This paper presents a simple theoretical argument to isolate the conditions under which a tropical cyclone can rapidly develop a warm-core thermal structure and subsequently approach a steady state. The theoretical argument is based on the balanced vortex model and, in particular, on the associated transverse circulation equation and the geopotential tendency equation. These second-order partial differential equations contain the diabatic forcing and three spatially varying coefficients: the static stability A, the baroclinity B, and the inertial stability C. Thus, the transverse circulation and the temperature tendency in a tropical vortex depend not only on the diabatic forcing but also on the spatial distributions of A, B, and C. Experience shows that the large radial variations of C are typically the most important effect. Under certain simplifying assumptions as to the vertical structure of the diabatic forcing and the spatial variability of A, B, and C, the transverse circulation equation and the geopotential tendency equation can be solved via separation of variables. The resultingradialstructureequationsretainthedynamicallyimportantradialvariationofCandcanbe solvedin terms of Green’s functions. These analytical solutions show that the vortex response to a delta function in the diabatic heating depends critically on whether the heating occurs in the low-inertial-stability region outside the radius of maximum wind or in the high-inertial-stability region inside the radius of maximum wind. This resultsuggeststhatrapidintensification isfavoredforstormsthathaveat leastsome oftheeyewallconvection inside the radius of maximum wind. The development of an eye partially removes diabatic heating from the high-inertial-stability region of the storm center; however, rapid intensification may continue if the eyewall heating continues to become more efficient. As the warm core matures and static stability increases over the inner core, conditions there become less favorable for deep upright convection and the storm tends to approach a steady state.

Rapid development of the tropical cyclone warm core

. The planetary boundary layer (PBL) governs the vertical transport of mass,
momentum, and moisture between the surface and the free atmosphere, and thus
the determination of PBL height (BLH) is recognized as crucial for air
quality, weather, and climate analysis. Although reanalysis products can
provide important insight into the global view of BLH in a seamless way, the BLH observed in situ on a global scale remains poorly understood due to the lack of
high-resolution (1 or 2 s) radiosonde measurements. The present study
attempts to establish a near-global BLH climatology at synoptic times (00:00
and 12:00 UTC) and in the daytime using high-resolution radiosonde
measurements over 300 radiosonde sites worldwide for the period 2012 to
2019, which is then compared against the BLHs obtained from four reanalysis
datasets, including ERA5, MERRA-2, JRA-55, and NCEP-2. The variations in
daytime BLH exhibit large spatial and temporal dependence, and as a result
the BLH maxima are generally discerned over the regions such as the western
United States and western China, in which the balloon launch times mostly
correspond to the afternoon. The diurnal variations in BLH are revealed with
a peak at 17:00 local solar time (LST). The most promising reanalysis product
is ERA5, which underestimates BLH by around 130 m as compared to radiosondes
released during daytime. In addition, MERRA-2 is a well-established product
and has an underestimation of around 160 m. JRA-55 and NCEP-2 might produce
considerable additional uncertainties, with a much larger underestimation of
up to 400 m. The largest bias in the reanalysis data appears over the
western United States and western China, and it might be attributed to the
maximal BLH in the afternoon when the PBL has risen. Statistical analyses
further indicate that the biases of reanalysis BLH products are positively
associated with orographic complexity, as well as the occurrence of static
instability. To our best knowledge, this study presents the first
near-global view of high-resolution radiosonde-derived boundary layer height
and provides a quantitative assessment of the four frequently used
reanalysis products.

/pdf/investigation-of-near-global-daytime-boundary-layer-height-2slz3bl2j6.pdf

Investigation of near-global daytime boundary layer height using high-resolution radiosondes: first results and comparison with ERA5, MERRA-2, JRA-55, and NCEP-2 reanalyses

Africa has a paucity of long term reliable meteorological ground station data and reanalysis products are used to provide the climate estimations that are important for climate change projections In this paper monthly observed precipitation records in the Logone catchment of the Lake Chad Basin are used to evaluate the performance of two global reanalysis products: the Climate Forecasting System Reanalysis (CFSR) and ERA Interim datasets



The two reanalysis products reproduced the monthly, annual and decadal cycle of precipitation and variability relatively accurately albeit with some discrepancies The catchment rainfall gradient was also well captured by the two products There are good correlations between the reanalysis and rain gauge datasets although significant deviations exist, especially for CFSR Both reanalysis products overestimated rainfall in 68% of the rain gauge stations ERA Interim produced the lowest bias and mean absolute error with average values of 2% and 65 mm month−1 respectively compared to 15% and 34 mm month−1 for the CFSR However, both reanalysis products systematically underestimated annual rainfall in the catchment during the period 1997–2002 for ERA Interim and 1998–2000 for CFSR This research demonstrates that evaluating reanalysis products in remote areas like the Logone catchment enables users to identify artefacts inherent in reanalysis datasets This will facilitate improvements in certain aspects of the reanalysis forecast model physics and parameterization to improve reanalysis dataset quality



This study concludes that the application of each reanalysis product in the catchment will depend on the purpose for which it is to be used and the spatial scale required

https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/met.1600

Evaluating global reanalysis precipitation datasets with rain gauge measurements in the Sudano-Sahel region: case study of the Logone catchment, Lake Chad Basin

. Aeolus is the first satellite mission to directly observe
wind profile information on a global scale. After implementing a set of bias
corrections, the Aeolus data products went public on 12 May 2020. However,
Aeolus wind products over China have thus far not been evaluated extensively by
ground-based remote sensing measurements. In this study, the Mie-cloudy and
Rayleigh-clear wind products from Aeolus measurements are validated against
wind observations from the radar wind profiler (RWP) network in China. Based
on the position of each RWP site relative to the closest Aeolus ground
tracks, three matchup categories are proposed, and comparisons between Aeolus
wind products and RWP wind observations are performed for each category
separately. The performance of Mie-cloudy wind products does not change much
between the three matchup categories. On the other hand, for Rayleigh-clear
and RWP wind products, categories 1 and 2 are found to have much smaller
differences compared with category 3. This could be due to the RWP site
being sufficiently approximate to the Aeolus ground track for categories 1 and
2. In the vertical, the Aeolus wind products are similar to the RWP wind
observations, except for the Rayleigh-clear winds in the height range of
0–1 km. The mean absolute normalized differences between the
Mie-cloudy (Rayleigh-clear) and the RWP wind components are 3.06 (5.45),
2.79 (4.81), and 3.32 (5.72) m/s at all orbit times and ascending and
descending Aeolus orbit times, respectively. This indicates that the wind
products for ascending orbits are slightly superior to those for descending
orbits, and the observation time has a minor effect on the comparison. From
the perspective of spatial differences, the Aeolus Mie-cloudy winds are
consistent with RWP winds in most of east China, except in coastal areas
where the Aeolus Rayleigh-clear winds are more reliable. Overall, the
correlation coefficient R between the Mie-cloudy (Rayleigh-clear) wind and RWP
wind component observation is 0.94 (0.81), suggesting that Aeolus wind
products are in good agreement with wind observations from the RWP network
in China. The findings give us sufficient confidence in assimilating the
newly released Aeolus wind products in operational weather forecasting in
China.

/pdf/technical-note-first-comparison-of-wind-observations-from-3e51vplas2.pdf

Technical note: First comparison of wind observations from ESA's satellite mission Aeolus and ground-based radar wind profiler network of China

In this paper, hourly observations of precipitation, wind, and PM2.5 and PM10 concentrations in Qinhuangdao from 2016 to 2018 were used to study the effects of precipitation and wind on PM2.5 and PM10 concentrations. The results show that precipitation has a certain wet scavenging effect on PM2.5 and PM10, and the scavenging effect on PM10 is greater than that on PM2.5. Precipitation above moderate rainfall is concentrated from May to September, and light rain in winter increases the concentration of pollutants. The changes of PM2.5 before and after precipitation are related to the initial concentration of PM2.5 before precipitation, precipitation intensity, and precipitation duration. The scavenging effect of precipitation on PM10 is closely related to the initial concentration of PM10 before precipitation. The higher the initial concentration of PM10 is, the greater the removal amount of precipitation will be. Moderate or above pollution weather mainly occurs in the northeast, southwest, and west wind meteorological conditions; the more westerly the wind, the more the pollution; north wind and northwest wind have the most obvious scavenging effect on PM2.5 and Pm10; when the wind speed increases to 2 m/s, the concentration of PM2.5 and PM10 can be reduced; when the wind speed is more than 4 m/s, the concentration of PM10 increases under the south wind, southeast wind, east wind, and northeast wind.

/pdf/analysis-of-the-influence-of-precipitation-and-wind-on-pm2-5-iv5gspn071.pdf

Analysis of the Influence of Precipitation and Wind on PM2.5 and PM10 in the Atmosphere

Vertical wind shear (VWS) is one of the key meteorological factors in modulating ground-level particulate matter with an aerodynamic diameter of 2.5 µm or less (PM2.5). Due to the lack of high-resolution vertical wind measurements, how the VWS affects ground-level PM2.5 remains highly debated. Here we employed the wind profiling observations from the fine-time-resolution radar wind profiler (RWP), together with hourly ground-level PM2.5 measurements, to explore the wind features in the planetary boundary layer (PBL) and their association with aerosols in Beijing for the period from December 1, 2018, to February 28, 2019. Overall, southerly wind anomalies almost dominated throughout the whole PBL or even beyond the PBL under polluted conditions during the course of a day, as totally opposed to the northerly wind anomalies in the PBL under clean conditions. Besides, the ground-level PM2.5 pollution exhibited a strong dependence on the VWS. A much weaker VWS was observed in the lower part of the PBL under polluted conditions, compared with that under clean conditions, which could be due to the strong ground-level PM2.5 accumulation induced by weak vertical mixing in the PBL. Notably, weak northbound transboundary PM2.5 pollution mainly appeared within the PBL, where relatively small VWS dominated. Above the PBL, strong northerlies winds also favored the long-range transport of aerosols, which in turn deteriorated the air quality in Beijing as well. This was well corroborated by the synoptic-scale circulation and backward trajectory analysis. Therefore, we argued here that not only the wind speed in the vertical but the VWS were important for the investigation of aerosol pollution formation mechanism in Beijing. Also, our findings offer wider insights into the role of VWS from RWP in modulating the variation of PM2.5, which deserves explicit consideration in the forecast of air quality in the future.

Vertical Wind Shear Modulates Particulate Matter Pollutions: A Perspective from Radar Wind Profiler Observations in Beijing, China

The atmospheric reanalysis datasets have been widely used to understand the variability of atmospheric water vapor on various temporal and spatial scales for climate change research. The difference among a variety of reanalysis datasets, however, causes the uncertainty of corresponding results. In this study, the climatology of atmospheric column-integrated water vapor for the period from 2000 to 2012 was compared among three latest third-generation atmospheric reanalyses including European Centre for Medium-range Weather Forecasts Interim Re-Analysis (ERA-Interim), Modern-Era Retrospective Analysis for Research and Applications (MERRA), and Climate Forecast System Reanalysis (CFSR), while possible explanation on the difference between them was given. The results show that there are significant differences among three datasets in the multi-year global distribution, variation of interannual cycle, long-term trend and so on, though high similarity for principal mode describing the variability of water vapor. Over oceans, the characteristics of long-term CWV variability are similar, whereas the main discrepancy among three datasets is located around the equatorial regions of the Intertropical Convergence Zone, the South Pacific Convergence Zone and warm cloud area, which is related with the difference between reanalysis models for the scheme of convective parameterization, the treatment of warm clouds, and the assimilation of satellite-based observations. Moreover, these CWV products are fairly consistent with observations (satellite-based retrievals) for oceans. On the other hand, there are systematic underestimations about 2.5 kg/m2 over lands for all three CWV datasets, compared with radiosonde observations. The difference between models to solve land-atmosphere interaction in complex environment, as well as the paucity in radiosonde observations, leads to significant water vapor gaps in the Amazon Basin of South America, central parts of Africa and some mountainous regions. These results would help better understand the climatology difference among various reanalysis datasets better, and more properly choose water vapor datasets for different research requirements.

A climatological comparison of column-integrated water vapor for the third-generation reanalysis datasets

Ice water path (IWP) is an important parameter to characterize tropical cyclones. The FY-3B satellite, with multiple passive microwave sensors onboard, offers a unique opportunity to monitor the variation of cloud IWP during the evolution of tropical cyclones. In this paper, by using the combined simultaneous measurements of the MicroWave atmospheric Humidity Sounder and MicroWave Radiometer Imager on FY-3B satellite, an improved IWP algorithm for tropical clouds is developed. The new algorithm seeks to better estimate ice-free background brightness temperature at 150 GHz using simultaneous observations at low microwave frequencies. This approach improves IWP retrieval accuracy particularly for high IWP clouds that often associated with tropical cyclones. The current algorithm was applied to FY-3B observations of two typhoons with different strengths, and the characteristics of IWP variation at the storms' different evolution stages were investigated. The results showed that IWP tends to vary ahead of the storm intensification or decay, suggesting that IWP can be potentially used to predict the change of storm intensity.

Estimating Ice Water Path in Tropical Cyclones With Multispectral Microwave Data From the FY-3B Satellite

The accurate simulation of typhoon hydrometeors remains a challenge. This study attempts to evaluate the performances of five microphysics schemes (MPSs) in the Weather Research and Forecasting (WRF) model in simulating the supertyphoon Neoguri in July 2014. The observed microwave brightness temperature, as well as retrieved data from the microwave radiometer imager (MWRI) onboard Chinese FY-3B satellite, are used to test hydrometeor simulations. In particular, two MWRI radiance indices, including the emission index (EI) and scattering index (SI), are used to assess the performance of five MPSs in simulating liquid and frozen hydrometeors, respectively. Overall, the WRF model can well reproduce the overall pattern of typhoon-produced precipitation, albeit with slightly overestimated precipitation in the inner rainband and underestimated precipitation in the stratiform rainband. Moreover, ice water paths (IWPs) from all five MPS simulations are higher than those estimated from MWRI retrieval in most areas, and the spatial pattern and values of IWP for the National Severe Storms Laboratory double-moment MPS (NSSL) are much closer to those for MWRI. The NSSL scheme reproduces a more realistic joint histogram distribution of SI and EI than other MPSs do, relative to the observation. Besides, the nonlinear Lucas–Kanade optical flow approach has been used to reflect the horizontal distribution of hydrometeors in the typhoon. The results show that the simulated EI and SI from the five MPSs show a systematic southwest bias of approximately about 10∼20 km and significant intensity bias in the convection area. Further model sensitivity tests confirm that the NSSL scheme generates more realistic graupel and supercooled water close to the observations among all MPSs. The findings suggest that satellite measurements would be helpful to assess MPSs in numeric weather models, especially for hydrometeor distributions in the whole typhoon system.

/pdf/satellite-based-assessment-of-various-cloud-microphysics-48ryl46hek.pdf

Ying Zhang

Papers

Vertical Wind Shear Modulates Particulate Matter Pollutions: A Perspective from Radar Wind Profiler Observations in Beijing, China

A climatological comparison of column-integrated water vapor for the third-generation reanalysis datasets

Estimating Ice Water Path in Tropical Cyclones With Multispectral Microwave Data From the FY-3B Satellite

Satellite-Based Assessment of Various Cloud Microphysics Schemes in Simulating Typhoon Hydrometeors