scholarly journals The 2009–2010 Arctic polar stratospheric cloud season: a CALIPSO perspective

2011 ◽  
Vol 11 (5) ◽  
pp. 2161-2177 ◽  
Author(s):  
M. C. Pitts ◽  
L. R. Poole ◽  
A. Dörnbrack ◽  
L. W. Thomason
Keyword(s):  
Cold Pool ◽  
Second Phase ◽  
Number Density ◽  
Synoptic Scale ◽  
Mountain Wave ◽  
Ice Clouds ◽  
Lower Altitude ◽  
Early Season ◽  
Frost Point ◽  
Polar Stratospheric Cloud

Abstract. Spaceborne lidar measurements from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) are used to provide a vortex-wide perspective of the 2009–2010 Arctic PSC (polar stratospheric cloud) season to complement more focused measurements from the European Union RECONCILE (reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) field campaign. The 2009–2010 Arctic winter was unusually cold at stratospheric levels from mid-December 2009 until the end of January 2010, and was one of only a few winters from the past fifty-two years with synoptic-scale regions of temperatures below the frost point. More PSCs were observed by CALIPSO during the 2009–2010 Arctic winter than in the previous three Arctic seasons combined. In particular, there were significantly more observations of high number density NAT (nitric acid trihydrate) mixtures (referred to as Mix 2-enh) and ice PSCs. We found that the 2009–2010 season could roughly be divided into four periods with distinctly different PSC optical characteristics. The early season (15–30 December 2009) was characterized by patchy, tenuous PSCs, primarily low number density liquid/NAT mixtures. No ice clouds were observed by CALIPSO during this early phase, suggesting that these early season NAT clouds were formed through a non-ice nucleation mechanism. The second phase of the season (31 December 2009–14 January 2010) was characterized by frequent mountain wave ice clouds that nucleated widespread NAT particles throughout the vortex, including Mix 2-enh. The third phase of the season (15–21 January 2010) was characterized by synoptic-scale temperatures below the frost point which led to a rare outbreak of widespread ice clouds. The fourth phase of the season (22–28 January) was characterized by a major stratospheric warming that distorted the vortex, displacing the cold pool from the vortex center. This final phase was dominated by STS (supercooled ternary solution) PSCs, although NAT particles may have been present in low number densities, but were masked by the more abundant STS droplets at colder temperatures. We also found distinct variations in the relative proportion of PSCs in each composition class with altitude over the course of the 2009–2010 Arctic season. Lower number density liquid/NAT mixtures were most frequently observed in the lower altitude regions of the clouds (below ~18–20 km), which is consistent with CALIPSO observations in the Antarctic. Higher number density liquid/NAT mixtures, especially Mix 2-enh, were most frequently observed at altitudes above 18–20 km, primarily downstream of wave ice clouds. This pattern is consistent with the conceptual model whereby low number density, large NAT particles are precipitated from higher number density NAT clouds (i.e. mother clouds) that are nucleated downstream of mountain wave ice clouds.

scholarly journals The 2009–2010 Arctic polar stratospheric cloud season: a CALIPSO perspective

2010 ◽  
Vol 10 (10) ◽  
pp. 24205-24243 ◽  
Author(s):  
M. C. Pitts ◽  
L. R. Poole ◽  
A. Dörnbrack ◽  
L. W. Thomason
Keyword(s):  
Cold Pool ◽  
Second Phase ◽  
Vortex Center ◽  
Number Density ◽  
Synoptic Scale ◽  
Mountain Wave ◽  
Ice Clouds ◽  
Lower Altitude ◽  
Frost Point ◽  
Polar Stratospheric Cloud

Abstract. Spaceborne lidar measurements from CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) are used to provide a vortex-wide perspective of the 2009–2010 Arctic polar stratospheric cloud (PSC) season to complement more focused measurements from the European Union RECONCILE (reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions) field campaign. The 2009–2010 Arctic winter was unusually cold at stratospheric levels, especially from mid-December 2009 until the end of January 2010, and was one of only a few winters from the past 52 years with synoptic-scale regions of temperatures below the frost point. More PSCs were observed by CALIPSO during the 2009–2010 Arctic winter than in the previous three Arctic seasons combined. In particular, there were significantly more observations of high number density nitric acid trihydrate (NAT) mixtures (referred to as Mix 2-enh) and ice PSCs. We found that the 2009–2010 season could roughly be divided into four periods with distinctly different PSC optical characteristics. The early season (15–30 December 2009) was characterized by patchy, tenuous PSCs, primarily low number density liquid/NAT mixtures. The second phase of the season (31 December 2009–14 January 2010) was characterized by frequent mountain wave ice clouds that nucleated widespread NAT particles throughout the vortex, including Mix 2-enh. The third phase of the season (15–21 January 2010) was characterized by synoptic-scale temperatures below the frost point which led to a rare outbreak of widespread ice clouds. The fourth phase of the season (22–28 January) was characterized by a major stratospheric warming that distorted the vortex, displacing the cold pool from the vortex center. This final phase was dominated by supercooled ternary solution (STS) PSCs, although NAT particles may have been present in low number densities, but were masked by the more abundant STS droplets at colder temperatures. We also found distinct variations in the relative proportion of PSCs in each composition class with altitude over the course of the 2009–2010 Arctic season. Lower number density liquid/NAT mixtures were most frequently observed in the lower altitude regions of the clouds (below ∼18–20 km), which is consistent with CALIPSO observations in the Antarctic. Higher number density liquid/NAT mixtures, especially Mix 2-enh, were most frequently observed at altitudes above 18–20 km, primarily downstream of wave ice clouds. This pattern is consistent with the conceptual model whereby low number density, large NAT particles are precipitated from higher number density NAT clouds (i.e. mother clouds) that are nucleated downstream of mountain wave ice clouds.

scholarly journals Accuracy and precision of polar lower stratospheric temperatures from reanalyses evaluated from A-Train CALIOP and MLS, COSMIC GPS RO, and the equilibrium thermodynamics of supercooled ternary solutions and ice clouds

2018 ◽  
Vol 18 (3) ◽  
pp. 1945-1975 ◽  
Author(s):  
Alyn Lambert ◽  
Michelle L. Santee
Keyword(s):  
Pressure Range ◽  
Equilibrium Thermodynamics ◽  
Polar Stratospheric Clouds ◽  
Ice Clouds ◽  
Warm Bias ◽  
Frost Point ◽  
Ternary Solutions ◽  
Accuracy And Precision ◽  
Temperature Reference ◽  
Stratospheric Clouds

Abstract. We investigate the accuracy and precision of polar lower stratospheric temperatures (100–10 hPa during 2008–2013) reported in several contemporary reanalysis datasets comprising two versions of the Modern-Era Retrospective analysis for Research and Applications (MERRA and MERRA-2), the Japanese 55-year Reanalysis (JRA-55), the European Centre for Medium-Range Weather Forecasts (ECMWF) interim reanalysis (ERA-I), and the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (NCEP-CFSR). We also include the Goddard Earth Observing System model version 5.9.1 near-real-time analysis (GEOS-5.9.1). Comparisons of these datasets are made with respect to retrieved temperatures from the Aura Microwave Limb Sounder (MLS), Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) Global Positioning System (GPS) radio occultation (RO) temperatures, and independent absolute temperature references defined by the equilibrium thermodynamics of supercooled ternary solutions (STSs) and ice clouds. Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) observations of polar stratospheric clouds are used to determine the cloud particle types within the Aura MLS geometric field of view. The thermodynamic calculations for STS and the ice frost point use the colocated MLS gas-phase measurements of HNO3 and H2O. The estimated bias and precision for the STS temperature reference, over the 68 to 21 hPa pressure range, are 0.6–1.5 and 0.3–0.6 K, respectively; for the ice temperature reference, they are 0.4 and 0.3 K, respectively. These uncertainties are smaller than those estimated for the retrieved MLS temperatures and also comparable to GPS RO uncertainties (bias  <  0.2 K, precision  >  0.7 K) in the same pressure range. We examine a case study of the time-varying temperature structure associated with layered ice clouds formed by orographic gravity waves forced by flow over the Palmer Peninsula and compare how the wave amplitudes are reproduced by each reanalysis dataset. We find that the spatial and temporal distribution of temperatures below the ice frost point, and hence the potential to form ice polar stratospheric clouds (PSCs) in model studies driven by the reanalyses, varies significantly because of the underlying differences in the representation of mountain wave activity. High-accuracy COSMIC temperatures are used as a common reference to intercompare the reanalysis temperatures. Over the 68–21 hPa pressure range, the biases of the reanalyses with respect to COSMIC temperatures for both polar regions fall within the narrow range of −0.6 K to +0.5 K. GEOS-5.9.1, MERRA, MERRA-2, and JRA-55 have predominantly cold biases, whereas ERA-I has a predominantly warm bias. NCEP-CFSR has a warm bias in the Arctic but becomes substantially colder in the Antarctic. Reanalysis temperatures are also compared with the PSC reference temperatures. Over the 68–21 hPa pressure range, the reanalysis temperature biases are in the range −1.6 to −0.3 K with standard deviations  ∼  0.6 K for the CALIOP STS reference, and in the range −0.9 to +0.1 K with standard deviations  ∼  0.7 K for the CALIOP ice reference. Comparisons of MLS temperatures with the PSC reference temperatures reveal vertical oscillations in the MLS temperatures and a significant low bias in MLS temperatures of up to 3 K.

scholarly journals Balloon borne Antarctic frost point measurements and their impact on polar stratospheric cloud theories

1988 ◽  
Vol 15 (8) ◽  
pp. 859-862 ◽  
Author(s):  
James M. Rosen ◽  
D. J. Hofmann ◽  
J. R. Carpenter ◽  
J. W. Harder ◽  
S. J. Oltmans
Keyword(s):  
Frost Point ◽  
Polar Stratospheric Cloud

scholarly journals Synoptic-Scale Flow and Valley Cold Pool Evolution in the Western United States

2009 ◽  
Vol 24 (6) ◽  
pp. 1625-1643 ◽  
Author(s):  
Heather Dawn Reeves ◽  
David J. Stensrud
Keyword(s):  
United States ◽  
Large Scale ◽  
Numerical Models ◽  
Western United States ◽  
Cold Pool ◽  
Synoptic Scale ◽  
Temperature Changes ◽  
Cold Pools ◽  
Upper Level ◽  
Forecast Problem

Abstract Valley cold pools (VCPs), which are trapped, cold layers of air at the bottoms of basins or valleys, pose a significant problem for forecasters because they can lead to several forms of difficult-to-forecast and hazardous weather such as fog, freezing rain, or poor air quality. Numerical models have historically failed to routinely provide accurate guidance on the formation and demise of VCPs, making the forecast problem more challenging. In some case studies of persistent wintertime VCPs, there is a connection between the movement of upper-level waves and the timing of VCP formation and decay. Herein, a 3-yr climatology of persistent wintertime VCPs for five valleys and basins in the western United States is performed to see how often VCP formation and decay coincides with synoptic-scale (∼200–2000 km) wave motions. Valley cold pools are found to form most frequently as an upper-level ridge approaches the western United States and in response to strong midlevel warming. The VCPs usually last as long as the ridge is over the area and usually only end when a trough, and its associated midlevel cooling, move over the western United States. In fact, VCP strength appears to be almost entirely dictated by midlevel temperature changes, which suggests large-scale forcing is dominant for this type of VCP most of the time.

scholarly journals Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling

2003 ◽  
Vol 3 (6) ◽  
pp. 5831-5873
Author(s):  
J. Reichardt ◽  
A. Dörnbrack ◽  
S. Reichardt ◽  
P. Yang ◽  
T. J. McGee
Keyword(s):  
Optical Data ◽  
Particle Nucleation ◽  
Number Density ◽  
Mountain Wave ◽  
Time Space ◽  
Early Afternoon ◽  
Lidar Measurements ◽  
Ground Based Lidar ◽  
Meteorological Modeling ◽  
Wave Induced

Abstract. The exceptional day-long observation of a polar stratospheric cloud (PSC) by two ground-based lidars at the Swedish research facility Esrange (67.9° N, 21.1° E) on 16 January 1997 is analyzed in terms of PSC dynamics and microphysics. Mesoscale meteorological modeling is utilized to resolve the time-space ambiguity of the lidar measurements. Microphysical properties of the PSC particles are retrieved by comparing the measured particle depolarization ratio and the PSC-averaged lidar ratio with theoretical optical data derived for different particle shapes. In the morning, nitric acid trihydrate (NAT) particles and then increasingly coexisting liquid ternary aerosol (LTA) were detected as outflow from a mountain wave-induced ice PSC upwind Esrange. The NAT PSC consisted of irregular-shaped particles with length-to-diameter ratios between 0.75 and 1.25, maximum dimensions from 0.7 to 0.9 μm, and a number density from 8 to 12 cm−3 and the coexisting LTA droplets had diameters from 0.7 to 0.9 μm, a refractive index of 1.39 and a number density from 7 to 11 cm−3. NAT activation was probably substantial (~53%) which appears to be the effect of the high cooling rates (>100 K/h) in the stratospheric mountain wave. The total amount of condensed HNO3 was in the range of 57–90% of the HNO3 gas reservoir. By early afternoon the mountain wave-induced ice PSC expanded above the lidar site. Its optical data indicate a decrease in minimum particle size from 4.3 to 1.9 μm with time, possibly due to a diminishing growth rate. Later on, following the cessation of particle nucleation upwind wave-processed LTA was observed only. Our study demonstrates that ground-based lidar measurements of PSCs can be comprehensively interpreted if combined with mesoscale meteorological data.

scholarly journals Detailed modeling of mountain wave PSCs

2003 ◽  
Vol 3 (3) ◽  
pp. 697-712 ◽  
Author(s):  
S. Fueglistaler ◽  
S. Buss ◽  
B. P. Luo ◽  
H. Wernli ◽  
H. Flentje ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Nitric Acid ◽  
Weather Prediction ◽  
Detailed Comparison ◽  
Data Interpretation ◽  
Analysis Data ◽  
The Arctic ◽  
Second Phase ◽  
Mountain Wave

Abstract. Polar stratospheric clouds (PSCs) play a key role in polar ozone depletion. In the Arctic, PSCs can occur on the mesoscale due to orographically induced gravity waves. Here we present a detailed study of a mountain wave PSC event on 25-27 January 2000 over Scandinavia. The mountain wave PSCs were intensively observed by in-situ and remote-sensing techniques during the second phase of the SOLVE/THESEO-2000 Arctic campaign. We use these excellent data of PSC observations on 3 successive days to analyze the PSCs and to perform a detailed comparison with modeled clouds. We simulated the 3-dimensional PSC structure on all 3 days with a mesoscale numerical weather prediction (NWP) model and a microphysical box model (using best available nucleation rates for ice and nitric acid trihydrate particles). We show that the combined mesoscale/microphysical model is capable of reproducing the PSC measurements within the uncertainty of data interpretation with respect to spatial dimensions, temporal development and microphysical properties, without manipulating temperatures or using other tuning parameters. In contrast, microphysical modeling based upon coarser scale global NWP data, e.g. current ECMWF analysis data, cannot reproduce observations, in particular the occurrence of ice and nitric acid trihydrate clouds. Combined mesoscale/microphysical modeling may be used for detailed a posteriori PSC analysis and for future Arctic campaign flight and mission planning. The fact that remote sensing alone cannot further constrain model results due to uncertainities in the interpretation of measurements, underlines the need for synchronous in-situ PSC observations in campaigns.

scholarly journals Mountain wave PSC dynamics and microphysics from ground-based lidar measurements and meteorological modeling

2004 ◽  
Vol 4 (4) ◽  
pp. 1149-1165 ◽  
Author(s):  
J. Reichardt ◽  
A. Dörnbrack ◽  
S. Reichardt ◽  
P. Yang ◽  
T. J. McGee
Keyword(s):  
Meteorological Data ◽  
Optical Data ◽  
Number Density ◽  
Mountain Wave ◽  
Microphysical Properties ◽  
Early Afternoon ◽  
Lidar Measurements ◽  
Ground Based Lidar ◽  
Meteorological Modeling ◽  
Wave Induced

Abstract. The day-long observation of a polar stratospheric cloud (PSC) by two co-located ground-based lidars at the Swedish research facility Esrange (67.9° N, 21.1° E) on 16 January 1997 is analyzed in terms of PSC dynamics and microphysics. Mesoscale modeling is utilized to simulate the meteorological setting of the lidar measurements. Microphysical properties of the PSC particles are retrieved by comparing the measured particle depolarization ratio and the PSC-averaged lidar ratio with theoretical optical data derived for different particle shapes. In the morning, nitric acid trihydrate (NAT) particles and then increasingly coexisting liquid ternary aerosol (LTA) were detected as outflow from a mountain wave-induced ice PSC upwind Esrange. The NAT PSC is in good agreement with simulations for irregular-shaped particles with length-to-diameter ratios between 0.75 and 1.25, maximum dimensions from 0.7 to 0.9 µm, and a number density from 8 to 12 cm-3 and the coexisting LTA droplets had diameters from 0.7 to 0.9 µm, a refractive index of 1.39 and a number density from 7 to 11 cm-3. The total amount of condensed HNO3 was in the range of 8–12 ppbv. The data provide further observational evidence that NAT forms via deposition nucleation on ice particles as a number of recently published papers suggest. By early afternoon the mountain-wave ice PSC expanded above the lidar site. Its optical data indicate a decrease in minimum particle size from 3 to 1.9 µm with time. Later on, following the weakening of the mountain wave, wave-induced LTA was observed only. Our study demonstrates that ground-based lidar measurements of PSCs can be comprehensively interpreted if combined with mesoscale meteorological data.

scholarly journals A Characterization of Cold Pools in the West African Sahel

2016 ◽  
Vol 144 (5) ◽  
pp. 1923-1934 ◽  
Author(s):  
M. Provod ◽  
J. H. Marsham ◽  
D. J. Parker ◽  
C. E. Birch
Keyword(s):  
Potential Temperature ◽  
West African ◽  
Energy Deficit ◽  
Squall Line ◽  
Cold Pool ◽  
The West ◽  
Early Season ◽  
African Monsoon ◽  
Cold Pools

Cold pools are integral components of squall-line mesoscale convective systems and the West African monsoon, but are poorly represented in operational global models. Observations of 38 cold pools made at Niamey, Niger, during the 2006 African Monsoon Multidisciplinary Analysis (AMMA) campaign (1 June–30 September 2006), are used to generate a seasonal characterization of cold pool properties by quantifying related changes in surface meteorological variables. Cold pools were associated with temperature decreases of 2°–14°C, pressure increases of 0–8 hPa, and wind gusts of 3–22 m s−1. Comparison with published values of similar variables from the U.S. Great Plains showed comparable differences. The leading part of most cold pools had decreased water vapor mixing ratios compared to the environment, with moister air, likely related to precipitation, approximately 30 min behind the gust front. A novel diagnostic used to quantify how consistent observed cold pool temperatures are with saturated or unsaturated descent from midlevels [fractional evaporational energy deficit (FEED)] shows that early season cold pools are consistent with less saturated descents. Early season cold pools were relatively colder, windier, and wetter, consistent with drier midlevels, although this was only statistically significant for the change in moisture. Late season cold pools tended to decrease equivalent potential temperature from the pre–cold pool value, whereas earlier in the season changes were smaller, with more increases. The role of cold pools may therefore change through the season, with early season cold pools more able to feed subsequent convection.

scholarly journals Validation of MODIS derived aerosol optical depth and an investigation on aerosol transport over the South East Arabian Sea during ARMEX-II

2009 ◽  
Vol 27 (6) ◽  
pp. 2285-2296 ◽  
Author(s):  
M. Aloysius ◽  
M. Mohan ◽  
S. Suresh Babu ◽  
K. Parameswaran ◽  
K. Krishna Moorthy
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Mass Concentration ◽  
Arabian Sea ◽  
Second Phase ◽  
The South ◽  
Monsoon Period ◽  
Lower Altitude ◽  
The North ◽  
Coarse Mode

Abstract. The influence of wind and humidity on aerosol optical depth (AOD) over the Arabian sea is being investigated using MODIS (Moderate Resolution Imaging Spectroradiometer) Level 3 (Collection-5) and NCEP (National Centres for Environmental Prediction) reanalysis data for the second phase of the Arabian Sea Monsoon Experiment (ARMEX-II) over the South East Arabian Sea (SEAS) in the pre-monsoon period (14 March–10 April 2003). In order to qualify MODIS data for this study, MODIS aerosol parameters were first compared with ship borne Microtops measurements. This showed correlations 0.96–0.97 in the case of spectral AODs and a correlation 0.72 for the angstrom exponents. The daily AOD data from MODIS and winds from NCEP reveal that the ship observed episodic enhancement and decay of AOD at the TSL (Time Series Location) during 23 March–6 April 2003 was caused by the southward drift of an aerosol pocket driven by an intensification and reduction of surface pressure in the North Western Arabian Sea with a low altitude convergence prevailing over SEAS. The AOD increase coincided with a decrease in the Angstrom exponent and the fine mode fraction suggesting the pocket being dominated by coarse mode particles. A partial correlation analysis reveals that the lower altitude wind convergence is the most influential atmospheric variable in modulating AOD over the ARMEX-II domain during the TSL period. However, surface winds at a distant zone in the north/north west upwind direction also had a moderate influence, though with a lag of two days. But this effect was minor since the winds were not strong enough to produce marine aerosols matching with the high AODs over the ARMEX-II domain. These findings and the similarity between MODIS column mass concentration and the ship borne QCM (Quartz Crystal Microbalance) measured coarse mode mass concentration, suggest that the aerosol pocket was mostly composed of coarse mode mineral dust in the lower atmospheric altitudes transported from the Arabian deserts.

scholarly journals Liquid particle composition and heterogeneous reactions in a mountain wave Polar Stratospheric Cloud

2005 ◽  
Vol 5 (5) ◽  
pp. 9547-9580
Author(s):  
D. Lowe ◽  
A. R. MacKenzie ◽  
H. Schlager ◽  
C. Voigt ◽  
A. Dörnbrack ◽  
...  
Keyword(s):  
Gas Phase ◽  
Large Scale ◽  
Heterogeneous Reactions ◽  
Mountain Wave ◽  
Transport Models ◽  
Particle Composition ◽  
Polar Stratospheric Cloud ◽  
Stratospheric Clouds ◽  
Equilibrium Calculations

Abstract. Mountain wave polar stratospheric clouds (PSCs) were detected on 8 February 2003 above the Scandinavian Mountains by in-situ instruments onboard the M55 Geophysica aircraft. The observations of PSC particle composition, backscatter and chlorine activation are studied with a recently developed dynamical microphysical non-equilibrium box model. Results from the microphysical model, run on quasi-lagrangian trajectories, show that the PSC is composed of supercooled ternary (H2O/HNO3/H2SO4) solutions (STS) particles, which are out of equilibrium with the gas phase. The optical properties of the PSC can well be simulated with the model. Up to 0.15 ppbv Cl2 can be released by the PSC within 2 h in reasonable agreement with the measured ClOx concentrations, but high solar zenith angles prevent a direct comparison. Equilibrium calculations commonly used in large scale chemistry transport models poorly represent the measured PSC particle composition and chlorine activation under mountain wave conditions.

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