwise away from the hurricane center. GWs with vertical wavelengths up to 14 km are generated. We find that GW activity is more frequent and intense during hurricane intensification than during weakening, particularly for the most intense GW activity. There are significant correlations between the change of stratospheric GW intensity and hurricane intensity. Therefore, the emergence of intensive stratospheric GW activity may be considered a useful proxy for identifying hurricane intensification.
Plain Language Summary
Accurate predictions of changes in hurricane intensity are essential to provide sufficient lead time for warning and evacuation. As a hurricane intensifies, gravity waves (GWs) are emitted into the stratosphere to partially rebalance the sudden energy changes. If a correlation between hurricane intensification and GWs is verified, observing stratospheric GWs with satellite instruments could provide a possible predictor of hurricane intensification. This approach is advantageous when clouds obscure the direct view from above by visible and infrared instruments into the inner state of the hurricane. This study uses mesoscale model simulations to test and verify the correlation between hurricane intensification and GWs and finds that stratospheric GW activity increases prior to peaks in hurricane intensity.
Key Points
High‐resolution weather research and forecast simulations for Hurricane Joaquin show spiral gravity waves (GWs) emanating into the stratosphere
Stratospheric GW activity is more frequent and intense before and during hurricane intensification than during weakening
This study provides further evidence that stratospheric GW activity is a valid proxy for hurricane intensification
Abstract
Sudden stratospheric warmings (SSWs) have been linked to surface temperature anomalies, but how these connect to changes in the likelihood of specific weather extremes and their associated ...weather patterns remains uncertain. While, on average, it is true that cold surface temperatures follow SSW events, particularly in Northern Europe, there is considerable event-to-event variability. Over the British Isles and Central Europe, only around 45% of SSWs are followed by a colder than average period and a negative phase of the North Atlantic Oscillation, cautioning against an over-generalised approach to surface anomalies associated with SSWs. Focussing on more hazardous weather, which in winter is associated with cold extremes, we use reanalysis data to consider how SSWs impact temperature-related hazards; namely the frequency of snowy days, frost days and spells of extreme cold weather in 12 major European cities. In general, SSWs are associated with an increased risk of snow across most of western Europe, and that this is particularly significant in milder, more maritime locations such as London where in reanalysis, snowfall days are 40% more likely after an SSW. However, there is considerable variation in surface temperature anomalies between SSW events; the third of SSWs with the warmest surface anomalies are statistically more likely to have a decreased risk of snow, frost and persistent cold spells compared with non-SSW time periods. These warmer events are associated with a different temperature anomaly pattern, which is consistent in both reanalysis data and large ensemble CMIP6 models. We further show that these warm surface temperature anomaly SSWs are becoming more frequent, a trend which is consistent with background global warming. The varied surface anomalies associated with SSWs highlights the need to study their impacts in a probabilistic sense, and motivates further work to enable better prediction of the impacts of a given event.
This paper investigates concentric traveling ionospheric disturbances (CTIDs) associated with the Tonga volcanic eruption. Results show that: (a) two types of CTIDs (CTID #1 and CTID #2) were ...identified that traveled radially from Tonga at the speed of 610–880 m/s (acoustic‐mode) and 300–380 m/s (Lamb‐mode), respectively. CTID #1 reached 3,800 and 5,000 km away from the eruption location toward the directions of New Zealand and Australia, respectively. CTID #2 propagated persistently for ∼9 hr over New Zealand and Australia. (b) The CTID #2 wavefront changed after 08:35 UT over New Zealand, possibly due to a combination of factors including the anisotropic propagation of CTID #2, the regional geomagnetic declination, and westward‐moving Lamb waves. (c) Topside total electron content (TEC) enhancement with a magnitude over two TECu was observed from COSMIC‐2 measurements. The enhancement agrees with CTID #1 peak from nearby ground‐based TEC observations and could be related to the upward propagation of the F layer’s CTID #1 signatures.
Plain Language Summary
The Tonga volcanic eruption on 15 January triggered various atmospheric waves that propagate from the Earth’s surface and throughout the atmosphere and ionosphere. In this study, we discuss two types of concentric traveling ionospheric disturbances (CTIDs, #1 and #2) propagating outward from the Tonga site based on measurements collected by ∼1,000 ground‐based global navigation satellite system receivers. Our analysis based on the CTID propagation speed showed that CTIDs #1 and #2 traveled at acoustic and Lamb wave modes, respectively. We also analyzed COSMIC‐2 satellite radio occultation observations and showed that CTID #1‐related enhancement signatures were observed at the topside ionosphere near the eruption site. Moreover, it is interesting to note that CTID #2 wavefront changed over New Zealand after 08:35 UT on 15 January likely followed the regional geomagnetic declination and westward‐moving Lamb waves.
Key Points
Two distinctive types of concentric traveling ionospheric disturbances (CTIDs #1 and #2) were identified, and they propagated radially outward from Tonga at the speed of 610–880 m/s (acoustic‐mode) and 300–380 m/s (Lamb‐mode), respectively
The wavefront of the long‐lasting CTID #2 changed after 08:35 UT over New Zealand, possibly due to the regional geomagnetic declination and westward‐moving Lamb waves
Distinctive total electron content (TEC) enhancement of over 2 TECu magnitude observed above 530 km near the eruption site could be associated with the upward propagation of the acoustic‐mode CTID #1 signatures in the F layer
Lee wave generation rates in the deep ocean Wright, Corwin J.; Scott, Robert B.; Ailliot, Pierre ...
Geophysical research letters,
16 April 2014, Letnik:
41, Številka:
7
Journal Article
Recenzirano
Odprti dostop
Using the world's largest data set of in situ ocean current measurements, combined with a high‐resolution topography roughness data set, we use a model‐assisted hierarchical clustering methodology to ...estimate the global lee wave generation rate at the ocean floor. Our analysis suggests that internal wave generation contributes 0.75±0.19 TW (±2 standard deviation) to the oceanic energy budget but with a strong dependence on the Brunt‐Väisäla (buoyancy) frequency climatology used. This estimate is higher than previous calculations and suggests that internal wave generation may be a much more significant contributor to the global oceanic mechanical energy budget than had previously been assumed. Our results imply that lee wave generation and propagation may be a dominant sink of at least half and potentially the overwhelming majority of ocean surface wind work on the geostrophic circulation.
Key Points
Internal wave generation may contribute 0.75±0.19 TW to oceanic energy budget
This estimate is much higher than previous calculations
Implies lee wave generation may be a dominant sink of wind work on surface
Atmospheric gravity waves play a key role in the transfer of energy and momentum between layers of the Earth's atmosphere. However, nearly all general circulation models (GCMs) seriously ...under-represent the momentum fluxes of gravity waves at latitudes near 60∘ S, which can lead to significant biases. A prominent example of this is the “cold pole problem”, where modelled winter stratospheres are unrealistically cold. There is thus a need for large-scale measurements of gravity wave fluxes near 60∘ S, and indeed globally, to test and constrain GCMs. Such measurements are notoriously difficult, because they require 3-D observations of wave properties if the fluxes are to be estimated without using significant limiting assumptions. Here we use 3-D satellite measurements of stratospheric gravity waves from NASA's Atmospheric Infrared Sounder (AIRS) Aqua instrument. We present the first extended application of a 3-D Stockwell transform (3DST) method to determine localised gravity wave amplitudes, wavelengths and directions of propagation around the entire region of the Southern Ocean near 60∘ S during austral winter 2010. We first validate our method using a synthetic wavefield and two case studies of real gravity waves over the southern Andes and the island of South Georgia. A new technique to overcome wave amplitude attenuation problems in previous methods is also presented. We then characterise large-scale gravity wave occurrence frequencies, directional momentum fluxes and short-timescale intermittency over the entire Southern Ocean. Our results show that highest wave occurrence frequencies, amplitudes and momentum fluxes are observed in the stratosphere over the mountains of the southern Andes and Antarctic Peninsula. However, we find that around 60 %–80 % of total zonal-mean momentum flux is located over the open Southern Ocean during June–August, where a large “belt” of increased wave occurrence frequencies, amplitudes and fluxes is observed. Our results also suggest significant short-timescale variability of fluxes from both orographic and non-orographic sources in the region. A particularly striking result is a widespread convergence of gravity wave momentum fluxes towards latitudes around 60∘ S from the north and south. We propose that this convergence, which is observed at nearly all longitudes during winter, could account for a significant part of the under-represented flux in GCMs at these latitudes.
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