scholarly journals Enhancement of ice-phase precipitation caused by thermal forcing produces ghost echoes over the Tibetan Plateau

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Yilun Chen ◽  
Aoqi Zhang ◽  
Shumin Chen ◽  
Chaoyong Tu ◽  
Weibiao Li ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Heavy Precipitation ◽  
Dynamic Factor ◽  
The Tibetan Plateau ◽  
Dual Frequency ◽  
Phase Precipitation ◽  
Thermal Forcing ◽  
Near Surface ◽  
Surface Precipitation ◽  
Ice Phase

AbstractWhether tall storms produce heavy precipitation is currently a controversial topic. Here, we used seven years of observations from the dual-frequency precipitation radar and found that there is a rare but unique vertical precipitation structure over the Tibetan Plateau. The radar echo peaks above the freezing height, which we refer to as a “ghost echo”. The existence of a ghost echo increases the echo-top height but suppresses the increase in droplet size below it, and therefore weakens the near-surface precipitation. Compared with normal echoes, ghost echoes appear more often in the afternoon. The potentially unstable environment produced by thermal forcing is the main cause of ghost echoes, rather than the dynamic factor of wind shear. The ghost echo, which is essentially a mechanism of ice-phase precipitation enhancement, represents a type of tall but weak precipitation. Its existence adds to our current perception of the nature of precipitation.

scholarly journals Effects of Liquid Phase Cloud Microphysical Processes in Mixed Phase Cumulus Clouds over the Tibetan Plateau

2019 ◽  
Author(s):  
Xiaoqi Xu ◽  
Chunsong Lu ◽  
Yangang Liu ◽  
Wenhua Gao ◽  
Yuan Wang ◽  
...  
Keyword(s):  
Liquid Phase ◽  
Tibetan Plateau ◽  
Large Scale ◽  
Precipitation Event ◽  
The Tibetan Plateau ◽  
Phase Precipitation ◽  
Physical Reason ◽  
Surface Precipitation ◽  
Skill Scores ◽  
Microphysical Processes

Abstract. Overprediction of precipitation over the Tibetan Plateau is often found in numerical simulations, which is thought to be related to coarse grid sizes or inaccurate large-scale forcing. In addition to confirming the important role of model grid sizes, this study shows that liquid-phase precipitation parameterization is another key culprit, and underlying physical mechanisms are revealed. A typical summer plateau precipitation event is simulated with the Weather Research and Forecasting (WRF) model by introducing different parameterizations of liquid-phase microphysical processes into the commonly used Morrison scheme, including autoconversion, accretion, and entrainment-mixing mechanisms. All simulations can reproduce the general spatial distribution and temporal variation of precipitation. The precipitation in the high-resolution domain is less overpredicted than in the low-resolution domain. The accretion process plays more important roles than other liquid-phase processes in simulating precipitation. Employing the accretion parameterization considering raindrop size makes the total surface precipitation closest to the observation which is supported by the Heidke skill scores. The physical reason is that this accretion parameterization can suppress fake accretion and liquid-phase precipitation when cloud droplets are too small to initiate precipitation.

scholarly journals Sediment transport processes across the Tibetan Plateau inferred from robust grain-size end members in lake sediments

2014 ◽  
Vol 10 (1) ◽  
pp. 91-106 ◽  
Author(s):  
E. Dietze ◽  
F. Maussion ◽  
M. Ahlborn ◽  
B. Diekmann ◽  
K. Hartmann ◽  
...  
Keyword(s):  
Grain Size ◽  
Sediment Transport ◽  
Tibetan Plateau ◽  
Transport Processes ◽  
The Tibetan Plateau ◽  
Dust Deposition ◽  
Northerly Wind ◽  
Near Surface ◽  
Depositional Processes ◽  
End Members

Abstract. Grain-size distributions offer powerful proxies of past environmental conditions that are related to sediment sorting processes. However, they are often of multimodal character because sediments can get mixed during deposition. To facilitate the use of grain size as palaeoenvironmental proxy, this study aims to distinguish the main detrital processes that contribute to lacustrine sedimentation across the Tibetan Plateau using grain-size end-member modelling analysis. Between three and five robust grain-size end-member subpopulations were distinguished at different sites from similarly–likely end-member model runs. Their main modes were grouped and linked to common sediment transport and depositional processes that can be associated with contemporary Tibetan climate (precipitation patterns and lake ice phenology, gridded wind and shear stress data from the High Asia Reanalysis) and local catchment configurations. The coarse sands and clays with grain-size modes >250 μm and <2 μm were probably transported by fluvial processes. Aeolian sands (~200 μm) and coarse local dust (~60 μm), transported by saltation and in near-surface suspension clouds, are probably related to occasional westerly storms in winter and spring. Coarse regional dust with modes ~25 μm may derive from near-by sources that keep in longer term suspension. The continuous background dust is differentiated into two robust end members (modes: 5–10 and 2–5 μm) that may represent different sources, wind directions and/or sediment trapping dynamics from long-range, upper-level westerly and episodic northerly wind transport. According to this study grain-size end members of only fluvial origin contribute small amounts to mean Tibetan lake sedimentation (19± 5%), whereas local to regional aeolian transport and background dust deposition dominate the clastic sedimentation in Tibetan lakes (contributions: 42 ± 14% and 51 ± 11%). However, fluvial and alluvial reworking of aeolian material from nearby slopes during summer seems to limit end-member interpretation and should be crosschecked with other proxy information. If not considered as a stand-alone proxy, a high transferability to other regions and sediment archives allows helpful reconstructions of past sedimentation history.

scholarly journals A numerical process study on the rapid transport of stratospheric air down to the surface over western North America and the Tibetan Plateau

2019 ◽  
Vol 19 (9) ◽  
pp. 6535-6549 ◽  
Author(s):  
Bojan Škerlak ◽  
Stephan Pfahl ◽  
Michael Sprenger ◽  
Heini Wernli
Keyword(s):  
Boundary Layer ◽  
Tibetan Plateau ◽  
Surface Ozone ◽  
Vertical Transport ◽  
The Tibetan Plateau ◽  
Near Surface ◽  
Air Mass ◽  
Ozone Concentrations ◽  
Rapid Transport ◽  
Upper Level

Abstract. Upper-level fronts are often associated with the rapid transport of stratospheric air along tilted isentropes to the middle or lower troposphere, where this air leads to significantly enhanced ozone concentrations. These plumes of originally stratospheric air can only occasionally be observed at the surface because (i) stable boundary layers prevent an efficient vertical transport down to the surface, and (ii) even if boundary layer turbulence were strong enough to enable this transport, the originally stratospheric air mass can be diluted by mixing, such that only a weak stratospheric signal can be recorded at the surface. Most documented examples of stratospheric air reaching the surface occurred in mountainous regions. This study investigates two such events, using a passive stratospheric air mass tracer in a mesoscale model to explore the processes that enable the transport down to the surface. The events occurred in early May 2006 in the Rocky Mountains and in mid-June 2006 on the Tibetan Plateau. In both cases, a tropopause fold associated with an upper-level front enabled stratospheric air to enter the troposphere. In our model simulation of the North American case, the strong frontal zone reaches down to 700 hPa and leads to a fairly direct vertical transport of the stratospheric tracer along the tilted isentropes to the surface. In the Tibetan Plateau case, however, no near-surface front exists and a reservoir of high stratospheric tracer concentrations initially forms at 300–400 hPa, without further isentropic descent. However, entrainment at the top of the very deep boundary layer (reaching to 300 hPa over the Tibetan Plateau) and turbulence within the boundary layer allows for downward transport of stratospheric air to the surface. Despite the strongly differing dynamical processes, stratospheric tracer concentrations at the surface reach peak values of 10 %–20 % of the imposed stratospheric value in both cases, corroborating the potential of deep stratosphere-to-troposphere transport events to significantly influence surface ozone concentrations in these regions.

scholarly journals Impact of topography on black carbon transport to the southern Tibetan Plateau during the pre-monsoon season and its climatic implication

2020 ◽  
Vol 20 (10) ◽  
pp. 5923-5943 ◽  
Author(s):  
Meixin Zhang ◽  
Chun Zhao ◽  
Zhiyuan Cong ◽  
Qiuyan Du ◽  
Mingyue Xu ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Black Carbon ◽  
Radiative Forcing ◽  
Monsoon Season ◽  
Radiative Heating ◽  
The Tibetan Plateau ◽  
Complex Topography ◽  
Meridional Transport ◽  
Near Surface ◽  
Mass Volume

Abstract. Most previous modeling studies about black carbon (BC) transport and its impact over the Tibetan Plateau (TP) conducted simulations with horizontal resolutions coarser than 20 km that may not be able to resolve the complex topography of the Himalayas well. In this study, the two experiments covering all of the Himalayas with the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) at the horizontal resolution of 4 km but with two different topography datasets (4 km complex topography and 20 km smooth topography) are conducted for pre-monsoon season (April 2016) to investigate the impacts of topography on modeling the transport and distribution of BC over the TP. Both experiments show the evident accumulation of aerosols near the southern Himalayas during the pre-monsoon season, consistent with the satellite retrievals. The observed episode of high surface BC concentration at the station near Mt. Everest due to heavy biomass burning near the southern Himalayas is well captured by the simulations. The simulations indicate that the prevailing upflow across the Himalayas driven by the large-scale westerly and small-scale southerly circulations during the daytime is the dominant transport mechanism of southern Asian BC into the TP, and it is much stronger than that during the nighttime. The simulation with the 4 km topography resolves more valleys and mountain ridges and shows that the BC transport across the Himalayas can overcome the majority of mountain ridges, but the valley transport is more efficient. The complex topography results in stronger overall cross-Himalayan transport during the simulation period primarily due to the strengthened efficiency of near-surface meridional transport towards the TP, enhanced wind speed at some valleys and deeper valley channels associated with larger transported BC mass volume. This results in 50 % higher transport flux of BC across the Himalayas and 30 %–50 % stronger BC radiative heating in the atmosphere up to 10 km over the TP from the simulation with the 4 km complex topography than that with the 20 km smoother topography. The different topography also leads to different distributions of snow cover and BC forcing in snow. This study implies that the relatively smooth topography used by the models with resolutions coarser than 20 km may introduce significant negative biases in estimating light-absorbing aerosol radiative forcing over the TP during the pre-monsoon season. Highlights. The black carbon (BC) transport across the Himalayas can overcome the majority of mountain ridges, but the valley transport is much more efficient during the pre-monsoon season. The complex topography results in stronger overall cross-Himalayan transport during the study period primarily due to the strengthened efficiency of near-surface meridional transport towards the TP, enhanced wind speed at some valleys and deeper valley channels associated with larger transported BC mass volume. The complex topography generates 50 % higher transport flux of BC across the Himalayas and 30 %–50 % stronger BC radiative heating in the atmosphere up to 10 km over the Tibetan Plateau (TP) than the smoother topography, which implies that the smooth topography used by the models with relatively coarse resolution may introduce significant negative biases in estimating BC radiative forcing over the TP during the pre-monsoon season. The different topography also leads to different distributions of snow cover and BC forcing in snow over the TP.

Recent Trends in Land Surface Temperature on the Tibetan Plateau

2006 ◽  
Vol 19 (12) ◽  
pp. 2995-3003 ◽  
Author(s):  
Yuichiro Oku ◽  
Hirohiko Ishikawa ◽  
Shigenori Haginoya ◽  
Yaoming Ma
Keyword(s):  
Tibetan Plateau ◽  
Surface Temperature ◽  
Air Temperature ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Precipitation Amount ◽  
Surface Air Temperature ◽  
The Tibetan Plateau ◽  
Near Surface ◽  
Diurnal Range

Abstract The diurnal, seasonal, and interannual variations in land surface temperature (LST) on the Tibetan Plateau from 1996 to 2002 are analyzed using the hourly LST dataset obtained by Japanese Geostationary Meteorological Satellite 5 (GMS-5) observations. Comparing LST retrieved from GMS-5 with independent precipitation amount data demonstrates the consistent and complementary relationship between them. The results indicate an increase in the LST over this period. The daily minimum has risen faster than the daily maximum, resulting in a narrowing of the diurnal range of LST. This is in agreement with the observed trends in both global and plateau near-surface air temperature. Since the near-surface air temperature is mainly controlled by LST, this result ensures a warming trend in near-surface air temperature.

Modeling the Effects of Lakes in the Tibetan Plateau on Diurnal Variations of Regional Climate and Their Seasonality

2020 ◽  
Vol 21 (11) ◽  
pp. 2523-2536
Author(s):  
Lingjing Zhu ◽  
Jiming Jin ◽  
Yimin Liu
Keyword(s):  
Tibetan Plateau ◽  
Regional Climate ◽  
Wrf Model ◽  
Surface Air Temperature ◽  
Diurnal Variations ◽  
The Tibetan Plateau ◽  
Near Surface ◽  
Local Climate ◽  
Lake Model ◽  
Physically Based

AbstractIn this study, we investigated the effects of lakes in the Tibetan Plateau (TP) on diurnal variations of local climate and their seasonal changes by using the Weather Research and Forecasting (WRF) Model coupled with a one-dimensional physically based lake model. We conducted WRF simulations for the TP over 2000–10, and the model showed excellent performance in simulating near-surface air temperature, precipitation, lake surface temperature, and lake-region precipitation when compared to observations. We carried out additional WRF simulations where all the TP lakes were replaced with the nearest land-use types. The differences between these two sets of simulations were analyzed to quantify the effects of the TP lakes on the local climate. Our results indicate that the strongest lake-induced cooling occurred during the spring daytime, while the most significant warming occurred during the fall nighttime. The cooling and warming effects of the lakes further inhibited precipitation during summer afternoons and evenings and motivated it during fall early mornings, respectively. This study lays a solid foundation for further exploration of the role of TP lakes in climate systems at different time scales.

scholarly journals Multiple-Scattering-Induced “Ghost Echoes” in GPM DPR Observations of a Tornadic Supercell

2016 ◽  
Vol 55 (8) ◽  
pp. 1653-1666 ◽  
Author(s):  
Alessandro Battaglia ◽  
Kamil Mroz ◽  
Simone Tanelli ◽  
Frederic Tridon ◽  
Pierre-Emmanuel Kirstetter
Keyword(s):  
Multiple Scattering ◽  
Ice Core ◽  
Extreme Case ◽  
Dual Frequency ◽  
Near Surface ◽  
Surface Precipitation ◽  
Triple Frequency ◽  
Rain Rates ◽  
Global Precipitation ◽  
Ku Band

AbstractEvidence of multiple-scattering-induced pulse stretching for the signal of both frequencies of the Dual-Frequency Precipitation Radar (DPR) on the Global Precipitation Measurement (GPM) mission Core Observatory satellite is presented on the basis of collocated ground-based WSR-88D S-band observations of an extreme case: a tornadic supercell. The ground-based observations clearly show a tilted convective core with a so-called bounded weak-echo region—that is, locations where precipitation is absent or extremely light at the ground while large amounts of liquid or frozen precipitation are present aloft. The satellite observations in this region show reflectivity profiles that extend all the way to the surface despite the absence of near-surface precipitation: these are here referred to as “ghost echoes.” Furthermore, the Ku- and Ka-band profiles exhibit similar slopes, which is a typical sign that the observed power is almost entirely due to multiple scattering. A novel microphysical retrieval that is based on triple-frequency (S–Ku–Ka) observations shows that a dense ice core located between 4 and 14 km with particle sizes exceeding 2.5 cm and integrated ice contents exceeding 7.0 kg m−2 is the source of the ghost echoes of the signal in the lower layers. The level of confidence of this assessment is strengthened by the availability of the S-band data, which provide the necessary additional constraints to the radar retrieval that is based on DPR data. This study shows not only that multiple-scattering contributions may become predominant at Ka already very high up in the atmosphere but also that they play a key role at Ku band within the layers close to the surface. As a result, extreme caution must be paid even in the interpretation of Ku-based retrievals (e.g., the TRMM PR dataset or any DPR retrievals that are based on the assumption that Ku band is not affected by multiple scattering) when examining extreme surface rain rates that occur in the presence of deep dense ice layers.

scholarly journals Opposite responses of the Indian Ocean to the thermal forcing of the Tibetan Plateau before and after the onset of the South Asian monsoon

2021 ◽  
pp. 1-56
Author(s):  
Yu Zhao ◽  
Anmin Duan ◽  
Guoxiong Wu
Keyword(s):  
Indian Ocean ◽  
Tibetan Plateau ◽  
South Asian ◽  
Asian Monsoon ◽  
Monsoon Onset ◽  
The Tibetan Plateau ◽  
Thermal Forcing ◽  
The North ◽  
Before And After ◽  
The Indian Ocean

AbstractThe atmospheric circulation changes dramatically over a few days before and after the onset of the South Asian monsoon in spring. It is accompanied by the annual maximum surface heating over the Tibetan Plateau. We conducted two sets of experiments with a coupled general circulation model to compare the response of atmospheric circulation and wind-driven circulation in the Indian Ocean to the thermal forcing of the Tibetan Plateau before and after the monsoon onset. The results show that the Tibetan Plateau's thermal forcing modulates the sea surface temperature (SST) of the Indian Ocean and the meridional circulation in the upper ocean with opposite effects during these two stages. The thermal forcing of the Tibetan Plateau always induces a southwesterly response over the northern Indian Ocean and weakens the northeasterly background circulation before the monsoon onset. Subsequently, wind-evaporation feedback results in a warming SST response. Meanwhile, the oceanic meridional circulation shows offshore upwellings in the north and southward transport in the upper layer crossing the equator, sinking near 15°S. After the monsoon onset, the thermal forcing of the Tibetan Plateau accelerates the background southwesterly and introduces a cooling response to the Indian Ocean SST. The response of oceanic meridional overturning circulation is limited to the north of the equator due to the location and structural evolution of the climatological local Hadley circulation. With an acceleration of the local Walker circulation, the underlying zonal currents also show corresponding changes, including a westerly drift along the equator, downwelling near Indonesia, offshore upwelling near Somalia, and a westward undercurrent.

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