Papers by Roberto Rondanelli
Geophysical Research Letters, 2006
Journal of Geophysical Research, 2008
This paper focuses on the relation between local sea surface temperature (SST) and convective pre... more This paper focuses on the relation between local sea surface temperature (SST) and convective precipitation fraction and stratiform rainfall area from radar observations of precipitation, using data from the Kwajalein atoll ground-based radar as well as the precipitation radar on board the TRMM satellite. We find that the fraction of convective precipitation increases with SST at a rate of about 6 to 12%/K and the area of stratiform rainfall normalized by total precipitation decreases with SST at rates between -5 and -28%/K. These relations are observed to hold for different regions over the tropical oceans and also for different periods of time. Correlations are robust to outliers and to undersampled precipitation regions. Kwajalein results are relatively insensitive to the parameters in the stratiform-convective classification algorithm. Quantitative differences between the results obtained using the two different radars could be explained by the smoothing in the reflectivity of convective regions due to the relatively large pixel size of the TRMM precipitation radar compared to the size of the convective clouds. Although a dependence on temperature such as the one documented is consistent with an increase in the efficiency of convective precipitation (and therefore consistent with one of the mechanisms invoked to explain the original Iris effect observations) this is but one step in studying the possibility of a climate feedback. Further work is required to clarify the particular mechanism involved.
Journal of Geophysical Research, 2010
In this paper we present radiative-convective simulations to test the idea that tropical 7 cirrus... more In this paper we present radiative-convective simulations to test the idea that tropical 7 cirrus clouds, acting as a negative feedback on climate, can provide a solution to the faint 8 young Sun paradox. We find that global mean surface temperatures above freezing can 9 indeed be found for luminosities larger than about 0.8 (corresponding to $2.9 Ga and 10 nearly complete tropical cirrus coverage). For luminosities smaller than 0.8, even though 11 global mean surface temperatures are below freezing, tropical mean temperatures are still 12 above freezing, indicating the possibility of a partially ice-free Earth for the Early 13 Archean. We discuss possible mechanisms for the functioning of this negative feedback. 14 While it is feasible for tropical cirrus to completely eliminate the paradox, it is similarly 15 possible for tropical cirrus to reduce the amounts of other greenhouse gases needed 16 for solving the paradox and therefore easing the constraints on CO 2 and CH 4 that appear to 17 be in disagreement with geological evidence. 18 Citation: Rondanelli, R., and R. S. Lindzen (2010), Can thin cirrus clouds in the tropics provide a solution to the faint young Sun 19 paradox?, 22 65 implies a drier atmosphere and a reduced greenhouse effect. 66 For instance, Kasting et al. [1988] found that T s remains 67 below freezing up until $2 Ga or S $ 0.85 S 0 . Moreover, 68 Pierrehumbert [2010] shows that including an ice-albedo 69 feedback the paradox is even more dramatic and the 70 solution for S = 0.75 S 0 is a snowball Earth with T s = 71 228 K (however, see Cogley and Henderson-Sellers [1984] 72 for arguments on a much reduced role for the ice-albedo 73 feedback on the early Earth). 74 [4] Sagan and Mullen [1972] first pointed out the exis-75 tence of the paradox and suggested that trace amounts of JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 115, XXXXXX, XXXXXX 1 of 12
Journal of Geophysical Research, 2010
1] Using TRMM VIRS data, we attempt to replicate the analysis made by to quantify the effect of m... more 1] Using TRMM VIRS data, we attempt to replicate the analysis made by to quantify the effect of methodological choices on the magnitude of the observed correlations between upper-level cloud cover and SST. Using brightness temperature thresholds to identify upper-level cloud, we recover a relatively small change in the normalized area of cirrus clouds with SST ($À6%/K compared to $À2%/K found by Su et al. ). We discuss the effect of several methodological choices on the magnitude of the signal, namely, the classification of cloudy regions into convective updrafts and anvil, the use of cloud weighted SST, and the truncation and sampling error of the orbital satellite data with respect to the evolution of mesoscale convective systems. Accounting for some of these methodological differences could resolve the discrepancy between the weak signal documented by and the stronger signal documented originally by and others, including the results reported in this comment.
Comment on ``Variations of tropical upper tropospheric clouds with sea surface temperature and implications for radiative effects'' by H. Su et al
Journal of Geophysical Research, 2010
Using TRMM VIRS data, we attempt to replicate the analysis made by Su et al. (2008) to quantify t... more Using TRMM VIRS data, we attempt to replicate the analysis made by Su et al. (2008) to quantify the effect of methodological choices on the magnitude of the observed correlations between upper-level cloud cover and SST. Using brightness temperature thresholds to identify upper-level cloud, we recover a relatively small change in the normalized area of cirrus clouds with SST (∼−6%/K compared to ∼−2%/K found by Su et al. (2008)). We discuss the effect of several methodological choices on the magnitude of the signal, namely, the classification of cloudy regions into convective updrafts and anvil, the use of cloud weighted SST, and the truncation and sampling error of the orbital satellite data with respect to the evolution of mesoscale convective systems. Accounting for some of these methodological differences could resolve the discrepancy between the weak signal documented by Su et al. (2008) and the stronger signal documented originally by Lindzen et al. (2001) and others, including the results reported in this comment.
Geophysical Research Letters, 2006
Journal of Geophysical Research, 2008
1] This paper focuses on the relation between local sea surface temperature (SST) and convective ... more 1] This paper focuses on the relation between local sea surface temperature (SST) and convective precipitation fraction and stratiform rainfall area from radar observations of precipitation, using data from the Kwajalein atoll ground-based radar as well as the precipitation radar on board the TRMM satellite. We find that the fraction of convective precipitation increases with SST at a rate of about 6 to 12%/K and the area of stratiform rainfall normalized by total precipitation decreases with SST at rates between À5 and À28%/K. These relations are observed to hold for different regions over the tropical oceans and also for different periods of time. Correlations are robust to outliers and to undersampled precipitation regions. Kwajalein results are relatively insensitive to the parameters in the stratiform-convective classification algorithm. Quantitative differences between the results obtained using the two different radars could be explained by the smoothing in the reflectivity of convective regions due to the relatively large pixel size of the TRMM precipitation radar compared to the size of the convective clouds. Although a dependence on temperature such as the one documented is consistent with an increase in the efficiency of convective precipitation (and therefore consistent with one of the mechanisms invoked to explain the original Iris effect observations) this is but one step in studying the possibility of a climate feedback. Further work is required to clarify the particular mechanism involved. Citation: Rondanelli, R., and R. S. Lindzen (2008), Observed variations in convective precipitation fraction and stratiform area with sea surface temperature,
Geophysical Research Letters, 2006
Here, we investigate the possibility of a significant atmospheric contribution to the tidal dissi... more Here, we investigate the possibility of a significant atmospheric contribution to the tidal dissipation of the Phobos-Mars system. We apply the classical tidal theory and we find that most of the gravitational forcing is projected onto the first symmetric Hough mode which has an equivalent depth of about 57 km and is significantly trapped in the vertical. Therefore, no significant dissipation occurs through the vertical propagation of energy and subsequent breaking of the tidal wave as the wave amplifies with height. Alternatively, from the energy stored in the first trapped mode we estimate that the time scale required for the dissipative mechanisms to account for the total dissipation of the tides is of order 102 s. This time scale is unrealistically short, since it would contradict observations of propagating thermal tides in Mars atmosphere. Therefore we conclude that the dissipation of the tidal potential that explains the observed acceleration of Phobos most likely occurs within the solid planet.
Journal of Geophysical Research, 2002
1] Rapid changes in surface ozone mixing ratios (up to 15 ppbv over 12 hours) at the Cerro Tololo... more 1] Rapid changes in surface ozone mixing ratios (up to 15 ppbv over 12 hours) at the Cerro Tololo (CT) station (70°W, 30°S, 2200 m) over the period 1996-2000 are analyzed. These changes explain most of the wintertime variability of the ozone data at CT. Since the wintertime data show no significant diurnal cycle, local circulations and in situ photochemical processes cannot account for the sudden changes in ozone. Rather, a synoptic-scale forcing of the changes is described on the basis of composite analyses of reanalysis data. Synoptic configurations associated with sudden changes in ozone were separated into W and D cases, according to the local evolution of humidity. W cases are characterized by humidity values in excess of 4 hPa lasting one or two days before the ozone maximum. D cases show no significant change in humidity before the ozone maximum. Both in W and in D cases, stratospheric air appears to be advected from polar latitudes to midlatitudes and subtropical latitudes during the development of cutoff lows and deep troughs. The origin of the air arriving at CT during a W and a D case study was assessed using mesoscale numerical simulations. The model calculations for the W case show a deep stratospheric intrusion reaching the lower troposphere in subtropical latitudes during the amplification and mature stages of a cutoff low. For D cases the stratospheric intrusion is mostly confined to midlatitudes and to an oceanic area far from the site of study. Analyses of trajectories show that in both cases, high ozone mixing ratios at the surface occur in connection with air parcels having a stratospheric history.
Journal of Geophysical Research, 2002
1] Rapid changes in surface ozone mixing ratios (up to 15 ppbv over 12 hours) at the Cerro Tololo... more 1] Rapid changes in surface ozone mixing ratios (up to 15 ppbv over 12 hours) at the Cerro Tololo (CT) station (70°W, 30°S, 2200 m) over the period 1996-2000 are analyzed. These changes explain most of the wintertime variability of the ozone data at CT. Since the wintertime data show no significant diurnal cycle, local circulations and in situ photochemical processes cannot account for the sudden changes in ozone. Rather, a synoptic-scale forcing of the changes is described on the basis of composite analyses of reanalysis data. Synoptic configurations associated with sudden changes in ozone were separated into W and D cases, according to the local evolution of humidity. W cases are characterized by humidity values in excess of 4 hPa lasting one or two days before the ozone maximum. D cases show no significant change in humidity before the ozone maximum. Both in W and in D cases, stratospheric air appears to be advected from polar latitudes to midlatitudes and subtropical latitudes during the development of cutoff lows and deep troughs. The origin of the air arriving at CT during a W and a D case study was assessed using mesoscale numerical simulations. The model calculations for the W case show a deep stratospheric intrusion reaching the lower troposphere in subtropical latitudes during the amplification and mature stages of a cutoff low. For D cases the stratospheric intrusion is mostly confined to midlatitudes and to an oceanic area far from the site of study. Analyses of trajectories show that in both cases, high ozone mixing ratios at the surface occur in connection with air parcels having a stratospheric history.
Mesoscale Wind Regimes in Chile at 30°S
Journal of Applied Meteorology, 2002
In November of 1999, four permanent surface stations were installed in the vicinity of the surfac... more In November of 1999, four permanent surface stations were installed in the vicinity of the surface ozone monitoring station on the summit of the Cerro Tololo (2200 m MSL) in Chile at 30°S. These stations were used to study the atmospheric flow conditions, which are important for the ...
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Papers by Roberto Rondanelli