Regional Rain Research Articles

Tropical Inversions near the 0°C Level

Abstract Soundings taken from the tropical western Pacific warm pool region during TOGA COARE reveal the common occurrence of temperature and moisture perturbations near the 0°C level. The perturbations frequently are characterized by shallow layers of increased stability (or occasionally temperature inversions) and reversals or inflections in the vertical profile of specific humidity. Similar temperature and moisture inversions have been observed elsewhere in the Tropics and midlatitudes but have not received much attention. Isothermal layers are known to exist just below the melting level in stratiform rain regions; however, not all stable layers observed over the warm pool are confined to precipitation systems. The perturbation in the specific humidity profile accounts for the often-observed double-peak structure in the apparent moisture sink Q2 in tie Tropics. Stratification of the data based on relative humidity criteria indicates that the stable layers near the 0°C level generally fall into two main...

A Class of Single- and Dual-Frequency Algorithms for Rain-Rate Profiling from a Spaceborne Radar. Part II: Tests from Airborne Radar Measurements

Abstract In Part I, four single-frequency (SF) algorithms and a dual-frequency (DF) algorithm for range profiling of the rain rate from a spaceborne radar were described and tested from numerical simulations. In Part II, performances of these algorithms are studied using data from a DF (X and Ka bands) near-nadir-pointing airborne radar. The data, gathered over ocean near Wallops Island in 1988, mimic future spaceborne radar measurements. Rain retrievals are performed for isolated and series of contiguous rain measurements within stratiform and convective rain regions overflown by the aircraft. General features and aspects specific to the experiment conditions are pointed out. The SF algorithms provide more or less scattered results according to their own sensitivities to uncorrected scaling errors. Improvement of the algorithms stability by constraining the total path-integrated attenuation from surface echo measurements is confirmed. The correlation between attenuation coefficients at both frequencies, ...

The Guinea–Congo lowland rain forest: an overview

In a paper entitled ‘Africa – the odd man out’ Richards (1973) pointed out that of the three main regions of tropical rain forest he recognised, namely American, African and Indo–Malaysian, the African rain forest stands out as distinct from the others. He took this view largely on the comparative poverty of its flora, the wider distribution of African plants, and the poor representation of certain plant groups such as palms, orchids and trees of the family Lauraceae. In addition, Africa is relatively poorly endowed with some life forms such as lianes and epiphytes. He attributed the uniqueness of tropical Africa to a number of possible factors. In the first place, differences may be due to climate since the uniformly high rainfall, humidity, temperatures, and absence of a regular dry season that occur in parts of the other two tropical regions are evidently rare or lacking in Africa. A distinct dry season, often of over two months, is nearly always present, and even in the central Congo basin there is usually at least one month when rainfall is less than 100 mm. Secondly, the impact of human beings on vegetation has been longer and more sustained in Africa than elsewhere, so much so that the presence of any truly primeval or so-called virgin forest is very questionable. However, it is unlikely that present day climatic factors and human interference can wholly account for the unique position of African rain forest, and historical reasons must also be sought. Thus it seems probable that the vicissitudes of climate, recorded as arid and pluvial periods in African lake sediments, have been much greater than those in the other two regions in question.

Cloud observations with a polarimetric 33 GHz and 95 GHz radar

The University of Massachusetts' Microwave Remote Sensing Laboratory (MIRSL) has developed a unique high spatial resolution multiparameter radar under sponsorship from the Department of Energy's Atmospheric Radiation Measurement (ARM) program. The Cloud Profiling Radar System (CPRS) uses a single one-meter diameter dielectric lens antenna to make collocated polarimetric and Doppler measurements at both 33 GHz and 95 GHz. The polarization of each transmitted pulse at either frequency can be selected on a pulse-to-pulse basis. The radar and supporting hardware are mounted on a truck that serves as a mobile laboratory. The truck-based platform permits CPRS to operate in remote locations and also serves as an economical means of transporting the system. This paper describes the CPRS hardware and presents preliminary vertically pointing observations of mixed-phase stratus clouds obtained in the summer of 1993 during the first field test of the system. Measurements show Mie scattering in the ice region, melting layer and rain region of the clouds observed. To illustrate CPRS potential for particle sizing, models of differential reflectivity and differential mean Doppler velocity are used to estimate median volume diameter,D 0, from dual-wavelength reflectivity and Doppler measurments of rain.

Long-range movements of small mammals in arid Australia: implications for land management

This study investigated movements of seven species of small mammals at study areas in arid Western Australia and Queensland. Populations of all species fluctuated dramatically in abundance over time, with the recapture rate for individuals averaging at a low 11.3%. Mean long-distance movements ranged from 1.04 km in the marsupial Sminthopsis hirtipes to 6.34 km in the native rodent Pseudomys hermannsburgensis ; the maximum distance recorded was 14 km. Long-range movements occurred independently of sex, age and reproductive status in all species, but tended to increase during or after rain in the study regions. Individuals moved toward areas of rainfall, probably because rains produce local increases in food resources. We suggest that long-range movements are crucial in allowing small mammals to exploit both permanent and ephemeral refugia of increased productivity, hence facilitating long-term persistence in regional areas. Although protection of fixed refugia can be achieved by land reservation, conservation goals for small mammals and other biota will be met more realistically by improving land management throughout the arid zone with the involvement and cooperation of all land users.

Pervasive small‐scale enhancements in mantle and polar rain precipitation

Short duration bursts—1–3 s or 0.05–0.15° MLAT—of 32 eV to several hundred eV electrons are regularly observed in the polar rain and mantle precipitation regions by the DMSP satellites. The spacing between bursts is typically 9–12 s (70–90 km) and is sometimes regular but more often irregular. Sometimes quasi‐periodic trains of 4 or 5 evenly spaced bursts occur. Electron spectra in the bursts are variable, but typically represent an enhancement of an order of magnitude in the spectral differential energy flux, but without showing signs of field‐aligned acceleration. Previous reports of bursty polar cap precipitation consisted of precipitation with large scale (hundreds of km) spatial inhomogeneity of plasma sheet origin under northward IMF conditions. The bursts described herein occur for southward as well as northward IMF Bz, and represent fine structure (7.5 km) within regions that are of magnetosheath origin and which are homogenous over larger spatial scales (>∼100 km). We suggest that the observed phenomena may be related to the nonstationary processes in the outer high latitude magnetosphere.

Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rainfall in tropical regions

Computation of attenuation, phase rotation, and cross-polarization of radio waves due to rain in tropical regions using finite element method is the subject of this work. Computations are made of the forward-scattering amplitudes of oblate spheroidal raindrops at 20 and 30 GHz, assuming plane waves at normal incidence to the raindrop axis. The forward-scattering amplitudes are employed to obtain the required attenuation, phase rotation, and cross-polarization using the rainfall rate data for Nigeria, a tropical African country. The results obtained in this work compare with those existing in the open literature.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

MOISTURE TRAJECTORIES ASSOCIATED WITH HEAVY RAINFALL IN THE APPALACHIAN REGION OF THE UNITED STATES

Synoptic data associated with a sample of 554 heavy rainfall events is utilized to carry out a trajectory analysis that identifies the movements of moisture towards regions of heavy rain. Both seasonal and regional variations are found in the moisture trajectories associated with heavy rain events occurring in three regions in the Appalachian study area. Numerous events in the region west of the mountain range are tied to westerly and south-southwesterly circulations that bring moisture from the Mississippi River Valley and the Gulf of Mexico during the warm and cool seasons, respectively. Many events southeast of the mountain range are associated with southerly to southeasterly circulations that advect moisture from the Atlantic Ocean. Because of orographic precipitation enhancement and a good exposure to the Gulf of Mexico and the Atlantic Ocean, the southern and southeastern slopes of the Appalachian mountains display high frequencies of heavy rainfall, particularly during the cool season. The interior...

A Numerical Study of the Genesis of Extratropical Convective Mesovortices. Part I: Evolution and Dynamics

Abstract The purpose of this study is to understand the genesis of extratropical convective mesovortices and the large-scale environmental features that influence the vortex formation. A hypothesis is proposed that mesovortices form in the stratiform rain regions of mesoscale convective systems (MCSs) due to the reduction of static stability that reduces the effective local Rossby radius in such regions. A conceptual model of the mesoscale convective cyclogenesis is introduced, which describes the three stages of the mesovortex formation. A modified version of the Pennsylvania State University/National Center for Atmospheric Research three-dimensional hydrostatic mesoscale model is used to simulate mesovortex genesis in analytically generated pre-MCS large-scale environments. The model simultaneously incorporates parameterized convection and a grid-resolvable convective scheme containing the effects of hydrostatic water loading, condensation (evaporation), freezing (melting), and sublimation. A control si...

The Form of Cyclonic Precipitation and Its Thermal Impact

A two-dimensional, parameterized kinematic cloud microphysics model is described and used to simulate the form of cyclonic precipitation and its thermal impact in three idealized situations. The first situation represents a strong, warm, or stationary front with a zone of freezing rain and ice pellets separating regions of rain and snow. The second represents a storm with initial surface temperatures slightly above 0°C, and in which precipitation at the ground changes from rain to snow as a result of cooling by melting and evaporation of hydrometeors. The third represents a shallow cloud in a sounding with all temperatures below0°C that initially produces freezing drizzle before a change to snow or ice pellets.

Multigigabit transmission through rain in a dual polarization frequency reuse system: an experimental study

An experimental terrestrial link was set up for the purpose of evaluating very-high-data-rate communications in dual-polarization frequency reuse systems. Possible applications are in the field of satellite communications. Two 3.2-Gb/s signals using staggered quadriphase shift keying (SQPSK) were transmitted on opposite senses of circular polarization over a 7-km path located in Crane rain region D3. Performance degradation of the demodulator as a function of cross-polarization discrimination (XPD) was evaluated and found to closely match simulation predictions. However, the relationship between XPD and rain attenuation was found to be more complex than thought previously, displaying a relatively slowly varying hysteresis effect as well as significant interactions with characteristics of the receive antenna. The latter effect suggests that careful control of antenna characteristics may be required if such high-data-rate techniques are to be employed in space-ground links. >

The transport and redistribution of atmospheric gases in regions of frontal rain

Gases emitted in the planetary boundary layer can be transported very efficiently to the free troposphere through vertical motion along a frontal surface. A mesoscale numerical model was used to simulate the vertical transport of a tracer by clouds during frontogenesis in a moist atmosphere (an evolving Eady wave) in order to illustrate such vertical transport conditions. It is shown that the efficient vertical transport of a tracer occurs only when clouds are present, either when a surface or an in-situ source is considered. Insoluble, partially soluble, and soluble tracers are studied in order to determine the relative importance of vertical transport and scavenging on their redistribution.

Mid-miocene post-disturbance vegetation dynamics and the emergence of cold desert/steppe vegetation in the northern intermountain region

The mesic broad-leaved and coniferous forests of the Middle Miocene of the northern Intermountain region of the United States contrast strongly with the semi-arid shrub/grassland steppe vegetation that comprises the extant vegetation. This contrast is a consequence of the progressive development of a regional rain shadow, beginning in the Late Miocene, coincident with the uplift of the Cascades to the west. It is generally assumed that the emergence of the extant vegetation was a consequence of a combination of in situ evolution of taxa in response to moisture and thermal stress and the immigration of taxa already adapted to such stressful environments. The study of stratigraphically sequential successional vegetation stages in a number of Middle Miocene floras in the northern Great Basin suggest that many elements of the extant vegetation of the region were already present as taxa adapted to the several characteristic environmental conditions of landscapes affected by volcanic disturbance.The Middle Miocene “climax” vegetation of southeastern Oregon and southwestern and southcentral Idaho, documented by paleobotanical and palynological data from floras such as Stinking Water (Oregon), Succor Creek (Oregon-Idaho), and Trapper Creek (Idaho), was a complex mosaic of vegetation types comprised of broad-leaved evergreen, mixed mesophytic, and mixed coniferous forest elements. These floras are preserved in volcaniclastic sediments. Palynological analysis of sequential samples from overlying strata indicate that the bulk of the sedimentary record at each of these sites records vegetation in varying stages of recovery following destruction of forests by local volcanism. The earliest seral stages following such events are characterized by taxa, including Artemisia, Sarcobatus, and other Malvaceae, Chenopodiaceae, Amaranthaceae, Compositae, and Gramineae that represent important components of the extant vegetation of the region.An ash-covered landscape, denuded of forest cover, is a highly stressful environment. Ash forms an edaphically dry and nutrient-poor substrate and such sites would be exposed to a significantly greater range of annual temperatures and much greater exposure than forested sites. Grasses, forbs, and shrubs that evolved in ways that permitted the colonization of such landscapes would be preadapted to the drier and less equable climates that would accompany the development of the Cascadian rain shadow. In addition, such successional areas also supported a mammalian fauna dominated by grazers in contrast to the browsing-dominated fauna of the climax forest mosaic. It would thus appear that the post-disturbance grass/forb/shrub communities provided an evolutionary proving ground for mammalian niches that now dominate the extant cold desert/steppe biome.

Transpolar auroras, their particle precipitation, and IMF By component

Transpolar auroras, their associated particle precipitation, and their occurrence with respect to the IMF By polarity are examined on the basis of DMSP F6 auroral images and the corresponding particle data. It is found that the transpolar arcs are located in the poleward edge of the soft particle precipitation region extending from either the dawn or dusk part of the auroral oval precipitation; they are not embedded in the polar rain region. This finding suggests that the transpolar arcs are located along the poleward boundary of the closed field line region (or the equatorward boundary of the open region) as suggested by Meng (1981). Further, the appearance of the extended precipitation region from the oval depends on the polarity of the IMF By, in the northern hemisphere morning sector for IMF By &lt; 0 or in the evening sector for IMF By &gt; 0. In general, the precipitating particle flux in the extended precipitation region is not high enough to produce appreciable luminosity. Thus only the transpolar arcs (associated with relatively intense precipitation) near the poleward boundary tend to become much more luminous, forming the so‐called “theta aurora.”

Mercury dispersal in water, sediments and aquatic biota of a gold mining tailing deposit drainage in pocone, Brazil

In the Pocone district, Brazil, Hg distribution was studied in a small watershed which drains tailings from a 10 yr old gold mining operation. Heavy regional rains are responsible for continuous weathering, thereby making it possible to transport Hg into the ecologically important Pantanal area. Mercury concentrations in creek sediments range from < 0.02 to 0.18 mg. kg−1. The highest concentrations occur close to the tailings deposit. Mercury concentrations in the water were always below the detection limit of the analytical method used (<0.04 µg. L−1). Suspended matter samples collected before, during and after a storm, showed a Hg peak value of 0.61 mg kg−1. about 30 min after the event. Dissolved Hg concentration still fell below the detection limit. Among the biota, molluscs accumulated moderately high concentrations of Hg, while macrophytes and fish did not. Mercury concentrations in molluscs were dependent on size, with larger animals presenting higher Hg concentration. We conclude that Hg present in the tailings shows low mobility and that its eventual transport into the drainage system is dependent on the erosion of fine material from the wastes during rains, resulting in a restricted contamination of the area and low Hg concentration in the biota.

Modern Pollen Rain in the Southeast Missouri Ozarks

-Bryophytic polsters and surface samples were collected from four sites in Shannon and Carter counties in the SE Missouri.Ozarks to determine modern pollen rain. Regional pollen rain and variation in the local pollen rain are reflected by modern pollen spectra. Regional pollen rain was calculated by averaging the percentages of the various taxa in the pollen spectra from the 10 samples collected. In this area the average regional pollen rain is dominated by Pinus (18.5), Quercus (51.5), Carya (4.4) and Ambrosia (8.7). The data are consistent with the mosaic of pine-oak and oak-hickory-pine forests characteristic of this region.

Modelling attenuation by rain in tropical regions

AbstractThe data in the CCIR data banks were employed for a statistical study of the relative performance of several rain attenuation prediction procedures in temperate and tropical regions. The results show that the models worked well, in general, when used for prediction at latitudes more than 30° from the equator, but, in the equatorial region, significant prediction errors were observed for all the models. Three sources of error were discovered. The most important is the use of too few rain climate zones to span the wide range of rain conditions present in the equatorial region. The second is an inadequate procedure for taking the naturally occurring vertical variations of specific attenuation into account. Finally, for the CCIR attenuation prediction model, the use of a universal shape for the cumulative distribution of path attenuation must be called into question.

Studies on the causes of forest decline in Nanshan, Chongqing

Nanshan is located in the south suburb of Chongqing, Sichuan province in China. It is about 10 km from the city of Chongqing. There are about 2000 ha of forest, mainly Masson pines (Pinus massoniana Lamb) which have exhibited decline since the beginning of the 1980s. Surveys of stands estimated that 85% of Masson pines are injured. Symptomology of Masson pines includes tip necrosis of needles, thin crown, reduced needle length, premature abscission, branch dieback, reduced radial growth. The foliage of broadleaf treesRobinia pseudoacacia L,Quercus dentata Thunb,Eucalyptus robusta Sm,Erythrina variegata var. orientalis (L) Merr,Faulownia fortunei (Seem) Hemsl,Rosa chinensis Jacq, also displayed necrotic lesions, both marginal and interveinous, most are brown or bleached. Foliage symptoms are similar to that produced in laboratory fumigation experiments with gaseous air pollutants SO2 or HF. The foliage injury intensity is related to the distance from the city. Forest in some localities furthest from the city exhibit approximately normal growth.Three monitoring sites had been selected in Nanshan forest area. At two sites pine trees were severely damaged. At another site they showed little damage. Atmospheric SO2 and fluoride concentrations had been examined. The average value of SO2 and fluoride concentrations at the two former sites were much higher than that at the latter site. The injury intensity was consistent with an increase in the concentrations of SO2 and fluoride. The sulphur and fluoride contents of tree leaves were also monitored. Sulphur contents of pine needles at the two former sites were generally more than that at the latter. The same tendency is observed in broadleaf trees. Higher levels of fluoride had been found in foliage of injured trees compared to unijured trees.Chongqing is also an acid rain region. The yearly average pH value of precipitation approaches to 4.0, and the frequency 100%. The pH values of acid rain at the three sites in Nanshan region are 4.17, 4.20, and 4.38 respectively. The difference is not significant. Also no significant difference in soil pH among the three sites is observed. It is suggested that acid rain and the acidification of soil are not implicated in the decline of Masson pines in Nanshan region.

Mesoscale Organization of Springtime Rainstorms in Oklahoma

Abstract Radar reflectivity and raingage data obtained during six springtimes indicate the types of mesoscale organization that occur in association with major rain events in Oklahoma (at least 25 mm of rain in 24 h over an area exceeding 12 500 km2). In these storms the primary rain area is found to be a contiguous region of precipitation 10s to 100s of km in scale that consists partly of deep convection and partly of stratiform rain. The patterns of rain formed by the convective and stratiform areas comprise a continuous spectrum of mesoscale structures. About two-thirds of the cases examined exhibited variations on the type of organization in which convective cells arranged in a moving line are followed by a region of stratiform rain. Storm organization was graded according to the degree to which it matched an idealized model of this “leading-line/trailing-stratiform” structure. The precipitation pattern was further graded according to whether its structure was relatively symmetric with respect to an a...

Airflow patterns in two mesoscale convective systems

Single Doppler observations from an operational 5-cm radar of two mesoscale convective systems show mesoscale kinematic structures of the order of tens of kilometers. Two cases observed during routine operational scanning illustrate the presence of various low-level jets and their relationship with precipitation. One case illustrates dual rear jets associated with a mesoscale convective system (MCS) observed on 17 July 1986. The MCS developed on a wave along a warm front and was in steady state for much of the observation period. This wave was not resolvable in the synoptic data. Primary features were a leading narrow convective rain band 20 km in width, a low reflectivity transition zone 30 km in width, with a trailing region of rain which included a bright band at a height of 4 km. From the operational PPI radial velocity images, the patterns showed three-dimensional kinematic structure which included a mid-tropospheric rearward flow and two “dry” rear inflow jets. These jets were deduced to flow toward the rear of the convective band and then diverge with one descending anti-cyclonically and the other ascending cyclonically. These jets were below the bright band found in the trailing rain region. A “warm” cross-flow was also observed ahead of the convective line. A second case illustrates a MCS that evolved much more rapidly. The presence of the rear jet preceded the full development of the trailing rain region. These two MCS cases illustrate not only the complex three-dimensional structure of these systems which are very difficult to interpret for the operational nowcaster but also the mesoscale analogy to the conveyor-belt model of synoptic precipitation systems.