Abstract. The global temperature responses to the eruptions of Mount Agung in 1963, El Chichón in 1982, and Mount Pinatubo in 1991 are investigated using nine currently available reanalysis data sets (JRA-55, MERRA, ERA-Interim, NCEP-CFSR, JRA-25, ERA-40, NCEP-1, NCEP-2, and 20CR). Multiple linear regression is applied to the zonal and monthly mean time series of temperature for two periods, 1979-2009 (for eight reanalysis data sets) and 1958-2001 (for four reanalysis data sets), by considering explanatory factors of seasonal harmonics, linear trends, QuasiBiennial Oscillation, solar cycle, and El Niño Southern Oscillation. The residuals are used to define the volcanic signals for the three eruptions separately, and common and different responses among the older and newer reanalysis data sets are highlighted for each eruption. In response to the Mount Pinatubo eruption, most reanalysis data sets show strong warming signals (up to 2-3 K for 1-year average) in the tropical lower stratosphere and weak cooling signals (down to −1 K) in the subtropical upper troposphere. For the El Chichón eruption, warming signals in the tropical lower stratosphere are somewhat smaller than those for the Mount Pinatubo eruption. The response to the Mount Agung eruption is asymmetric about the equator with strong warming in the Southern Hemisphere midlatitude upper troposphere to lower stratosphere. Comparison of the results from several different reanalysis data sets confirms the atmospheric temperature response to these major eruptions qualitatively, but also shows quantitative differences even among the most recent reanalysis data sets. The consistencies and differences among different reanalysis data sets provide a measure of the confidence and uncertainty in our current understanding of the volcanic response. The results of this intercomparison study may be useful for validation of climate model responses to volcanic forcing and for assessing proposed geoengineering by stratospheric aerosol injection, as well as to link studies using only a single reanalysis data set to other studies using a different reanalysis data set.
Using the MST radar observations at Gadanki (13.5°N, 79.2°E), a tropical station, the altitude of major convective outflow in the troposphere is identified and is considered to represent the convective tropopause. This is found to match well with the altitude of local minimum of potential temperature lapse rate obtained from simultaneous radiosonde observations. The convective tropopause altitudes are also compared with the cloud top altitudes obtained using satellite brightness temperature (BT) data and are found to match in the case of deep convection. The thickness of the tropical tropopause layer follows very closely the convective tropopause altitude and has little dependence on the cold point tropopause altitude. The thickness of the tropopause layer is found to shrink when convection reaches high altitudes. This occurs mainly during the monsoon months of July, September, and October.
[1] The variations of the cold point tropopause (CPT), convective tropopause (COT), lapse rate tropopause (LRT), and tropical tropopause layer (TTL) from subdaily to seasonal timescales are studied using high-resolution radiosonde observations from April 2006 to December 2008 over a tropical station Gadanki (13.5°N, 79.2°E), in the Indian monsoon region. The correlations between temperatures and altitudes of the different tropopauses and between TTL thickness and satellite brightness temperature (TBB) are estimated. Diurnal behavior of CPT, LRT, and COT is also investigated. The seasonal variation of the CPT at Gadanki shows notable differences when compared to Western Pacific region, though major features remain similar. CPT temperature at Gadanki goes below 191 K more frequently during December to May than during June to November. The TTL thickness, which is the difference between CPT altitude and COT altitude, is small during summer monsoon and is strongly correlated with TBB on seasonal scale. The CPT altitude and temperature show large variation by as much as ∼1 km and ∼3 K, respectively, even on subdaily scale. During deep convection (TBB < 240) the CPT is found to ascend (∼0.6-0.8 km) in some events and descend (∼1 km) in some other events. Interestingly, during clear sky conditions (TBB > 240), increase in the CPT altitude with increase in CPT temperature is noticed on some occasions. Strong correlation between LRT (and COT) altitude and temperature from subdaily to seasonal timescale is noticed in contrast to CPT altitude and temperature. However, the correlation between TBB and CPT, LRT, and COT degrades from seasonal to subdaily timescale.
AB STRACTCon stel la tion Ob serv ing Sys tem for Me te o rol ogy Ion o sphere and Cli mate (COS MIC), con sist ing of six Low Earth Or bit (LEO) Global Po si tion Sys tem (GPS) re ceiv ers, on board the Formosat Sat el lite 3 (FORMOSAT-3) is pro vid ing dense ob ser va tions of den sity, refractivity, tem per a ture and wa ter va por pro files of the neu tral at mo sphere since mid dle of July 2006. Spe cial ra dio sonde (Väisälä) cam paign was con ducted at Gadanki (13.48°N, 79.18°E), a trop i cal site in In dia, dur ing July 2006 to March 2007 to val i date these me te o ro log i cal pa ram e ters. Co-lo cated Nd: YAG Ray leigh lidar was also op er ated dur ing the over pass of COS MIC and is uti lized to val i date the tem per a tures in the height range of 30 to 40 km. A to tal of 142 over passes oc curred dur ing the above men tioned pe riod within 300 km dis tance from Gadanki out of which 41 over passes oc curred within a time dif fer ence of ±4 hours of ra dio sonde launch. In ad di tion, 18 over passes oc curred within the time dif fer ence of ±4 hours of lidar op er a tion. A de tailed com par i son has been made with all these over passes for the refractivity, tem per a ture and wa ter va por ob tained from COS MIC. The wa ter va por com par i son has shown gen er ally a good agree ment with a mean dif fer ence of 5 -10% be low 6 -7 km. Al though there is a colder bias be tween COS MIC and ra dio sonde, a very good com par i son in tem per a ture is also found be tween 10 and 27 km with a mean dif fer ence of less than 1 K (RMS dif fer ence is only 0.64 K). There ex ists a large dif fer ence in tem per a ture of about 8 K be tween 30 and 40 km (be tween COS MIC and lidar). Pos si ble rea sons for these large dif fer ences are given. There was one event that oc curred just over Gadanki for which a de tailed com par i son has been made with spe cial em pha sis on wa ter va por re triev als. Sen si tiv ity test is also done on the frac tional dif fer ence in N for the event that occurred on 24 July 2006 between COSMIC (1D-var) and radiosonde and found that pressure plays a key role than temperature in determining the refractivity. Atmos. Ocean. Sci., 20, 59-70, doi: 10.3319/ TAO.2008.01.23.01(F3C) IN TRO DUC TIONRa dio occultation soundings of the sig nals from the Global Po si tion ing Sys tem Sat el lites (GPS) are be ing used to ob tain ver ti cal pro files of at mo spheric tem per a ture, pressure and wa ter va por for cli mate re search and weather predic tion (Kursinski et al. 1997). The GPS Ra dio occultation tech nique has emerged as a pow er ful tool for ex plor ing the earth's at mo sphere from ground to a height of around 40 km and also in the ion o sphere af ter the suc cess ful launch of GPS/MET which has pro vided a 'proof of con cept' of GPS Ra dio Occultation (RO) tech nique. Sev eral mis sions such as Oers ted and SAC-C (Hajj et al. 2004) fol lowed GPS/
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