Abstract
The distribution of angular momentum of planets and their host stars provides important information on the formation and evolution of the planetary system. However, mysteries still remain, ...partly due to bias and uncertainty of the current observational data sets and partly due to the fact that theoretical models for the formation and evolution of planetary systems are still underdeveloped. In this study, we calculate the spin angular momentum of host stars and the orbital angular momentum of their planets using data from the NASA Exoplanet Archive along with detailed analysis of observation dependent biases and uncertainty ranges. We also analyze the angular momentum of the planetary system as a function of star age to understand their variation in different evolutionary stages. In addition, we use a population of planets from theoretical model simulations to reexamine the observed patterns and compare the simulated population with the observed samples to assess variations and differences. We found the majority of exoplanets discovered thus far do not have the angular momentum distribution similar to that of planets in our solar system, though this could be due to the observation bias. When filtered by the observational biases, the model simulated angular momentum distributions are comparable to the observed pattern in general. However, the differences between the observation and model simulation in the parameter (angular momentum) space provide more rigorous constraints and insights on the issues that needed future improvement.
Upper tropospheric water vapor (UTWV) plays a critical role in amplifying global warming caused by increasing greenhouse gases, yet it is one of the most poorly simulated quantities in climate ...models. It is not clear what physical processes play a central role in controlling the model errors in UTWV. We diagnose the UTWV simulation errors from AMIP models submitted to the CMIP5 project by using “A-Train” satellite observation and reanalysis data. We identify the relative contributions of errors in relative humidity (RH), temperature, and large-scale circulation (represented by vertical pressure velocity at 500 hPa, ω
500
) to the modeled UTWV errors over the tropics (30°N–30°S). It is found that models generally have positive biases in UTWV, except over the continental convective regions where negative biases predominate. The errors in the patterns and amplitudes of climatological UTWV are highly correlated with those in RH and ω
500
. The fractional UTWV errors show large positive errors over the large-scale descending regimes (0 < ω
500
< 40 hPa/day) where large model spreads also exist. The seasonal cycle of hemispherically averaged UTWV closely resembles that of ω
500
. The errors for UTWV interannual anomalies are abundant over the climatologically deep convective regions (SST > 300 K or ω
500
< −30 hPa/day) and these errors are positive (negative) where anomalous descent (ascent) occurs during El Niño. We find that the water vapor errors are dominated by the errors in RH rather than in temperature throughout the troposphere, while temperature errors play an important role for water vapor errors near the tropopause.
Abstract
The climate of a planet can be strongly affected by its eccentricity due to variations in the stellar flux. There are two limits for the dependence of the inner habitable zone boundary (IHZ) ...on eccentricity: (1) the mean stellar flux approximation (
S
IHZ
∝
1
−
e
2
), in which the temperature is approximately constant throughout the orbit, and (2) the maximum stellar flux approximation (
S
IHZ
∝ (1 −
e
)
2
), in which the temperature adjusts instantaneously to the stellar flux. Which limit is appropriate is determined by the dimensionless parameter
Π
=
C
BP
, where
C
is the heat capacity of the planet,
P
is the orbital period, and
B
=
∂
Ω
∂
T
s
, where Ω is the outgoing long-wave radiation and
T
s
is the surface temperature. We use the Buckingham Π theorem to derive an analytical function for the IHZ in terms of eccentricity and Π. We then build a time-dependent energy balance model to resolve the surface temperature evolution and constrain our analytical result. We find that Π must be greater than about ∼1 for the mean stellar flux approximation to be nearly exact and less than about ∼0.01 for the maximum stellar flux approximation to be nearly exact. In addition to assuming a constant heat capacity, we also consider the effective heat capacity including latent heat (evaporation and precipitation). We find that for planets with an Earthlike ocean, the IHZ should follow the mean stellar flux limit for all eccentricities. This work will aid in the prioritization of potentially habitable exoplanets with nonzero eccentricity for follow-up characterization.
Present‐day shortcomings in the representation of upper tropospheric ice clouds in general circulation models (GCMs) lead to errors in weather and climate forecasts as well as account for a source of ...uncertainty in climate change projections. An ongoing challenge in rectifying these shortcomings has been the availability of adequate, high‐quality, global observations targeting ice clouds and related precipitating hydrometeors. In addition, the inadequacy of the modeled physics and the often disjointed nature between model representation and the characteristics of the retrieved/observed values have hampered GCM development and validation efforts from making effective use of the measurements that have been available. Thus, even though parameterizations in GCMs accounting for cloud ice processes have, in some cases, become more sophisticated in recent years, this development has largely occurred independently of the global‐scale measurements. With the relatively recent addition of satellite‐derived products from Aura/Microwave Limb Sounder (MLS) and CloudSat, there are now considerably more resources with new and unique capabilities to evaluate GCMs. In this article, we illustrate the shortcomings evident in model representations of cloud ice through a comparison of the simulations assessed in the Intergovernmental Panel on Climate Change Fourth Assessment Report, briefly discuss the range of global observational resources that are available, and describe the essential components of the model parameterizations that characterize their “cloud” ice and related fields. Using this information as background, we (1) discuss some of the main considerations and cautions that must be taken into account in making model‐data comparisons related to cloud ice, (2) illustrate present progress and uncertainties in applying satellite cloud ice (namely from MLS and CloudSat) to model diagnosis, (3) show some indications of model improvements, and finally (4) discuss a number of remaining questions and suggestions for pathways forward.
We examine the spatial distributions of CMIP6‐simulated cloud liquid water path (CLWP) and content (CLWC) against MODIS and CloudSat synthesized data over the tropical and subtropical Pacific. Three ...subsets of models are categorized based on their treatments of frozen ice‐radiative interactions. CLWP/CLWC are generally well simulated in subset with separately‐calculated radiative effects of cloud ice and falling ice (SON2). Too much warm clouds above 750 hPa are produced in either subset with total frozen ice radiative effects (SON1) or subset without radiative effects of falling ice (NOS) and thus CLWP/CLWC are overestimated over the open ocean including the trade‐wind regions. Stratocumulus clouds off the coasts of North and South America are severely underestimated in NOS models. We attribute the overestimates of clouds above the trade‐wind boundary layers to anomalous ascending motion associated with warmer sea surface temperature and weaker surface wind stress linked to indirect effects of falling ice‐radiation interactions.
Plain Language Summary
We explore how different formulations of frozen particle radiative effects in global climate models have effects on the simulation of warm clouds in the subtropical and tropical Pacific. Coupled Model Intercomparison Project Phase 6 (CMIP6) models are divided into three subsets for this study. We find that models with a separated treatment of floating ice and falling ice radiative effects (SON2) perform better than models with floating ice radiative effects only (NOS) or combined frozen ice radiative effects (SON1) in terms of biases of cloud liquid water content and cloud liquid water path against satellite measurements. This study suggests that biases in broad‐scale meteorological environments such as anomalous ascending motion, warmer sea surface temperature and weaker surface wind stress may cause excessive amounts of warm clouds above the trade‐wind boundary layers in NOS and SON1, thereby leading to excessive cloud liquid water.
Key Points
CloudSat‐MODIS synthesized estimates of warm cloud liquid water path/content (CLWP/CLWC) are used to evaluate three CMIP6 model subsets
CLWP/CLWC are simulated well with separately‐calculated radiative effects of cloud ice and falling ice over subtropical and tropical Pacific
Produce too much liquid water above 750 hPa over the trade‐wind regions in subsets with cloud ice only or total frozen ice radiative effects
This study investigates the climatology of vertical distributions of cloud liquid water content, ice water content, and cloud fraction (CFR) associated with eight different cloud types, by utilizing ...the combined CloudSat radar and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations lidar measurements. The geographical and seasonal variations of these cloud properties for each cloud type are also analyzed. The cloud water content (CWC) of each cloud type is sorted by three parameters obtained from colocated satellite observations to investigate the relationships between large‐scale conditions and the vertical structure of clouds. Results show that different cloud types have different altitudes of CWC and CFR peaks, and the altitude of CFR peak does not always overlap with that of CWC peak. Each type of cloud shows a clear asymmetric pattern of spatial distribution between Northern Hemisphere (NH) and Southern Hemisphere (SH). Stratocumulus and stratus clouds make the greatest contribution to the liquid water path, while the ice water path is mostly contributed by deep convective cloud over the tropics and nimbostratus over the middle and high latitudes. Over both middle and high latitudes, clouds have larger seasonal variation in the NH than in the SH. Over ocean, large CWCs of deep convective cloud, cirrus, and altostratus are above 7 km, and are associated with high convective available potential energy (>2000 J/kg), warm sea surface temperature (>303 K), and relatively high precipitation (>1 mm/h). Over land, most of the middle and high clouds have similar CWC distributions compared to those over ocean, but altocumulus and low clouds are quite different from those over ocean.
Key Points
Climatology of vertical distributions of cloud LWC, IWC, and cloud fraction
Geographical and seasonal variations of cloud properties for eight cloud types
Relation between large‐scale parameters and cloud vertical structure
Local primary emission, transport, and secondary formation of aerosols constitute the major atmospheric particulate matter (PM) over a certain region. To identify and quantify major sources of ...ambient PM is important for pollution mitigation strategies, especially on a city scale. We developed two source apportionment methods to make the first‐order estimates of local primary contribution ratio (LCR) of PM2.5 (PM with diameter less than 2.5 μm) using the high‐density (about 1/km2) network observations with high sampling frequency (about 1 hr). Measurements of PM2.5 mass concentration from 169 sites within a 20 km × 20 km domain are analyzed. The two methods developed here are mainly based on the spatial and temporal variations of PM2.5 within an urban area. The accuracy of our developed methods is subject to the assumptions on the spatial heterogeneity of primary and secondary formed aerosols as well as those from long‐range transport to a city. We apply these two methods to a typical industrial city in China in winter of 2015 with frequent severe haze events. The local primary pollution contributions calculated from the two methods agree with each other that they are often larger than 0.4. The LCR range is from 0.4 to 0.7, with an average value of 0.63. Our study indicates the decisive role of locally emitted aerosols in the urban severe haze formation during the winter time. It further suggests that reductions of local primary aerosol emissions are essential to alleviate the severe haze pollution, especially in industrial cities.
Key Points
Two approaches are developed to quantify the local contribution from primary emissions to haze using high‐density site observations
Both methods indicate the importance of local primary emissions in haze formation in an industrial city with contribution ratios of 0.4‐0.7
Local primary emission contribution ratio increases with mean pollution level during the winter of an industrial city
Robotic-assisted total hip arthroplasty (R-THA) affords precision yet uncertain clinical benefits. This study compares dislocation rates and related revisions between R-THA and manual total hip ...arthroplasty (M-THA). Secondarily we evaluated cup position, patient-reported outcome measures (PROMs), and postoperative complications.
A three-surgeon cohort study was conducted on 2247 consecutive patients (1724 M-THA and 523 R-THA) who received a primary THA between January 2014 and June 2020 at a single hospital. Demographics, PROMs, emergency department visits, readmissions, and 90-day complications were collected via the Michigan Arthroplasty Registry Collaborative Quality Initiative. Chart review yielded instability occurrence with an average follow-up of 4 years. Multivariate regression analysis was performed, and a sample of 368 radiographs, including all dislocations, were assessed.
There were significantly lower rates of dislocation in R-THA (0.6%) vs M-THA (2.5%; Multivariate odds ratio 3.74, P < .046). All cases of unstable R-THA were successfully treated conservatively, whereas 46% of unstable M-THA were revised for recurrent instability. Cup anteversion (25.6° ± 5.4° R-THA vs 20.6° ± 7.6° M-THA) was greater, and cup inclination (42.5° ± 5.3° R-THA vs 47.0° ± 6.7° M-THA) was lower in the R-THA group (P < .05). No significant differences were noted for demographics, PROMs, or other complications (P > .05).
R-THA resulted in less than one-fourth the dislocation rate compared to M-THA and no revision for instability. It was associated with no difference in PROMs or other early complications. The influence of R-THA on stability goes beyond simply cup positioning and deserves further study.
PDF
