Stratospheric aerosols measurements at CEILAP, Argentina: Two
Contents
1. tropospheric aerosols and cirrus clouds This instrument is located to 18 meters over the sea level Table I shows principal lidar characteristics 6 TABLE I Principal characteristics of CEILAP lidar Parameters Laser wavelength Energy Frequency Mirrors diameter Magnitude Nd YAG 532 nm 300 mJ max 10 Hz 50 cm Newtonian 8 cm Cassegrain lt 1 5 mrad Photomultipliers Analogical photocurrent Field of view Detector Signal processing For the present study two tropospheric aerosols lidar measurements was employed One conducted in November 16 2000 at 02 20 55 LT and the other in June 22 2001 at 02 04 00 LT Lidar measurements consist of vertical profiles of returned signals at a resolution of 300m Measurements processing was conducted using the BackScatter Process Application BSPA software developed by the Camagiiey Lidar Station team 7 8 The molecular backscattering was calculated using the nearest in time aerological soundings from Buenos Opt Pura Apl 41 2 101 107 2008 103 Aires They were November 17 2000 at 00 00 GMT and June 22 2001 at the 12 00 GMT Backscattering aerosol profiles were derived for each day The SNR was calculated for each one of the two lidar soundings For making the lidar profiles resolution compatible with the SAGE II aerosol extinction profiles the backscatter profiles originally at 300m were integrated to a r2. PTICA PURA Y APLICADA www sedoptica es Stratospheric aerosols measurements at CEILAP Argentina Two case studies Mediciones de Aerosoles Estratosf ricos en CEILAP Argentina Dos casos de estudio Ren Estevan Juan Carlos Antu a and Mario B Lavorato Camag ey Lidar Station Meteorlogical Center of Camag ey INSMET Carretera Nuevitas Km 7 2 PO Box 134 Camagiiey 70100 Cuba Division Radar Laser CEILAP CITEFA CONICET J B de La Salle 4397 B1603ALO Villa Martelli Argentina Email rene met cmw inf cu Recibido Received 20 Jul 2007 Version revisada Revised version 30 Oct 2007 Aceptado Accepted 10 Nov 2007 ABSTRACT CEILAP lidar located at Buenos Aires Argentina 34 6 S and 58 5 W was usually employed for atmospheric boundary layer tropospheric aerosols and cirrus clouds measurements We conducted two cases study to evaluate the potential of such lidar for lower stratospheric aerosols measurements Two lidar profiles were processed using the appropriated software developed at Camagiiey Lidar Station The results show clear evidence of the presence of stratospheric aerosols in the backscattering profiles above the tropopause level Signal noise relationship are employed as a quality control and discrimination procedure for determining the capability to retrieve stratospheric aerosols information from such measurements One comparison between space time coincident exti
3. Fig 3 SAGE Il and CEILAP lidar coincident profiles corresponding to June 2001 at 532 nm Sociedad Espa ola de ptica Pdf downloaded from http www thepdfportal com estevanopa412008_66101 pdf PTICA PURA Y APLICADA www sedoptica es Fig 4 Backtrajectories in the upper troposphere and lower stratosphere for two SAGE II measurements on June 24 2001 a Case No 2 and b Case No 4 Table II shows the AOD values at two wavelengths for both lidar and sunphotometer measurements Although both instruments measure at slightly different wavelengths the proximity among the pairs 532 nm and 1064 nm for lidar versus 500 nm and 1020 for the sunphotometer guarantee no significant differences by this reason TABLE III AOD measurements both from sunphotometer and lidar for November 16 2000 and June 22 2001 x 16 11 2000 22 06 2001 ae 532nm 4 06X 107 2 85X 107 1064nm 2 10x10 1 48x10 Suno 500nm 6 61X 107 7 63 X 107 1020nm 3 81x107 4 85x10 All the AOD values from both instruments are in the same magnitude order with reasonable values In all cases the AOD measured by the sunphotometer show higher values than the one measured by lidar The reason is associated to the fact that the sunphotometer provides an integrated measurement in the whole column while the lidar do not measure at the very low level near the surface Other reason for differences in AOD between lidar and
4. processing O Sociedad Espa ola de ptica Pdf downloaded from http www thepdfportal com estevanopa412008_ 66101 pdf PTICA PURA Y APLICADA www sedoptica es stratospheric aerosols lidar measurements is suitable to processing tropospheric lidar aerosols measurements This type of study open the possibility of recovering stratospheric aerosols backscattering profiles from originally designed tropospheric lidar measurements Acknowledgements Authors thank the NASA Langley Research Center and the NASA Langley Radiation and Aerosols Opt Pura Apl 41 2 101 107 2008 107 Branch for providing the SAGE II dataset This work has been supported by the Cuban National Climate Change Research Program grant 01303177 O Sociedad Espa ola de ptica Pdf downloaded from http www thepdfportal com estevanopa412008_66101 pdf
5. 66101 pdf PTICA PURA Y APLICADA www sedoptica es REFERENCES AND LINKS 1 J C Antu a Efectos Clim ticos de las erupciones volc nicas pp 3 19 in Riesgos Clim ticos e Impacto Ambiental C Garcia Legaz F Valero Edts Editorial Complutense Madrid In Spanish 2003 2 A Robock Volcanic eruptions and climate Rev Geophys 38 191 219 2000 3 G L Stenchikov I Kirchner A Robock H F Graf J C Antu a R G Grainger A Lambert L Thomason Radiative forcing from the 1991 Mount Pinatubo volcanic eruption J Geophys Res 103 13837 13857 1998 4 A Robock J Mao The volcanic signal in surface temperature observations J Climate 8 1086 1103 1995 5 SPARC Assessment of Stratospheric Aerosols L Thomason Th Peter Edts SPARC Report No 4 2006 6 M Lavorato P Cesarano E Quel P H Flamant Dual backscatter lidar is operated in Buenos Aires 34 6 S 58 5 W for determine the atmospheric parameters in cirrus clouds tropospheric aerosols and ABL Proc 21 International Laser Radar Conference pp 75 78 2002 7 BSPA Backscatter Process Application Manual de Usuario Certificaci n de deposito legal facultativo de Obras Protegidas CENDA Registro 2366 2004 2004 8 R Estevan J C Antu a Updated Camagtiey lidar dataset validation with SAGE IP Opt Pura Apl 39 85 90 2006 9 H J ger T Deshler Lidar backscatter to ex
6. 8 102 Sociedad Espa ola de ptica Pdf downloaded from http www thepdfportal com estevanopa412008_ 66101 pdf PTICA PURA Y APLICADA www sedoptica es stratospheric aerosols layer to be located at lower altitudes For such a goal we used two upper tropospheric aerosols lidar measurements conducted at the Centro de Investigaciones L ser y sus Aplicaciones CEILAP located near Buenos Aires Argentina 6 Both measurements are processed and the vertical profiles of stratospheric aerosols backscatter coefficients are derived The analysis of the signal to noise ratio SNR explains the capability of the tropospheric designed measurements for providing information on stratospheric aerosols Profiles of aerosol backscatter coefficients were converted to aerosol extinction profiles The comparison of space coincident SAGE II aerosols extinction profiles with one the lidar derived aerosols extinction profiles demonstrated that the lidar derived profile is representative of the stratospheric aerosols The comparison of the aerosol optical depth AOD derived from lidar and sunphotometer show a good agreement between both instruments The paper pointed out the possibility of recovering stratospheric aerosols profiles from some original designed tropospheric lidar measurements 2 Instruments and Dataset The CEILAP lidar 34 6 S and 58 5 W Buenos Aires Argentina was designed for measurements of Atmospheric Boundary Layer ABL
7. de retrodispersi n sobre el nivel de la tropopausa La relaci n se al ruido se ha empleado como control de calidad y procedimiento de discriminaci n para determinar la posibilidad de obtener informaci n de aerosoles estratosf ricos de est s mediciones Se realiz una comparaci n entre perfiles de extinci n coincidentes en tiempo y espacio entre el lidar y SAGE II El AOD obtenido a partir de los perfiles de extinci n por aerosoles fue comparado con mediciones realizadas con el fot metro solar ubicado en CEILAP perteneciente a AERONET Los resultados corroboran las posibilidades del lidar para de estas mediciones as como la efectividad del algoritmo de procesamiento empleado Se demuestran las ventajas de emplear sondeos aerol gicos para obtener los perfiles de retrodispersi n molecular en lugar de emplear modelos de densidad estad sticos basados en sondeos medios o atm sfera est ndar Se analiza el origen de los aerosoles estratosf ricos medidos por el lidar de CEILAP utilizando an lisis de retrotrayectorias Esto permite explicar la similitud o no de los perfiles de extinci n por aerosoles estratosf ricos entre el lidar y SAGE II teniendo en cuenta el origen de las masas de aire muestreadas por ambos instrumentos Palabras clave Aerosoles Estratosf ricos Lidar SAGE IL CEILAP Opt Pura Apl 41 2 101 107 2008 101 O Sociedad Espa ola de ptica Pdf downloaded from http www thepdfportal com estevanopa412008_
8. easurements at altitudes of 10 15 and 20 km reveal the variability of the transport at such levels in the region This variability is in general higher at the level of 10 km in the vicinity of the tropopause decreasing in direction to the 20 km level Figure 4 shows the backtrajectories for the case 2 and 4 that appear in Figure 3 In case 4 the Figure 4 shows that the transport was completely zonal For this case Fig 3 shows a good agreement between the lidar and the SAGE II profiles While for case 2 the Fig 4 shows that the transport have a noticeable meridional component most notorious in the upper troposphere around 10 km Fig 3 shows for case 2 that precisely in the upper troposphere are the biggest disagreement between SAGE II and lidar profiles The explanation for such behavior is well Opt Pura Apl 41 2 101 107 2008 known banded structure of the stratospheric aerosols in non volcanic conditions 14 The detailed analysis of the backtrajectories for the other cases not shown demonstrated that in general the SAGE II sampled air masses at the level of 10km came from different latitudinal bands that the one sampled at the CEILAP lidar site Helgrt Km 1E 05 1E03 1E 01 1E 05 1 03 1E01 1E05 1E 03 1E 01 logalEstincion km logulEstin cion km logalEstincion km 55 35 Helgtt Km 1 05 103 1E 01 1E 05 1E 03 1E01 1 05 1 E03 1E 01 logulEstin cion km h bgalExtncion km logulExtin cion km h
9. ering values are reasonable with the characteristic of an abrupt increase at the lower levels and a more smooth decay toward the stratosphere The presence of aerosols well in to the stratosphere above the tropopause is evident showing the possibility for deriving stratospheric aerosols backscatter profiles from some of the measurements originally designed for tropospheric aerosols 16 11 2000 22 06 2001 Altitude km Backscatter m sr Altitude km Figure 1 b shows the SNR in logarithmic scale plotted versus altitude As it is expected it spans over several ranges of magnitude An important feature is that yet at around 20 km the signal is ten times the value of the noise That is the reason why at that altitude the returned signal profile still contains information in this case about the stratospheric aerosols This is the criteria that should be applied to evaluate the capability of tropospheric lidar aerosol measurements to provide also information on stratospheric aerosols In order to determine the possible sources of aerosols was employed the backtrajectory analysis for the two lidar measurement days Figure 2 a shows the behavior for November 16 2000 showing that air masses traveled fundamentally over land This could explain the presence of tropospheric aerosols Fig 1 a 16 11 2000 even below of 5 km due fundamentally to an important contribution from air pollution over land Figu
10. esolution of 500 meters then the resulting backscattering profiles were converted to extinction profiles 8 For backscatter to extinction conversion procedure was employed the Jager coefficients 9 10 These values have been averaged in the heights range of TP 15 15 20 20 25 and 25 30 km for periods of four months To convert 532 nm extinction profile at 1064 nm wavelength was used Angstrom exponents from the same author 9 10 Aerosol extinction profiles from the SAGE II instrument version 6 20 were downloaded from the LARC Langley Research Center NASA on Internet 11 Used profiles are from the wavelengths of 525 and 1020nm with a vertical resolution of 500m Coincident measurements between SAGE II and the CEILAP lidar were selected using the next spatio temporal criteria 6 degrees in latitude and 72 hours In longitude no coincident criteria was established allowing all the SAGE II measurements inside the predefined latitudinal band In the case of lidar measurement at November 16 2000 no coincident measurements were found However for June 22 2001 a total of 6 coincident measurements were found which appear in Table II This table contain the time location and tropopause TP altitude for each one of the SAGE II coincident profiles Hourly values of AOD from the CEILAP sunphotometer were downloaded from AERONET website 12 for 500 and 1020 nm respectively The AOD hourly values belong to November 16 2000 a
11. nction profiles from lidar and SAGE II is conducted AOD calculated from the lidar derived aerosols extinction profiles were compared with the AOD measured by the AERONET sun photometer lidar operating at CEILAP Results corroborate the lidar capabilities for such measurements as well as the effectiveness of the processing algorithm We also documented the advantage of using aerological sounding to derive the molecular backscattering profile instead of using statistical density models based on mean soundings or the standard atmosphere The source of the stratospheric aerosols measured by the CEILAP lidar was analyzed using back trajectories analysis It allows explaining the agreements and disagreements of the lidar and SAGE II stratospheric aerosols extinction profiles taking into account the sources of the air masses sampled by both instruments Keywords Stratospheric Aerosols Lidar SAGE II CEILAP RESUMEN El lidar de CEILAP ubicado en Buenos Aires Argentina 34 6 S and 58 5 O ha sido empleado usualmente para mediciones de capa fronteriza planetaria aerosoles troposf ricos y nubes cirros Se analizaron dos casos de estudio para evaluar el potencial de este lidar para mediciones de aerosoles estratosf ricos bajos Se procesaron dos perfiles de lidar empleando el software apropiado desarrollado en la Estaci n Lidar de Camag ey Los resultados muestran una clara evidencia de la presencia de aerosoles estratosf ricos en los perfiles
12. nd June 22 2001 The AOD data was averaged for each day The sunphotometer located at CEILAP is a CIMEL CE 138 belonging to AERONET network 12 TABLE II SAGE II coincident profiles belonging to June 2001 No Day Time Lat S Lon W TP Km 1 24 01 39 37 40 43 134 71 9 91 2 24 19 17 16 38 44 37 55 10 32 3 24 20 53 25 38 23 61 37 11 79 4 24 22 29 35 38 02 85 23 12 98 5 25 00 00 54 37 87 109 28 10 83 6 25 01 45 53 37 63 133 08 10 14 O Sociedad Espa ola de ptica Pdf downloaded from http www thepdfportal com estevanopa412008_ 66101 pdf PTICA PURA Y APLICADA www sedoptica es Back trajectories were calculated using the HYSPLIT HYbrid Single Particle Lagrangian Integrated Trajectory model Version 4 8 12 13 For determining the back trajectories at each one of the SAGE II aerosol extinction profiles location and at the CEILAP lidar site the model was run backward for 72 hours using reanalysis dataset at the levels of 10 15 and 20 km for the stratosphere end 2 5 5 and 7 5 km for the troposphere 3 Results The vertical profiles of aerosol backscattering coefficients from the CEILAP lidar for both days are shown in Figure 1 a Tropopause altitudes for each day are denoted with an arrow and the altitude by its side The profiles resemble clearly the typical structure of tropospheric aerosols in the middle and upper troposphere Backscatt
13. not comprise a complete measurement set stratosphere several climatic effects have been data does no P p documented 1 2 The most relevant effect of the Consequently many parameters required a nir volcanic stratospheric clouds is the influence over scientific r intercomparison purposes are derived ihe earth radiative balance as has been shown f r indirectly from the base measurements Additional example after the most intense eruption of twenty difficulties arise from the spatio temporal gaps in the century the Mount Pinatubo eruption in June 12 16 datasets In particular few lidar sites have measured 1991 B 4 i stratospheric aerosols in the Southern Hemisphere 5 The objective of the present paper is to demonstrate that under certain circumstances it is possible to recover stratospheric aerosols Both ground and space based measurements of stratospheric aerosols have played a decisive role in providing the information necessary for the studies conducted up to the present In particular lidars and j ee the SAGE I and II Stratospheric Aerosols and Gas information from upper tropospheric lidar aerosols Experiment I and II satellite instruments provided measurements That is particularly possible tor the biggest spatio temporal coverage 5 measurements conducted in the middle and high latitude because the altitude of the tropopause decrease from the equator to the poles causing the Opt Pura Apl 41 2 101 107 200
14. re 2 b shows conditions for June 22 2001 in this case the air masses traveled mainly over maritime regions with low aerosol content That is the cause why in the corresponding profile in Fig 1 a there are no aerosols below 5 km for this date 16 11 2000 22 06 2001 2 log SNR Fig 1 a Vertical profiles of the backscatter aerosols coefficient calculated using aerological soundings Tropopause altitudes are denoted by the arrows for each profile b Vertical profiles of the SNR in logarithmic scale Opt Pura Apl 41 2 101 107 2008 104 Pdf downloaded from http www thepdfportal com estevanopa412008_ 66101 pdf O Sociedad Espa ola de ptica PTICA PURA Y APLICADA www sedoptica es Fig 2 Backtrajectories in the lower troposphere a November 16 2000 and b June 22 2001 4 Sage II and sunphotometer comparisons SAGE II and CEILAP lidar coincident profiles at 532 nm wavelength are shown in Fig 3 In the upper right corner of each graphic appears the corresponding number listed on Table II In general we appreciate the good agreement between SAGE II and lidar profiles mainly for day 24 cases 2 3 and 4 in Fig 3 almost two days after the lidar measurement The agreement is better in the case 4 than the rest For the case of the 1064 nm the plots not shown reveal similar features with better agreements for cases 3 and 4 Backtrajectories for locations of the SAGE II m
15. sunphotometer are related with that lidar measurements are carry out during night when atmospheric conditions are very different to the day Opt Pura Apl 41 2 101 107 2008 106 The largest differences are 22 06 2001 in this case the lidar signal begin from 5500 m altitude versus 2500 m for day 16 11 2000 In last date the lidar AOD include information of part of ABL Lidar AOD for day 16 are greater than day 22 due the polluted continental air masses figure 2a However sunphotometer AOD for day 22 are greater than day 16 this can be associated to the fact in part that day 22 sunphotometer measurements initiate to 13 41 5 Conclusions It has been demonstrated that certain CEILAP lidar tropospheric aerosols measurements could be processed for deriving stratospheric aerosols profiles This capability is associated with the good SNR of some measurements at levels above the stratospheric aerosols layer in the lidar location The resulting lidar profiles of aerosol backscatter coefficients show reasonable values Comparisons of the lidar derived aerosols extinction profile and AOD with independent instruments show good agreements in general The comparison conducted with coincident SAGE II aerosol extinction profiles reveals the importance of considering the transport for understanding the degree of agreement of both instruments It has been shown that the BSPA algorithm and software designed and implemented for
16. tinction mass and area conversions for stratospheric aerosols based on midlatitude balloonborne size distribution measurements Geophys Res Lett 29 1929 2002 10 H J ger T Deshler Correction to Lidar backscatter to extinction mass and area conversions for stratospheric aerosols based on midlatitude balloonborne size distribution measurements Geophys Res Lett 30 1382 2003 11 LARC 2006 http www sage2 larc nasa gov data v6_data 12 AERONET http aeronet gsfc nasa gov index html 13 R R Draxler G D Rolph HYSPLIT HY brid Single Particle Lagrangian Integrated Trajectory Model access via NOAA ARL READY Website http www arl noaa gov ready hysplit4 html NOAA Air Resources Laboratory Silver Spring MD 2003 14 G D Rolph Real time Environmental Applications and Display sYstem READY Website http www arl noaa gov ready hysplit4 html NOAA Air Resources Laboratory Silver Spring MD 2003 15 C R Trepte L W Thomason G S Kent Banded structure in stratospheric aerosol distribution Geophys Res Lett 21 2397 240 1994 1 Introduction Together with the important advances in the As is well know the stratospheric aerosols play an roca u y o oia wee important role in climate and atmospheric chemistry Doer ien a have bead poled OW Under volcanic perturbed conditions in the mainly associated with the fact that existing aerosol i i ata
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