We review observations on the coupling between Earth's surface disturbances and the upper atmosphere. In particular, we focus on the upper atmospheric responses to atmospheric acoustic‐gravity waves ...generated during impulsive surface disturbance events including earthquakes, tsunamis, volcanic eruptions, and explosions. We review the theoretical background for the generation and propagation of atmospheric acoustic‐gravity waves from surface disturbance events as well as of the ionospheric plasma response to such acoustic‐gravity waves. We review a variety of observational techniques that have been successfully utilized to detect upper atmospheric perturbations induced by surface disturbances and summarize the state‐of‐the‐art knowledge on the coupling processes learnt from these observations. Finally, we touch on some most recent advances in the field and propose directions for future research.
Plain Language Summary
Earthquakes, tsunamis, volcanic eruptions, and chemical and nuclear explosions on or under the ground create sudden and violent motions of the ground or ocean surface. While ground shakings during some massive earthquakes can be felt by people who live thousands of kilometers away from the epicenters, the shakings can also be detected from the atmosphere hundreds of kilometers above the ground (upper atmosphere). Similarly, tsunamis, volcanic eruptions, and explosions can have footprints in the upper atmosphere as well. These footprints have been successfully detected by a variety of observational techniques. This paper reviews the observational results and the current understanding of the physical mechanisms behind the coupling between the ground/ocean and the upper atmosphere. In addition, future research directions are proposed in order to address the open questions.
Key Points
The upper atmosphere can respond to Earth's surface disturbances via acoustic‐gravity waves
The responses have been detected by a variety of remote sensing and in situ observations
Outstanding questions remain to understand the surface‐upper atmosphere coupling processes
In the context of the International GNSS Service (IGS), several IGS Ionosphere Associated Analysis Centers have developed different techniques to provide global ionospheric maps (GIMs) of vertical ...total electron content (VTEC) since 1998. In this paper we present a comparison of the performances of all the GIMs created in the frame of IGS. Indeed we compare the
classical
ones (for the ionospheric analysis centers CODE, ESA/ESOC, JPL and UPC) with the new ones (NRCAN, CAS, WHU). To assess the quality of them in fair and completely independent ways, two assessment methods are used: a direct comparison to altimeter data (VTEC-altimeter) and to the difference of slant total electron content (STEC) observed in independent ground reference stations (dSTEC-GPS). The main conclusion of this study, performed during one solar cycle, is the consistency of the results between so many different GIM techniques and implementations.
In this study, we analyzed signals transmitted by the U.S. Wide Area Augmentation System (WAAS) geostationary (GEO) satellites using the Variometric Approach for Real-Time Ionosphere Observation ...(VARION) algorithm in a simulated real-time scenario, to characterize the ionospheric response to the 24 August 2017 Falcon 9 rocket launch from Vandenberg Air Force Base in California. VARION is a real-time Global Navigation Satellites Systems (GNSS)-based algorithm that can be used to detect various ionospheric disturbances associated with natural hazards, such as tsunamis and earthquakes. A noise reduction algorithm was applied to the VARION-GEO solutions to remove the satellite-dependent noise term. Our analysis showed that the interactions of the exhaust plume with the ionospheric plasma depleted the total electron content (TEC) to a level comparable with nighttime TEC values. During this event, the geometry of the satellite-receiver link is such that GEO satellites measured the depleted plasma hole before any GPS satellites. We estimated that the ionosphere relaxed back to a pre-perturbed state after about 3 h, and the hole propagated with a mean speed of about 600 m/s over a region of 700 km in radius. We conclude that the VARION-GEO approach can provide important ionospheric TEC real-time measurements, which are not affected by the motion of the ionospheric pierce points (IPPs). Furthermore, the VARION-GEO measurements experience a steady noise level throughout the entire observation period, making this technique particularly useful to augment and enhance the capabilities of well-established GNSS-based ionosphere remote sensing techniques and future ionospheric-based early warning systems.
The Jet Propulsion Laboratory (JPL) develops JPL-GIM, a software for generating global ionospheric maps (GIMs) of total electron content (TEC) using measurements from multiple Global Navigation ...Satellite System (GNSS) constellations. Within this overview paper, we delve into the current state and the most recent enhancements of JPL-GIM. An adaptable Kalman filter provides maps with user-defined temporal and spatial resolutions, while concurrently delivering essential covariance data for uncertainty assessment. Furthermore, multiple shell models offer a versatile framework to balance accuracy and computational efficiency. We present the five operational JPL GIM products (JPLG, JPRG, JPLI, JPLD, JPRT), highlighting JPLG and JPRG, our products routinely delivered to the International GNSS Service (IGS), and introduce a new near-real-time product (JPRT). As an added demonstration of JPL-GIM’s capabilities, we present a very-high-resolution (2-minute, multi-GNSS, 1000-station) configuration to showcase JPL-GIM’s ability to resolve long-lasting effects of the 2022 Hunga Tonga-Hunga Ha’apai eruption. Validations using independent datasets confirm the accurate reproduction of ionospheric variations across all latitudinal bands.
This study presents a novel approach to estimating the intensity of hurricanes using temperature profiles from Global Positioning System radio occultation (GPSRO) measurements. Previous research has ...shown that the temperature difference between the ocean surface and the eyewall outflow region defines hurricanes' thermodynamic efficiency, which is directly proportional to the storm's intensity. Outflow temperatures in the eyewall region of 27 hurricanes in 2004–2011 were obtained from GPSRO observations. These observations, along with ocean surface temperatures from NASA Modern Era‐Retrospective Analysis for Research and Applications, made it possible to estimate hurricane intensities using a simplified hurricane model. Our preliminary results are quantitatively consistent with best‐track values from the National Hurricane Center within 9.4%. As a by‐product of our study, we present for the first time GPSRO vertical temperature profiles in the vicinity of the eyewall region of hurricanes, which we compared with collocated temperature profiles from the European Centre for Medium‐Range Weather Forecasts Reanalysis Interim (ERA‐Interim). Some of the GPSRO data sets reveal a double tropopause in the vicinity of the eyewall—a characteristic that we do not see in ERA‐Interim. We conclude that GPSRO observations can be of supplementary assistance in augmenting existing data sets used in hurricane intensity estimation. GPSROs' cloud‐penetrating capability and high vertical resolution can be useful in providing soundings in the area close to the eyewall region of hurricanes revealing detailed information about their thermal structure, potentially advancing our current knowledge of their dynamics, evolution, and physics.
Key Points
First estimates of hurricane intensity using GPS
Hurricanes' eyewall vertical thermal structure observed with GPS
GPS shows promise in augmenting current hurricane data sets
In the upper troposphere (UT), Global Navigation Satellite System (GNSS) Radio Occultations (ROs) provide accurate air temperatures (<0.5 K) every ∼200 m vertically. We use RO observations from ...01/2002 until 12/2018 at 300, 250, and 200 hPa to quantify the tropical upper tropospheric amplification (defined as the ratio of temperature trends in the UT relative to the surface). We compare the RO‐derived results against Atmospheric Infrared Sounder (AIRS), Coupled Model Intercomparison Project Phase 6 (CMIP6) Atmospheric Model Intercomparison Project (AMIP) models, Modern‐Era Retrospective Analysis for Research and Applications version 2 (MERRA‐2), and European Center for Medium‐range Weather Forecasts Re‐Analysis Interim (ERA‐Interim) data. We find that CMIP6 AMIP models show excellent agreement with independent AIRS and RO observations on the magnitude of the UT warming and show warming that is significantly faster than both reanalyses above 250 hPa. Additionally, AIRS and CMIP6 AMIP present excellent agreement with the RO‐measured tropical tropospheric amplification.
Plain Language Summary
In the upper troposphere, Global Navigation Satellite System Radio Occultations (GNSS‐RO) measure the air's refractive index, which depends primarily on the air's temperature. We use these GNSS‐RO temperatures from 01/2002 until 12/2018 at 200, 250, and 300 hPa in the tropics (where the atmosphere experiences the largest amplification in response to surface warming). Routinely, climate models are used to simulate how much the upper atmosphere has warmed in response to surface warming. However, there appears to be a disagreement between observations and models, which today we try to understand. The GNSS‐RO observations have a unique feature of being able to measure the air temperature every 200 m, and show us that that climate models are in close agreement with the GNSS‐RO and other infrared observations. In other words, GNSS‐RO observations show that the upper atmosphere warms faster and the amplification due to surface warming is stronger than what current reanalysis estimate. Independent infrared observations of the Earth's upper troposphere also support the GNSS‐RO findings and are also in very close agreement with the climate models. Interestingly, the reanalysis indicates that at 200 hPa there is no warming observed, contrary to what GNSS‐RO, infrared, and climate models reveal.
Key points
Coupled model intercomparison project phase 6 (cmip6) atmospheric model intercomparison project (AMIP) models agree with independent radio occultation and infrared data on the magnitude of the tropical upper tropospheric temperature trends
Radio occultations reveal faster tropical upper tropospheric warming than both modern‐era retrospective analysis for research and applications version 2 (MERRA‐2) and European Center for Medium‐Range Weather Forecasts Re‐Analysis Interim (ERA‐Interim) (above 250 hPa) reanalyses
ERA‐Interim presents decreasing tropical upper troposphere amplification with altitude, unlike the amplification shown by radio occultations
The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record. The event generated a ...broad range of atmospheric waves observed globally by various ground-based and spaceborne instrumentation networks. Most prominent is the surface-guided Lamb wave (Formula: see text0.01 Hz), which we observed propagating for four (+three antipodal) passages around the Earth over six days. Based on Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption. The Hunga eruption produced remarkable globally-detected infrasound (0.01-20 Hz), long-range (~10,000 km) audible sound, and ionospheric perturbations. Seismometers worldwide recorded pure seismic and air-to-ground coupled waves. Air-to-sea coupling likely contributed to fast-arriving tsunamis. We highlight exceptional observations of the atmospheric waves.
We assess the detection of the August 4, 2020 chemical explosion in Beirut, Lebanon (33°N, 35°E). We use ionospheric total electron content (TEC) observations from a regional network of ground‐based ...Global Positioning System (GPS) receivers to study the ionospheric variability and wave perturbations generated by the Beirut explosion. Our analysis reveals that the induced wave structures arrived in the ionosphere 10 ± 2 min after the explosion, which is a strong indication of acoustic gravity wave activity. These wave structures are characterized with ΔTEC of 0.06 TECU moving at ∼750 m/s in south‐east direction away from the explosion epicenter. The continuous wavelet analysis we applied shows a dominant wave periodicity of 1.5–2.5 min (6.78–11 mHz) in the ionosphere. Furthermore, we use measurements from ERA‐interim analysis to establish the ambient neutral atmospheric conditions before the Beirut explosion event. Finally, the observed ionospheric wave perturbations appear to be in good agreement with the expected arrival of acoustic gravity waves generated following the explosion.
Key Points
Detection and characterization of ionospheric perturbations generated by the 2020 Beirut explosion
Signatures of acoustic gravity wave activity generated by the event are observed
Lower and upper atmospheric coupling due to anthropogenic explosion is investigated
We analyze the spatial‐temporal variability of the mesosphere/lower thermosphere (MLT) temperature at ±15N/S over 14 years, using measurements from the Sounding of the Atmosphere using Broadband ...Emission Radiometry (SABER) instrument. We report that during the Madden‐Julian Oscillation season (November–April) the MLT region exhibits temperature variations with dominant periodicities at 40 and 60 days with amplitudes as large as 5.0 K. These intraseasonal oscillations (ISOs) are expressed across all longitudes, having superimposed zonal wave‐like structures that resemble waves 3 and 4 with amplitudes as large as 5.0 K. The cold and warm ISO phases are ubiquitous and repeatable from year to year over the 14‐year satellite record. We show that the MLT ISO exhibits the characteristics of a propagating wave carrying the embedded zonal wave‐like structures. At 20 km an ISO signal also exists with similar characteristics as the MLT ISO, suggesting a potential connection with the lower atmosphere.
Plain Language Summary
We find that the Earth's temperature in the low‐latitude mesosphere/lower thermosphere (MLT) region appears to increase and decrease by 5.0 K every 60 days. This behavior is present in every year from 2002 until 2016, and it affects all longitudes. Such an event was not possible before to observe, due to a limited number of ground‐based stations that monitor the Earth's MLT region. In our analysis, we used satellite observations from 2002 to 2016 that covered all longitudes. The instrument we used was the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). Interestingly, superimposed within these intraseasonal oscillations (ISOs), the MLT region is noticed to also vary as a function of longitude. These variations represent waves that travel around the Earth's atmosphere increasing and decreasing the Earth's MLT region by 5.0 K. Interestingly, when such oscillations are present in the MLT region, the lower stratosphere presents similar variability at the same periodicities, which makes us to believe that there may be a potential influence of the lower to upper atmosphere. Our results provide a unique picture of the MLT's thermal structure as a function of longitude, which is important in model simulations of the dynamic structure of the MLT region.
Key Points
The mesosphere/lower thermosphere (MLT) region displays intraseasonal oscillations (ISOs) at 40 and 60 days that are ubiquitous and repeatable from year to year
The MLT ISO exhibits zonal variations that resemble wave 3 and 4 structures in the temperatures
When the MLT ISO is present, the lower stratosphere also shows ISOs with similar periodicities and longitudinal structures
We assess the impact that the Global Positioning System radio occultations (GPSRO) measurements have on complementing different data sets in characterizing the lower‐to‐middle tropospheric humidity ...in cloudy conditions over both land and oceans using data from 1 August 2006 to 31 October 2006. We use observations from rawinsondes, Global Positioning System radio occultations (GPSRO), Atmospheric Infrared Sounder (AIRS), and the European Center for Medium‐Range Weather Forecasts Reanalysis Interim (ERA‐Interim). During the selected time period, Constellation Observing System for Meteorology, Ionosphere, and Climate data were not assimilated in ERA‐Interim. From each data set, we estimate a zonally averaged tropospheric specific humidity profile at tropical, middle, and high latitudes. Over land, we use rawinsondes as the ground truth and quantify the specific humidity differences and root‐mean‐square‐errors (RMSEs) of the GPSRO, AIRS, and ERA‐Interim profiles. GPSRO are beneficial in retrieving lower tropospheric humidity than upper tropospheric profiles, due to their loss of sensitivity at high altitudes. Blending GPSRO with ERA‐Interim produces profiles with smaller humidity biases outside the tropics, but GPSRO data do not improve the humidity RMSE when compared to rawinsondes. Combining GPSRO with AIRS leads to smaller humidity bias at the tropics and high latitudes, while reducing humidity's RMSEs. Over oceans, no rawinsonde information is available, and we use ERA‐Interim as a reference. Combining GPSRO with AIRS leads to smaller humidity RMSEs than AIRS. We conclude that cross‐comparisons and synergies among multi‐instrument observations are promising in advancing our knowledge of the tropospheric humidity in cloudy conditions. GPSRO data can contribute to improving humidity retrievals over cloud‐covered regions, especially over land and within the boundary layer.
Key Points
First results showing multi‐dataset comparisons of humidity over clouds
Study the impact of GPSRO in retrieving tropospheric humidity over clouds
Emphasize on synergies among different datasets to improve humidity retrievals
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