Wind Amplitudes Research Articles

Exploring the time variability of the solar wind using LOFAR pulsar data

High-precision pulsar timing is highly dependent on the precise and accurate modelling of any effects that can potentially impact the data. In particular, effects that contain stochastic elements contribute to some level of corruption and complexity in the analysis of pulsar-timing data. It has been shown that commonly used solar wind models do not accurately account for variability in the amplitude of the solar wind on both short and long timescales. In this study, we test and validate a new, cutting-edge solar wind modelling method included in the enterprise software suite (widely used for pulsar noise analysis) through extended simulations. We use it to investigate temporal variability in LOFAR data. Our model testing scheme in itself provides an invaluable asset for pulsar timing array (PTA) experiments. Since, improperly accounting for the solar wind signature in pulsar data can induce false-positive signals, it is of fundamental importance to include in any such investigations. We employed a Bayesian approach utilising a continuously varying Gaussian process to model the solar wind. It uses a spherical approximation that modulates the electron density. This method, which we refer to as a solar wind Gaussian process (SWGP), has been integrated into existing noise analysis software, specifically enterprise . Our Validation of this model was performed through simulations. We then conduct noise analysis on eight pulsars from the LOFAR dataset, with most pulsars having a time span of $ 11$ years encompassing one full solar activity cycle. Furthermore, we derived the electron densities from the dispersion measure values obtained by the SWGP model. Our analysis reveals a strong correlation between the electron density at 1 AU and the ecliptic latitude (ELAT) of the pulsar. Pulsars with $|ELAT|< 3^ circ $ exhibit significantly higher average electron densities. Furthermore, we observed distinct temporal patterns in the electron densities in different pulsars. In particular, pulsars within $|ELAT|< 3^ circ $ exhibit similar temporal variations, while the electron densities of those outside this range correlate with the solar activity cycle. Notably, some pulsars exhibit sensitivity to the solar wind up to $45^ circ $ away from the Sun in LOFAR data. The continuous variability in electron density offered in this model represents a substantial improvement over previous models, that assume a single value for piece-wise bins of time. This advancement holds promise for solar wind modelling in future International Pulsar Timing Array (IPTA) data combinations.

Evolution of Dew and Rain Water Resources in Gujarat (India) between 2005 and 2021

The present study, carried out in Gujarat (India) between 2005 and 2021, aims to prepare dew and rain maps of Gujarat over a long period (17 years, from 2005 to 2021) in order to evaluate the evolution of the potential for dew and rain in the state. The ratio of dew to precipitation is also determined, which is an important metric that quantifies the contribution of dew to the overall water resources. Global warming leads, in general, to a reduction in precipitation and non-rainfall water contributions such as dew. The study shows, however, a rare increase in the rainfall and dew condensation, with the latter related to an increase in relative humidity and a decrease in wind amplitudes. Rain primarily occurs during the monsoon months, while dew forms during the dry season. Although dew alone cannot resolve water scarcity, it nonetheless may provide an exigent and unignorable contribution to the water balance in time to come. According to the site, the dew–rain ratios, which are also, in general, well correlated with dew yields, can represent between 4.6% (Ahmedabad) and 37.2% (Jamnagar). The positive trend, observed since 2015–2017, is expected to continue into the future.

Tidal Control of Equatorial Vertical E × B Drift Under Solar Minimum Conditions

AbstractObservations show that equatorial ionospheric vertical drifts during solar minimum differ from the climatology between late afternoon and midnight. By analyzing WACCM‐X simulations, which reproduce this solar cycle dependence, we show that the interplay of the dominant migrating tides, their propagating and in situ forced components, and their solar cycle dependence impact the F‐region wind dynamo. In particular, the amplitude and phase of the propagating migrating semidiurnal tide (SW2) in the F‐region plays a key role. Under solar minimum conditions, the SW2 tide propagate to and beyond the F‐region in the winter hemisphere, and consequently its zonal wind amplitude in the F‐region is much stronger than that under solar maximum conditions. Furthermore, its phase shift leads to a strong eastward wind perturbation near local midnight. This in turn drives a F‐region dynamo with an equatorial upward drift between 18 and 1 hr local times.

Zeitlin Truncation of a Shallow Water Quasi‐Geostrophic Model for Planetary Flow

AbstractIn this work, we consider a Shallow‐Water Quasi Geostrophic equation on the sphere, as a model for global large‐scale atmospheric dynamics. This equation, previously studied by Verkley (2009, https://doi.org/10.1175/2008jas2837.1) and Schubert et al. (2009, https://doi.org/10.3894/james.2009.1.2), possesses a rich geometric structure, called Lie‐Poisson, and admits an infinite number of conserved quantities, called Casimirs. In this paper, we develop a Casimir preserving numerical method for long‐time simulations of this equation. The method develops in two steps: first, we construct an N‐dimensional Lie‐Poisson system that converges to the continuous one in the limit N → ∞; second, we integrate in time the finite‐dimensional system using an isospectral time integrator, developed by Modin and Viviani (2020, https://doi.org/10.1017/jfm.2019.944). We demonstrate the efficacy of this computational method by simulating a flow on the entire sphere for different values of the Lamb parameter. We particularly focus on rotation‐induced effects, such as the formation of jets. In agreement with shallow water models of the atmosphere, we observe the formation of robust latitudinal jets and a decrease in the zonal wind amplitude with latitude. Furthermore, spectra of the kinetic energy are computed as a point of reference for future studies.

Effect of background wind and dissipation processes on the semidiurnal component of atmospheric solar tides

The equations governing the neutral wind velocities and temperature, which depict the oscillations of atmospheric tides, incorporate various elements of the atmosphere. These factors comprise background wind, temperature profiles, and the atmosphere’s composition, including ozone, oxygen, carbon dioxide, water, etc. The current work describes the method of solution of the atmospheric tidal model and investigates the effects of background wind and dissipation processes on the migrating semidiurnal tides during the March equinox. Thermal heating due to water vapour absorption in the troposphere, ozone in the stratosphere and oxygen absorption in the thermosphere is considered in this model. Furthermore, the model takes into account the various dissipation processes (i.e. ion drag and Hall coefficients, Newtonian cooling, divergence of momentum and heat fluxes due to molecular and eddy diffusion) and background wind. The semidiurnal tidal features obtained from the present model match well with the Global Scale Wave Model (GSWM-98). The bar charts are presented to quantify the effects of different parameters on horizontal winds for altitudes below 100 km and above 100 km, separately. It reveals that the background wind plays a vital role in deciding the semidiurnal tidal amplitudes of zonal and meridional winds. Momentum and heat flux coefficients also have a significant influence on semidiurnal tides. At higher altitudes (>100 km), the ion drag reduces the amplitude of semidiurnal tides considerably.

Revisiting the effect of increasing horizontal resolution on the evolution of El Niño in a coupled model

The ENSO (El Niño southern oscillation) in the tropical Pacific plays a crucial role in regulating the Indian summer monsoon. Many mechanisms have been proposed to explain the positive and negative feedback associated with the ENSO through air-sea interaction in the tropical Pacific. Historical run data at varying oceanic and atmospheric resolutions from the MPI-ESM model is analyzed and compared with observations to determine the possible reasons for the much earlier onset and delayed withdrawal of ENSO in the coupled model. Increasing the resolution of the oceanic and atmospheric components of the coupled model helps in well-resolving the annual cycle of sea surface temperature in the tropical Pacific. There is a significant improvement in the early onset and late withdrawal of El Niño in the coupled model with increasing horizontal resolution of the model components. The weak subsurface propagation along the 20 °C isotherm in the equatorial Pacific improves on increasing the horizontal resolution of the coupled model. Similar to observations, there is a clear eastward extension of convection, 20° east of the dateline, in the equatorial tropical Pacific in the coupled model during ENSO years. Increasing the resolution of the oceanic and atmospheric components of the coupled model improves the simulation of convective activity over the western Pacific along with the improved magnitude of anomalous zonal wind strength during El Niño years. However, the presentation of convective activity over the equatorial Pacific deteriorated on increasing atmospheric resolution further to T255 due to the enhanced value of the interannual amplitude of intraseasonal zonal wind around the international dateline. Also, the coupled model does not capture the accurate eastward propagation of the Madden Julian Oscillation envelope over the western Pacific. While higher resolutions showed improvement in the representation of El Niño events in terms of their number and duration, challenges persisted in accurately capturing the frequency of these events and their related triggering mechanisms. Understanding the intricate interplay of factors influencing the evolution of El Niño requires further research and progress in modeling strategies.

The Holton–Tan mechanism under stratospheric aerosol intervention

Abstract. The teleconnection between the quasi-biennial oscillation (QBO) and the Arctic stratospheric polar vortex, or the Holton–Tan (HT) relationship, may change in a warmer climate or one with stratospheric aerosol intervention (SAI) compared to the present-day climate (PDC). Our results from an Earth system model indicate that, under both global warming (based on RCP8.5 emission scenario) and SAI scenarios, the HT relationship weakens in early winter (November–December), although it is closer to PDC under SAI than under the RCP8.5 scenario. In contrast, the HT relationship in the middle to late winter period (January–February) does not change considerably in response to either RCP8.5 or SAI scenarios compared to PDC. While the weakening of the HT relationship under the RCP8.5 scenario is likely due to the weaker QBO wind amplitudes at the Equator, another physical mechanism must be responsible for the weaker HT relationship under SAI scenarios, since the amplitude of the QBO wind is comparable to the PDC. The strength of the polar vortex does not change under the RCP8.5 scenario compared to PDC, but it becomes stronger under SAI; we attribute the weakening of the HT relationship under SAI to a stronger polar vortex. In general, the changes in the HT relationship cannot be explained by changes to the critical line; the changes in the residual circulation (particularly due to the gravity wave contributions) are important in explaining the changes in the HT relationship under RCP8.5 and SAI scenarios.

Emergence of Madden-Julian oscillation precipitation and wind amplitude changes in a warming climate

The Madden-Julian oscillation (MJO) has profound impacts on weather and climate phenomena, and thus changes in its activity have important implications under human-induced global climate change. Here, the time at which the MJO change signal emerges from natural variability under anthropogenic warming is investigated. Using simulations of the Community Earth System Model version 2 large ensemble forced by the shared socioeconomic pathways SSP370 scenario, an increase in ensemble mean MJO precipitation amplitude and a smaller increase in MJO circulation amplitude occur by the end of the 21st century, consistent with previous studies. Notably, the MJO precipitation amplitude change signal generally emerges more than a decade earlier than that of MJO wind amplitude. MJO amplitude changes also emerge earlier over the eastern Pacific than other parts of the tropics. Our findings provide valuable information on the potential changes of MJO variability with the aim of improving predictions of the MJO and its associated extreme events.

Bursting Phenomenon and Chaos Phase Control in Plant Dynamics

New complex features of a Pinus family plant subjected to wind load by proposing an analog electronic simulator with an active R C realization that mimics the real-time dynamics of the system was examined in this paper. Findings reveal that the periodic or chaotic dynamics of the system depends on the favored initial conditions. We see the dynamical behavior of the plant showing transition from periodic to chaotic states. This is very beneficial because it allows for the observation that when the value of the wind amplitude ratio changes continuously, the plant behavior may change in a discontinuous way. It also helps to understand the impact of wind on the plant dynamics, in particular, and in forest in general, which is very crucial for understanding several plant communities. We show that plants exhibit multiple forms (periodic/chaotic) of repetitive spiking oscillations reflecting the phenomenon of bursting. For the periodic bursting oscillations, we observe that after each peak of excitation due to the wind load, the plant returns directly to its state of rest, whereas the chaotic bursting oscillations break the energy of the wind into decreasing value packets and its occurrence has the merit of reducing the effects of wind energy on the plant; this action ensures the stability of the plant even in chaotic cases. We also observe that the numerical study based on the isospike technique permits efficient discovery and separation between periodic and chaotic orbits visited during the temporal evolution. We also establish through the chaos phase-control techniques that various chaotic oscillations disappeared after applying the chaos phase control strategy in the system compared to the uncontrolled case. Moreover, the chaos phase-control strategy to the system is introduced to instantly inform how the correct choice of the phase minimizes the effects of the wind and thus eliminates chaotic behavior of the plant by simply driving it towards a variety of periodic orbits.

Comparison of Madden-Julian oscillation in three super El Niño events

This paper investigated the characteristics of Madden-Julian Oscillation (MJO) in three super El Niño events (i.e., 1982/83, 1997/98 and 2015/16 El Niño events) based on reanalysis data. MJO with apparent eastward propagation can be observed during the developing stages of these three super El Niño events. Enhanced MJO zonal wind was observed over the western Pacific, especially in 1997/98 and 2015/16 El Niño events, which is mainly attributed to the effects of tropical background circulation and extratropical anomalous circulation. During the mature stages of 1982/83 and 1997/98 El Niño events, MJO with noticeable eastward propagation cannot be observed, and the MJO zonal wind amplitude at 850 hPa was weakened (enhanced) over the Indian Ocean and western Pacific (central and eastern Pacific). However, MJO zonal wind amplitude over the central and eastern Pacific was enhanced and the prominent eastward propagation was also found in the mature stage of 2015/16 El Niño. The eastward propagation of MJO was also observed during the decaying stages of the three super El Niño events, but its intensity was weaker compared with the developing and mature stages. The abnormal activity of MJO during the mature and decaying stages may be closely related to the characteristics in circulation and moisture anomalies caused by El Niño and the seasonal cycle of circulation and moisture. In addition, this study found that the RMM index and MJO zonal wind amplitude may lead to contradictory results in identifying the characteristics of MJO activity, especially during the developing and decaying stages.

Primary and Secondary Gravity Waves and Large‐Scale Wind Changes Generated by the Tonga Volcanic Eruption on 15 January 2022: Modeling and Comparison With ICON‐MIGHTI Winds

AbstractWe simulate the primary and secondary atmospheric gravity waves (GWs) excited by the upward movement of air generated by the Hunga Tonga‐Hunga Ha'apai (hereafter “Tonga”) volcanic eruption on 15 January 2022. The Model for gravity wavE SOurce, Ray trAcing and reConstruction (MESORAC) is used to calculate the primary GWs and the local body forces/heatings generated where they dissipate. We add these forces/heatings to the HIgh Altitude Mechanistic general Circulation Model (HIAMCM) to determine the secondary GWs and large‐scale wind changes that result. We find that a wide range of medium to large‐scale secondary GWs with concentric ring structure are created having horizontal wind amplitudes of u′, v′ ∼ 100–200 m/s, ground‐based periods of τr ∼ 20 min to 7 hr, horizontal phase speeds of cH ∼ 100–600 m/s, and horizontal wavelengths of λH ∼ 400–7,500 km. The fastest secondary GWs with cH ∼ 500–600 m/s are large‐scale GWs with λH ∼ 3,000–7,500 km and τr ∼ 1.5–7 hr. They reach the antipode over Africa ∼9 hr after creation. Large‐scale temporally and spatially varying wind changes of ∼80–120 m/s are created where the secondary GWs dissipate. We analyze the Tonga waves measured by the Michelson Interferometer for Global High‐resolution Thermospheric Imaging (MIGHTI) on the National Aeronautics and Space Administration Ionospheric Connection Explorer (ICON), and find that the observed GWs were medium to large‐scale with cH ∼ 100–600 m/s and λH ∼ 800–7,500 km, in good agreement with the simulated secondary GWs. We also find good agreement between ICON‐MIGHTI and HIAMCM for the timing, amplitudes, locations, and wavelengths of the Tonga waves, provided we increase the GW amplitudes by ∼2 and sample them ∼30 min later than ICON.

A novel metric for assessing wind and solar power complementarity based on three different fluctuation states and corresponding fluctuation amplitudes

Assessing complementarity is a foundational work to combine wind and solar power to mitigate their fluctuations. Correlation coefficient is the most commonly used index to assess complementarity. But correlation coefficient mainly quantifies the synchronous and reverse correlations between wind and solar power. Moreover, it ignores the fluctuation amplitudes of wind and solar power, which would misestimate the complementarity. To address the issue, a novel complementarity index is proposed considering both the fluctuation states and corresponding fluctuation amplitudes. The present study firstly divides the fluctuations of wind and solar power into synchronous, reverse, and discrepancy fluctuation states. Then the degrees of the three different fluctuation states are obtained according to the score rules considering the fluctuation amplitudes. Finally, the novel complementarity index is jointly determined by these fluctuation degrees. Validation results show that the proposed index successfully avoids the misestimation scenarios caused by using correlation coefficient to assess complementarity. Then the proposed index is applied to analyze the complementarity of wind and solar power in China on hourly, daily, and monthly time scales. The complementarity index is generally −0.11–0 on the hourly time scale in most regions of Jilin, Heilongjiang, Liaoning, Inner Mongolia, northern Gansu, southern Xinjiang, and the North China Plain, showing greater complementarity than other onshore regions. But the complementarity index is generally 0–0.3 in most of the aforementioned regions on the monthly time scale, implying that the complementarity on the monthly time scale is smaller than that on the hourly time scale. The complementarity indices in most offshore regions are −0.1–0, −0.12–0 and −0.2–0, respectively, on the hourly, daily, and monthly time scales. Further analysis reveals that the complementarity between wind and solar power would be overestimated once the fluctuation amplitude is ignored. Additionally, the proposed complementarity index can be used to optimize the installed capacity ratio of wind and solar power in a hybrid system. The proposed complementarity metric contributes to a better and more accurate understanding of the complementarity between wind and solar power. Furthermore, the proposed metric can be readily applied to assess the complementarity of other renewable power generations.

Projected Changes in the Seasonal Cycle of Madden‐Julian Oscillation Precipitation and Wind Amplitude

AbstractAlthough recent studies have examined the responses of annual‐ and seasonal‐mean Madden‐Julian oscillation (MJO) activity to global warming, little is known about the seasonal cycle changes that determine the timing of the peak MJO influence on local weather and climate. By analyzing the Community Earth System Model version 2 large ensemble at the end of the 21st century, we report changes in both the phase and amplitude of the seasonal cycle of MJO precipitation over the tropical Indian Ocean and southwestern Pacific. While the seasonal delay in phase of the MJO is related to the seasonal delay of total precipitation, with contributions from surface latent heat flux and circulation changes, the amplification in seasonal amplitude is consistent with the increase in MJO amplitude due to mean temperature increases. The shifts in phase of the seasonal cycle of the MJO under global warming may influence the predictability of extreme events.

Coastal Sea Level Observations Record the Twentieth-Century Enhancement of Decadal Climate Variability

Abstract Changes in the amplitude of decadal climate variability over the twentieth century have been noted, with most evidence derived from tropical Pacific sea surface temperature records. However, the length, spatial coverage, and stability of most instrumental records are insufficient to robustly identify such nonstationarity, or resolve its global spatial structure. Here, it is found that the long-term, stable, observing platform provided by tide gauges reveals a dramatic increase in the amplitude and spatial coherence of decadal (11–14-yr period) coastal sea level (ζ) variability between 1960 and 2000. During this epoch, western North American ζ was approximately out of phase with ζ in Sydney, Australia, and led northeastern U.S. ζ by approximately 1–2 years. The amplitude and timing of changes in decadal ζ variability in these regions are consistent with changes in atmospheric variability. Specifically, central equatorial Pacific wind stress and Labrador Sea heat flux are highly coherent and exhibit contemporaneous, order-of-magnitude increases in decadal power. These statistical relationships have a mechanistic underpinning: Along the western North American coastline, equatorial winds are known to drive rapidly propagating ζ signals along equatorial and coastal waveguides, while a 1–2-yr lag between Labrador Sea heat fluxes and northeastern United States ζ is consistent with a remotely forced, buoyancy-driven, mechanism. Tide gauges thus provide strong independent support for an increase in interbasin coherence on decadal time scales over the second half of the twentieth century, with implications for both the interpretation and prediction of climate and sea level variability. Significance Statement Decadal climate variability influences the frequency and severity of many natural hazards (e.g., drought), with considerable human and ecological impacts. Understanding observed changes and predicting future impacts relies upon an understanding of the physical processes and any changes in their variability and relationship over time. However, identifying such changes requires very long observational records. This paper leverages a large set of tide gauge records to show that decadal time scale coastal sea level variability increased dramatically in the second half of the twentieth century, in widely separated geographic locations. The increase was driven by a shift in the amplitude, spatial pattern, and interbasin coherence of atmospheric pressure, wind, and sea surface temperature variability.

Response of the American equatorial ionization anomaly to 2016 Arctic sudden stratospheric warming events

Apart from the rapid ionospheric response to geomagnetic forcing originating from the Sun during extreme space weather events, forcing from the lower atmosphere below still exerts a significant influence on the ionosphere during quiet-time conditions. This study examines the ionospheric response of the equatorial ionization anomaly (EIA) in the American sector to the combined influence of the cascades of sudden stratospheric warming (SSW) events and the geomagnetic storms that coexisted with them during the period of January–March 2016. We adopted a multi-instrument and multi-modeling approach with the study locations spanning ±40° geomagnetic latitudes. Our results showed a hemispheric asymmetry in the total electron content and change in total electron content (ΔTEC) distribution with higher enhancement clearly visible in the Northern Hemisphere in comparison to the Southern Hemisphere (NH). Semidiurnal signatures were observed in both ΔTEC and equatorial electrojet parameters for some days. The double-peak zonal mean zonal wind amplitude days supported the formation of the reverse fountain effects. The different SSW peak temperature days also showed either positive or negative ionospheric response. Generally, orientation of the prompt penetration electric field (PPEF) and their strengths at either daytime or nighttime played a weak role in the ionosphere response during some of the geomagnetic storms. The negative and positive ionospheric responses under geomagnetic storm conditions were ascribed to changes in the composition of the thermosphere, prompt penetration electric field (PPEF), and traveling atmospheric disturbances (TADs).

Rapid Volcanic Modification of the E‐Region Dynamo: ICON's First Glimpse of the Tonga Eruption

AbstractThe 15 January 2022 Hunga Tonga‐Hunga Ha'apai volcano eruption drove global atmospheric waves that propagated into space and impacted the ionosphere. Here we show immediate large‐scale electrodynamic effects of the eruption using observations from the National Aeronautics and Space Administration's Ionospheric Connection Explorer. We report extreme zonal and vertical ion drifts thousands of kilometers away from Tonga within an hour of the eruption, before the arrival of any atmospheric wave. The measured drifts were magnetically connected to the ionospheric E‐region just 400 km from Tonga, suggesting that the expanding wavefront created strong electric potentials which were transmitted along Earth's magnetic field. A simple theoretical model suggests that the observed drifts are consistent with an expanding wave with a large (>200 m/s) neutral wind amplitude. These observations are the first direct detection in space of the immediate electrodynamic effects of a volcanic eruption and will help constrain future models of impulsive lower atmospheric events.

The Impact of the Quasi‐Biennial Oscillation on the Mesosphere and Ionosphere

AbstractWe studied the responses of the mesosphere and ionosphere to the quasi‐biennial oscillation (QBO) in the stratosphere using meteor radar zonal wind observations over monitoring station Kototabang (KB, 0.2°S, 100.3°E), global zonal wind data from the thermosphere and ionosphere extension of the Whole Atmosphere Community Climate Model (WACCM‐X), equatorial electrojet (EEJ) data over the monitoring station Jicamarca (12°S, 77°W) and global total electron content (TEC) maps. The Fourier fitting method was applied to obtain the monthly mean amplitudes of zonal wind, TEC and EEJ. The least squares fitting method was utilized to perform a spectral analysis. Our data indicate that the QBOs of the stratosphere and mesosphere are present in the zonal winds between 20 and 40 km and 82 and 96 km at KB. The QBO is also present in the global TEC at 40°S to 40°N latitude and is characterized by the equatorial ionization anomaly (EIA). We propose that the QBOs in the mesosphere are linked to the QBOs in the ionosphere through the modulation of the E region dynamo by neutral winds and the equatorial ionospheric fountain effect. This model is verified by the QBO signals in the EEJ and diurnal tides in the E region of the ionosphere. The absence of QBO signals in the zonal wind at 250 km confirms that QBO signals in the TEC are not modulated by the zonal wind in the F region ionosphere, which further substantiates the model.

Long‐Term Study of Quasi‐16‐day Waves Based on ERA5 Reanalysis Data and EOS MLS Observations From 2005 to 2020

AbstractThis study uses the latest ERA5 reanalysis data and Earth Observing System microwave limb sounder (MLS) observations to investigate the climatological characteristics of quasi‐16‐day waves (Q16DWs) with different zonal wavenumbers. The fitted temperature amplitudes deduced from ERA5 reanalysis data and from MLS observations are highly consistent with each other, even in fine spatial‐temporal structures. The westward‐propagating wave with wavenumber 1 (W1) and the eastward‐propagating waves with wavenumbers 1 (E1) and 2 (E2) are identified as the most dominant propagating components according to the statistical analyses of their fitted temperature and wind amplitudes. All three waves exhibit significant intra‐annual and interannual variations. Their amplitudes in winter/spring and autumn/summer are strong, moderate, or weak. The W1 wave is more intense in boreal winter than in austral winter, while the E2 wave is the opposite, and the E1 wave is equally strong in boreal and austral winters. Their interannual variabilities measured by the ratios of peak amplitudes in temperature, zonal wind, and meridional wind range from 1.64 to 2.15, indicating significant variability. The presence of intense wave activities is always accompanied by a positive squared refractive index. We suggest that the squared refractive index contributes greatly to the global distribution characteristics of the Q16DWs. The W1 wave in the troposphere is more likely to travel upward and reach the stratosphere and mesosphere, while the intense E1 and E2 waves in the stratosphere and mesosphere may come from the upper atmosphere or be excited in situ.

Changes to tropical eastern North Pacific intraseasonal variability under global warming, implications for tropical cyclogenesis

Changes to the tropical eastern North Pacific Intraseasonal Oscillation (ISO) at the end of the 21st century and implications for tropical cyclone (TC) genesis are examined in the Shared Socioeconomic Pathways (SSP585) scenario of the Coupled Model Intercomparison Project phase 6 (CMIP6) data set. Multimodel mean composite low-level wind and precipitation anomalies associated with the leading intraseasonal mode indicate that precipitation amplitude increases while wind amplitude weakens under global warming, consistent with previous studies for the Indo-Pacific warm pool. The eastern North Pacific intraseasonal precipitation/wind pattern also tends to shift southwestward in a warmer climate, associated with weaker positive precipitation anomalies near the coast of Mexico and Central America during the enhanced convection/westerly wind phase. Implications for the modulation of TC genesis by the leading intraseasonal mode are then explored using an empirical genesis potential index (GPI). In the historical simulation, GPI shows positive anomalies in the eastern North Pacific in the convectively enhanced phase of the ISO. The ISO’s modulation of GPI weakens near the coast of Mexico and Central America with warming, associated with a southward shift of GPI anomalies. Further examination of the contribution from individual environmental variables that enter the GPI shows that relative humidity and vorticity changes during ISO events weaken positive GPI anomalies near the Mexican coast with warming and make genesis more favorable to the southwest. The impact of vertical shear anomaly changes is also to favor genesis away from the coast. These results suggest a weaker modulation of TCs near the Mexican Coast by the ISO in a warmer climate.

A New Mechanism for the Generation of Quasi‐6‐Day and Quasi‐10‐Day Waves During the 2019 Antarctic Sudden Stratospheric Warming

AbstractUsing the Modern‐Era Retrospective analysis for Research and Applications version 2 reanalysis and Aura Microwave Limb Sounder geopotential height and temperature observations, two unusual planetary waves (PWs) with westward zonal wavenumber 1 (W1) and periods of ∼6.0 and ∼9.6 days are identified during a rare Antarctic sudden stratospheric warming (SSW) event in September 2019, which follow a strong W1 PW with period of ∼7.4 days. It is found that the W1 ∼7.4‐day wave is actually the representation of the climatological W1 quasi‐6‐day wave before the September equinox, which peaks on September 10, 2019. Meanwhile, a strong zonally symmetric wave with period of ∼32.2 days occurs in the Southern Hemisphere with a maximum zonal wind amplitude of ∼27 m/s at 65°S and 48 km. Interestingly, the frequencies and zonal wavenumbers of the W1 ∼7.4‐day, ∼6.0‐day, ∼9.6‐day and zonally symmetric ∼32.2‐day waves exactly satisfy the nonlinear interaction theory between PWs. We thus proposed for the first time the occurrence of nonlinear interaction between a W1 ∼7.4‐day wave and a zonally symmetric ∼32.2‐day wave, which generates two W1 PWs with periods of ∼6.0 and ∼9.6 days. The Eliassen‐Palm flux diagnostics suggest that the zonally symmetric ∼32.2‐day wave also contributes to the wind deceleration during this SSW. Moreover, the baroclinic/barotropic instabilities related to the vertical shear in the zonal wind during the SSW considerably enhance the PW activities in the Antarctic stratosphere. The climatological variations of the instabilities and critical layers in the mesosphere can also influence the propagation of these three W1 PWs.