CN113779770B - Assessment method for influence of cyclone on North sea ice - Google Patents
Assessment method for influence of cyclone on North sea ice Download PDFInfo
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Abstract
The invention discloses a method for evaluating the influence of a cyclone on North sea ice, which comprises the steps of downloading atmospheric analysis data to obtain a variable field and a basic field at the moment of cyclone occurrence; precisely determining the influence range of the cyclone; subtracting the basic field from the variable field at the moment of cyclone occurrence, and calculating the disturbance field of the variable in the cyclone range; performing iterative spatial smoothing on the disturbance field, and calculating a non-cyclone component of the disturbance field; adding non-cyclone components in the cyclone range to the basic field, and calculating a variable field after cyclone removal; and taking the cyclone generation time and the variable field after cyclone removal as the atmospheric forced field of the North sea ice numerical mode respectively, calculating the North sea ice change under two conditions, and then calculating the difference of the two sea ice changes to obtain the net influence of the cyclone on the North sea ice. The assessment method of the influence of the cyclone on the North sea ice net is provided.
Description
Technical Field
The invention relates to an evaluation method for the change of arctic sea ice influenced by cyclone, in particular to an evaluation method for the change of arctic sea ice caused by measuring cyclone activity.
Background
Arctic is an important component of the global climate system, being a sensitive and critical area of global change. In recent decades, and especially in the 21 st century, the arctic environment has changed rapidly. Rapid North sea ice reduction is one of the main features of North climate change. Since satellite observation in 1979, arctic sea ice has shown a significant trend to decrease, and in the last decade, the arctic sea ice range, sea ice thickness, and the proportion of years of ice have all been in a rapid trend to decrease. Meanwhile, weather changes cause extreme weather events to occur frequently at medium and high latitudes. Cyclone is a common weather-scale event that affects arctic sea ice significantly. In general, cyclones can cause not only local strong winds, but also a large amount of warm wet air flow. Thinning and reduction of sea ice results in a more rapid and vigorous response of sea ice to cyclone. However, the net effect of the cyclone on arctic sea ice is not clear. Under the conditions that the North sea ice is rapidly reduced and the activities of people in the North are increasingly increased, the method for measuring the net influence of the cyclone on the North sea ice is particularly important, so that the influence of different cyclones on the North sea ice can be researched, the physical mechanism of the influence can be explored, and more accurate North sea ice forecast products can be provided for the activities of people in the North, such as navigation of a ship, in the North sea ice channel.
The influence of the cyclone on the North Pole sea ice is generally studied, and the influence of the cyclone on the North Pole sea ice is mainly reflected by analyzing the integral change of the sea ice area, the sea ice volume, the sea ice density, the sea ice thickness or the sea ice drifting speed before and after the cyclone passes through the border, but the quantitative result obtained by the method comprises the influence of the cyclone and the atmospheric background field on the North Pole sea ice. That is, the existing method cannot quantitatively express the influence of the pure cyclone on the arctic sea ice, and can cause the influence of the cyclone on the arctic sea ice to be overestimated or underestimated, thereby affecting the accuracy of short-term prediction of the arctic sea ice.
Disclosure of Invention
Aiming at the problems that the influence of the cyclone on the North sea ice is quicker and the influence degree is larger, the invention provides the assessment method for the influence of the cyclone on the North sea ice, which can quantitatively obtain the influence degree of different cyclones on the North sea ice, discuss the physical mechanism of the cyclone, and provide important support for improving the short-term forecast level of the North sea ice.
According to the method, the influence range of the cyclone is determined, the airless cyclone field of the atmospheric variable is obtained by removing the arctic cyclone, and the sea ice density, the sea ice thickness and the sea ice drift speed change caused by the atmospheric background field are obtained by the arctic sea ice numerical mode. And subtracting the influence of the atmospheric background field on the sea ice from the North pole sea ice numerical mode result when the cyclone exists, and more accurately acquiring the influence of the cyclone on the North pole sea ice. By analyzing the net effect of the cyclones on the arctic sea ice, the physical mechanism of the effect of different cyclones on the arctic sea ice can be explored, and the short-term prediction level of the arctic sea ice is improved.
The technical scheme adopted for solving the technical problems is as follows: a method of assessing the net effect of a cyclone on arctic sea ice comprising the steps of:
step 1, acquiring arctic atmosphere analysis data of a cyclone occurrence period to obtain a real field of the cyclone occurrence moment; acquiring atmospheric analysis data of the same region of the historical year and the cyclone generation period to obtain a basic field;
step 2, according to sea level air pressure and a real field of a 10m wind field, obtaining boundary points of a cyclone influence range by constructing a polar coordinate system grid, mapping the boundary points into longitude and latitude grids, and determining the cyclone influence range;
step 3, in the cyclone influence range, the real field and the basic field of each atmospheric variable are differenced to obtain a disturbance field, and iterative space smoothing is carried out on the disturbance field to obtain a non-cyclone field of all the atmospheric variables;
and 4, respectively obtaining a variation condition of the North sea ice with the cyclone influence and a variation condition of the North sea ice without the cyclone influence according to the real field obtained in the step 1 and the airless field of the atmospheric variable obtained in the step 3, and making a difference between the two results to obtain the net influence of the cyclone on the North sea ice.
The real field comprises 8 atmospheric variables of sea level air pressure, a 10m wind speed u component, a 10m wind speed v component, a 2m air temperature, a 2m specific humidity, precipitation, long wave and short wave radiation under the ground, and corresponding longitude and latitude coordinate grid data.
The basic field comprises 8 atmospheric variables of sea level air pressure, a 10m wind speed u component, a 10m wind speed v component, a 2m air temperature, a 2m specific humidity, precipitation, long wave and short wave radiation under the ground, and corresponding longitude and latitude coordinate grid data, and the average value of the time dimensions of the 8 atmospheric variables is calculated to obtain the basic field of the 8 atmospheric variables.
The step 2 specifically comprises the following steps:
2.1, selecting a certain moment when the cyclone occurs, and acquiring longitude and latitude coordinates of the cyclone center and the sea level air pressure P of the closed isobar line of the outermost layer of the cyclone according to the real field of the sea level air pressure at the moment e ；
2.2, taking the cyclone center as a pole, guiding a ray along the longitude line of the cyclone center in the positive and negative directions as a polar axis, establishing a grid of a polar coordinate system, re-projecting sea level air pressure and a 10m wind field under the longitude and latitude coordinates at a selected moment to the polar coordinate system, and calculating the component v of the 10m wind speed under the polar coordinate system in the polar angle direction θ (r, θ), where r represents the polar diameter and θ represents the polar angle;
2.3, determining a ray at intervals of a set angle by taking a pole as an endpoint in a polar coordinate system grid, and determining a boundary point of a cyclone influence range in the direction along the increasing direction of the pole diameter for each ray according to the wind speed and the sea level air pressure;
2.4, among a plurality of boundary points of the cyclone influence range, when the sea level air pressure of the boundary point in a certain direction is less than P e In this direction, the first one is selected to satisfy the sea level pressure p=p, starting from the pole in the direction of increasing the pole diameter e The grid points at the position are used as boundary points after the direction correction;
2.5, re-projecting the obtained coordinates of the plurality of boundary points into longitude and latitude grids of the atmospheric variable to obtain the longitude and latitude coordinates of the boundary points, and sequentially connecting the plurality of boundary points to obtain a cyclone influence range at a selected moment;
and 2.6, repeating the steps 2.1 to 2.5 by using the sea level air pressure real field at other moments, and acquiring the cyclone influence ranges of all cyclone occurrence moments.
The spatial resolution of the polar coordinate system grid in the polar diameter direction and the polar angle direction is 10km and 1 degree respectively.
In the step 2.3, the boundary point of the cyclone influence range in the direction is determined according to the wind speed of 10m and the sea level air pressure, and the method specifically comprises the following steps: the first one satisfies v at the same time θ <Threshold 1, sea level air pressure P>Threshold value 2 and wind speed U<The point of the threshold 3 condition is noted as the boundary point of the cyclone influence range in this direction at the selected moment.
The step 3 specifically comprises the following steps:
3.1, subtracting a corresponding basic field from a real field of a certain atmospheric variable in the cyclone influence range at a certain selected moment to obtain a disturbance field of the atmospheric variable in the cyclone influence range at the moment;
3.2 calculating the spatial variance sigma of the atmospheric variable disturbance field within the cyclone influence range 1 2 ；
3.3, carrying out space smoothing on the atmospheric variable disturbance field in the cyclone influence range to obtain a new disturbance field,and calculating the spatial variance sigma in the cyclone influence range after the spatial smoothing 2 2 ；
3.4, calculating the spatial variance change before and after the spatial smoothing:
Δσ 2 ＝|σ 2 2 –σ 1 2 |
3.5, repeating the steps 3.2 to 3.4, and performing iterative spatial smoothing until the spatial variance changes delta sigma 2 The atmospheric variable after the space smoothing is the non-cyclone component at the moment when the atmospheric variable is smaller than the set threshold value;
3.6, adding the non-cyclone component of the atmospheric variable to the basic field of the atmospheric variable in the cyclone influence range at the moment to obtain the background field of the atmospheric variable with the cyclone influence removed at the moment;
3.7, replacing the atmospheric variable values at the same time and the same position in the real field by using the background field of the atmospheric variable in the cyclone influence range at the time to obtain an atmospheric variable airless field after removing the selected cyclone influence at the time;
3.8, repeating the steps 3.1 to 3.7 by using the real field and the basic field of the atmospheric variable at other moments and the cyclone influence range of the same moment obtained in the step 2, and carrying out iterative processing on the atmospheric variable at all moments to obtain the airless fields of the atmospheric variable at all cyclone occurrence moments;
and 3.9, repeating the steps 3.1-3.8, traversing all the atmospheric variables, and obtaining the airless fields of all the atmospheric variables at all the moments.
The spatial smoothing is achieved by the following formula:
where (L, K) represents the grid position that the t-th iteration spatial smoothing needs to calculate,is the result after the t-th iteration of a certain atmospheric variable at the (L, K) position.
The step 4 specifically comprises the following steps:
4.1, acquiring the spatial distribution of sea ice density, sea ice thickness and sea ice drift speed with cyclone influence according to the atmospheric variable real field acquired in the step 1 as an atmospheric forced field in a north pole sea ice numerical mode;
4.2, using the atmospheric variable cyclone-free field obtained in the step 3 as an atmospheric forced field, and operating the north pole sea ice numerical mode which is the same as that of the step 4.1 to obtain the space distribution of sea ice density, sea ice thickness and sea ice drift speed without cyclone influence;
4.3, subtracting the sea ice density, the sea ice thickness and the sea ice drift velocity of the corresponding moment and the corresponding grid obtained in the step 4.2 from the sea ice density, the sea ice thickness and the sea ice drift velocity of each grid at a certain moment to obtain the net influence of the cyclone at the moment on the sea ice density, the sea ice thickness and the sea ice drift velocity of all grids; if the result is negative, the net effect of the cyclone on the sea ice concentration, the sea ice thickness and the sea ice drift velocity is to reduce the sea ice concentration, the sea ice thickness or the sea ice drift velocity; if the result is positive, the net effect of the cyclone on the sea ice concentration, the sea ice thickness and the sea ice drift velocity is to increase the sea ice concentration or the sea ice thickness or the sea ice drift velocity;
and 4.4, repeating the step 4.3, and traversing all moments to obtain the net influence of the cyclone at all moments on the sea ice density, the sea ice thickness and the sea ice drift speed of all grids.
Step 4 also includes visualizing the net effect of the cyclone on all grid sea ice concentration, sea ice thickness, and sea ice drift velocity: and selecting positive values and negative values of net influences of different colors representing sea ice concentration, sea ice thickness and sea ice drift speed, wherein the larger the absolute value is, the darker the corresponding color is, so that the net influence of the cyclone on the sea ice at a certain position is that the sea ice concentration, the sea ice thickness and the sea ice drift speed are increased or reduced.
The invention has the following beneficial effects and advantages:
obtaining a net impact metric of cyclone on arctic sea ice is of great importance in studying the physical mechanism of arctic weather scale events affecting sea ice and improving the short-term forecast level of arctic sea ice. The invention realizes the assessment method of the effect of the cyclone on the North sea ice, and the method for removing the North cyclone and the North sea ice numerical mode are utilized to effectively filter the effect of the atmospheric background field on the North sea ice from the North sea ice change when the cyclone is affected, so as to obtain the net effect of the cyclone on the North sea ice.
The method has the following specific beneficial effects:
first, the invention can analyze data by using the atmosphere issued by any mechanism, is not limited by time resolution, space resolution and data format, and can ensure the real-time property, easy acquisition and processing convenience of the data.
Second, the invention filters out the influence of the atmospheric background field on the arctic sea ice during the cyclone transit from the arctic sea ice change during the cyclone transit, and more accurately quantifies the influence of the cyclone on the arctic sea ice.
Thirdly, the method is suitable for obtaining the influence of different cyclones on the arctic sea ice, and can further analyze the influence mechanism of the different cyclones on the arctic sea ice according to the diagnosis variable output by the arctic sea ice numerical mode, so that the short-term prediction level of the arctic sea ice is improved.
Fourth, the data processing of the invention realizes batch processing through programming, and the operation is simple, thereby avoiding introducing artificial errors and greatly improving the data processing efficiency.
Fifth, the invention is suitable for the mechanism research of the rapid change of the arctic sea ice by the arctic weather scale event, and is helpful for improving the short-term forecast level of the arctic sea ice.
Drawings
FIG. 1 is a flow chart of a method for evaluating the net effect of a cyclone on arctic sea ice;
FIG. 2 graph of actual field (a, c) and field after cyclone removal (b, d) results for sea level barometric pressure, 10m wind speed and 2m air temperature at 6/8/2012 (UTC);
FIG. 3 is a graph of the spatial distribution of North sea ice concentration at 12 (UTC) at 8/6/2012 without (b) cyclone effects and the net effect of the cyclone on North sea ice concentration (c) results;
FIG. 4 is a graph of the spatial distribution of North sea ice thickness at 2012, 8, 6, and 12 (UTC) without (b) cyclone effects and the net effect of the cyclone on North sea ice thickness (c) results;
fig. 5 is a graph of the spatial distribution of the arctic sea ice drift velocity at 12 (UTC) at 8, 2012 without the influence of (b) the cyclone and the net influence of the cyclone on the arctic sea ice drift velocity (c).
Detailed Description
The present invention will be described in further detail with reference to examples.
A method of assessing the net effect of a cyclone on arctic sea ice comprising the steps of:
(1) Acquiring data
The method comprises the steps of firstly, acquiring arctic atmosphere analysis data of a cyclone occurrence period, wherein the arctic atmosphere analysis data comprise 8 atmosphere variables such as sea level air pressure, a 10m wind speed u component, a 10m wind speed v component, a 2m air temperature, a 2m specific humidity, precipitation, ground downward long wave and short wave radiation and the like, and corresponding longitude and latitude coordinate grid data, so that a real field of the 8 atmosphere variables at the cyclone occurrence moment is obtained;
step two, acquiring atmospheric analysis data of the same area in the same period as the cyclone occurrence period in the historical year, wherein the atmospheric analysis data comprise 8 atmospheric variables such as sea level air pressure, a 10m wind speed u component, a 10m wind speed v component, a 2m air temperature, a 2m specific humidity, precipitation, ground downward long wave radiation, short wave radiation and the like, and corresponding longitude and latitude coordinate grid data, and respectively calculating average values of the time dimensions of the 8 atmospheric variables to obtain a basic field of the 8 atmospheric variables;
(2) Determining accurate cyclone impact range
Thirdly, selecting a certain moment when the cyclone occurs, and acquiring longitude and latitude coordinates of the cyclone center and the sea level air pressure P of the closed isobar line of the outermost layer of the cyclone according to the real field of the sea level air pressure at the moment e ；
Fourthly, taking the cyclone center as a pole, guiding a ray along the longitude direction of the cyclone center in the positive and negative directions as a polar axis, establishing a polar coordinate system grid, respectively setting the spatial resolutions of the new grid in the polar diameter direction and the polar angle direction to be 10km and 1 DEG, and setting the sea level air pressure under the longitude and latitude coordinates at the selected momentAnd re-projecting the 10m wind field under the polar coordinate system, and calculating the component v of the 10m wind speed under the polar coordinate system in the polar angle direction θ (r,θ)；
Fifthly, determining 24 rays at intervals of 15 degrees by taking a pole as an endpoint in the polar coordinate system grid established in the fourth step, wherein v is satisfied for each ray along the increasing direction of the pole diameter at the first time θ <3m·s -1 Sea level air pressure P>(P e -3) hPa and wind speed U<5m·s -1 The point of the condition is preliminarily marked as the boundary point of the cyclone influence range in the direction at the selected moment;
sixth, if the sea level air pressure at the boundary point in a certain direction is less than P at the boundary point of the 24 cyclone influence ranges obtained in the fifth step e In this direction, the first one satisfies the sea level air pressure p=p, starting from the pole in the direction of increasing the pole diameter e The grid points at the position are used as boundary points after the direction correction;
a seventh step of re-projecting the 24 boundary point coordinates obtained in the fifth step and the sixth step into an original longitude and latitude grid of an atmospheric variable to obtain 24 boundary point longitude and latitude coordinates, and sequentially connecting the 24 boundary points to obtain a cyclone influence range with accurate selected moment;
eighth, repeating the third step to the seventh step by using the sea level air pressure real field at other moments, and performing iterative processing on all moments to obtain precise cyclone influence ranges of all cyclone occurrence moments;
(3) Removing cyclones
A ninth step of subtracting the corresponding 2m air temperature basic field obtained in the second step from the real field of the 2m air temperature obtained in the first step aiming at a certain selected moment, and combining the cyclone influence range of the moment obtained in the eighth step to obtain a disturbance field of the 2m air temperature in the cyclone influence range of the moment;
tenth step, calculating the space variance sigma of 2m air temperature disturbance field in the cyclone influence range 1 2 ；
Eleventh, performing space smoothing on the 2m air temperature disturbance field in the cyclone influence range to obtain a new disturbance field, and calculating the space smoothed cyclone influence rangeSpatial variance sigma 2 2 ；
The twelfth step, calculating the space variance change before and after the space smoothing, the calculating method is as follows:
Δσ 2 ＝|σ 2 2 –σ 1 2 |
thirteenth, repeating the tenth to twelfth steps, performing iterative spatial smoothing until the spatial variance changes by delta sigma 2 The temperature field of 2m after the space smoothing is the non-cyclone component at the moment when the temperature field is smaller than a specific threshold value;
fourteenth step, adding the non-cyclone component of the air temperature of 2m obtained in the thirteenth step with the basic field of the air temperature of 2m in the cyclone range to obtain the background field of the air temperature of 2m which removes the influence of the cyclone at the moment;
a fifteenth step of replacing the 2m air temperature at the same moment and the same position in the real field by the background field of the 2m air temperature obtained in the fourteenth step to obtain a 2m air temperature after the influence of the selected cyclone is removed at the moment, namely a non-cyclone field of the 2m air temperature;
sixteenth, using the real field and the basic field of the air temperature of 2m at other moments and the accurate cyclone influence range of the same moment obtained in the eighth step, repeating the ninth to fifteenth steps, and performing iterative processing on the air temperature of 2m at all moments to obtain the non-cyclone field of the air temperature of 2m at all cyclone occurrence moments;
seventeenth, replacing the air temperature of 2m in the ninth to sixteenth steps with other atmospheric variables obtained in the first step, and performing iterative processing on the rest 7 atmospheric variables to obtain airless fields of all 8 atmospheric variables;
(4) Acquiring net effect of cyclone on arctic sea ice
Eighteenth, using the real field of the atmospheric variable obtained in the first step as an atmospheric forced field of a north pole sea ice numerical mode to obtain the spatial distribution of sea ice density, sea ice thickness and sea ice drift velocity with cyclone influence;
nineteenth, using the atmospheric variable non-cyclone field obtained in the seventeenth step as an atmospheric forced field, and operating the same North polar sea ice numerical mode as the eighteenth step to obtain the spatial distribution of sea ice density, sea ice thickness and sea ice drift speed without cyclone influence;
the twenty-first step is to calculate the net influence of the cyclone at the moment on the sea ice density of each grid at each moment by subtracting the sea ice density of the corresponding moment and the sea ice density of the corresponding grid obtained in the nineteenth step from the sea ice density of the sea ice acquired in the eighteenth step;
the twenty-first step is repeated, the twentieth step is repeated, iteration processing is carried out on all grids at all moments, and the net influence of cyclone at all moments on sea ice concentration of all grids is calculated;
twenty-second, establishing a drawing window, visualizing the net influence of the cyclone on the sea ice density of all grids, and intuitively representing the net influence of the cyclone on the sea ice at the position by using an image to increase or decrease the sea ice density;
and repeating the twenty-third step and the twentieth step to the twenty-second step, replacing the sea ice density with the sea ice thickness obtained in the eighteenth step and the nineteenth step to obtain the net influence of the cyclone on the sea ice thickness, and visually representing the net influence of the cyclone on the sea ice at the position by using an image to increase or decrease the sea ice thickness.
And repeating the twenty-fourth step and the twentieth step to the twenty-second step, replacing the sea ice density with the sea ice drifting speed obtained in the eighteenth step and the nineteenth step to obtain the net influence of the cyclone on the sea ice drifting speed, and visually representing the net influence of the cyclone on the sea ice at the position by using an image to increase or decrease the sea ice drifting speed.
In the first step to the second step, 8 atmospheric variables such as sea level air pressure, a 10m wind speed u component, a 10m wind speed v component, a 2m air temperature, a 2m specific humidity, precipitation, ground downward long wave and short wave radiation and the like are respectively expressed in hPa, m.s -1 、m·s -1 、℃、kg·kg -1 、m·s -1 、W·m -2 And W.m -2 。
In the tenth to twelfth steps, the spatial variance is a variance of all grid point variable values of the atmospheric variable calculated at the moment in the cyclone influence range.
In the eleventh step, the spatial smoothing is calculated as follows:
where (L, K) represents the lattice point position that needs to be calculated for the t-th iteration spatial smoothing,is the result after the t-th iteration of a certain atmospheric variable at the (L, K) position.
In the thirteenth step, the specific threshold values of 8 atmospheric variables such as sea level air pressure, 10m wind speed u component, 10m wind speed v component, 2m air temperature, 2m specific humidity, precipitation, ground downward long wave and short wave radiation are respectively 1.0X10 -4 hPa、1.0×10 - 4 m·s -1 、1.0×10 -4 m·s -1 、1.0×10 -5 ℃、1.0×10 -10 kg·kg -1 、1.0×10 -20 m·s -1 、1.0×10 -4 W·m -2 And 1.0X10 -4 W·m -2 。
In the eighteenth step and the nineteenth step, the atmospheric forced field of the numerical mode of the North sea ice used must be a part or all of 7 atmospheric variables such as a 10m wind speed u component, a 10m wind speed v component, a 2m air temperature, a 2m specific humidity, precipitation, long wave and short wave radiation facing downwards, and the like.
In the eighteenth and nineteenth steps, the time resolution of the spatial distribution of the sea ice concentration, the sea ice thickness and the sea ice drift velocity obtained is 6 hours or more.
In the twenty-first step, if the result is a negative value, the net influence of the cyclone on the sea ice concentration, the sea ice thickness or the sea ice drift velocity is that the sea ice concentration, the sea ice thickness or the sea ice drift velocity is reduced; if the result is positive, it means that the net effect of the cyclone on the sea ice concentration, sea ice thickness, or sea ice drift velocity is to increase the sea ice concentration, sea ice thickness, or sea ice drift velocity.
In the twentieth step, if the absolute value of the result is larger, the net influence of the cyclone on the sea ice at the position is larger.
In the twenty-second and twenty-third steps, visualizing the net effect of the cyclone on sea ice concentration, sea ice thickness, and sea ice drift velocity includes differentiating the net effect data for each grid sea ice concentration, sea ice thickness, and sea ice drift velocity with a color and displaying a land overlay thereon.
And selecting positive values and negative values of net influences of different colors representing sea ice density, sea ice thickness and sea ice drift speed, wherein the larger the absolute value is, the darker the corresponding color is.
As shown in fig. 1, which is a flowchart of this example, the specific implementation steps of the method for evaluating the effect of cyclone on the net ice of arctic sea include the following:
and step one, acquiring arctic atmosphere analysis data of a cyclone generation period, wherein the arctic atmosphere analysis data comprises sea level air pressure, 10m wind speed u and v component data, 2m air temperature, 2m specific humidity, precipitation, and ground downward long wave and short wave radiation, so as to obtain a real field of the cyclone generation moment. These several data may be obtained from the analytical data product issued by any institution, but it must be ensured that all data come from the same atmospheric analytical data set.
The present example used JRA-55 analytical data issued by the Japan Meteorological corporation with a spatial resolution of 1.25 deg. x 1.25 deg., a temporal resolution of 3h and a format of GRIB1. The data downloaded in this example is 4-12 days 8 of 2012, and the downloaded data set covers the entire arctic region. The sea level barometric pressure, 10m wind speed and 2m air temperature profiles at 12 days 8, 6, 2012 (UTC) are shown as a and c in fig. 2.
And secondly, acquiring atmospheric analysis data of the same region of the historical year and the cyclone generation period, wherein the atmospheric analysis data comprise sea level air pressure, 10m wind speed u and v component data, 2m air temperature, 2m specific humidity, precipitation, long wave and short wave radiation facing downwards, calculating an average value in a time dimension, and calculating a basic field of each variable.
The downloaded data time is 8 months 4-12 days and the year is 1995-2006, and the downloaded data set covers the whole arctic region. The climatic mean in 1995-2006 was calculated as the base field.
And thirdly, determining the sea level air pressure of the central position and the outermost closed isobars of the cyclone according to the sea level air pressure at the moment of occurrence of the cyclone.
And fourthly, carrying out polar coordinate re-projection on the sea level air pressure and the 10m wind field at the moment of cyclone occurrence, taking the cyclone center as a pole, guiding a ray from the cyclone center to the direction of the north pole as a polar axis, resampling the spatial resolution to be 10km multiplied by 1 DEG, and calculating the 10m wind speed component under a polar coordinate system.
And fifthly, taking a pole as an endpoint, determining 24 rays at intervals of 15 degrees, determining the boundary of the cyclone along the increasing direction of the pole diameter according to the wind speed and the sea level air pressure, and sequentially connecting the 24 boundary points to obtain the influence range of the cyclone. The red thick solid line in fig. 2 shows the cyclone impact boundary determined at this time.
And sixthly, subtracting the basic field from the real field in the cyclone range to obtain the disturbance field in the cyclone range.
Seventhly, carrying out iterative space smoothing on a disturbance field in a cyclone range, and calculating the space variance change of the space smoothing of two adjacent times, wherein the space smoothing calculation method comprises the following steps:
where (L, K) represents the lattice point position that needs to be calculated for the t-th iteration spatial smoothing,is the result after the t-th iteration of a certain atmospheric variable at the (L, K) position.
The method for calculating the spatial variance change of two adjacent spatial smoothing steps in the cyclone range is as follows:
Δσ 2 ＝|σ t 2 –σ t-1 2 |
in sigma t 2 Sum sigma t-1 2 The spatial variance in the cyclonic region after the t-th iteration and the t-1 th iteration are shown, respectively.
And eighth, stopping the space smoothing when the space variance change of the two adjacent times of space smoothing is smaller than a specific threshold value, and obtaining the non-cyclone component from the flat field.
And a ninth step of adding the non-cyclone component obtained in the eighth step to a basic field in the cyclone range to obtain an atmospheric variable field for removing the cyclone influence. B and d in fig. 2 show the sea level air pressure, 10m wind field and 2m air temperature spatial distribution after cyclone removal at 12 days 8, 6, 2012 (UTC).
And tenth, respectively taking the atmospheric variable field at the moment of cyclone occurrence and the atmospheric variable field after cyclone removal obtained in the ninth step as an atmospheric forced field in a North pole sea ice numerical mode, and calculating the North pole sea ice change condition when the cyclone exists or does not exist, wherein the difference between the two is the net influence of the cyclone on the North pole sea ice. The a, b, c in fig. 3, 4 and 5 are the spatial distribution of sea ice concentration, sea ice thickness and sea ice drift velocity with and without cyclones at 12 (UTC) of 8/6/2012, respectively, and the difference between the two, i.e. the net effect of the final acquired cyclone on arctic sea ice. After the difference results with or without cyclone influence are visualized, the influence degree of the cyclone on the sea ice in different sea areas of the north pole can be intuitively and clearly obtained.
In addition to the examples described above, other embodiments of the invention are possible. All technical schemes formed by equivalent substitution or equivalent transformation fall within the protection scope of the invention.
Claims (9)
1. A method of assessing the net effect of a cyclone on arctic sea ice comprising the steps of:
step 1, acquiring arctic atmosphere analysis data of a cyclone occurrence period to obtain a real field of the cyclone occurrence moment; acquiring atmospheric analysis data of the same region of the historical year and the cyclone generation period to obtain a basic field;
step 2, according to sea level air pressure and a real field of a 10m wind field, obtaining boundary points of a cyclone influence range by constructing a polar coordinate system grid, mapping the boundary points into longitude and latitude grids, and determining the cyclone influence range;
step 3, in the cyclone influence range, the real field and the basic field of each atmospheric variable are differenced to obtain a disturbance field, and iterative space smoothing is carried out on the disturbance field to obtain a non-cyclone field of all the atmospheric variables;
the step 3 specifically comprises the following steps:
3.1, subtracting a corresponding basic field from a real field of a certain atmospheric variable in the cyclone influence range at a certain selected moment to obtain a disturbance field of the atmospheric variable in the cyclone influence range at the moment;
3.2 calculating the spatial variance sigma of the atmospheric variable disturbance field within the cyclone influence range 1 2 ；
3.3, performing space smoothing on the atmospheric variable disturbance field in the cyclone influence range to obtain a new disturbance field, and calculating the space variance sigma in the cyclone influence range after space smoothing 2 2 ；
3.4, calculating the spatial variance change before and after the spatial smoothing:
Δσ 2 ＝|σ 2 2 –σ 1 2 |
3.5, repeating the steps 3.2 to 3.4, and performing iterative spatial smoothing until the spatial variance changes delta sigma 2 The atmospheric variable after the space smoothing is the non-cyclone component at the moment when the atmospheric variable is smaller than the set threshold value;
3.6, adding the non-cyclone component of the atmospheric variable to the basic field of the atmospheric variable in the cyclone influence range at the moment to obtain the background field of the atmospheric variable with the cyclone influence removed at the moment;
3.7, replacing the atmospheric variable values at the same time and the same position in the real field by using the background field of the atmospheric variable in the cyclone influence range at the time to obtain an atmospheric variable airless field after removing the selected cyclone influence at the time;
3.8, repeating the steps 3.1 to 3.7 by using the real field and the basic field of the atmospheric variable at other moments and the cyclone influence range of the same moment obtained in the step 2, and carrying out iterative processing on the atmospheric variable at all moments to obtain the airless fields of the atmospheric variable at all cyclone occurrence moments;
3.9, repeating the steps 3.1-3.8, traversing all the atmospheric variables, and obtaining the airless fields of all the atmospheric variables at all the moments;
and 4, respectively obtaining a variation condition of the North sea ice with the cyclone influence and a variation condition of the North sea ice without the cyclone influence according to the real field obtained in the step 1 and the airless field of the atmospheric variable obtained in the step 3, and making a difference between the two results to obtain the net influence of the cyclone on the North sea ice.
2. The method of assessing the net effect of a cyclone on arctic sea ice of claim 1, wherein said real field comprises 8 atmospheric variables of sea level barometric pressure, 10m wind speed u component, 10m wind speed v component, 2m air temperature, 2m specific humidity, precipitation, ground down long wave and short wave radiation, and corresponding longitude and latitude coordinate grid data.
3. A method of assessing the net effect of a cyclone on arctic sea ice as claimed in claim 1 wherein said basic field comprises 8 atmospheric variables of sea level air pressure, 10m wind speed u component, 10m wind speed v component, 2m air temperature, 2m specific humidity, precipitation, ground down long wave and short wave radiation, and corresponding longitude and latitude coordinate grid data, and averaging the time dimensions of the 8 atmospheric variables to obtain a basic field of the 8 atmospheric variables.
4. The method for evaluating the net effect of a cyclone on ice on arctic sea according to claim 1, wherein said step 2 is specifically as follows:
2.1, selecting a certain moment when the cyclone occurs, and acquiring longitude and latitude coordinates of the cyclone center and the sea level air pressure P of the closed isobar line of the outermost layer of the cyclone according to the real field of the sea level air pressure at the moment e ；
2.2, taking the cyclone center as a pole, guiding a ray along the longitude line of the cyclone center in the positive and negative directions as a polar axis, establishing a grid of a polar coordinate system, re-projecting sea level air pressure and a 10m wind field under the longitude and latitude coordinates at a selected moment to the polar coordinate system, and calculating the component v of the 10m wind speed under the polar coordinate system in the polar angle direction θ (r, θ), where r represents the polar diameter and θ represents the polar angle；
2.3, determining a ray at intervals of a set angle by taking a pole as an endpoint in a polar coordinate system grid, and determining a boundary point of a cyclone influence range in the direction along the increasing direction of the pole diameter for each ray according to the wind speed and the sea level air pressure;
2.4, among a plurality of boundary points of the cyclone influence range, when the sea level air pressure of the boundary point in a certain direction is less than P e In this direction, the first one is selected to satisfy the sea level pressure p=p, starting from the pole in the direction of increasing the pole diameter e The grid points at the position are used as boundary points after the direction correction;
2.5, re-projecting the obtained coordinates of the plurality of boundary points into longitude and latitude grids of the atmospheric variable to obtain the longitude and latitude coordinates of the boundary points, and sequentially connecting the plurality of boundary points to obtain a cyclone influence range at a selected moment;
and 2.6, repeating the steps 2.1 to 2.5 by using the sea level air pressure real field at other moments, and acquiring the cyclone influence ranges of all cyclone occurrence moments.
5. The method of claim 4, wherein the polar grid has spatial resolutions of 10km and 1 ° in the polar and polar directions, respectively.
6. The method of claim 4, wherein the step 2.3 of determining the boundary point of the cyclone influence range in the direction according to the wind speed of 10m and the sea level air pressure is as follows: the first one satisfies v at the same time θ <Threshold 1, sea level air pressure P>Threshold value 2 and wind speed U<The point of the threshold 3 condition is noted as the boundary point of the cyclone influence range in this direction at the selected moment.
7. The method of assessing the net effect of a cyclone on arctic sea ice of claim 1, wherein said spatial smoothing is accomplished by the formula:
where (L, K) represents the grid position that the t-th iteration spatial smoothing needs to calculate,is the result after the t-th iteration of a certain atmospheric variable at the (L, K) position.
8. The method for evaluating the net effect of a cyclone on ice on arctic sea according to claim 1, wherein said step 4 is specifically as follows:
4.1, acquiring the spatial distribution of sea ice density, sea ice thickness and sea ice drift speed with cyclone influence according to the atmospheric variable real field acquired in the step 1 as an atmospheric forced field in a north pole sea ice numerical mode;
4.2, using the atmospheric variable cyclone-free field obtained in the step 3 as an atmospheric forced field, and operating the north pole sea ice numerical mode which is the same as that of the step 4.1 to obtain the space distribution of sea ice density, sea ice thickness and sea ice drift speed without cyclone influence;
4.3, subtracting the sea ice density, the sea ice thickness and the sea ice drift velocity of the corresponding moment and the corresponding grid obtained in the step 4.2 from the sea ice density, the sea ice thickness and the sea ice drift velocity of each grid at a certain moment to obtain the net influence of the cyclone at the moment on the sea ice density, the sea ice thickness and the sea ice drift velocity of all grids; if the result is negative, the net effect of the cyclone on the sea ice concentration, the sea ice thickness and the sea ice drift velocity is to reduce the sea ice concentration, the sea ice thickness or the sea ice drift velocity; if the result is positive, the net effect of the cyclone on the sea ice concentration, the sea ice thickness and the sea ice drift velocity is to increase the sea ice concentration or the sea ice thickness or the sea ice drift velocity;
and 4.4, repeating the step 4.3, and traversing all moments to obtain the net influence of the cyclone at all moments on the sea ice density, the sea ice thickness and the sea ice drift speed of all grids.
9. The method of claim 1, wherein step 4 further comprises visualizing the net effect of the cyclone on all grid sea ice concentration, sea ice thickness and sea ice drift velocity: and selecting positive values and negative values of net influences of different colors representing sea ice concentration, sea ice thickness and sea ice drift speed, wherein the larger the absolute value is, the darker the corresponding color is, so that the net influence of the cyclone on the sea ice at a certain position is that the sea ice concentration, the sea ice thickness and the sea ice drift speed are increased or reduced.
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