Geophysical Research Letters最新文献

A factor of 2 difference is found between microwave brightness temperature (TB) observations and simulations from vector radiative transfer models. A physical explanation of this difference is related to the calibration process. In principle, for the calibration of polarimetric instruments of a total power radiometer, the radiation should be only half of the values derived from Planck function but in the actual calibration process, a full value is used. When this full value is converted to a TB it is approximately, but not exactly, twice the TB simulated by a vector radiative transfer model. This inconsistency is verified by simulations of three conically scanning microwave imagers (WindSat, AMSR2 and MWRI) and one cross-track scanning microwave sounder (AMSU-A). This difference cannot be compensated simply by dividing a factor of 2 to the processed TBs, especially at high frequencies or at low physical temperatures due to the nonlinear property of Planck function.

Although Cloud-radiative feedback (CRF) has been investigated in terms of its modulation of extreme precipitation over tropical oceans, the specific timeframe of CRF variability and the associated processes driving extreme rainfall over Asian monsoon regions remain unclear. Based on observational analyses and model sensitivity experiments, this study reveals that longwave CRF at the quasi-biweekly timescale is most closely linked to the intensity of persistent (≥3-day) heavy rainfall events in southern China and northern India by efficiently maintaining the large-scale convective perturbations. When CRF is disabled, the quasi-biweekly convective anomalies supporting extreme precipitation are weakened. Additional assessments of Coupled Model Intercomparison Project historical simulations confirm that models with more accurate quasi-biweekly longwave CRF exhibit smaller biases in capturing the amplitude of persistent heavy rainfall. These results have implications for improving model capability in simulating and forecasting quasi-biweekly CRF to mitigate the risks of extreme precipitation events in monsoonal Asia.

Knowing the structure of the crust is critical to understanding a planet's geologic evolution. Crustal thickness inversions rely on bulk density estimates, which are primarily affected by porosity. Due to the absence of high-resolution gravity data, Mercury's crustal porosity has remained unknown. Here, we use a model that was calibrated to the Moon to relate Mercury's impact crater population and long-wavelength crustal porosity in the cratered terrains. Therein, porosity is created by large impacts and then decreased as the surface ages due to pore compaction by smaller impacts and overburden pressure. Our models fit independent gravity-derived porosity estimates in the northern regions, where data is well resolved. Porosity in the cratered terrains is found to be 9%–18% with an average and standard deviation of 13% $��\pm �$ 2%, indicating lunar-like crustal bulk densities of 2,565 $��\pm �$ 70 kg $��m^{�-�3�}�$ from which updated crustal thickness maps are constructed.

Mercury's surface undergoes large temperature gradients between day and night, which repeats periodically over the same longitudes due to its 3:2 spin-orbit resonance. This effect combined with the orbit's eccentricity, creates hot and cold geographic longitudes. The planet is covered with a highly porous regolith, allowing exospheric atoms to diffuse in depth. By using a 1-D diffusion model, we studied the subsurface precipitation of gas over the cold and hot longitudes to understand gas retention. This work identifies the cold longitudes as favorable regions to form subsurface reservoirs closer to the surface. Moreover, subsurface reservoirs of adsorbates increase two to three times faster over cold longitudes than over hot longitudes, depending on the surface binding energy distribution of the atoms. We suggest that this result may be related to the observation that Mercury's sodium exosphere persists at later local times over the cold pole.

The mesoscale spectrum describes the distribution of kinetic energy in the Earth's atmosphere between length scales of 10 and 400 km. Since the first observations, the origins of this spectrum have been controversial. At synoptic scales, the spectrum follows a −3 spectral slope, consistent with two-dimensional turbulence theory, but a shallower −5/3 slope was observed at the shorter mesoscales. The cause of the shallower slope remains obscure, illustrating our lack of understanding. Through a novel coarse-graining methodology, we are able to present a spatio-temporal climatology of the spectral slope. We find convection and orography have a shallowing effect and can quantify this using “conditioned spectra.” These are typical spectra for a meteorological condition, obtained by aggregating spectra where the condition holds. This allows the investigation of new relationships, such as that between energy flux and spectral slope. Potential future applications of our methodology include predictability research and model validation.

The ocean response to Antarctic Ice Sheet (AIS) mass loss has been extensively studied using numerical models, but less attention has been given to the atmosphere. We examine the global atmospheric response to AIS meltwater in an ensemble of experiments performed using two fully coupled climate models under a pre-industrial climate. In response to AIS meltwater, the experiments yield cooling from the surface to the tropopause over the subpolar Southern Ocean, warming in the Southern Hemisphere polar stratosphere, and cooling in the upper tropical troposphere. Positive feedbacks, initiated by disrupted ocean-atmosphere heat exchange, result in a change in the top-of-atmosphere radiative balance caused primarily through surface and near-surface albedo changes. Changes in the atmospheric thermal structure alter the jet streams aloft. The results highlight the global influence of AIS melting on the climate system and the potential for impacts on mid-latitude climate patterns and delayed regional warming signals.

Simulations based on physical models of the thermosphere-ionosphere system suggest that the ionosphere will sink as the thermosphere cools and contracts in response to increasing greenhouse gas concentrations. As a consequence, long-term trends can be expected in ionospheric parameters such as: total electron content (TEC), the critical frequency of the F2 layer, foF2, and its peak height, hmF2. Since early 1990s, foF2 and hmF2, though to a lesser extent, have been widely analyzed to find these trends. This study shows long-term TEC trends for the period 1999–2023 from available global International GNSS service TEC maps. Using F30, F10.7 or MgII as proxies to filter out the effect of solar EUV, the trends are negative, not only for the mean global value but also for most regions with very few exceptions. This would align with the greenhouse effect hypothesis, even though our results show higher negative trend values than expected theoretically.

The magnetopause is the boundary between the Earth's magnetosphere and the solar wind. Magnetosheath high-speed jets can impact the magnetopause, causing local indentation and subsequently rebound. However, the comprehensive response of the magnetopause to the impact of a high-speed jet remains unclear. In this study, we establish that the full spatiotemporal response pattern of the magnetopause to the impact of an isolated magnetosheath high-speed jet can be characterized as an “Indentation-Rebounce-Relaxation” sequence from a statistical view. Based on the pressure balance, we estimate the spatial and temporal scales of the entire response process to range from 0.5 to 3.2 Earth radii and 0.9–4.7 min, respectively. Furthermore, we find that the interaction between the magnetopause and the high-speed jet during the rebounce phase distorts the magnetopause, subsequently generating pairs of field-aligned currents. These generated field-aligned currents may flow to the ionosphere, potentially contributing to magnetosphere-ionosphere coupling.

Introduction: The relationship between several adipokines and COVID-19 severity has lately been evaluated, results being inconclusive. Therefore, we aimed to assess the association between adipokines in COVID-19 and its severity.

Methods: A search was performed in PubMed, Scopus, and Embase using predefined keywords. The Newcastle of Ottawa Scale (NOS) was used for the quality assessment of included studies. The main summary outcome was the mean difference (MD) in adipokine levels.

Results: A total of 8 studies involving 473 individuals were included. A significant MD in serum adiponectin levels was demonstrated in mild vs. severe COVID-19 patients (-5.734 [95% CI -11.215 - -0.252]), with no significant MD in mild vs. moderate (-7.117 [95% CI -19.546 - 5.313]), or moderate vs. severe COVID-19 (-1.846 [95% CI -4.516 - 0.824]). Moreover, no significant MD was found in adiponectin and leptin levels when comparing COVID-19 patients vs. controls (-12.675 [95% CI -36.159 - 10.808]) and (8.034 [95% CI -10.403 - 26.471]), respectively.

Conclusion: Adiponectin levels were significantly increased in patients with severe compared to mild COVID-19. However, no significant MD was found in adiponectin levels in mild vs. moderate and moderate vs. severe COVID-19 patients, nor in adiponectin and leptin levels in COVID-19 patients vs. controls.