Dissipation Stage Research Articles

Moisture source identification for precipitation associated with tropical cyclone development over the Indian Ocean: a Lagrangian approach

In this study, we investigated the moisture sources for precipitation through a Lagrangian approach during the genesis, intensification, and dissipation phases of all tropical cyclones (TCs) that occurred over the two hemispheric sub-basins of the Indian Ocean (IO) from 1980 to 2018. In the North IO (NIO), TCs formed and reached their maximum intensity on both sides of the Indian Peninsula, to the east in the Bay of Bengal (BoB), and to the west in the Arabian Sea (AS). The oceanic areas where TCs occurred were their main moisture sources for precipitation associated with TCs. Additionally, for TCs over the BoB, continental sources from the Ganges River basin and the South China Sea also played a notable role; for TCs over the AS, the Somali Low-Level jet (along the African coast in a northerly direction) also acted as an essential moisture transport. In the South IO (SIO), the western, central, and eastern basins were identified as the preferred areas for the genesis and development of TCs. During TC activity, the central IO and the Wharton and Perth basins mostly supplied atmospheric moisture. The Mascarene High circulation was the main moisture transport mechanism for the precipitation of TCs formed in the SIO basin. In both basins, during their intensification process, TCs gained more moisture (even more intensely when reaching the hurricane category) than during the genesis or dissipation stages. Additionally, the modulation during monsoonal seasons of the moisture contribution to the TCs was more noticeable over the NIO basin than for the SIO. Overall, the moisture uptake for precipitation from the sources for TCs occurred slightly faster in the NIO basin than in the SIO basin.

Comparison between biogas and pure methane as the fuel of a polygeneration system including a regenerative gas turbine cycle and partial cooling supercritical CO2 Brayton cycle: 4E analysis and tri-objective optimization

The present study aims at utilizing the waste energy from a regenerative gas turbine cycle (GTC) for the production of hydrogen in a proton exchange membrane electrolysis unit (PEMEU), freshwater in a reverse osmosis desalination unit (RODU), and hot steam in a heat recovery steam generator (HRSG). The waste heat of the GTC is first recuperated in a partial cooling supercritical CO2 Brayton cycle (SCBC) to supply the required electricity for the PEMEU and RODU. Then, the residual heat is recuperated in the HRSG to produce hot steam. The waste heat of the SCBC is recovered by two thermoelectric generators in the heat dissipation stages of the cycle. The system is assessed and optimized from thermodynamic, economic, and environmental aspects for the two cases of utilizing methane and biogas as fuel. The optimization results indicate that biogas is superior from an economic aspect as the unit cost of polygeneration and economic cost rate in the case of biogas are 32.5% lower than the case of methane as fuel. On the other hand, employing methane as the fuel brings about lower environmental impacts as it causes a 29% lower environmental cost rate than the case of biogas as fuel. There is quite a narrow difference between the exergy efficiency of the two cases from 40.45% in the case of biogas to 40.72% in the case of methane as fuel. Moreover, the heat loss recovery of the GTC ameliorates the exergy efficiency by 11.96% points in the biogas case.

Transport of substantial stratospheric ozone to the surface by a dying typhoon and shallow convection

Abstract. Stratospheric ozone transported to the troposphere is estimated to account for 5 %–15 % of the tropospheric ozone sources. However, the chances of intruded stratospheric ozone reaching the surface are low. Here, we report an event of a strong surface ozone surge of stratospheric origin in the North China Plain (NCP, 34–40∘ N, 114–121∘ E) during the night of 31 July 2021. The hourly measurements reveal surface ozone concentrations of up to 80–90 ppbv at several cities over the NCP from 23:00 LST (Local Standard time, = UTC +8 h) on 31 July to 06:00 LST on 1 August 2021. The ozone enhancement was 40–50 ppbv higher than the corresponding monthly mean. A high-frequency surface measurement indicates that this ozone surge occurred abruptly, with an increase reaching 40–50 ppbv within 10 min. A concurrent decline in surface carbon monoxide (CO) concentrations suggests that this surface ozone surge might have resulted from the downward transport of a stratospheric ozone-rich and CO-poor air mass. This is further confirmed by the vertical evolutions of humidity and ozone profiles based on radiosonde and satellite data respectively. Such an event of stratospheric impact on surface ozone is rarely documented in view of its magnitude, coverage, and duration. We find that this surface ozone surge was induced by a combined effect of dying Typhoon In-fa and shallow local mesoscale convective systems (MCSs) that facilitated transport of stratospheric ozone to the surface. This finding is based on analysis of meteorological reanalysis and radiosonde data, combined with high-resolution Weather Research and Forecasting (WRF) simulation and backward trajectory analysis using the FLEXible PARTicle (FLEXPART) particle dispersion model. Although Typhoon In-fa on the synoptic scale was at its dissipation stage when it passed through the NCP, it could still bring down a stratospheric dry and ozone-rich air mass. As a result, the stratospheric air mass descended to the middle-to-low troposphere over the NCP before the MCSs formed. With the pre-existing stratospheric air mass, the convective downdrafts of the MCSs facilitated the final descent of stratospheric air mass to the surface. Significant surface ozone enhancement occurred in the convective downdraft regions during the development and propagation of the MCSs. This study underscores the substantial roles of weak convection in transporting stratospheric ozone to the lower troposphere and even to the surface, which has important implications for air quality and climate change.

Relative sea level and wave energy changes recorded in a micro-tidal barrier in southern Brazil

AbstractConstructional sedimentary history of coastal barriers can provide insights regarding meteorological and oceanographic processes, and relative sea-level changes. We investigated the Holocene evolution of a segment of the Rio Grande do Sul Coastal Plain in southernmost Brazil. Data were obtained from ground-penetrating radargrams, optically stimulated luminescence dating, altimetry measurements, Google Earth imagery, and aerial photographs. These data allowed a qualitative and quantitative analysis of the beach profiles recorded in the radargrams. From which eolian, backshore/foreshore, breaker bars, and upper and lower shoreface radar facies were identified. The beach-related radar facies are recorded in twenty-eight progradational sand units (sigmoidal bodies). These units record increments of relatively steady deposition bounded by erosional surfaces produced by anomalous, high-magnitude storm events taking place about every 250 years. The upper shoreface strata include two to three breaker bars. Several pieces of evidence (number of breaker bars, upper shoreface gradient and progradation rate) suggest an alternation between dissipative and intermediate stages of barrier morphodynamics and a decrease of wave energy from 2 ka onwards. The barrier prograded during the last 7.1 ka, and initially, barrier progradation occurred because of a normal regression during a relative sea-level rise followed by a stillstand. Later, barrier progradation took place as a forced regression driven by a relative sea-level fall.

Atmosphere Condition Analysis on Hail Event (Case Study : Pelalawan on September 23rd, 2019)

<p align="justify">Hail in Pulau Muda Village, Pelalawan Regency, Riau Province, occured on September 23rd 2019 when the entire Riau area was covered by smoke due to forest and land fires phenomenon. The hail was not accompanied by extreme rain and did not cause material harm. However, a study of atmospheric conditions before, during, and after the hail occurred is needed to reference for early warning of future events. The result was analyzed descriptively on the radar products, satellite images and observation parameters. CMAX and VCUT of radar product generated from RainbowV5.9 showed that at 06.02 UTC there was a single CB cloud, which its maximum reflectivity core was 60 dBZ at 5 km height. Both the core reflectivity and its height decreased by the time as the cloud dissipated. Himawari-8 RGB images and cloud top temperature time series processed by SATAID showed a significant decrease of cloud top temperature reached -75<sup>o</sup>C at 06.00 UTC where the cloud had large ice particles with strong updraft and dissipated within 1 hour into thin cirrus and medium-low clouds. ECMWF ERA5 Reanalysis data processed by GrADS showed that surface air temperature, RH, and CAPE index has a different value from h-1 to h+1 of hail occurrence. Vertical profile showed the single CB cloud had much amount of ice particles and also strong updrafts that the maximum value of updraft was 0,202 m/s at the development stage. In contrast, the maximum value of downdraft was 0,032 m/s in the dissipation stage of the cloud.</p>

Research on shutdown control strategy of hybrid DC system

The hybrid DC system combined with line commutated converter (LCC) and hybrid modular multilevel converter (HY-MMC), which is named LCC-HY-MMC, has technical advantages and economy. Shutdown is a key problem that any DC system needs to face. In order to ensure that the DC system and the sub-module capacitors of HY-MMC can be discharged quickly during shutdown stage, a complete shutdown control strategy is proposed in this paper. From the characteristics of shutdown, it can be basically regarded as three stages: DC energy feedback stage, controllable dissipation stage of sub-module capacitor energy and uncontrollable dissipation stage of sub-module capacitor energy. Finally, based on the 200 MW/ 200 kV digital simulation model built in the electromagnetic transient simulation software PSCAD/EMTDC, the effectiveness of the proposed method is verified.

Analysis of Energy Evolution Characteristics of Salt Rock Under Different Loading Rates

The existing uniaxial compression test results of salt rock under different loading rates are used to study its energy evolution characteristics during deformation and failure in this study. First of all, the influence of loading rate on the total energy density, elastic energy density, and dissipated energy density is analyzed. Afterward, the relationship between the number and size of fragments, crushing intensity after rock destruction, and energy density of each part is discussed. The results show that the energy evolution process of salt rock during deformation and failure contains three stages, namely, energy accumulation stage, energy dissipation stage, and energy release stage. With the increase in loading rate, the total energy density and dissipated energy density gradually decrease, whereas the elastic energy density increases. When the volume of rock remains constant, the greater the dissipated strain energy, the more the number of fragments will be produced after rock failure. When the dissipated strain energy remains unchanged, the larger the dissipated strain energy (surface free energy) is, the smaller the number and the larger the size of fragments will be produced. When the total strain energy is constant, the splash rate of the fragments increases with increasing elastic strain energy ratio.

Influences of an entrainment–mixing parameterization on numerical simulations of cumulus and stratocumulus clouds

Abstract. Different entrainment–mixing processes can occur in clouds; however, a homogeneous mixing mechanism is often implicitly assumed in most commonly used microphysics schemes. Here, we first present a new entrainment–mixing parameterization that uses the grid mean relative humidity without requiring the relative humidity of the entrained air. Then, the parameterization is implemented in a microphysics scheme in a large eddy simulation model, and sensitivity experiments are conducted to compare the new parameterization with the default homogeneous entrainment–mixing parameterization. The results indicate that the new entrainment–mixing parameterization has a larger impact on the number concentration, volume mean radius, and cloud optical depth in the stratocumulus case than in the cumulus case. This is because inhomogeneous and homogeneous mixing mechanisms dominate in the stratocumulus and cumulus cases, respectively, which is mainly due to the larger turbulence dissipation rate in the cumulus case. Because stratocumulus clouds break up during the dissipation stage to form cumulus clouds, the effects of this new entrainment–mixing parameterization during the stratocumulus dissipation stage are between those during the stratocumulus mature stage and the cumulus case. A large aerosol concentration can enhance the effects of this new entrainment–mixing parameterization by decreasing the cloud droplet size and evaporation timescale. The results of this new entrainment–mixing parameterization with grid mean relative humidity are validated by the use of a different entrainment–mixing parameterization that uses parameterized entrained air properties. This study sheds new light on the improvement of entrainment–mixing parameterizations in models.

An Analysis of the Microstructure of the Melting Layer of a Precipitating Stratiform Cloud at the Dissipation Stage

In this study, we investigated the macro- and microstructures of layered precipitation clouds in spring in Jilin Province, China. The premise of the campaign was to observe cloud particles in the melting layer (ML). The weather was developed under the influence of the Mongolia cyclone, which brought a large range of precipitation to the northeast. Combining the Droplet Measurement Technology (DMT) and Particle Measuring Systems (PMS) data, small particles accounted for the majority of all particles at each level above and below the ML. In our observations, both ice crystals (50–300 μm) and snowflakes (>300 μm) had two peaks between −5 and −2 °C. The high concentration of ice crystals at a temperature of −2.65 °C (4865 m) attained a maximum value of 287 L−1 and snowflakes with 47 L−1, which was similar to the previous studies. The Hallett–Mossop ice multiplication process operated most effectively at the temperature of −5 °C in this study. Even at the cloud dissipation stage, new droplets were still generated between −5 and −6 °C, providing abundant liquid water content (LWC) for the upper cloud. Although irregulars were observed, needles and spheres dominated in the observed cloud region of low LWC (<0.1 g m−3) at temperatures of −6 to −3 °C. These cloud conditions fit into the Hallett–Mossop criteria.

ПОВЕДЕНИЕ ГРУНТОВ И ДИССИПАТИВНЫХ ГЕОЛОГИЧЕСКИХ СТРУКТУР ПРИ ОБРАЗОВАНИИ ОПОЛЗНЕВОГО БЛОКА

The peculiarities of soil state and strength and its role as a “weak” layer in the groundmass are often represented as the main factor that determines the occurrence of a landslide or its activation. These concepts are usually extended both to shallow shear landslides and liquefaction-flow types, as well as to deep block landslides, such as compression-extrusion type, with the release of so-called “the main deformable horizon” of soils in the latter. The formation of a new landslide block is accompanied by the occurrence of destructive displacements in the landslide cirque, involving in displacements of the whole slope. Such events are common in urbanized areas, on slopes with the development of deep compression-extrusion landslides. This article discusses the mechanism of formation of a landslide block and the geological features of transformation of the stress-strain state of the ground mass. New data on the behavior of soils at various stages of dissipation are presented, including the case when the dissipative geological structure is separated from the bedrock in the form of a landslide block.

Energy balance and acoustic emission in titanium Grade 2 under fatigue

This work is devoted to the study of fatigue crack propagation features in titanium Grade 2 in order to develop effective methods for fatigue crack detection and prediction of its propagation rate. Two characteristic stages of heat dissipation are identified during fatigue crack growth. Also the stored energy during fatigue crack propagation is calculated by experimental data of mechanical work and heat dissipation. The stored energy rate is smoother than heat dissipation rate and it slows down when approaching the moment of damage. Cluster analysis of the signal allows us to identify two most probable clusters. The correlation between the acoustic emission energy and heat dissipation was found to be a harbinger of the approaching transition from stable to unstable crack growth. The relation between fatigue crack growth rate and the processes of energy dissipation and acoustic emission can be used in development of intelligent monitoring systems for assessment of current state of structure.

Evaluation and Analysis of Dust Storm Activity in Tianwen-1 Landing Area Based on the Moderate Resolution Imaging Camera Observations and Mars Daily Global Maps

The first Mars exploration mission from China (Tianwen-1) was launched on 23 July 2020 with the goal of “orbiting, landing, and roving”. The occurrence of dust storm activities is an important criterion of assessing atmospheric risk for the Tianwen-1 landing process. Dust storm activities from Mars Year (MY) 24 to MY32 in southern Utopia Planitia were identified. Most dust storms only appeared in one Mars Daily Global Map (MDGM), with a lifetime of less than or equal to solar longitude (Ls) = 0.5°. Only if the lifetime of a dust storm is greater than or equal to Ls = 1° can it reach the primary landing ellipse. From Ls = 0–50°, dust storms are mostly in the diffusion stage with a maximum speed of movement of 2479 km/Ls. Then, the speed gradually decreases to the minimum value of 368 km/Ls when the dust storm is in the dissipation stage. If a dust storm moves at an average speed of 750 km/Ls, the safe landing zone is a circle within a radius of 750 km centered on the primary landing ellipse. From March to May 2021, eight dust storms were identified in the Moderate Resolution Imaging Camera (MoRIC) mosaics. Because there was no dust storm activity in MoRIC mosaic on 13 May 2021, we concluded that there would be no dust storm in the primary landing ellipse on 15 May (MY36, Ls = 45.1°). Therefore, the landing time of the Tianwen-1 probe was finally determined as 15 May, which successfully landed in the south of the Utopia Planitia, and the in-situ investigation was carried out by the Zhurong Mars rover.

Source apportionment of PM2.5 during haze episodes in Shanghai by the PMF model with PAHs

Positive matrix factorization (PMF) is a commonly used receptor model for PM2.5 source apportionment, relying on tracers to identify emission sources. Adding organic tracers such as polycyclic aromatic hydrocarbons (PAHs) to PMF model could enhance the performance of constraining emission sources. In this study, the PMF with PAHs was applied to 112 PM2.5 samples, including full-year and haze episodes during 2015–2016 in Shanghai. Compared to the original PMF, the PMF with PAHs newly identified the industry source and revised of the contributions of biomass burning and coal combustion. The PMF with PAHs were used to reconstruct the source apportionment of PM2.5 in four winter haze episodes. Taking the first two haze episodes (defined as P1and P2) as examples of frequent air mass changes, the P1 accumulation stage was successively affected by local and northwest sources. Vehicle (35.3%) and secondary particles (25.7%) were the primary contributors to PM2.5, due to local accumulation. Industry sources obtained a 25.9% increment under the effect from the northwest sources. P2 was successively controlled by the southwest and northwest sources from the clean stage to the dissipation stage. Significantly increased contributions of biomass burning and industry sources to PM2.5 were observed. Compared to other episodes, the P2 accumulation stage had the highest coal-combustion proportion (5.6%) under the influence of the northwest sources from Shaanxi, Shanxi, and Henan. Moreover, the toxicities of different emission sources were evaluated based on PAHs and BaPeq. Coal combustion, biomass burning, and vehicle sources were the three major contributors, especially coal combustion, contributing 17.1–66.8% to PAHs and 22.6–66.4% to BaPeq but less than 5.6% to PM2.5. We believe that these results will help policymakers by providing insights into the reduction in emission sources for regulation in urban environments and the mitigation of health risks.

Comparing pyrometry and thermography in ballistic impact experiments

Thermal analyses of projectile impact and subsequent combustion are investigated for aluminum projectiles using a high-velocity impact ignition system. Temperature measurements are compared using pyrometry and thermography. The implementation of these techniques is discussed, as well as their benefits and limitations in ballistic experiments. Results show pyrometry is best for measuring temperatures in the immediate vicinity surrounding the impact location, while thermography better quantifies temperature dissipation downstream from impact as the combusting debris cloud disperses. Temperatures comparable to the predicted adiabatic flame temperature are observed with the pyrometer. For thermography, emphasis is placed on the treatment of emissivity in temperature calculations. Three combustion stages are identified in the thermography data and attributed to 1) ignition and growth of the combustion front, 2) thermal dissipation due to initial particle burnout, and 3) a slower dissipation stage caused by reduced heat exchange between the burning debris cloud and surroundings.

The impact of initial concentration of selected pharmaceuticals on their early stage of dissipation in soils

The impact of initial concentration of selected pharmaceuticals on their early stage of dissipation in soils

A Review of Coastal Fog Microphysics During C-FOG

Our goal is to provide an overview of the microphysical measurements made during the C-FOG (Toward Improving Coastal Fog Prediction) field project. In addition, we evaluate microphysical parametrizations using the C-FOG dataset. The C-FOG project is designed to advance understanding of liquid fog formation, particularly its development and dissipation in coastal environments, so as to improve fog predictability and monitoring. The project took place along eastern Canada’s (Nova Scotia and Newfoundland) coastlines and open water environments from August−October 2018, where environmental conditions play an important role for late-season fog formation. Visibility, wind speed, and atmospheric turbulence along coastlines are the most critical weather-related factors affecting marine transportation and aviation. In the analysis, microphysical observations are summarized first and then, together with three-dimensional wind components, used for fog intensity (visibility) evaluation. Results suggest that detailed microphysical observations collected at the supersites and aboard the Research Vessel Hugh R. Sharp are useful for developing microphysical parametrizations. The fog life cycle and turbulence-kinetic-energy dissipation rate are strongly related to each other. The magnitudes of three-dimensional wind fluctuations are higher during the formation and dissipation stages. An array of cutting-edge instruments used for data collection provides new insight into the variability and intensity of fog (visibility) and microphysics. It is concluded that further modifications in microphysical observations and parametrizations are needed to improve fog predictability of numerical-weather-prediction models.

An enhanced plasma injection method for triggering a 10 cm-magnitude high-pressure SF6 gas gap for a megavolt ultrafast bypass switch.

Aiming at developing a megavolt ultrafast bypass switch (UFBPS) that operates at a very low working coefficient, an enhanced plasma injection (EPI) method was proposed, which ejected high-density plasmas up to several centimeters in height in a high-pressure SF6 and thus has an extremely strong triggering ability. The EPI method employed a thin polytetrafluoroethylene microcavity embedded inside the ground electrode and a metal wire electrically exploded inside the microcavity, generating a high-density metal vapor plasma that was rapidly ejected outward from the nozzle and inducing a breakdown of the residual gas gap. In this study, the ejected plasma properties by EPI and main influencing factors were examined and the EPI triggering ability was experimentally verified. The results showed that EPI evolution presented three stages: ellipsoid-shaped, mushroom-shaped, and dissipation stages. In 0.5-MPa SF6, when the trigger energy was 960J and the exploded aluminum wire was 300 µm in radius, the EPI maximum height reached over 9cm within 0.7ms, with an initial evolution velocity >800m/s. Then, an EPI cavity array was set to repetitively trigger a 10 cm-magnitude SF6 gas gap at 0.5 MPa, with a theoretical breakdown voltage >2 MV. The gas gap was successfully triggered with an average trigger delay of 538 µs when a DC 100 kV voltage (undervoltage ratio <5%) was applied. These results indicated that EPI was an effective method for triggering megavolt-magnitude high-pressure SF6 gas gaps at a low undervoltage ratio and meeting the submillisecond trigger requirement of the UFBPS.

Variations of water vapor transport and water vapor-hydrometeor-precipitation conversions during a heavy rainfall event in the Three-River-Headwater region of the Tibetan Plateau

A summertime torrential heavy rainfall event which was occurred in the eastern Three-River-Headwater region (TRHR) of the Tibet Plateau (TP) was simulated by the Weather Research and Forecasting (WRF) model. Variations of three-dimensional water vapor transport and water vapor-hydrometeor-precipitation conversions were analyzed in complex terrains. The results show that: before and in the beginning of the precipitation, the surface evaporation (ES) in the forenoon is the most important water vapor source of hydrometeor formation (Micss), and is much larger than water vapor flux convergence (Qvac). During the developmental stage in the afternoon, Qvac surpasses ES, and contributes the most hydrometeor mainly through condensation (Qcon) for the sporadic precipitation on the mountains, which is related to the convergence of the vertically integrated water vapor flux (IWVF) belts from the northern lower altitude under the topography-forced and thermal-driven uplift with the southerly water vapor flux. During the mature stage at night, the northerly and southerly water vapor fluxes merge and transport eastward downhill, converge further with another easterly stronger IWVF belt, leading to the local heavy rainfall on the lower topography slope. The hydrometeor generated by Qcon and deposition (Qdep) is the primary source of heavy precipitation, while the weak precipitation is prone to directly come from the hydrometeor convergence (Qhc) and local hydrometeor consumption (Qhl). During the dissipative stage before the dawn, the persistence of precipitation is significantly through the consumption of local accumulated water vapor (Qvl) and hydrometeor (Qhl). This study is helpful to provide scientific reference for the rational development and utilization of local cloud water resources and the local disastrous weather prevention and reduction.

An observational and modeling study of a sea fog event over the yellow and east China seas on 17 March 2014

The Moderate Resolution Imaging Spectroradiometer (MODIS) satellite imagery, weather charts, objectively reanalyzed data, the observational data and station sounding data were analyzed to investigate a sea fog event occurred over the Yellow and East China Seas on March 17, 2014. The sounding profiles, weather situations and the related meteorological factors during the development and dissipation stages of this sea fog event were documented. Weather Research Forecast (WRF) model was applied to simulate this sea fog case. The simulated horizontal atmospheric visibility, cloud water, humidity, and vertical wind profile during the different stages of this fog event were analyzed. During the development stage of this sea fog, a southerly lower-jet with 16–18 ms-1, an inversion layer and a cold center over the Yellow Sea were detected. The relative humidity in the fog area was above 95%. The specific humidity over the East China Sea was higher than that over the Yellow Sea. Southerly was dominated in fog area. However, during the dissipation stage of this sea fog, westerly replaced the southerly and at the lower level, southerly jet disappeared. A dry air area formed over the Shandong Peninsula and moved eastwards. Moreover, the WRF modeling result showed that the simulated atmospheric horizontal visibility and cloud water were approximately consistent with the MODIS satellite imagery. Most of cloud water concentrated below 200–400 m, and the cloud water in the southern part of fog area extended to a higher height than the northern part. While both of air temperature and dew-point temperature were close to sea surface temperature.

Study on permeability and collapsibility characteristics of sandy loess in northern Loess Plateau, China

To explore the permeability and collapsibility characteristics of sandy loess in northern Loess Plateau of China, the in-situ tests were carried out by monitoring information of moisture content and collapse deformation in the soil layers. The laws in conditions of simulated rainfall infiltration and saturated infiltration were compared and analyzed. The main results are as follows. (1) The water infiltrates with funnel-shaped. The moisture content decreases with the increase of depth under simulated rainfall infiltration. All sandy loess layers can be nearly saturated under saturated infiltration. (2) The water infiltrating in sandy loess site is fast. The infiltration rate decreases with depth as a power function. (3) The proportion of water lateral migration in sandy loess site is small. For simulated rainfall infiltration, the development of cracks experienced three stages of appearing, expanding and keeping. For saturated infiltration, the development of cracks experienced the process of appearing, expanding, local small cracks cutting the main cracks and the later cracks developing makes the early cracks have trend of bending and closing. (4) The differential collapse deformation is most obvious near the test pit boundary and the maximum collapse deformation occurs in the test pit center. The collapse deformation caused by rainfall infiltration is only 11.6% of saturated infiltration. (5) Two conditions must be satisfied at the same time to fully activate the collapsibility of sandy loess. Firstly, the moisture content variation reaches the initial collapse threshold of moisture content increment. Secondly, the moisture state reaching the initial collapse moisture content increment must be kept for enough time. (6) The evaluation of site collapsibility type and the calculation of ground collapsibility value can be carried out according to the formula Δs=∑i=1nαβδsihi, the parameter β and α is selected according to the evaluation type, application condition and depth. (7) The seepage force drives the silt components moving and changes the original structure of sandy loess, which makes the water holding capacity in infiltration stage and water loss capacity in dissipation stage shows in layered distribution along the depth. (8) The water dissipation of sandy loess site is accompanied by settlement and lasts for a long time. The water dissipation rate decreased exponentially with time. In practical application, the adverse effect of water dissipation on ground deformation and pile bearing capacity cannot be ignored. The research finally provides a new understanding for the mechanism of water physical action and deformation response of sandy loess. It is of great significance for correcting and adding the evaluation method of site collapsibility type and ground collapsibility value in sandy loess areas.