We present simultaneous observations of VLF emissions with periodic (2 or 4 s) bursts by Van Allen Probe near geomagnetic equator and Kannuslehto and Lovozero ground-based sites. The repetition period and ground–spacecraft delay are consistent with guided whistler wave propagation between conjugate ionospheres. In contrast to lightning whistlers, the group velocity dispersion is not accumulated from one burst to another, thus implying a nonlinear mechanism of its compensation. Two regimes are observed. In one regime, Poynting flux direction alternates in the magnetosphere, and the burst period is twice lower than on the ground, that corresponds to single wave packet bouncing along the field line. This regime is switched to the other one, with burst period unchanged in the magnetosphere but halved on the ground. In the second regime, no alternating Poynting flux direction is observed. This second regime corresponds to two symmetrically propagating wave packets synchronously meeting at the equator.

Recently, Anderson et al. (2012, https://doi.org/10.1126/science.1222978, 2017, https://doi. org/10.1073/pnas.1619318114) and Anderson and Clapp (2018, https://doi.org/10.1039/C7CP08331A) proposed that summertime convectively injected water vapor over North America could lead to stratospheric ozone depletion through halogenic catalytic reactions. Such ozone loss would reduce the ozone column and increase erythemal daily dose (EDD). Using 10 years of observations over the North American monsoon region from the Aura Ozone Monitoring Instrument, we find that the column ozone and EDD has a ~0.8–0.9 spatial correlation with lower stratospheric water vapor measured by the Aura Microwave Limb Sounder. We show that this correlation appears to be due to the elevation of the monsoonal tropopause and associated monsoonal convection. The increase in tropopause altitude reduces the ozone column and increases EDD. We see no apparent evidence of substantial heterogeneous chemical ozone loss in lower stratospheric ozone coincident with the stratospheric monsoonal water vapor enhancement.

Lossless compression can reduce climate data storage by 30-40%. In general, further reductions require lossy compression that also reduces precision. Fortunately, geoscientific models and measurements generate false precision (scientifically meaningless data bits) that can be eliminated without sacrificing scientifically meaningful data. We introduce Bit Grooming, a lossy compression algorithm that removes the bloat due to false- precision, those bits and bytes beyond the meaningful precision of the data. We evaluated Bit Grooming against competitors Linear Packing, Layer Packing, and GRIB2/JPEG2000.

The net surface water flux (evaporation minus precipitation minus runoff, E-P-R) of the Atlantic Ocean is approximately 0.4 – 0.6 Sv (1 Sv = 10^9 kg s-1) larger than that of the Pacific Ocean, as shown in atmospheric and oceanic reanalyses and by oceanographic estimates. This asymmetry is linked to the asymmetry in sea surface salinity and the existence of the Atlantic Meridional Overturning Circulation. It is shown that the reason for the asymmetry in E-P-R is greater precipitation per unit area over the Pacific south of 30N, while evaporation rates are similar over both basins. It is further argued that the Pacific Ocean is anomalous compared to the Atlantic and Indian Oceans in terms of atmospheric moisture flux convergence and precipitation across the tropics and subtropics. To clarify the mechanism by which water vapour is exported out of the Atlantic basin and imported into the Pacific, we use an air mass trajectory model driven by ERA-Interim reanalysis. Using 12-hourly releases of 14-day back trajectories on the boundaries of ocean drainage basins over the period 2010-2014, we are able to partition the atmospheric moisture fluxes between basins according to their origins (i.e. last contact with the boundary layer). We show that at most a quarter of the E-P-R asymmetry is explained by higher moisture export to the Arctic and Southern basins from the Atlantic than from the Pacific. The main contributions come from differences in the longitudinal atmospheric transport of moisture between the Atlantic, Indian and Pacific basins. In particular, during the Asian summer monsoon the recurvature of the low level flow in the Somali Jet results in a much weaker westward moisture transport from the Indian into the Atlantic basin than across Central America (where it is similar to the zonal average) while there is stronger eastward transport from the Indian to Pacific basins. The net effect is stronger moisture convergence into the Pacific, but weaker into the Atlantic. In contrast to previous thinking, the role of the moisture flux across Central America in the asymmetry, albeit significant, is not dominant.

The spatio-temporal distribution characteristics of thermospheric mass density have been given more attention with an increasing demand for spacecraft launches and low Earth orbital prediction. More and more patterns of spatial structure and temporal variation are being discovered. Notwithstanding these developments, the study of spatio-temporal coupling in characteristics analysis remains quite limited. In this study, we use a co-clustering method to explore and analyze the spatio-temporal coupling structural characteristics of thermospheric mass density. The processed GOCE satellite dataset is divided into 5 temporal clusters and 20 spatial clusters by the co-clustering method. In terms of spatial structure, the density has an obvious zonal distribution structure and hemispheric asymmetry. Moreover, due to the influence of the Earth’s magnetic field, there is an average angle about 2.00° between the band structure and the latitudinal circle. In terms of temporal structure, the temporal patterns of density can be grouped into five period types, namely the quiet period, the moderate activity period, the event period, the oscillation period and the recovery period. And significant positive correlation can be found between the F10.7 indices and the temporal density variation. This study explores the spatial structure and temporal pattern of thermospheric mass density and its driving forces from the perspective of spatio-temporal coupling based on a statistical method, which can provide a new idea of spatio-temporal coupling method for spatio-temporal evolution of thermospheric mass density.

The Solar Dynamics Observatory (SDO) is a solar mission in an inclined geosynchronous orbit. Since commissioning, images acquired by Atmospheric Imaging Assembly (AIA) instrument on-board the SDO have frequently displayed “spikes”, pixel regions yielding extreme number of digital counts. These are theorized to occur from energetic electron collisions with the instrument detector system. These spikes are regularly removed from AIA Level 1.0 images to produce clean and reliable data. A study of historical data has found over 100 trillion spikes in the past decade. This project correlates spike detection frequency with radiation environment parameters in order to generate an augmented data product from SDO. We conduct a correlation study between SDO/AIA data and radiation belt activity within the SDO’s orbit. By extracting radiation “spike” data from the SDO/AIA images, we produce a comprehensive data product which is correlated not only with geomagnetic parameters such as Kp, Ap and Sym-H but also with the electron and proton fluxes measured by the GOES-14 satellite. As a result, we find that AIA spikes are highly correlated with the GOES-14 electrons detected by the MAGED and EPEAD instruments at the equator (where the two satellites meet) with Spearman’s Correlation values of ρ=0.73 and ρ=0.53 respectively, while a weaker correlation of ρ=0.47 is shown with MAGPD protons for the two year period where both missions returned data uninterruptedly. This correlation proves that the SDO spike data can be proven useful for characterizing the Van Allen radiation belt, especially at areas where other satellites cannot.

We describe new publicly-available, multi-year formaldehyde (HCHO) data records from the Ozone Mapping and Profiler Suite (OMPS) nadir mapper (NM) instruments on the Suomi NPP and NOAA-20 satellites. The OMPS-NM instruments measure backscattered UV light over the globe once per day, with spatial resolutions close to nadir of 50 × 50 km² (OMPS/Suomi-NPP) and 17 × 17 km² or 12 × 17 km² (OMPS/NOAA-20). After a preliminary instrument line shape and wavelength calibration using on-orbit observations, we use the backscatter measurements in a direct spectral fit of radiances, in combination with a nadir reference spectrum collected over a clean area, to determine slant columns of HCHO. The slant columns are converted to vertical columns using air mass factors derived through scene-by-scene radiative transfer calculations. Finally, a correction is applied to account for background HCHO in the reference spectrum, as well as any remaining high-latitude biases. We investigate the consistency of the OMPS products from Suomi NPP and NOAA-20 using long-term monthly means over 12 geographic regions, and also compare the products with publicly-available TROPOMI HCHO observations. OMPS/Suomi-NPP and OMPS/NOAA-20 monthly mean HCHO vertical columns are highly consistent (r = 0.98), with low proportional (2 %) and offset (2×10¹⁴ molecules cm⁻²) biases. OMPS HCHO monthly means are also well-correlated with those from TROPOMI (r = 0.92), although they are consistently 10±16 % larger in polluted regions (columns >8×10¹⁵ molecules cm⁻²). These differences result primarily from differences in air mass factors.

Surface charging properties of a non-conducting surface that has a deep cavity and is in contact with the solar wind plasma are investigated by means of the particle-in-cell plasma simulations. The modeled topography is intended with a portion of irregular surfaces found on solid planetary bodies. The simulations have revealed unconventional charging features in that the cavity bottom is charged up to positive values even without any electron emission processes such as photoemission, provided that the surface location is accessible to a portion of incoming solar wind ions. The major driver of the positive charging is identified as drifting ions of the solar wind plasma, and an uncommon current ordering where ion currents exceed electron currents is established at the innermost part of the deep cavity. This also implies that the cavity bottom surface may have a positive potential of several hundred volts, corresponding to the kinetic energy of the ions. The present study also clarifies the role of photoelectrons in developing the distinctive charging environment inside the cavity. The photoemitted electrons can no longer trigger positive charging at the cavity bottom, but rather exhibit the effect of relaxing positive potentials caused by the solar wind ions. The identified charging process, which are primarily due to the solar wind ions, are localized at the depths of the cavity and may be one possible scenario for generating intense electric fields inside the cavity.

This work uses the Specified Dynamics-Whole Atmosphere Community Climate Model with Ionosphere/Thermosphere eXtension (SD-WACCM-X) to determine and explain the seasonality of the migrating semidiurnal tide (SW2) components of tropical upper mesosphere and lower thermosphere (UMLT) temperature, zonal-wind and meridional-wind. This work also quantifies aliasing due to SW2 in satellite-based tidal estimates. Results show that during equinox seasons, the vertical profile of tropical UMLT temperature SW2 and zonal wind SW2’s amplitudes have a double peak structure while they, along with meridional wind SW2, have a single peak structure in their amplitudes in June solstice. Hough mode reconstruction reveals that a linear combination of 5 SW2 Hough modes cannot fully reproduced these features. Tendency analysis reveals that for temperature, the adiabatic term, non-linear advection term and linear advection term are important. For the winds, the classical terms, non-linear advection term, linear advection term and gravity wave drag are important. Results of our alias analysis then indicate that SW2 can induce an ~60% alias in zonal-mean and DW1 components calculated from sampling like that of the Thermosphere Ionosphere Mesosphere Energetics and Dynamics satellite and the Aura satellite. This work concludes that in-situ generation by wave-wave interaction and/or by gravity waves play significant roles in the seasonality of tropical UMLT temperature SW2, zonal wind SW2 and meridional wind SW2. The alias analysis further adds that one cannot simply assume SW2 in the tropical UMLT is negligible.

Recent worldwide heatwaves have shattered temperature records in many regions. In this study, we applied a dynamical downscaling method on the high-resolution version of the Max Planck Institute Earth System Model (MPI-ESM-1-2-HR) to obtain projections of the summer thermal environments and heatwaves in the Pearl River Delta (PRD) considering three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, and SSP5-8.5) in the middle and late 21st century. Results indicated that relative to the temperatures in the 2010s, the mean increases in the summer daytime and nighttime temperatures in the 2040s will be 0.7–0.8 °C and 0.9–1.1 °C, respectively. In the 2090s, they will be 0.5–3.1 °C and 0.7–3.4 °C, respectively. SSP1-2.6 is the only scenario in which the temperatures in the 2090s are expected to be lower than those in the 2040s. Compared with those in the 2010s, hot extremes are expected to be more frequent, more intense, more extensive, and longer-lasting in the future in the SSP2-4.5 and SSP5-8.5 scenarios. In the 2010s, a heatwave occurred in the PRD lasted for 6 days on average, with a mean daily maximum temperature of 34.4 °C. In the 2040s, the heatwave duration and intensity are expected to increase by 2–3 days and 0.2–0.4 °C in all three scenarios. In the 2090s, the increase in these values will be 23 days and 36.0 °C in SSP5-8.5. Moreover, a 10-year extreme high temperature in the 2010s is expected to occur at a monthly frequency from June to September.

The autumn precipitation in the central region of China (APCC) can exert great influences to the production and people’s livelihood. With the use of reanalysis data from 1979−2020, we found a simultaneous relationship between the interannual variability of APCC and the second mode of the 200-hPa meridional wind field over the Eurasian continent, which featured a ‘+-+’ wave-like pattern in autumn (denoted by EC-a). When EC-a is in a positive phase, the coupling of the positive geopotential height with anticyclonic anomalies in the upper level and low sea level pressure over the central China provides a conducive moisture and dynamic condition for precipitation, which is reversed in the negative phase. As indicated by the diagnostic equation, the local vertical motion anomaly is mainly dependent on the temperature advection anomaly by the perturbed wind acting on mean temperature. The strengthened anticyclonic wind shear over East Asia reinforces the southeasterly, which induces warmer air to move northward, resulting in a positive temperature advection and hence enhancing local ascending motion. Moreover, wave flux analysis and numerical simulations show that the EC-a wave train could be triggered by an abnormal dipole pattern SST over the North Atlantic Ocean, which acts as a critical pacemaker on the variability of EC-a.

In response to north-south pressure gradients set by the annual march of the Sun, a cross-equatorial flow that turns to become a low-level Somali jet at around $10^{\circ}$ N is established in the lower troposphere over the Indian ocean. This flow plays a fundamental role in the Indian monsoon. A mechanistic understanding of drivers of this flow is lacking. Here we present a seasonal-mean analysis of the Kinetic Energy (KE) budget of the low-level flow using high spatiotemporal resolution ERA5 reanalysis to identify sources and sinks of KE. We find that the largest KE generation occurs around east African orography where the Somali jet forms while a significant KE is also generated over western Ghats and the Madagascar Island (‘hot spots’). These regions are distant from core monsoon precipitation regions, suggesting that local circulations driven by condensation do not directly produce the bulk of KE during monsoons. A unique KE balance supports the generation of Somali jet, with KE generation balanced by nonlinear KE advection as it forms. Over oceans, KE generation occurs mainly due to cross-isobaric meridional winds in the boundary layer. In contrast, over east African highlands and western Ghats KE generation maximizes just above the boundary layer and mainly occurs due to interaction of flow with orography. We propose a simple decomposition of lower tropospheric KE generation into contributions from surface pressure, orography and free-tropospheric gradients that corroborates the important role played by surface pressure gradients once adjusted for effects of orography.

This study examines how the congestus mode of tropical convection is expressed in numerical simulations of radiative-convective equilibrium (RCE). We draw insights from the ensemble of cloud-resolving models participating in the RCE Model Intercomparison Project (RCEMIP) and from a new ensemble of two-dimensional RCE simulations. About half of the RCEMIP models produce a congestus circulation that is distinct from the deep and shallow circulation modes. In both ensembles, congestus strength is associated with large-scale convective aggregation. Aggregation dries out the upper troposphere, which allows moist congestus outflow to undergo strong radiative cooling. The cooling generates divergence that promotes continued congestus overturning (a positive feedback). This mechanism is fundamentally similar to the driving of shallow circulations by radiative cooling at the top of the surface boundary layer. Aggregation and congestus invigoration are also associated with enhanced static stability throughout the troposphere. Changes in entrainment cooling are found to play an important role in stability enhancement, as has been suggested previously. A modeling experiment shows that enhanced stability is not necessary for congestus invigoration; rather, invigoration itself contributes to midlevel stability enhancement via its impact on the vertical profile of radiative cooling. When present, congestus circulations have a large impact on the mean RCE atmospheric state; for this reason, their inconsistent representation in models and their impact on the real tropical atmosphere warrant further scrutiny.