Evolution Of Planetary Boundary Layer Research Articles

Retrievals of atmospheric boundary layer temperature and moisture profiles by using Atmospheric Emitted Radiance Interferometer (AERI) measurements in Shouxian

The ground-based Atmospheric Emitted Radiance Interferometer (AERI) was deployed in Shouxian, China in 2008 to measure down-welling infrared radiances with high resolution. Based on AERI observations, we propose a new method for retrieving vertical temperature and water vapor profiles in the planetary boundary layer (PBL). The method exclusively uses NCEP-2, a global reanalysis data as a first-guess profile in an iterative recursive algorithm. The PBL profiles of temperature and moisture under clear sky conditions in Shouxian have been retrieved using this new method. Compared with coincident radiosonde measurements, we find that AERI is able to obtain more accurate temperature and water vapor profiles in the PBL. The retrieval results with high temporal resolution can be used to monitor the PBL stability and evolution.

Investigation of the Planetary Boundary Layer in the Swiss Alps Using Remote Sensing and In Situ Measurements

The development of the planetary boundary layer (PBL) has been studied in a complex terrain using various remote sensing and in situ techniques. The high-altitude research station at Jungfraujoch (3,580 m a.s.l.) in the Swiss Alps lies for most of the time in the free troposphere except when it is influenced by the PBL reaching the station, especially during the summer season. A ceilometer and a wind profiler were installed at Kleine Scheidegg, a mountain pass close to Jungfraujoch, located at an altitude of 2,061 m a.s.l. Data from the ceilometer were analyzed using two different algorithms, while the signal-to-noise ratio of the wind profiler was studied to compare the retrieved PBL heights. The retrieved values from the ceilometer and wind profiler agreed well during daytime and cloud-free conditions. The results were additionally compared with the PBL height estimated by the numerical weather prediction model COSMO-2, which showed a clear underestimation of the PBL height for most of the cases but occasionally also a slight overestimation especially around noon, when the PBL showed its maximum extent. Air parcels were transported upwards by slope winds towards Jungfraujoch when the PBL was higher than 2,800 m a.s.l. during cloud-free cases. This was confirmed by the in situ aerosol measurements at Jungfraujoch with a significant increase in particle number concentration, particle light absorption and scattering coefficients when PBL-influenced air masses reached the station in the afternoon hours. The continuous aerosol in situ measurements at Jungfraujoch were clearly influenced by the local PBL development but also by long-range transport phenomena such as Saharan dust or pollution from the south.

EXPLORING THE DYNAMICS OF CAPPED INVERSION FROM SODAR DATA

The time evolution of planetary boundary layer can be studied from sodar data. Normally most of the sound wave transmitted above gets backscattered from a single inversion layer. However, during turbulent atmospheric conditions, there are multiple layers from where the signal gets backscattered with varying echo strengths. The present work describes a methodology for computer analysis of multilayered structures. Two distinct backscatter heights are extracted from observed echograms. This noisy measurement is filtered to estimate the layer heights using an a priori system model. The process and measurement noise covariances used by the filter algorithm are tuned from physical considerations to get good filter performance. Data from sodar installed at Maitree station of Antarctica with capping over an inversion layer is used to prove the concept.

A multisensor evaluation of the Asymmetric Convective Model, Version 2, in Southeast Texas

There currently exist a number of planetary boundary layer (PBL) schemes that can represent the effects of turbulence in daytime convective conditions, although these schemes remain a large source of uncertainty in meteorology and air quality model simulations. This study evaluates a recently developed combined local and nonlocal closure PBL scheme, the Asymmetric Convective Model, version 2 (ACM2), against PBL observations taken from radar wind profilers, a ground-based lidar, and multiple daytime radiosonde balloon launches. These observations were compared against predictions of PBLs from the Weather Research and Forecasting (WRF) model version 3.1 with the ACM2 PBL scheme option, and the Fifth-Generation Meteorological Model (MM5) version 3.7.3 with the Eta PBL scheme option that is currently being used to develop ozone control strategies in southeast Texas. MM5 and WRF predictions during the regulatory modeling episode were evaluated on their ability to predict the rise and fall of the PBL during daytime convective conditions across southeastern Texas. The MM5 predicted PBLs consistently underpredicted observations, and were also less than the WRF PBL predictions. The analysis reveals that the MM5 predicted a slower rising and shallower PBL not representative of the daytime urban boundary layer. Alternatively, the WRF model predicted a more accurate PBL evolution improving the root mean square error (RMSE), both temporally and spatially. The WRF model also more accurately predicted vertical profiles of temperature and moisture in the lowest 3 km of the atmosphere. Inspection of median surface temperature and moisture time-series plots revealed higher predicted surface temperatures in WRF, and more surface moisture in MM5. These could not be attributed to surface heat fluxes, and thus the differences in performance of the WRF and MM5 models are likely due to the PBL schemes. Implications: An accurate depiction of the diurnal evolution of the planetary boundary layer (PBL) is necessary for realistic air quality simulations, and for formulating effective policy. The meteorological model used to support the southeast Texas O3 attainment demonstration made predictions of the PBL that were consistently less than those found in observations. The use of the Asymmetric Convective Model, version 2 (ACM2), predicted taller PBL heights and improved model predictions. A lower predicted PBL height in an air quality model would increase precursor concentrations and change the chemical production of O3 and possibly the response to control strategies.

Evolution of planetary boundary layer under different weather conditions, and its impact on aerosol concentrations

A field experiment was conducted in Tianjin, China from September 9–30, 2010, focused on the evolution of Planetary Boundary Layer (PBL) and its impact on surface air pollutants. The experiment used three remote sensing instruments, wind profile radar (WPR), microwave radiometer (MWR) and micro-pulse lidar (MPL), to detect the vertical profiles of winds, temperature, and aerosol backscattering coefficient and to measure the vertical profiles of surface pollutants (aerosol, CO, SO2, NOx), and also collected sonic anemometers data from a 255-m meteorological tower. Based on these measurements, the evolution of the PBL was estimated. The averaged PBL height was about 1000–1300m during noon/afternoon-time, and 200–300m during night-time. The PBL height and the aerosol concentrations were anti-correlated during clear and haze conditions. The averaged maximum PBL heights were 1.08 and 1.70km while the averaged aerosol concentrations were 52 and 17μg/m3 under haze and clear sky conditions, respectively. The influence of aerosols and clouds on solar radiation was observed based on sonic anemometers data collected from the 255-m meteorological tower. The heat flux was found significantly decreased by haze (heavy pollution) or cloud, which tended to depress the development of PBL, while the repressed structure of PBL further weakened the diffusion of pollutants, leading to heavy pollution. This possible positive feedback cycle (more aerosols→lower PBL height→more aerosols) would induce an acceleration process for heavy ground pollution in megacities.

Application of Lidar Data to Assist Airmass Discrimination at the Whistler Mountaintop Observatory

AbstractA ground-based lidar system that has been deployed in Whistler, British Columbia, Canada, since the spring of 2010 provides a means of evaluating vertical aerosol structure in a mountainous environment. This information is used to help to determine when an air chemistry observatory atop Whistler Mountain (2182 m MSL) is within the free troposphere or is influenced by the valley-based planetary boundary layer (PBL). Three case studies are presented in which 1-day time series images of backscatter data from the lidar are analyzed along with concurrent meteorological and air-chemistry datasets from the mountaintop site. The cases were selected to illustrate different scenarios of diurnal PBL evolution that are expected to be common during their respective seasons. The lidar images corroborate assumptions about PBL influence as derived from analysis of diurnal trends in water vapor, condensation nuclei, and ozone. Use of all of these datasets together bolsters efforts to determine which atmospheric layer the site best represents, which is important when evaluating the provenance of air samples.

Lidar and microwave radiometer observations of planetary boundary layer structure under light wind weather

The planetary boundary layer (PBL) structures on four light wind days at Suzhou city, China were analyzed with both micropulse lidar (MPL) and passive microwave radiometer (MWR). The planetary boundary layer height (PBLH) was estimated with the first-derivation method from the lidar observations. The lidar-observed PBLH and microwave radiometer observations were used to estimate the lapse rate in a simple encroachment model. Under light wind conditions in this area, the nocturnal PBLH is about 300 to 400 m. The maximum of PBLH was about 800 to 1000 m. The daytime PBL development could be divided into three periods: growing, maintenance, and decay. The PBLH is nearly linear in the growing period with a growth ratio of about 110 to 120 m/h. The encroachment model lapse rate was calculated from the MPL and MWR observations. The lapse rate γ is estimated in the four days and the average is about 0.0010 ?startKend?/m. The vertical structure of air temperature and humidity were also analyzed with the microwave radiometer observations. Diurnal variations of relative humidity in the boundary layer partly explain the light fog appearing at night during this period.

Large‐eddy simulations of surface influences on planetary boundary layer development in southwest Western Australia

AbstractObservations from near‐simultaneous atmospheric soundings released over contrasting land surfaces in the southwest of Western Australia during December 2005 (austral summer) and August 2007 (late austral winter or early spring) have shown higher planetary boundary layer (PBL) heights over native vegetation as compared to agricultural land. The large‐eddy simulation technique is used to investigate the drivers behind these observed differences in PBL, and sensitivity tests are carried out with modified soil moisture and vegetation cover. It is shown that the differences in PBL for the December case are mainly driven by the change in vegetation cover, while a soil moisture gradient also played a role for the August case. The mixing diagram approach is used to further quantify the relative contributions of surface and entrainment fluxes on the growth of the PBL and it is shown that, while dry‐air entrainment plays an important role in PBL development, it is the higher surface Bowen ratio which drives the more vigorous PBL development over the native vegetation. It is also shown that the enhanced PBL development over the native vegetation leads to the preferential formation of shallow convective clouds for the August case. Copyright © 2012 Royal Meteorological Society

해안지형의 복잡성에 따른 해풍침투 변화가 대기경계층에 미치는 영향 분석

In order to clarify the relation between sea breeze penetration and Planetary Boundary Layer development in southeastern part of the Korean Peninsula, several numerical assessments were carried out using atmospheric numerical model WRF(Weather Research and Forecasting). Compared with onset time of sea breeze at eastern coast area(Uljin), the time at southern coast region(Masan) with complex costal line tend to delay for several hours. The penetration patterns of sea breeze between two coastal regions are some different due to the shape of their coastal line and back ground topography. Intensified valley wind due to high topography of lee side of Uljin can help penetration of sea breeze at early time. So penetration of sea breeze at early time often prevent PBL to develop at Uljin and lower PBL height last for a day time. But because of late penetration of sea breeze at Masna, PBL Height dramatically decrease after 1500LST. The distribution of front genesis function based on the heat and momentum variation are explained obviously the sea breeze penetration patterns and agreed well with the PBL height distribution.

Atmospheric Aerosol Characterization Over Naples During 2000–2003 EARLINET Project: Planetary Boundary-Layer Evolution and Layering

The evolution of the planetary boundary layer and the influence of local circulation phenomena over Naples (southern Italy, 40.838° N, 14.183° E, 118 m above sea level) have been studied by systematic lidar measurements of aerosol optical properties and vertical distributions carried out from May 2000 to August 2003, in the course of the EARLINET project. In particular, our data show the development of aerosol layers typically located in the range between 1,000 and 2,300 m, with variable thickness. The optical properties of the observed layers have been determined. In order to analyse the evolution of the planetary boundary layer, detailed observations of complete diurnal cycles have also been performed. The analysis of lidar measurements of vertical profiles of wind speed and wind direction and air mass back-trajectories allowed us to characterize the sea-breeze circulation influence on both the planetary boundary-layer evolution and the observed aerosol vertical distribution.

Sensitivity of the PBL and Precipitation in 12-Day Simulations of Warm-Season Convection Using Different Land Surface Models and Soil Wetness Conditions

Abstract A coupled land surface–atmospheric model that permits grid-resolved deep convection is used to examine linkages between land surface conditions, the planetary boundary layer (PBL), and precipitation during a 12-day warm-season period over the central United States. The period of study (9–21 June 2002) coincided with an extensive dry soil moisture anomaly over the western United States and adjacent high plains and wetter-than-normal soil conditions over parts of the Midwest. A range of possible atmospheric responses to soil wetness is diagnosed from a set of simulations that use land surface models (LSMs) of varying sophistication and initial land surface conditions of varying resolution and specificity to the period of study. Results suggest that the choice of LSM [Noah or the less sophisticated simple slab soil model (SLAB)] significantly influences the diurnal cycle of near-surface potential temperature and water vapor mixing ratio. The initial soil wetness also has a major impact on these thermodynamic variables, particularly during and immediately following the most intense phase of daytime surface heating. The soil wetness influences the daytime PBL evolution through both local and upstream surface evaporation and sensible heat fluxes, and through differences in the mesoscale vertical circulation that develops in response to horizontal gradients of the latter. Resulting differences in late afternoon PBL moist static energy and stability near the PBL top are associated with differences in subsequent late afternoon and evening precipitation in locations where the initial soil wetness differs among simulations. In contrast to the initial soil wetness, soil moisture evolution has negligible effects on the mean regional-scale thermodynamic conditions and precipitation during the 12-day period.

Aerosol Lidar observations and model calculations of the Planetary Boundary Layer evolution over Greece, during the March 2006 Total Solar Eclipse

Abstract. An investigation of the Planetary Boundary Layer (PBL) height evolution over Greece, during the solar eclipse of 29 March 2006, is presented. Ground based observations were carried out using lidar detection and ranging devices and ground meteorological instruments, to estimate the height of the mixing layer (ML) before, during and after the solar eclipse in northern and southern parts of Greece exhibiting different sun obscuration. Data demonstrate that the solar eclipse has induced a decrease of the PBL height, indicating a suppression of turbulence activity similar to that during the sunset hours. The changes in PBL height were associated with a very shallow entrainment zone, indicating a significant weakening of the penetrative convection. Heat transfer was confined to a thinner layer above the ground. The thickness of the entrainment zone exhibited its minimum during the maximum of the eclipse, demonstrative of turbulence mechanisms suppression at that time. Model estimations of the PBL evolution were additionally conducted using the Comprehensive Air Quality Model with extensions (CAMx) coupled with the Weather Research and Forecasting model (WRF). Model-diagnosed PBL height decrease during the solar eclipse due to vertical transport decay, in agreement with the experimental findings; vertical profiles of atmospheric particles and gaseous species showed an important vertical mixing attenuation.

Convective Planetary Boundary Layer Interactions with the Land Surface at Diurnal Time Scales: Diagnostics and Feedbacks

Abstract The convective planetary boundary layer (PBL) integrates surface fluxes and conditions over regional and diurnal scales. As a result, the structure and evolution of the PBL contains information directly related to land surface states. To examine the nature and magnitude of land–atmosphere coupling and the interactions and feedbacks controlling PBL development, the authors used a large sample of radiosonde observations collected at the southern Atmospheric Research Measurement Program–Great Plains Cloud and Radiation Testbed (ARM-CART) site in association with simulations of mixed-layer growth from a single-column PBL/land surface model. The model accurately predicts PBL evolution and realistically simulates thermodynamics associated with two key controls on PBL growth: atmospheric stability and soil moisture. The information content of these variables and their influence on PBL height and screen-level temperature can be characterized using statistical methods to describe PBL–land surface coupling over a wide range of conditions. Results also show that the first-order effects of land–atmosphere coupling are manifested in the control of soil moisture and stability on atmospheric demand for evapotranspiration and on the surface energy balance. Two principal land–atmosphere feedback regimes observed during soil moisture drydown periods are identified that complicate direct relationships between PBL and land surface properties, and, as a result, limit the accuracy of uncoupled land surface and traditional PBL growth models. In particular, treatments for entrainment and the role of the residual mixed layer are critical to quantifying diurnal land–atmosphere interactions.

Strong capping inversion over the Tokyo metropolitan area associated with airborne Asian dust

[1] Lidar measurements in the Tokyo metropolitan area showed that the optical thickness of airborne Asian dust rapidly increased on the morning of April 28, 2005, owing to the arrival of a thick Asian dust layer (ADL), which settled on the planetary boundary layer (PBL). Radiosonde measurements showed that atmospheric temperature in the lower troposphere increased considerably after the arrival of the ADL to the extent that the increment rate reached 12 K/day. Strong capping inversion (CI) was thus formed between the ADL and the PBL with the maximum rate of 0.1 K/m. It was mainly caused by the appearance of a deep isentropic layer that well corresponded to the ADL, indicating that the Asian dust-laden heated and well-mixed air layer led to the temperature increment and consequently induced the CI. The CI inhibited the PBL evolution and caused a higher aerosol concentration in the PBL in the metropolitan area.

Effects of Implementing MODIS Land Cover and Albedo in MM5 at Two Contrasting U.S. Regions

Abstract This study implements a new land-cover classification and surface albedo from the Moderate Resolution Imaging Spectroradiometer (MODIS) in the fifth-generation Pennsylvania State University–National Center for Atmospheric Research (PSU–NCAR) Mesoscale Model (MM5) and investigates its effects on regional near-surface atmospheric state variables as well as the planetary boundary layer evolution for two dissimilar U.S. regions. Surface parameter datasets are determined by translating the 17-category MODIS classes into the U.S. Geological Survey (USGS) and Simple Biosphere (SiB) categories available for use in MM5. Changes in land-cover specification or associated parameters affected surface wind, temperature, and humidity fields, which, in turn, resulted in perceivable alterations in the evolving structure of the planetary boundary layer. Inclusion of the MODIS albedo into the simulations enhanced these impacts further. Area-averaged comparisons with ground measurements showed remarkable improvements in near-surface temperature and humidity at both study areas when MM5 is initialized with MODIS land-cover and albedo data. Influence of both MODIS surface datasets is more significant at a semiarid location in the southwest of the United States than it is in a humid location in the mid-Atlantic region. Intense summertime surface heating at the semiarid location creates favorable conditions for strong land surface forcing. For example, when the simulations include MODIS land cover and MODIS albedo, respective error reduction rates were 6% and 11% in temperature and 2% and 2.5% in humidity in the southwest of the United States. Error reduction rates in near-surface atmospheric fields are considered important in the design of mesoscale weather simulations.

An Empirical Investigation of Convective Planetary Boundary Layer Evolution and Its Relationship with the Land Surface

Abstract Relationships among convective planetary boundary layer (PBL) evolution and land surface properties are explored using data from the Atmospheric Radiation Measurement Program Cloud and Radiation Test Bed in the southern Great Plains. Previous attempts to infer surface fluxes from observations of the PBL have been constrained by difficulties in accurately estimating and parameterizing the conservation equation and have been limited to multiday averages or small samples of daily case studies. Using radiosonde and surface flux data for June, July, and August of 1997, 1999, and 2001, a conservation approach was applied to 132 sets of daily observations. Results highlight the limitations of using this method on daily time scales caused by the diurnal variability and complexity of entrainment. A statistical investigation of the relationship among PBL and both land surface and near-surface properties that are not explicitly included in conservation methods indicates that atmospheric stability in the layer of PBL growth is the most influential variable controlling PBL development. Significant relationships between PBL height and soil moisture, 2-m potential temperature, and 2-m specific humidity are also identified through this analysis, and it is found that 76% of the variance in PBL height can be explained by observations of stability and soil water content. Using this approach, it is also possible to use limited observations of the PBL to estimate soil moisture on daily time scales without the need for detailed land surface parameterizations. In the future, the general framework that is presented may provide a means for robust estimation of near-surface soil moisture and land surface energy balance over regional scales.

Summer mistral at the exit of the Rhône valley

The paper examines the three-dimensional structure and dynamics of the mistral at the Rhône valley exit on 28 June 2001. The mistral refers to a severe wind that develops along the Rhône valley in southern France. This summer mistral event was documented in the framework of the ESCOMPTE field experiment. The dynamical processes driving the circulation of the mistral in the Rhône valley and particularly wake formation and planetary boundary layer (PBL) inhomogeneity at the scale of Rhône valley delta are investigated. Several important data sources are used (airborne Doppler lidar, radiosondes and surface stations) as well as non-hydrostatic mesoscale simulations. This paper analyses experimentally, numerically and theoretically the mechanism of wake formation. It shows that the flow impinging on the Alpine range and the Massif Central becomes supercritical all along the ridge line, including the Rhône valley and continues to accelerate in the lee regions until a hydraulic jump occurs. It leads to the formation of wakes behind and close to the mountain peaks. Compared to the Massif Central wake, the origin of the western Alps wake is rather complicated. In this study, the observations and simulations suggest a combined wall separation/gravity wave breaking mechanism to explain the western Alps wake. Indeed, it is shown that in addition to the flow descending the western Alps slopes and experiencing a strong hydraulic jump, the point where the mistral flow separates from the eastern flank of the Rhône valley located at about 44°N is associated with a ‘flank-shock’ which is an oblique hydraulic jump (i.e. the downstream Froude number is supercritical). Wake formation in the lee of the Alps and the Massif Central causes large inhomogeneity of the PBL with differences between land and sea. In the Massif Central and western Alps wakes, the continental PBL is deeper (1.8 km) than in the mistral flow (1 km), which is consistent with a subcritical regime associated with enhanced turbulent mixing. The supercritical air flow, descending the Massif Central and Alps slopes and transitioning to subcritical flow, increases the near-surface air temperature due to the föhn effect. Over the Mediterranean, the surface heat fluxes are slightly negative (between −50 and 0 W m−2) and the main source of PBL turbulence is mechanical (wind shear). The PBL depth within the mistral flow does not vary over land (1 km), whereas the absence of convection but also of strong winds prevent PBL development over the sea in the wakes of the Massif Central and the Alps (PBL depth of about 0.5 km). Copyright © 2005 Royal Meteorological Society

PBL Stratiform Cloud Inhomogeneities Thermally Induced by the Orography: A Parameterization for Climate Models

Abstract This paper proposes a parameterization for use in climate models of the orographic variance and associated thermal circulation's impact on the macroscopic behavior of planetary boundary layer (PBL) stratiform clouds. Orographically induced inhomogeneities in the PBL cloud field can significantly alter the area-averaged cloud-radiative properties and consequently the PBL evolution. Current climate models do not include this effect. The design of the parameterization is based on a systematic set of experiments in which a cloud system resolving model (CSRM) explicitly simulates the diurnally varying interactions between PBL clouds and the orography for a variety of configurations. Analyses of the results suggest that the orographic effect on PBL clouds is parameterizable to a large extent due to a quasi equilibrium between cloud-radiative, turbulent, and mesoscale processes. Parameterizability holds in the range of parameters for which stratiform clouds play a dominant role in the PBL dynamics (clou...

Impact of Orographically Induced Spatial Variability in PBL Stratiform Clouds on Climate Simulations

Abstract This paper examines the impact of orographically induced mesoscale heterogeneities on the macroscopic behavior of planetary boundary layer (PBL) stratiform clouds, and implements and tests a physically based parameterization of this effect in the University of California, Los Angeles (UCLA), atmospheric general circulation model (AGCM). The orographic variance and associated thermal circulations induce inhomogeneities in the cloud field that can significantly alter the PBL evolution; an effect that has been largely ignored in existing climate models. The impact of this effect on AGCM simulations is examined and the mechanisms at work are studied by analyzing a series of Cloud System Resolving Model (CSRM) simulations. Both the CSRM and AGCM results show that, in the absence of the orographic effect, the continental PBL tends to be in one of two regimes: the solid regime characterized by a cold and overcast PBL and the broken regime characterized by a low time-mean cloud incidence and a large-ampl...

Fire effects on surface‐atmosphere energy exchange in Alaskan black spruce ecosystems: Implications for feedbacks to regional climate

Although fire is crucial to the functioning and diversity of boreal forests, the second largest biome on Earth, there are few detailed studies of the effects of disturbance on surface‐atmosphere interactions in these regions. We conducted tower‐based micrometeorological measurements in summer over six recently burned black spruce stands that varied in age between 0 and 14 years. Results are presented for nonprecipitating conditions. There was an initial reduction of minimum albedo following fire from ∼0.09 to 0.06 followed by a rapid increase to 0.135 as the cover of successional vegetation increased. For clear‐sky conditions near local solar noon, the combined effects of increased surface temperature due to a reduced surface‐atmospheric coupling and albedo reduced midday net radiation by 9.3% (∼70 W m−2) for the first decade of succession. The average daily net radiation declined by 5.5%. Near noon, the relative partitioning of net radiation into ground heat flux doubled compared to nearby unburned stands, although on a daily basis the increase was only significant for the first few years following fire. Reduced net radiation, enhanced ground heat flux, and reduced Bowen ratio values following the first decade of succession could lead to a midday reduction of approximately 80 W m−2 in sensible heat flux compared to an unburned stand. Across a fire‐scar boundary, the contrast in sensible heating and roughness is sufficiently large to induce mesoscale circulations and possibly trigger convective development. Because fire scars frequently exceed 104 ha, locally cooler conditions would prevail with suppressed planetary boundary layer development. Given the abundance of fire disturbance throughout interior Alaska, these effects may contribute to the regional climate patterns.