On Convection Bands Within Pacific Coast Storms and Their Relation to Storm Structure

Mechanisms of near-cloud turbulence (NCT) occurring at two different altitudes within the upper-level outflow of tropical cyclone (TC) “Hagibis” in the northwestern Pacific Ocean on 11 October 2019 are investigated using observations and high-resolution numerical simulations. Two NCT regions located several hundred kilometers from the TC center are the focus of this study. These include the 1) top half of cirrus anvil cloud near z = 14 km at 0330 UTC and 2) the anticyclonic outflow at a lower altitude within the TC anvil at z = 11 km later at 0850 UTC. In region 1, the simulated NCT occurred within banded cirrus, which was observed by a geostationary satellite, was organized by horizontal convective rolls resulting from differential thermal advection and enhanced vertical shear within the radial outflow of the TC. In region 2, simulated NCT collocated with observed light-to-moderate turbulence occurred in the radial outflow in the northwestern quadrant of the northward-moving TC that was located along the anticyclonic shear side of the midlatitude jet. Here, strong radial accelerations within the TC outflow toward areas of inertial instability generated the Kelvin–Helmholtz billows, which resulted in localized convective instability with 1-km deep convective overturning in the half bottom of anvil cloud. Simulated turbulence intensities represented by the eddy dissipation rate (EDR) derived from both subgrid-scale turbulent kinetic energy (TKE) and resolved TKE from model domains with subkilometer horizontal grid spacing were in agreement with observed EDR from the aircraft data. Significance Statement We investigated a case of upper-level turbulence encounter that was reported in hundreds of kilometers away from the center of super Typhoon [tropical cyclone (TC)] Hagibis in the northwestern Pacific Ocean. We conducted a high-resolution numerical simulation to understand how small-scale turbulence can be generated in the northwestern quadrant of the anticyclonic upper-level outflow of the TC. The main objective of this paper is to examine processes that induce turbulence near the base of accelerated radial outflows of the TC emerged by the interaction between the TC and upper-level jet stream in midlatitude. This is very important for the aviation industry to safely avoid possible areas of turbulence encounters along the flight routes between East Asia and North America across the northwestern Pacific Ocean.

The Intertropical Convergence Zone (ITCZ) is a band of vigorous convection and high precipitation formed by the confluence of southeasterly and northeasterly trade winds, and acts as a barrier to cross‐equatorial dust transport. We investigate the provenance of dust in the surface sediments of 16 cores collected along a 131.5°W transect from the equator to 16°N in the central Pacific. The results reveal well‐defined Asian dust signals north of 7°N and mixed Asian–South American source signals south of 6°N. We propose the southernmost latitude with an intact Asian source signal (7°N) as the present‐day mean ITCZ position in terms of dust provenance in the central Pacific. This geochemically defined mean ITCZ position reflects differences in thermal and dust fluxes between hemispheres and can be used as a reference for quantitatively assessing ITCZ displacement in the sedimentary down‐core records back to ca. 14 Ma.

The spatial resolution gap between global or regional climate models and the requirements for local impact studies motivates the need for climate downscaling. For impact studies that involve glacier modelling, the sparsity or complete absence of climate monitoring activities within the regions of interest presents a substantial additional challenge. Downscaling methods for this application must be independent of climate observations and cannot rely on tuning to station data. We present new, computationally-efficient methods for downscaling precipitation and temperature to the high spatial resolutions required to force mountain glacier models. Our precipitation downscaling is based on an existing linear theory for orographic precipitation, which we modify for large study regions by including moist air tracking. Temperature is downscaled using an interpolation scheme that reconstructs the vertical temperature structure to estimate surface temperatures from upper air data. Both methods are able to produce output on km to sub-km spatial resolution, yet do not require tuning to station measurements. By comparing our downscaled precipitation (1 km resolution) and temperature (200 m resolution) fields to station measurements in southern British Columbia, we evaluate their performance regionally and through the annual cycle. Precipitation is improved by as much as 30% (median relative error) over the input reanalysis data and temperature is reconstructed with a mean bias of 0.5°C at locations with high vertical relief. Both methods perform best in mountainous terrain, where glaciers tend to be concentrated.

The new generation of weather observatory satellites, namely Global Precipitation Measurement (GPM) constellation satellites, is the lead observatory of the 10 highly advanced earth orbiting weather research satellites. Indeed, GPM is the first satellite that has been designed to measure light rain and snowfall, in addition to heavy tropical rainfall. This work compares the final run of the Integrated Multi-satellitE Retrievals for GPM (IMERG) product, the post real time of TRMM and Multi-satellite Precipitation Analysis (TMPA-3B42) and the Era-Interim product from the European Centre for Medium Range Weather Forecasts (ECMWF) against the Iran Meteorological Organization (IMO) daily precipitation measured by the synoptic rain-gauges over four regions with different topography and climate conditions in Iran. Assessment is implemented for a one-year period from March 2014 to February 2015. Overall, in daily scale the results reveal that all three products lead to underestimation but IMERG performs better than other products and underestimates precipitation slightly in all four regions. Based on monthly and seasonal scale, in Guilan all products, in Bushehr and Kermanshah ERA-Interim and in Tehran IMERG and ERA-Interim tend to underestimate. The correlation coefficient between IMERG and the rain-gauge data in daily scale is far superior to that of Era-Interim and TMPA-3B42. On the basis of daily timescale of bias in comparison with the ground data, the IMERG product far outperforms ERA-Interim and 3B42 products. According to the categorical verification technique in this study, IMERG yields better results for detection of precipitation events on the basis of Probability of Detection (POD), Critical Success Index (CSI) and False Alarm Ratio (FAR) in those areas with stratiform and orographic precipitation, such as Tehran and Kermanshah, compared with other satellite/model data sets. In particular, for heavy precipitation (>15 mm/day), IMERG is superior to the other products in all study areas and could be used in future for meteorological and hydrological models, etc.

This paper assesses extreme precipitation events, which are one of the most impactful hydrological circulation events for policy decisions. In extreme analysis, samples of block maxima or peaks over threshold (POT) are used. However, annual maximum series (AMS), a type of block maxima, has been employed more often than POT. This study deals with problems that often occur in extreme analysis with long historical records and large ensembles of climate simulations. The following work is carried out: (1) AMS analysis is compared with POT analysis using long-term historical precipitation records at meteorological stations in Tokyo and Nagoya. With a carefully selected threshold, the generalized Pareto distribution keeps a more stable shape parameter than the generalized extreme value (GEV) distribution for AMS and gives relatively reliable return levels along with accumulated observation; and (2) a method using 60-year maxima is introduced to manage a very large set of AMS samples to which both the Gumbel distribution and the GEV distribution cannot fit well. Figures to obtain the 100-year return level are prepared based on the Gumbel distribution through the examination of relationships among past and future statistics of 1- to 3-day precipitation with a large ensemble of climate simulations called d4PDF. It is interesting that there are common statistical characteristics among the 1-day, 2-day, and 3-day precipitations.

Water vapour plays a key role in the Earth's energy balance. Almost 50% of the absorbed solar radiation at the surface is used to cool the surface, through evaporation, and warm the atmosphere, through release of latent heat. Latent heat is the single largest factor in warming the atmosphere and in transporting heat from low to high latitudes. Water vapour is also the dominant greenhouse gas and contributes to a warming of the climate system by some 24°C (Kondratev 1972). However, water vapour is a passive component in the troposphere as it is uniquely determined by temperature and should therefore be seen as a part of the climate feedback system. In this short overview, we will first describe the water on planet Earth and the role of the hydrological cycle: the way water vapour is transported between oceans and continents and the return of water via rivers to the oceans. Generally water vapour is well observed and analysed; however, there are considerable obstacles to observing precipitation, in particular over the oceans. The response of the hydrological cycle to global warming is far reaching. Because different physical processes control the change in water vapour and evaporation/precipitation, this leads to a more extreme distribution of precipitation making, in general, wet areas wetter and dry areas dryer. Another consequence is a transition towards more intense precipitation. It is to be expected that the changes in the hydrological cycle as a consequence of climate warming may be more severe that the temperature changes.

A climatology of the prefrontal westerly trough of southern Australia is presented, based on data for the 10-yr period 1976–85. Trough formation was confined to the longitudes of the Australian continent in the warmer months of the year. An average of approximately 15 troughs/yr were observed, evenly distributed each month from September to April, with appreciable interannual variability in incidence. Troughs formed in advance of a major Southern Ocean cold front in a region of differential thermal advection. Genesis occurred primarily over the west of the continent in spring and autumn, but over southeastern Australia in summer. Variability in the location of formation at different times of year was related to the seasonal shift of the subtropical ridge over the continent, the shape of the southern continental coastline, and periods of low zonal-index flow. A class of troughs prone to rapid intensification after formation was also identified.

The local atmospheric response to a realistic shift of the Oyashio Extension SST front in the western North Pacific is analyzed using a high-resolution (HR; 0.25°) version of the global Community Atmosphere Model, version 5 (CAM5). A northward shift in the SST front causes an atmospheric response consisting of a weak surface wind anomaly but a strong vertical circulation extending throughout the troposphere. In the lower troposphere, most of the SST anomaly–induced diabatic heating is balanced by poleward transient eddy heat and moisture fluxes. Collectively, this response differs from the circulation suggested by linear dynamics, where extratropical SST forcing produces shallow anomalous heating balanced by strong equatorward cold air advection driven by an anomalous, stationary surface low to the east. This latter response, however, is obtained by repeating the same experiment except using a relatively low-resolution (LR; 1°) version of CAM5. Comparison to observations suggests that the HR response is closer to nature than the LR response. Strikingly, HR and LR experiments have almost identical vertical profiles of . However, diagnosis of the diabatic quasigeostrophic vertical pressure velocity (ω) budget reveals that HR has a substantially stronger response, which together with upper-level mean differential thermal advection balances stronger vertical motion. The results herein suggest that changes in transient eddy heat and moisture fluxes are critical to the overall local atmospheric response to Oyashio Front anomalies, which may consequently yield a stronger downstream response. These changes may require the high resolution to be fully reproduced, warranting further experiments of this type with other high-resolution atmosphere-only and fully coupled GCMs.

In this chapter, we illustrate and discuss two distinct groups of microporous phases: the cancrinite group and the C-S-H compounds of the tobermorite and gyrolite families. The compounds in the first group present a three-dimensional purely tetrahedral framework with, apart from a single exception, Si:Al ratio equal to 1; in the mineralogical classifications they are included among feldspathoids and are generally “regarded …… distinct from zeolites, in part, at least, because of the presence of large volatile anions” (Coombs et al. 1998). The members of the second group are characterized by mixed frameworks built up by silicon (and aluminum) tetrahedra and calcium polyhedra. A common feature of both groups is the modular character of their frameworks, which are built up through various stacking ways of a single module (as in the minerals of the cancrinite-davyne family) and two or more modules as in the case of the C-S-H phases. ### Structural aspects The minerals belonging to the cancrinite group (Merlino 1984; Deer et al. 2004) are feldspathoids with a Si:Al ratio equal to 1, with the only exception of cancrisilite, which has Si:Al = 7:5 (Khomyakov et al. 1991a,b). The available structural data for the phases with Si: Al = 1 indicate that silicon and aluminum regularly alternate in the tetrahedral sites, in accordance with the Loewenstein rule. The structural cavities host alkaline and earth-alkaline cations, and a wide variety of extra-framework anions, as well as H2O molecules. Their framework is characterized by layers containing six-membered rings of tetrahedra (Fig. 1⇓). Every ring is linked to three similar rings in the preceding layer and to three rings in the succeeding one. If the position of the rings in the first layer is called “A,” and the two possible alternative positions in the adjacent layers are “B” and …

In Part I of this study, structural features of a convective rainband associated with the Mei-Yu front on 25 June 1987 over northwestern Taiwan are investigated. The dynamic and thermodynamic structures and momentum budgets of the convective rainband will be reported in Part II. Dual-Doppler data were collected from CP-4 and TOGA Doppler radars positioned along the northwest coast of Taiwan during the Taiwan Area Mesoscale Experiment (TAMEX). Fields of the system-relative wind and reflectivity were derived in a horizontal domain of 40 km × 36 km using the objective analysis scheme with a 1-km grid spacing in all three directions. There were ten analysis levels in the vertical ranging from 0.8 to 9.8 km. Vertical velocities were computed from the anelastic continuity equation by integrating downward with variational adjustment. Results show that the low-level jet (LLJ) in the boundary layer provides large vertical shear ahead of the cold front. The orientation of the jet is in the direction almost parallel to the cold front. The depth of the cold air associated with the Mei-Yu front is rather shallow (1–2 km), in agreement with other TAMEX case studies reported in the literature. To the south of the front, winds are from the southwest in the lower troposphere and veer with height in the middle and upper troposphere. The southwest monsoon flow at low levels transports high-θe, environmental air toward the wind-shift line. Behind the front, the northwesterly flow dominates, carrying much cooler air from northern China. The low-level convergence enhances lifting, resulting in a narrow band of convection on the warm side of the front. The length of the rainband analyzed is 5–10 km wide and 50 km long and is composed of many cells. Each cell is accompanied by the moderate convective updraft (6–8 m s−1) and weak downdraft (2–4 m s−1). The precipitation is deep but not intense on the warm side of the front. The maximum reflectivity within the rainband is less than 42 dBZ. The precipitation cores are elongated southeastward in the direction parallel to the environmental shear vector between the lower and middle layers. By contrast, the precipitation behind the front is weak and shallow, showing stratiform precipitation. Because the system traveled very slowly within the domain of interest, up to 200 mm of rainfall in 24 h occurred on the west coast of central Taiwan.

This study investigates the performance of the latest version of RegCM4 in simulating summer precipitation over South Korea, comparing nine sensitivity experiments with different combinations of convective parameterization schemes (CPSs) between land and ocean. In addition to the gross pattern of seasonal and monthly mean precipitation, the northward propagation of the intense precipitation band and statistics from extreme daily precipitation are thoroughly evaluated against gridded and in situ station observations. The comparative analysis of 10-year simulations demonstrates that no CPS shows superiority in both quantitative and qualitative aspects. Furthermore, a nontrivial discrepancy among the different observation datasets makes a robust assessment of model performance difficult. Regardless of the CPS over the ocean, the simulations with the Kain–Fritsch scheme over land show a severe dry bias, whereas the simulations with the Tiedtke scheme over land suffer from a limited accuracy in reproducing spatial distributions due to the excessive orographic precipitation. In general, the simulations with the Emanuel scheme over land are better at capturing the major characteristics of summer precipitation over South Korea, despite not all statistical metrics showing the best performance. When applying the Emanuel scheme to both land and the ocean, precipitation tends to be slightly overestimated. This deficiency can be alleviated by using either the Tiedtke or Kain–Fritsch schemes over the ocean instead. As few studies have applied and evaluated the Tiedtke and Kain–Fritsch schemes to the Korean region within the RegCM framework, and this study introduces the potential of these new CPSs compared with the more frequently selected Emanuel scheme, which is particularly beneficial to RegCM users.