Atmospheric Boundary Layer Temperature Research Articles

The Air‐Sea Response During Hurricane Irma's (2017) Rapid Intensification Over the Amazon‐Orinoco River Plume as Measured by Atmospheric and Oceanic Observations

AbstractHurricane Irma (2017) underwent rapid intensification (RI) while passing over the Amazon‐Orinoco River plume in the tropical Atlantic. The freshwater discharge from the plume creates a vertical salinity gradient that suppresses turbulent heat flux from the cool, ocean subsurface. The stability within the plume reduces sea surface temperature (SST) cooling and promotes energetic air‐sea fluxes. Hence, it is hypothesized that this ocean feature may have facilitated Irma's RI through favorable upper ocean conditions. This hypothesis is validated using a collection of atmospheric and oceanic observations to quantify how the ocean response influences surface flux and atmospheric boundary layer thermodynamics during Hurricane Irma's RI over the river plume. Novel aircraft‐deployed oceanic profiling floats highlight the detailed evolution of the ocean response during Irma's passage over the river plume. Analyses include quantifying the ocean response and identifying how it influenced atmospheric boundary layer temperature, moisture, and equivalent potential temperature (θE). An atmospheric boundary layer recovery analysis indicates that surface fluxes were sufficient to support the enhanced boundary layer θE (moist entropy) observed, which promotes inner‐core convection and facilitates TC intensification. The implicit influence of salinity stratification on Irma's intensity during RI is assessed using theoretical intensity frameworks. Overall, the findings suggest that the salinity stratification sustained SST during Irma's passage, which promoted energetic air‐sea fluxes that aided in boundary layer recovery and facilitated Irma's intensity during RI. Examination of the air‐sea coupling over this river plume, corresponding atmospheric boundary layer response, and feedback on TC intensity was previously absent in literature.

Shallow-cloud impact on climate and uncertainty: A simple stochastic model

AbstractShallow clouds are a major source of uncertainty in climate predictions. Several different sources of the uncertainty are possible—e.g., from different models of shallow cloud behavior, which could produce differing predictions and ensemble spread within an ensemble of models, or from inherent, natural variability of shallow clouds. Here, the latter (inherent variability) is investigated, using a simple model of radiative statistical equilibrium, with oceanic and atmospheric boundary layer temperatures,ToandTa, and with moistureqand basic cloud processes. Stochastic variability is used to generate a statistical equilibrium with climate variability. The results show that the intrinsic variability of the climate is enhanced due to the presence of shallow clouds. In particular, the on-and-off switching of cloud formation and decay is a source of additional climate variability and uncertainty, beyond the variability of a cloud-free climate. Furthermore, a sharp transition in the mean climate occurs as environmental parameters are changed, and the sharp transition in the mean is also accompanied by a substantial enhancement of climate sensitivity and uncertainty. Two viewpoints of this behavior are described, based on bifurcations and phase transitions/statistical physics. The sharp regime transitions are associated with changes in several parameters, including cloud albedo and longwave absorptivity/carbon dioxide concentration, and the climate state transitions between a partially cloudy state and a state of full cloud cover like closed-cell stratocumulus clouds. Ideas of statistical physics can provide a conceptual perspective to link the climate state transitions, increased climate uncertainty, and other related behavior.

Response of Surface Wind Divergence to Mesoscale SST Anomalies under Different Wind Conditions

Abstract The response of the atmospheric boundary layer to mesoscale sea surface temperature (SST) is often characterized by a link between wind stress divergence and downwind SST gradients. In this study, an idealized simulation representative of a storm track above a prescribed stationary SST field is examined in order to determine in which background wind conditions that relationship occurs. The SST field is composed of a midlatitude large-scale frontal zone and mesoscale SST anomalies. It is shown that the divergence of the surface wind can correlate either with the Laplacian of the atmospheric boundary layer temperature or with the downwind SST gradient. The first case corresponds to background situations of weak winds or of unstable boundary layers, and the response is in agreement with an Ekman balance adjustment in the boundary layer. The second case corresponds to background situations of stable boundary layers, and the response is in agreement with downward mixing of momentum. Concerning the divergence of the wind stress, it generally resembles downwind SST gradients for stable and unstable boundary layers, in agreement with past studies. For weak winds, a correlation with the temperature Laplacian is, however, found to some extent. In conclusion, our study reveals the importance of the large-scale wind conditions in modulating the surface atmospheric response with different responses in the divergences of surface wind and wind stress.

Evaluation of Parameterizations of Incoming Longwave Radiation in the High-Mountain Region of the Tibetan Plateau

AbstractAccurate evaluations of incoming longwave radiation (Lin) parameterization have practical implications for glacier and river runoff changes in high-mountain regions of the Tibetan Plateau (TP). To identify potential means of accurately predicting spatiotemporal variations in Lin, 13 clear-sky parameterizations combined with 10 cloud corrections for all-sky atmospheric emissivity were evaluated at five sites in high-mountain regions of the TP through temporal and spatial parameter transfer tests. Most locally calibrated parameterizations for clear-sky and all-sky conditions performed well when applied to the calibration site. The best parameterization at five sites is Dilley and O’Brien’s A model combined with Sicart et al.’s A for cloud-correction-incorporated relative humidity. The performance of parameter transferability in time is better than that in space for the same all-sky parameterizations. The performance of parameter transferability in space presents spatial discrepancies. In addition, all all-sky parameterizations show a decrease in performance with increasing altitude regardless of whether the parameters of all-sky parameterizations were recalibrated by local conditions or transferred from other study sites. This may be attributable to the difference between screen-level air temperature and the effective atmospheric boundary layer temperature and to different cloud-base heights. Nevertheless, such worse performance at higher altitudes is likely to change because of terrain, underlying surfaces, and wind systems, among other factors. The study also describes possible spatial characteristics of Lin and its driving factors by reviewing the few studies about Lin for the mountain regions of the TP.

The Time Scales of Variability of Marine Low Clouds

AbstractMultidecade global regressions of inversion strength, vertical velocity, and sea surface temperature (SST) on low cloud amount, from subdaily to multiyear time scales, refute the dominance of seasonal inversion strength on marine low cloud variability. Multiday low cloud variance averaged over the eastern Pacific and Atlantic stratocumulus regions [5 × 10−2 (cloud amount)2] is twice the subdaily variance and 5 times larger than the multimonth variance. The broad multiday band contains most (60%) of the variance, despite strong seasonal (annual) and diurnal spectral peaks. Multiday low cloud amount over the eastern tropical and midlatitude oceans is positively correlated to inversion strength, with a slope of 2%–5% K−1. Anecdotes show multiday low cloud and inversion strength anomalies propagate equatorward from midlatitudes. Previously shown correlations of low clouds to strong inversions and cool SST on monthly and longer time scales in the stratocumulus regions imply positive cloud-radiative feedbacks, with e-folding time scales of 300 days for SST and 14 days for atmospheric boundary layer temperature. On multimonth time scales, removing the effect of SST on low clouds reduces the low cloud amount explained by inversion strength by a factor of 3, but SST has a small effect at other time scales. Contrary to their positive correlation in the stratocumulus cloud decks, low clouds are anticorrelated to inversion strength over most of the tropics on daily and subdaily time scales.

Ground-based microwave temperature profilers: Potential and experimental data

Calculated (potential) and experimental parameters (accuracy, vertical resolution, and calibration) of ground-based temperature profilers are analyzed. At the moment, single-channel scanning microwave profilers (MTP-5) are widely used for atmospheric boundary layer temperature profile measurements, and multifrequency microwave radiometers (MP-3000A, RPG-HATPRO, and MICRORADCOM) are used for tropospheric temperature profiling. Data of the MICRORADCOM profiler, which operated from January 1, 2014, to January 1, 2015, in Dolgoprudny, Moscow oblast, are considered in more detail.

Influence of small-scale North Atlantic sea surface temperature patterns on the marine boundary layer and free troposphere: a study using the atmospheric ARPEGE model

A high-resolution global atmospheric model is used to investigate the influence of the representation of small-scale North Atlantic sea surface temperature (SST) patterns on the atmosphere during boreal winter. Two ensembles of forced simulations are performed and compared. In the first ensemble (HRES), the full spatial resolution of the SST is maintained while small-scale features are smoothed out in the Gulf Stream region for the second ensemble (SMTH). The model shows a reasonable climatology in term of large-scale circulation and air–sea interaction coefficient when compared to reanalyses and satellite observations, respectively. The impact of small-scale SST patterns as depicted by differences between HRES and SMTH shows a strong meso-scale local mean response in terms of surface heat fluxes, convective precipitation, and to a lesser extent cloudiness. The main mechanism behind these statistical differences is that of a simple hydrostatic pressure adjustment related to increased SST and marine atmospheric boundary layer temperature gradient along the North Atlantic SST front. The model response to small-scale SST patterns also includes remote large-scale effects: upper tropospheric winds show a decrease downstream of the eddy-driven jet maxima over the central North Atlantic, while the subtropical jet exhibits a significant northward shift in particular over the eastern Mediterranean region. Significant changes are simulated in regard to the North Atlantic storm track, such as a southward shift of the storm density off the coast of North America towards the maximum SST gradient. A storm density decrease is also depicted over Greenland and the Nordic seas while a significant increase is seen over the northern part of the Mediterranean basin. Changes in Rossby wave breaking frequencies and weather regimes spatial patterns are shown to be associated to the jets and storm track changes.

Using Surface Stations to Improve Sounding Retrievals from Hyperspectral Infrared Instruments

Having an accurate atmospheric thermodynamic state is critical for environmental research, particularly the vertical temperature and moisture profiles within the atmospheric boundary layer. This paper investigates the synergistic use of spaceborne hyperspectral infrared radiance measurement and traditional surface observation to conduct the best estimation of atmospheric temperature and water vapor profiles. Comparing the retrieval results from the original spaceborne observation stand-alone algorithm, atmospheric boundary layer temperature and moisture retrievals appear to be improved through the inclusion of the surface observation in the new developed algorithm. The statistics of retrieval performance by comparing with radiosonde observation suggest that the improvement is not only at the lowest surface level but also within the planetary boundary layer. This implies the benefit of surface observation in the atmospheric sounding retrieval algorithm, and the boundary layer thermodynamic structure could be retrieved optimally from the use of both spaceborne and ground-based observations.

Study of liquid water in clouds with the “Microradkom” radiometric system

Results of the study of liquid water in thin clouds and mist with the multichannel microwave radiometric system “Microradkom” are presented in the paper. The system includes four microwave radiometers: multichannel with frequencies of 53–58 GHz (temperature profiling in troposphere); one-channel scanning with a frequency of 56.6 GHz (profiling of atmospheric boundary layer temperature); one-channel radiometer with a frequency of 22.235 GHz (reduced sensitivity of 0.04 K for measurements of the integral water vapor); one-channel radiometer with a frequency of 37.5 GHz (reduced sensitivity of 0.02 K for measurements of the integral liquid water), and automated meteorological station and video system for cloud observations. Measurements were conducted in Dolgoprudny, Moscow oblast, from February, 2012, to January, 2014.

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.

Observations of atmospheric boundary layer temperature profiles with a small unmanned aerial vehicle

AbstractSmall Unmanned Meteorological Observer (SUMO) unmanned aerial vehicles (UAVs) were used to observe atmospheric boundary layer temperature profiles in the vicinity of McMurdo Station, Antarctica during January and September 2012. The observations from four flight days are shown and exhibit a variety of boundary layer temperature profiles ranging from deep, well-mixed conditions to strong, shallow inversions. Repeat UAV profiles over short periods of time (tens of minutes to several hours) revealed rapid changes in boundary layer structure. The success of the SUMO flights described here demonstrates the potential for using small UAVs for Antarctic research.

CheapAML: A Simple, Atmospheric Boundary Layer Model for Use in Ocean-Only Model Calculations

Abstract A model of the marine atmospheric boundary layer is developed for ocean-only modeling in order to better represent air–sea exchanges. This model computes the evolution of the atmospheric boundary layer temperature and humidity using a prescribed wind field. These quantities react to the underlying ocean through turbulent and radiative fluxes. With two examples, the authors illustrate that this formulation is accurate for regional and global modeling purposes and that turbulent fluxes are well reproduced in test cases when compared to reanalysis products. The model builds upon and is an extension of Seager et al.

The Diurnal Behavior of Evaporative Fraction in the Soil–Vegetation–Atmospheric Boundary Layer Continuum

AbstractThe components of the land surface energy balance respond to periodic incoming radiation forcing with different amplitude and phase characteristics. Evaporative fraction (EF), the ratio of latent heat to available energy at the land surface, supposedly isolates surface control (soil moisture and vegetation) from radiation and turbulent factors. EF is thus supposed to be a diagnostic of the surface energy balance that is constant or self-preserved during daytime. If this holds, EF can be an effective way to estimate surface characteristics from temperature and energy flux measurements. Evidence for EF diurnal self-preservation is based on limited-duration field measurements. The daytime EF self-preservation using both long-term measurements and a model of the soil–vegetation–atmosphere continuum is reexamined here. It is demonstrated that EF is rarely constant and that its temporal power spectrum is wide; thus emphasizing the role of all diurnal frequencies associated with reduced predictability in its daylight response. Oppositely, surface turbulent heat fluxes are characterized by a strong response to the principal daily frequencies (daily and semi-daily) of the solar radiative forcing. It is shown that the phase lag and bias between the turbulent flux components of the surface energy balance are key to the shape of the daytime EF. Therefore, an understanding of the physical factors that affect the phase lag and bias in the response of the components of the surface energy balance to periodic radiative forcing is needed. A linearized model of the soil–vegetation–atmosphere continuum is used that can be solved in terms of harmonics to explore the physical factors that determine the phase characteristics. The dependency of these phase and offsets on environmental parameters—friction velocity, water availability, solar radiation intensity, relative humidity, and boundary layer entrainment—is then analyzed using the model that solves the dynamics of subsurface and atmospheric boundary layer temperatures and heat fluxes in a continuum. Additionally, the asymptotical diurnal lower limit of EF is derived as a function of these surface parameters and shown to be an important indicator of the self-preservation value when the conditions (also identified) for such behavior are present.

The International polar year (IPY) circumpolar flaw lead (CFL) system study: Overview and the physical system

The Circumpolar Flaw Lead (CFL) system study is a Canadian‐led International Polar Year (IPY) initiative with over 350 participants from 27 countries. The study is multidisciplinary in nature, integrating physical sciences, biological sciences and Inuvialuit traditional knowledge. The CFL study is designed to investigate the importance of changing climate processes in the flaw lead system of the northern hemisphere on the physical, biogeochemical and biological components of the Arctic marine system. The circumpolar flaw lead is a perennial characteristic of the Arctic throughout the winter season and forms when the mobile multi‐year (MY) pack ice moves away from coastal fast ice, creating recurrent and interconnected polynyas in the Norwegian, Icelandic, North American and Siberian sectors of the Arctic. The CFL study was 293 days in duration and involved the overwintering of the Canadian research icebreaker CCGS Amundsen in the Cape Bathurst flaw lead throughout the annual sea‐ice cycle of 2007–2008. In this paper we provide an introduction to the CFL project and then use preliminary data from the field season to describe the physical flaw lead system, as observed during the CFL overwintering project. Preliminary data show that ocean circulation is affected by eddy propagation into Amundsen Gulf (AG). Upwelling features arising along the ice edge and along abrupt topography are also detected and identified as important processes that bring nutrient rich waters up to the euphotic zone. Analysis of sea‐ice relative vorticity and sea‐ice area by ice type in the AG during the CFL study illustrates increased variability in ice vorticity in late autumn 2007 and an increase in new and young ice areas in the AG during winter. Analysis of atmospheric data show that a strong northeast–southwest pressure gradient present over the AG in autumn may be a synoptic‐scale atmospheric response to sensible and latent heat fluxes arising from areas of open water persisting into late November 2007. The median atmospheric boundary layer temperature profile over the Cape Bathurst flaw lead during the winter season was stable but much less so when compared to Russian ice island stations.

Effective atmospheric boundary layer temperature from longwave radiation measurements

The atmospheric boundary layer (ABL) temperature is derived from concurrent measurements of two pyrgeometers, one standard pyrgeometer sensitive to the 3–50 μm wavelength range and one modified pyrgeometer sensitive only in the atmospheric window from 8–14 μm. By combining the measurements from the two instruments we retrieve the effective ABL temperature from the radiation emitted by the atmospheric water vapor contained in the atmospheric boundary layer. Measurements from five sites in Switzerland are analyzed, and salient features of the effective ABL temperature and its seasonal and diurnal variability are discussed. The measurements at Davos, Payerne, Zimmerwald, and Locarno‐Monti show a stable inversion layer during the night and the transition to a convective state during daylight, while at Jungfraujoch no systematic features of the effective ABL temperature are detected because of its locations on a high mountain ridge. The four lower‐altitude sites also show distinct diurnal and seasonal patterns of the ABL temperature with respect to 2 m air temperature. The largest inversion situations occur in winter at Davos, with ABL temperatures on average 5.6 K higher than the 2 m air temperatures. The amplitude of ABL variability is also largest at Davos in winter, with an average diurnal variation of 4.1 K between the early morning and the afternoon. Estimates of clear‐sky longwave downward emissions obtained by using a parametrization with the Brutsaert formula can be noticeably improved by using the effective ABL temperature instead of the 2 m air temperature.

Aerosol impact and correction on temperature profile retrieval from MODIS

Aerosols over desert areas can impact the temperature profile retrieval using infrared remote sensing techniques. Retrievals from Moderate Resolution Imaging Spectroradiometer (MODIS) Infrared (IR) radiances over the Gobi region in China show that atmospheric temperatures above the top of the boundary layer can be retrieved with a root mean square error (rmse) better than 2 K. In the boundary layer, the error in the temperature retrieval is largely due to limited spectral information and uncertainty of the radiative transfer model. The error in the retrieved atmospheric boundary layer temperature is positively correlated with aerosol optical depth (AOD) and estimated errors of skin temperature and surface IR emissivities. Taking into account the aerosol effect in the radiative transfer model, the temperature retrievals from MODIS are improved by approximately 0.38 K in the boundary layer depending on the aerosol optical depth (AOD).

Satellite remote sounding of atmospheric boundary layer temperature inversions over the subtropical eastern Pacific

We describe atmospheric temperature inversions and height‐resolved water vapor fields over the wintertime subtropical northeastern Pacific Ocean in observations by the satellite‐borne Atmospheric Infrared Sounder (AIRS) experiment. A comparison with model analyses shows good agreement in temperature. Water vapor comparisons with operational radiosondes at four sites in California and Hawaii during December 2002–January 2003 have low biases in the 1000–700 and 700–500 hPa layers. Maps of inversion frequency, and, water vapor at 1000–700 and 700–500 hPa over the subtropical northeast Pacific during 1–16 January 2003–when high pressure and clear conditions prevail–show inversions occurring at a local minimum in water vapor at 1000–700 hPa. Water vapor at 700–500 hPa has a broad minimum extending from Baja California to Hawaii, with inversions found on its eastern half. These observations illustrate the potential of the AIRS data for describing a climatology of temperature and water vapor in subtropical oceanic regions.

Investigation of atmospheric boundary layer temperature, turbulence, and wind parameters on the basis of passive microwave remote sensing

The MTP‐5, a microwave temperature profiler, has been widely used since 1991 for investigation of the atmospheric boundary layer (ABL). The MTP‐5 is an angular scanning single‐channel instrument with a central frequency of about 60 GHz, designed to provide continuous, unattended observations. It can measure the thermal emission of the atmosphere with high sensitivity (0.03 K at 1 s integration time) from different zenith angles. On the basis of this measurement, it is possible to retrieve temperature profiles at the altitude range up to 600 m, to calculate wind speed and wind direction at the lowest 250 m, and to get information about some parameters of atmospheric turbulence. This report presents some applications of the MTP‐5 instrument data collected in 1998–2001 within a number of international field projects: the dynamics of ABL temperature inversion in a mountain valley (Mesoscale Alpine Program (MAP)), as well as along an island coast (north part of Sakhalin Island, Russia‐Japan Project); continuous measurements of the ABL temperature profile provided from a special scientific train that crossed the territory of Russia (the Transcontinental Observations of the Chemistry of the Atmosphere Project (TROICA)); and simultaneous measurements of the ABL temperature profile provided over the central and northern part of Moscow in a continuous mode (the Global Urban Research Meteorology and Environment Project (GURME)). In 1999, two MTP‐5 instruments were installed on a platform that was rotating in the azimuth direction at the 310 m Obninsk Meteorological Research Tower (Meteo Tower) to validate the method and microwave equipment for measurement of wind speed and wind direction and investigation of atmospheric turbulence. Spectral analyses of the integrated signal provided an opportunity to estimate the inertial subrange low‐frequency limit and its height dependence for thermal turbulence at the lowest 200 m layer. Wavelet analysis of the signal made it possible to determine the convective thermic and other coherent structures; also to estimate energy and to provide visualization of the transformation processes of those structures during changing ABL stability. For a wide spectrum of ABL models the integrated character of radiometric data is more representative than in situ data. The measurement cycle for main wind is about 45 min, with an accuracy of about 1–2 m/s for wind speed and 10–20° for wind direction. Measurements at different levels of the Meteo Tower of vertical wind speed were in good agreement with in situ data. The possibility of manufacturing the microwave instrument for simultaneous measurements of the temperature profile and wind parameters in the ABL will be also discussed in this report.