Water vapor measurements at ALOMAR over a solar cycle compared with model calculations by LIMA (original) (raw)
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Journal of the Atmospheric Sciences, 2014
By analyzing the almost-decade-long record of water vapor measurements from the Microwave Limb Sounder (MLS) instrument on the NASA Aura satellite and by detailed diagnostic analysis of the results from state-of-the art climate model simulations, this study confirmed the conceptual picture of the interannual variation in equatorial stratospheric water vapor discussed in earlier papers (e.g., Geller et al.). The interannual anomalies in water vapor are strongly related to the dynamical quasi-biennial oscillation (QBO), and this study presents the first QBO composite of the time-height structure of the equatorial water vapor anomalies. The anomalies display upward propagation below about 10 hPa in a manner analogous to the annual ''tape recorder'' effect, but at higher levels they show clear downward propagation. This study examined these variations in the Model for Interdisciplinary Research on Climate (MIROC)-AGCM and in four models in phase 5 of the Coupled Model Intercomparison Project (CMIP5) that simulate realistic QBOs. Diagnostic budget analysis of the MIROC-AGCM data and comparisons among the CMIP5 model results demonstrate (i) the importance of temperature anomalies at the tropopause induced by the QBO for lowerstratospheric water vapor variations and (ii) that upper-stratospheric water vapor anomalies are largely driven by advection of the mean vertical gradient of water content by the QBO interannual fluctuations in the vertical wind.
Variations of stratospheric water vapor over the past three decades
We examine variations in water vapor in air entering the stratosphere through the 15 tropical tropopause layer (TTL) over the past three decades in satellite data and in a trajectory 16 model. Most of the variance can be explained by three processes that affect the TTL: the quasi-17 biennial oscillation, the strength of the Brewer-Dobson circulation, and the temperature of the 18 tropical troposphere. When these factors act in phase, significant variations in water entering the 19 stratosphere are possible. We also find that volcanic eruptions, which inject aerosol into the 20 TTL, affect the amount of water entering the stratosphere. While there is clear decadal 21 variability in the data and models, we find little evidence for a long-term trend in water entering 22 the stratosphere through the TTL over the past 3 decades. 23 24
Simulations of the Interannual Variability of Stratospheric Water Vapor
Journal of the Atmospheric Sciences, 2002
Observations and model results indicate that the quasi-biennial oscillation (QBO) modulation of stratospheric water vapor results from two causes. Dynamical redistribution of water vapor from the QBO-induced mean meridional circulation dominates the observed variability in the middle and upper stratosphere. In the lower stratosphere, the QBO water vapor variability is dominated by a ''tape recorder'' that results from the dehydration signal accompanying the QBO variation of the tropical cold point tropopause. It is suggested that another low frequency tape recorder exists due to ENSO modulations of the tropical tropopause, but insufficiently long observations of stratospheric water vapor exist to identify this in the observations.
The relationship between tropospheric wave forcing and tropical lower stratospheric water vapor
Atmospheric Chemistry and Physics, 2008
Using water vapor data from HALOE and SAGE II, an anti-correlation between planetary wave driving (here expressed by the mid-latitude eddy heat flux at 50 hPa added from both hemispheres) and tropical lower stratospheric (TLS) water vapor has been obtained. This appears to be a manifestation of the inter-annual variability of the Brewer-Dobson (BD) circulation strength (the driving of which is generally measured in terms of the mid-latitude eddy heat flux), and hence amount of water vapor entering the stratosphere. Some years such as 1991 and 1997 show, however, a clear departure from the anti-correlation which suggests that the water vapor changes in TLS can not be attributed solely to changes in extratropical planetary wave activity (and its effect on the BD circulation). After 2000 a sudden decrease in lower stratospheric water vapor has been reported in earlier studies based upon satellite data from HALOE, SAGE II and POAM III indicating that the lower stratosphere has become drier since then. This is consistent with a sudden rise in the combined mid-latitude eddy heat flux with nearly equal contribution from both hemispheres as shown here and with the increase in tropical upwelling and decrease in cold point temperatures found by . The low water vapor and enhanced planetary wave activity (in turn strength of the BD circulation) has persisted until the end of the satellite data records. From a multi-variate regression analysis applied to 27 years of NCEP and HadAT2 (radiosonde) temperatures (up to 2005) with contributions from solar cycle, stratospheric aerosols and QBO removed, the enhancement wave driving after 2000 is estimated to contribute up to 0.7 K cooling to the overall TLS temperature change during the period 2001-2005 when compared to the period 1996-2000. NCEP cold point temperature show an average decrease of nearly 0.4 K from changes in the wave driving, which is consistent with observed mean TLS water vapor changes of about −0.2 ppm after 2000.
Geophysical Research Letters, 1996
Stratospheric n]casurcmcnts of }120 and C}14 by the. A[nmphcric Trace Molcctrlc Spectroscopy (&l'MOS) I;ouritv [1 ansform spcclromclcr on the AI'I .AS-3 Shulllc flight in Novcmhcr 1994 have been examined 10 invcs(igatc the altitude and gcogmphic va[ i ability of }120 and the quantity H = (}120 -1 20 14) in the tropics and at n]ict-latitudes (8-49['N) in the norlhcm hcmisphcrc. '1'hc mcasutcmcnts inclicalc an average value of 7.18 ~ 0.43 ppmv for total bydrcsgcn H bctwccn altitudes of abcsul 18 to 35 knl, concsprsndin,g 10 an average water vapor mixing ratio of 3,81 ~ 0.29 ppnw entering the stratosphere. '1'hc 1120 vcr[ical distribution in the tropics cxhitrits a wave-like structure in the 16-25 km altitucle ran:c. suggestive of seasonal variations in the water vapor transported fro]ll
Bulletin of the American Meteorological Society, 1974
Observational data from the lower stratosphere are examined to determine to what extent an upper limit can be placed on the water-vapor content of that region of the atmosphere, a quantity which is presently in controversy by half an order of magnitude. Presented herein are the details of a systematic search of 37 winter months (November 1964-December 1971) of Northern Hemispheric 30-mb and 50-mb synoptic maps, as well as a search of over 170,000 individual radiosonde 30-mb temperature soundings for the same period. In addition, the results of a search of all available high-latitude Northern Hemispheric meteorological rocket data and a study of the 30-mb climatology for Jan Mayen Island are presented. The results of these studies are compared with the results of a careful literature search, as well as an inquiry to an airline pilot's volunteer organization, for reports of stratospheric cloud observations. The extreme sparsity of such observations, even with allowance for possible obscuring effects of tropospheric cloud cover, leads to the conclusion that water-vapor saturation is seldom reached in the lower stratosphere of the Northern Hemisphere. This conclusion, coupled with the results of the fairly extensive stratospheric observational data mentioned above, appears to be inconsistent with the concept of an average "moist" (10 ppm or greater) lower stratosphere. From the results of the present investigation, it may be inferred that the average 30-mb and 50-mb water-vapor mixing ratios, for the dates investigated, is almost certainly less than 11 ppm, and probably less than 6-8 ppm. The data appear to constitute reasonable evidence for setting an upper limit on the average 30-mb water-vapor mixing ratio at approximately the 6-8 ppm level for high latitudes in the Northern Hemispheric winter. These 30-mb results fall in between the values quoted by investigators reporting a "dry" (a few ppm mixing ratio) and "moist" (^10 ppm mixing ratio) lower stratosphere, and thus appear to provide a reasonably definitive choice on the question, independent of instru
Geophysical Research Letters, 1998
Observations of stratospheric water vapour, made by the Microwave Limb Sounder (MLS) during the 1992 and 1993 Arctic and 1992 Antarctic late winters have now been produced using version 4 of the retrieval software. These improved measurements are analysed as equivalent latitude zonal means. Major interhemispheric differences are revealed in the water vapour content of the vortex in the lower stratosphere. This technique emphasises mixing ratio gradients at the edges of both polar vortices, and a local maximum at the edge of the Antarctic vortex. There are some small interhemispheric differences in mixing ratios in mid-latitudes, but they are not strongly related to the dehydration of the Antarctic vortex. A mixing ratio gradient across the interior of the Antarctic vortex at 530K indicates it is not isentropically mixed. A strong local maximum in mixing ratio at the centre of the Antarctic vortex in the mid-stratosphere indicates it is not well mixed in the mid-stratosphere also. There is little evidence of significant structure inside the Arctic vortex.
Journal of Geophysical Research, 2008
1] A quasi 5-day signature in different middle atmospheric parameters such as the horizontal wind, the temperature, the pressure, the occurrence rate of Polar Mesospheric Summer Echoes (PMSEs) and Noctilucent Clouds (NLCs) or the ozone concentration has been found during the last decades since the 1970s. These effects were interpreted in terms of the impact of a 5-day planetary normal mode (1,1) of Rossby waves. In the mesosphere the quasi 5-day variation is predominantly a summer phenomenon occurring in high and middle latitudes. Water vapor measurements were carried out by means of the microwave technique in high latitudes at ALOMAR (69.29°N, 16.03°E), Norway, for the year 2003. The observations revealed a clear signature of a quasi 5-day variation. Using our real-date Leibniz-Institute Middle Atmosphere (LIMA) model of the Institute of Atmospheric Physics in Kühlungsborn, Germany, in a case study for the same period we found a very clear quasi 5-day signal in the distribution of the minor constituents and particularly in the water vapor mixing ratio in middle to high northern latitudes in the late spring and summer season. A similar finding is valid for the southern hemisphere half a year later. The variations of the minor constituents are triggered by the wind system resulting from the dynamical part of the model. The calculations satisfactorily reproduce the observed water vapor concentrations. In particular, the annual variation including intraannual variations is reflected by the model. We discuss the findings in terms of dynamics and chemistry.